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Your Brain Is a Time Machine: Why we need to talk about time

From space-time to the way minds keep time, getting to grips with the temporal is complex but rewarding, shows a new book

By Anil Ananthaswamy

31 May 2017

Neural circuits wire themselves to external stimuli to keep time

Herbert List/Magnum

“TIME is a road without any bifurcations, intersections, exits, or turnarounds.” With that, neuroscientist Dean Buonomano sets up the meat of his new book, Your Brain is a Time Machine – and an intriguing difference between the way we animals navigate time as opposed to space.

Natural time is what physicists fuss about. Is time real? Or is the passage of time an illusion, and do all moments in time exist in much the same way that all coordinates of space exist? Neuroscientists, on the other hand, fuss about clock time and subjective time.

To explain natural time, physicists and philosophers back eternalism, according to which the past, present and future are all equally real. “There is absolutely nothing particularly special about the present: under eternalism now is to time as here is to space,” writes Buonomano.

The other main explanation of natural time is presentism, according to which only the present moment is real – a view that tallies with our sense of subjective time. The past is gone, the future hasn’t happened yet. “Neuroscientists are implicitly presentists,” says Buonomano. “But despite its intuitive appeal, presentism is the underdog… in physics and philosophy.”

“Mental time travel is a human capacity. But to do it, biology first had to figure out how to keep time”

Buonomano decides it is time to simultaneously tackle the physics and the neuroscience of time. The title of the book is derived from the now well-regarded idea that our brains are prediction machines. Whenever we perceive something, theory says that what we perceive is not objective reality, but rather the brain’s best guess as to what’s causing the sensations impinging on the body. But popular accounts of the theory often ignore one dimension of the prediction machinery: time.

Buonomano points out that the brain is continuously making real-time predictions, not just of “what will happen next” but also of “when it will happen”. To do so, the brain needs complicated machinery for keeping time – to predict not just what will happen within microseconds, but what might happen in seconds, minutes, hours, even days, weeks, months and years.

This ability to predict the long-term future is reliant on memory. In fact, that’s really the main evolutionary use for memory, as a storehouse of the information needed to predict the future. With memory and cognition, our brains became time machines – we could travel back and forth in time. This mental time travel is a human capacity, distinguishing us from other animals, hence the book’s title. Scrub jays, oddly, seem to demonstrate similar abilities, but proof of mental time travel in animals is hard to come by as yet.

To indulge in mental time travel, biology first had to figure out how to keep time, not unlike how scientists in the 17th century invented the pendulum clock. Christiaan Huygens’s high-quality pendulum clocks were the first to keep time more accurately than clocks within the human brain.

Buonomano’s book is full of delicious details about the myriad ways in which cells – neurons and other types – tell the time. For example, there’s the complicated sounding suprachiasmatic nucleus, a cluster of neurons at the base of the hypothalamus that acts as a master circadian clock. Circadian clocks depend on pendulum-like oscillations of the levels of specific proteins. One of which is aptly named period.

But unlike our clocks, which can tell time over a vast range of intervals, the brain has no single clock. For example, lesions in the suprachiasmatic nucleus don’t alter the brain’s ability to discern temporal patterns at the scale of seconds: there are different clocks for that. If there’s one clear message about the neuroscience of timekeeping, it’s that neural circuits can wire themselves in response to regular external stimuli. In other words, they can keep time, all sorts of time.

Reading Buonomano’s book, it’s hard not to marvel at how time and timekeeping pervade our existence – whether in the form of the clocks and instruments we build or through the mechanisms inherent in our brains. Buonomano creates a sense of wonder about just how complex the temporal brain is and about what a spectacular job it does of timekeeping.

Buonomano writes lucidly, in an almost matter-of-fact fashion, choosing crystalline clarity over flowery prose. So the occasional writerly sentences stand out, for example, when he writes: “The duration of the beat of a hummingbird’s wing is as concealed to our sensory organs as is the drifting of the continents.”

Buonomano’s clear writing is most apparent when he writes about the physics of time. Given that his expertise is neuroscience, this is no small feat. His explanation for why Einstein’s special theory of relativity implies the existence a block universe – a 4D manifold of space-time in which here, there and everywhere exist alongside the past, present and future – makes a masterful case for eternalism.

Special relativity destroys the notion of simultaneity – the idea that two observers moving with respect to each other could agree on the timing of events. When speeds get close to the speed of light, the temporal order of events can be perceived differently by different observers.

Buonomano writes: “If we assume that all events that ave ever or will ever occur are permanently located at some point in the block universe… then the relativity of simultaneity becomes no more puzzling than the fact that two objects in space can appear to be aligned or not depending on where you are standing. Two telephone poles along a highway appear aligned if you are standing on the side f the road, but not if you are in the middle of the road – it is a question of perspective.” And so it is with time.

But eternalism clashes with our subjective experience of the flow of time: in other words, physics clashes with neuroscience. While it’s true that we feel the passing of time, and thus instinctively favour presentism, Buonomano points out that our notions of subjective time are intricately linked to our notions of space. He shows this with the metaphors we use to talk about time: “That was a refreshingly SHORT commercial. We have been studying time for a LONG time… I’m looking FORWARD to your reply; in HINDSIGHT that was a terrible idea.” For timekeeping, the brain co-opts the neural circuits that are used to represent space, thus treating time and space similarly, in a curious analogy to special relativity.

This leads to one of the most intriguing questions raised in the book: could our theories about physics be informed by the very architecture of our brain? “Now that we know that the brain itself spatializes time, it is also worth asking if the acceptance of eternalism has benefited from the fact that it resonates with the architecture of the organ responsible for choosing between eternalism and presentism,” writes Buonomano.

“Could our theories about physics be informed by the very architecture of our brain?”

The state of scientific knowledge about time is such that no straight answers are forthcoming. The book, a compelling read for the most part, somewhat peters out towards the end, with more questions raised than answers. Understandably so. “Our subjective sense of time sits at the center of a perfect storm of unsolved scientific mysteries: consciousness, free will, relativity, quantum mechanics, and the nature of time,” writes Buonomano.

Your Brain Is a Time Machine can be disquieting, as the implications settle in, for example, of inhabiting a universe in which all moments exist. But the book ultimately leads to an internal quieting, as one realises that all the profound scientific discoveries of the past century or so are struggling with a common enemy: time.

Your Brain Is a Time Machine: The neuroscience and physics of time

Dean Buonomano

W. W. Norton (Buy from Amazon *)

This article appeared in print under the headline “All the time in the world…”

(*When you buy through links on this page we may earn a small commission, but this plays no role in what we review or our opinion of it.)

• neuroscience /

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• Pixar shorts

Time Travel Mater

Time Travel Mater is the eleventh short film in the Cars Toons series, which was first aired on June 5 on Disney Channel. It was officially premiered ten days later, on June 15 at the Disneyland Resort in Blue Sky Cellar at Disney California Adventure park to celebrate the opening of Cars Land , and first aired on ABC the next day. It is included on the DVD and Blu-ray of Pixar Short Films Collection Volume 2 . The episode features Mater telling a story according to which he time traveled, back to the beginnings of Radiator Springs , thus reusing part of the abandoned concept of the unmade Tall Tale made by Scott Morse , Backwards to the Forwards . Stanley, the founder of Radiator Springs, appears alive in this episode when Mater time travels. It is the third production of Pixar Canada . The music is composed by Mark Watters .

• 5 External links
• 6 References

Lightning McQueen and Mater were in front of the Courthouse when Lizzie drives by. She says good morning to Lightning and Mater in a rude way, but she says it in a nice way to the statue of Stanley . Lightning McQueen asks Mater how Lizzie and Stanley met. Mater replies by telling one of his stories, which "all started last week."

The story starts with him putting up a new town sign with a clock on it. The sign falls on Mater, and the clock ends up on his "nose." Mater sneezes, and then disappears.

He ends up inside the Tail Light Caverns. He exits the caverns to go tell everyone back in town. However, when he does, he can't find the town, but he does see a car at a nearby spring. When Mater gets closer to the car, he discovers that it's Stanley! Stanley asks Mater if he needs a radiator cap. When Mater says no, Stanley leaves to go to California in search of customers. Mater realizes that if Stanley didn't stay, there wouldn't be a Radiator Springs in the future! So, he goes to the present, gets McQueen, and they both go back to the past, where Mater removes McQueen's radiator cap and calls out to Stanley, saying that there's a car that needs a radiator cap (McQueen). So, Stanley gives McQueen a new radiator cap. Two cars that also need radiator caps enter the scene, and Stanley leads them to the spring, where the cars get a "drink." Mater suggests that Stanley build a town right next to "this here radiator spring." Stanley likes the idea, and even comes up with a name for the town right then and there: Radiator Springs . While Stanley was planning how to build the town, Mater and McQueen travel to the future to speed things up a bit.

Mater and McQueen then travel to 1927. Stanley shows them the town. Then, Stanley takes note of a Model T (which turns out to be Lizzie) that arrives in town. Lizzie breaks down, so Mater helps her out. Lizzie sees McQueen and appears to be falling in love with him, and Mater realizes that if Lizzie falls in love with McQueen, then she won't fall in love with Stanley, and then Stanley will leave town, and there'd be no Radiator Springs! But then Lizzie asks McQueen to get out of the way, revealing that she had her eye on Stanley, not McQueen, as Mater thought. McQueen introduces Lizzie and Stanley. Stanley took Lizzie to his spring so that she could get a drink. Then he took her to get a new radiator cap. Then, McQueen and Mater leave.

They reappear in Radiator Springs at the time that Lizzie and Stanley get married. After getting married, they went honeymooning at Comfy Caverns. Then, Mater and McQueen leave, and Mater finishes his story.

McQueen says that there's no such thing as time travel, but then Lizzie comes and thanks McQueen for introducing her and Stanley. Mater says, "And that's how you make history."

• Larry the Cable Guy : Mater
• Keith Ferguson : Lightning McQueen
• John Michael Higgins : Stanley
• Katherine Helmond: Lizzie
• This is the final Mater's Tall Tales episode.
• The first and, so far, only Cars Toons: Mater's Tall Tales episode with Lizzie in it, and actually the first time she played a role as a secondary tritagonist.
• The first episode without any pitties and without Mia and Tia in it. This may be due to the fact that being modernized cars, they weren't even built (born) yet.
• The only episode not to have Mater say something similar to his line: "Don't you remember? You was there too!"
• The first episode (and only time in Mater's Tall Tales) with Lightning McQueen in his World Grand Prix paint job. It is also the first time it has shown McQueen's hood open, showing his motor.
• Tail Light Caverns, Stanley's early settlement, and Comfy Caverns, all places which had never been seen before, are sets that come from Cars Land . Their appearance in the short enables to establish them as canon, and perhaps to promote the attraction.
• This is the second Cars Toons: Mater's Tall Tales episode that has Mater's story in black and white. The first one is Mater Private Eye . However, in this episode, it's not Mater's whole story that's in black and white. After Mater drives out of the Tail Light Caverns, everything was in sepia tones (a common color tone used in "flashback" sequences). When he and McQueen time travel to when Stanley's early settlement was made, everything was in black and white. When Mater and McQueen time travel to when Lizzie and Stanley get married, the entire color scheme is an homage to the two color Technicolor processes that were used in movies from 1917 to 1936 .
• The alternating color schemes used in this story seem to be an homage to how photographs of each particular time period looked. This gave each era that Mater visits its own unique visual identity. It was likely implemented to avoid confusion.
• Also, the clock on Mater's "nose" is a reference to Cars 2 when the lemons planted a bomb on his "nose."
• The story of Radiator Springs seen in Time Travel Mater was used before the movie Cars . [1]
• Mater's "Whoa!" when he notices he's in the Tail Light Caverns is the same sound he makes when he sees the moon in Moon Mater .
• The scream that Mater makes when he sees that there would be no town in the future if Stanley doesn't stay is the same scream he makes when he is fighting the I-Screamer in Monster Truck Mater .
• This short is on the Pixar Short Films Collection Volume 2 DVD and Blu-Ray.

Gallery [ ]

External links [ ]

References [ ]

• 1 Sar-Chasm
• 3 The Emotions

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• Philos Trans R Soc Lond B Biol Sci
• v.364(1521); 2009 May 12

Mental time travel and the shaping of the human mind

Thomas suddendorf.

1 Department of Psychology, University of Queensland, St Lucia, Queensland 4072, Australia

Donna Rose Addis

2 Department of Psychology, University of Auckland, Private Bag 92019, Auckland 1142, New Zealand

Michael C. Corballis

Episodic memory, enabling conscious recollection of past episodes, can be distinguished from semantic memory, which stores enduring facts about the world. Episodic memory shares a core neural network with the simulation of future episodes, enabling mental time travel into both the past and the future. The notion that there might be something distinctly human about mental time travel has provoked ingenious attempts to demonstrate episodic memory or future simulation in non-human animals, but we argue that they have not yet established a capacity comparable to the human faculty. The evolution of the capacity to simulate possible future events, based on episodic memory, enhanced fitness by enabling action in preparation of different possible scenarios that increased present or future survival and reproduction chances. Human language may have evolved in the first instance for the sharing of past and planned future events, and, indeed, fictional ones, further enhancing fitness in social settings.

1. Introduction

Clive Wearing is an English musician. As an acknowledged expert on early music, he had built up a musical career with the BBC when he was infected at the age of 46 with the herpes simplex virus. This effectively destroyed his hippocampus and left him profoundly amnesic. The nature of his amnesia illustrates the distinction between semantic memory, which is memory for enduring facts about the world, and episodic memory, which is a personal record of the past ( Tulving 1983 ). Wearing's semantic memory is largely intact, as is his procedural memory. He retains a normal vocabulary, recognizes his wife and family, and can still play the piano and conduct a choir. His episodic memory, though, is profoundly impaired. He has sufficient short-term memory to be able to converse but quickly forgets about topics he spoke about or experienced just moments earlier. He is continually under the impression that he has just woken up, or recovered from being dead. His conscious experience is entirely of the present, and is well captured in the book, Forever today , written by his wife Deborah ( Wearing 2005 ).

Neuropsychological evidence reveals that deficits in episodic and semantic memory are doubly dissociated, implying distinct mechanisms. As with Clive Wearing, most cases of amnesia, especially those resulting from damage to the hippocampus, are characterized by severe deficits in episodic memory, while semantic memory remains largely intact ( Scoville & Milner 1957 ; Tulving et al . 1988 ; VarghaKhadem et al . 1997 ; Aggleton & Brown 1999 ). Indeed, the very term ‘memory’ is usually taken to mean episodic memory, as when William James wrote ‘Memory requires more than the mere dating of an event in the past. It must be dated in my past’ ( James 1890 , p. 650). Yet in a degenerative condition known as semantic dementia, semantic memory is grossly impaired, leaving episodic memory surprisingly unaffected ( Hodges & Graham 2001 ).

Retrieval of episodic memories involves the conscious reliving of past events, a sort of mental journey into the past ( Tulving 1983 ). In recent years, evidence has accumulated that the episodic memory system is also involved in mental travel into the future, suggesting a general concept of mental time travel (Suddendorf & Corballis 1997 , 2007 ). Conceiving of future events, of course, involves a process of active construction of events that have not yet occurred, but the more general process of mental time travel highlights the evidence that episodic memory, too, is better conceived as a conscious act of construction, rather than a faithful re-enactment of the past. Indeed, if the only function of episodic memory was to record the past, it might be expected to function in a reproductive manner, similar to a video recorder ( Suddendorf & Corballis 1997 ). However, the slew of errors and distortions that episodic memory is vulnerable to shows us this is not the case ( Schacter 1999 ; Schacter & Addis 2007 ). The primary role of episodic memory, then, may be to provide information from the past for the simulation of the future. Indeed, natural selection can only work on what memory can offer for present and future fitness rather than on the accuracy of the past record per se ( Suddendorf & Corballis 1997 ; Suddendorf & Busby 2005 ).

In spite of the dissociation between semantic and episodic memory, there must be some links between them. The encoding of episodic memories must to some extent depend on semantic memories that are already in place ( Tulving 2002 ); a remembered visit to a restaurant, for example, must depend in part on one's knowledge of what a restaurant is and what happens there. Indeed, descriptions of episodic memories and future simulations comprise both episodic and semantic details that are woven together into a narrative of the experience (e.g. Levine et al . 2002 ; Addis et al . 2008 ). Individual episodes, having drawn on semantic elements, are then related to the self in subjectively sensed time. This allows the experience of an event to be stored separately from the semantic system, and retrieved in what Tulving called ‘episodic retrieval mode’ ( Tulving 2002 ). Just as they are during encoding, retrieved episodic memories are interwoven with elements of semantic memory. The episodic details of an event are not retrieved in isolation of the context that semantic information can provide ( Levine et al . 2002 ). This would apply, we suggest, not only to the reconstruction of past events, but also to the construction of future ones, and even to story-telling—the construction of fictional episodes that permeate folklore, literature, stage drama, film and television ( Hassabis et al . 2007 b ; Suddendorf & Corballis 2007 ).

In this paper, we review neuroscientific evidence for the continuity of mental time travel into the past and future, and consider what, if anything, might be uniquely human about mental time travel. We go on to suggest that human language may have evolved primarily for the communication of episodes, whether from the past or the imagined future, or indeed in the form of fiction. We conclude with some speculation as to when and why mental time travel evolved in hominin evolution.

2. Neuropsychological and neuroimaging evidence

The title of Deborah Wearing's book, Forever today , also captures the fact that Clive Wearing is as unable to imagine future events as he is incapable of remembering past ones. It is becoming clear that this is true of other profoundly amnesic patients as well ( Tulving 1985 ; Klein et al . 2002 ; Rosenbaum et al . 2005 ; Hassabis et al . 2007 b ). In one study, for example, patients with bilateral hippocampal damage and intact premorbid semantic memory were given cue words and short descriptions of scenarios, and asked to generate new experiences from them. Their scores for the detail and coherence of the imagined scenarios fell well below those of a control group ( Hassabis et al . 2007 b ). Interestingly, this study suggests that the hippocampus may play a critical role, not only in terms of retrieving details from episodic memory to be used for an imagined scenario, but also the integration of such details into a coherent event. Moreover, it seems that such processes are not unique to imagining future events per se , but apply more generally to the construction of any fictitious scenario ( Rosenbaum et al . 2005 ; Hassabis et al . 2007 b ).

Consistent with neuropsychological data, functional brain imaging also reveals a strong overlap in brain activity between backward and forward mental time travel. In one study, positron emission tomography revealed activity in the frontal poles and medial temporal lobes, including hippocampal and parahippocampal regions, to tasks involving both the remembered past and the imagined future episodes ( Okuda et al . 2003 ). Although most areas showed equivalent activation to both the past and the future tasks, areas in the anteromedial pole showed greater activation to future than to past tasks, and greater activation to both tasks, the more distant the episode in time. A more recent study showed that hippocampal activity, too, was greatly increased for future events that were more distant from the present ( Addis & Schacter 2008 ). These effects may reflect the degree of construction required, with higher levels of construction for more distant events.

Based on this, and on another work using functional magnetic resonance imaging ( Addis et al . 2007 ; Szpunar et al . 2007 ), Schacter et al . (2007) identify a ‘core network’ that is used not just for remembering the past, but that functions adaptively and is even more actively recruited when integrating information from past experiences to construct mental simulations about possible future events. The prominent components of this network include regions of the medial prefrontal cortex, the lateral and medial parietal cortex (including precuneus and retrosplenial cortex), and the lateral and medial temporal lobes, including notably the hippocampus. Activity is intercorrelated across these regions and with activity in the hippocampal formation. While some recent studies challenge this finding, reporting more activity for past than future events ( Hassabis et al . 2007 a ; Botzung et al . 2008 ; D'Argembeau et al . 2008 ), it is important to note that, in these studies, future events are not being imagined during the scan. Rather, they are constructed outside of the scanner and then recalled during the scan. Memories of imagined events are typically less detailed than memories of real experiences, and thus recruit fewer hippocampal resources during retrieval. This further supports the core network being more actively recruited when one must use episodic memory to construct and imagine a new event online.

Moreover, these findings challenge the traditional view that the role of the hippocampus is to hold episodic memories for a limited period of time until they are consolidated in other neocortical areas ( Squire 1992 ; Squire et al . 2004 ). The alternative view, more consistent with these and other recent results, is that the hippocampus is always necessary for the retrieval of detailed episodic experiences, including remote ones ( Moscovitch et al . 2005 ). By this account, the extent of hippocampal involvement probably depends on the vividness of the internal representation, whether of past episodes or imagined future ones ( Hassabis et al . 2007 b ). Confirming this, Addis & Schacter (2008) also found more detailed representations to be associated with increased posterior hippocampal activity. This probably reflects the retrieval of information, necessary when remembering as well as imagining events. By contrast, future event detail was associated with greater activity in the anterior hippocampus, possibly reflecting the recombination of details into a coherent event.

The reported phenomenological richness of imagined events ( D'Argembeau & Van der Linden 2004 ), as well as the number of imagined events reported ( Spreng & Levine 2006 ), decreases with temporal distance into both the past and the future. There are further parallels in the development of mental time travel into past and future across the lifespan, both in terms of initial emergence ( Busby & Suddendorf 2005 ) and eventual decline ( Addis et al . 2008 ). The neural and cognitive evidence linking episodic memory to imagining the future is increasingly recognized (e.g. Hassabis & Maguire 2009 ; Schacter & Addis 2009 ).

3. Uniquely human?

In a detailed account of the nature of episodic memory, Tulving (1983) proposed that it was uniquely human. It was later proposed more generally that mental time travel was unique to our species and that the main adaptive advantage must lie with foresight (Suddendorf & Corballis 1997 , 2007 ). This does not mean that non-human animals do not behave in a manner oriented to the future. The futures of animals and their offspring often depend on instinctive behaviours, such as food caching, migrations and nest building, as well as on learned behaviours and semantic memory ( Suddendorf & Corballis 2007 ). Semantic knowledge can be important for prospection, but must be distinguished from episodic future thinking. For example, knowledge of where Paris is located, what language is spoken there and how to get there will clearly enhance the prospects of making a trip to that city. Episodic memories of experiences in Paris, though, allow conscious construction of imagined future events there, including, perhaps, friends that one might meet there, places one might revisit, specific restaurants and, perhaps, specific dishes, and so forth. More generally, episodic memory provides a vocabulary from which to construct possible scenarios, and compare them off-line in order to optimize future behaviour. This ability to act with specific, individually anticipated future events in mind may account for why human behaviour is so immensely flexible and, as we shall argue further below, why humans have evolved open-ended communication systems.

The claim that only humans are capable of episodic memory and episodic foresight has posed a challenge to animal researchers. One of the difficulties has been to demonstrate memory that is truly episodic, and not merely semantic or procedural. For example, does the dog that returns to where a bone is buried remember actually burying it, or does it simply know where it is buried? One suggestion is that episodic memory in non-human animals might be defined in terms of what happened, where it happened and when it happened—the so-called www criteria. It has been proposed that scrub jays ( Aphelcoma coerulescens ) meet these criteria, because of experimental evidence that they can select the locations of food they have previously cached not only according to the type of food that is stored there, but also according to how long it has been stored, implying that they remember when it was stored. For example, they will recover recently cached worms in preference to nuts, since fresh worms are more palatable, but if the worms have been cached for too long they will retrieve nuts, because the worms will have decayed and become unpalatable ( Clayton & Dickinson 1998 ). Furthermore, if another jay observes them caching food, they will later re-cache it, presumably to prevent the observer stealing the food. They will only do this, however, if they have themselves stolen food in the past ( Emery & Clayton 2001 ). Clayton and colleagues ( Clayton et al . 2003 ) concluded that scrub jays can not only remember the what, where and when of past events, but also anticipate the future by taking steps to avoid future theft.

A recent study suggests that meadow voles ( Microtus pennsylvanicus ), too, have a similar capacity ( Ferkin et al . 2008 ). Male voles were first allowed to explore two chambers, one containing a pregnant female 24 hours pre-partum, and the other containing a female that was neither lactating nor pregnant. Twenty-four hours later, they were again given access to the chambers, now empty and clean, and spent more time exploring the chamber that had contained the previously pregnant female than the one that had housed the other female. This suggests that they had remembered the pregnant female and her location, and understood that she would now be in post-partum oestrus, a state of heightened sexual receptivity. In another condition, they first explored a chamber containing a female in post-partum oestrus and another containing a female that was neither lactating nor pregnant, and was not in oestrus. Twenty-four hours later, they were again allowed to explore the now-empty cages, and showed no preference for the chamber that had housed the female in oestrus. This suggests that they realized the female would no longer be in a state of heightened receptivity.

Several other recent experiments have documented that various species of mammals and birds may pass the www criteria (for reviews, see Dere et al . 2005 ; Zentall 2006 ; Suddendorf & Corballis 2007 ). If this entails that these species can travel mentally in time, then we are in need of a fundamental reconsideration of animal welfare and ethics ( Lea 2001 ; Suddendorf & Corballis 2007 ). The extent to which animals live in the present has a major impact on their capacity for suffering—if they can mentally revisit a past traumatic event or anticipate future pain, as humans do, then considerations for their welfare would need to take this into account when attempting to minimize their suffering (see Mendl & Paul 2008 for a detailed discussion).

It remains possible, though, that these ingenious studies do not prove that the animals actually remember or anticipate episodes. For example, associative memory might be sufficient to link an object with a location, and a time tag or ‘use-by’ date might then be attached to the representation of the object to update information about it ( Suddendorf & Corballis 2007 ). Moreover, ‘how long ago’ can be empirically distinguished from ‘when’, so the ability of scrub jays to recover food depending on how long ago it was cached need not actually imply that they remember when it was cached. As evidence for this, a recent study suggests that rats can learn to retrieve food in a radial maze on the basis of how long ago it was stored, but not on when it was stored, suggesting that ‘episodic-like memory in rats is qualitatively different from episodic memory in humans’ ( Roberts et al . 2008 ).

More generally, the www criteria may not be sufficient to demonstrate true episodic memory. Most of us know where we were born, when we were born and, indeed, what was born, but this is semantic memory, not episodic memory ( Suddendorf & Busby 2003 ). Conversely, one can imagine past and future events and be factually wrong about what, where and when details (in fact, we are often mistaken). This double dissociation, then, strongly suggests that we should not equate mental time travel with www memory.

Non-human animals and very young children may be limited in their foresight in a number of different ways ( Suddendorf & Corballis 2007 ). One variant on the claim to human uniqueness is the so-called Bischof-Köhler hypothesis, which states that only humans can flexibly anticipate their own future mental states of need and act in the present to secure them ( Bischof 1978 ; Bischof-Köhler 1985 ; Suddendorf & Corballis 1997 ). Again, an experiment with scrub jays has been claimed as a counterexample. The birds were prefed with one type of food for three hours and then allowed to cache the prefed and an alternative food. They were subsequently prefed with the alternative food before being allowed to recover what they had cached. On the second and third trials, the birds cached more of the food on which they were satiated, on the apparent understanding that they would be hungry for this food at later recovery, thus challenging the Bischof-Köhler hypothesis ( Correia et al . 2007 ). Closer analysis of the data, however, suggests that this interpretation is misleading. Although the birds cached a greater proportion of food for which they would later be hungry, the absolute number of items stored did not change in any meaningful way. The six birds in the critical condition cached an average of 0.7 items of the prefed food on the first trial, and 1.2 items and 0.8 items on the second and third trials, respectively. Thus, they did not increasingly store the food that was more desirable in the future ( Suddendorf & Corballis 2008 ).

The most promising challenge to the Bischof-Köhler hypothesis so far comes from the great apes. In one study, orang-utans ( Pongo abelii ) and bonobos ( Pan paniscus ) learned to use a tool to extract grapes from an apparatus in a test room. They were later given a choice of tools, some appropriate and others inappropriate for extracting grapes, and significantly chose appropriate ones for later access to the test room ( Mulcahy & Call 2006 ). In a similar experiment, two chimpanzees ( Pan troglodytes ) and an orang-utan were shown, on a single trial, how to use a plastic hose as a straw to obtain juice from an apparatus, and on subsequent trials, prior to access to the test room an hour later, chose this tool in preference to others. In one critical condition, the animals were offered grapes, their favourite food, along with the other tools, and chose the hose more often than the grapes, suggesting that obtaining a large amount of fruit juice in the future may have been valued more than a small instant grape reward ( Osvath & Osvath 2008 ). In both the studies, the experimenters took pains to rule out alternative explanations, such as simple association between tool and later reward, but there continue to be some methodological concerns (see Suddendorf 2006 and Suddendorf et al . in press for critical analyses).

So far, examples of putative mental time travel in non-human species appear limited to situations with a strong instinctive component. They do suggest ways in which animals might adapt their behaviour to maximize future reward, but, so far, they have little of the flexibility and generality of mental time travel in humans. Humans can simulate virtually any event and evaluate it in terms of likelihood and desirability. It has been argued that this human faculty may be likened to a theatre production in that we employ mental analogues to a stage, a playwright, actors, a set, a director, an executive producer and a broadcaster ( Suddendorf & Corballis 2007 ). These sophisticated mental roles may be employed to simulate future events, just as readily as to imagine the minds of others (theory of mind) and entirely fictional stories ( Suddendorf & Corballis 1997 ; Buckner & Carroll 2007 ; Hassabis et al . 2007 b ). Animals may be restricted in their capacity to travel mentally in time by limits in any of these domains. For example, just as a playwright is responsible for creating new stories, mental simulations of novel future events require open-ended generativity—our ability to combine and recombine a limited set of items into virtually unlimited ways (something not evident in any of the animal studies). Our memories for episodes are made up of combinations of people, actions, objects and places, along with qualities such as time of day, season, emotional states, and so forth. Imagined future events are similarly constructed, and we may, in fact, compose different scenarios depending on various contingencies, such as the weather, or who is likely to show up. Indeed, it may be the generative component that most clearly distinguishes mental time travel in humans from future-directed capacities in other species. This generativity is also characteristic of other human faculties such as navigation, number, theory of mind and language ( Corballis 2003 ). Language is often regarded as the most distinct of human faculties (e.g. Hauser et al . 2002 ), and much of what humans talk about (or broadcast) are the mental simulations of past events and future possibilities ( Szagun 1978 ).

4. Language

Testing for episodic memory in humans is normally reliant on language, which is why it is difficult to devise ways of testing for it in non-human animals. This raises the possibility that the evolution of language itself is intimately connected with the evolution of mental time travel. Language is exquisitely designed to express ‘who did what to whom, what is true of what, where, when and why’, as Pinker (2003) put it—a combination of w 's that goes well beyond the www criteria—and these are precisely the qualities needed to recount episodic memories. The same applies to the expression of future events—who will do what to whom, or what will happen to what, where, when and why, and what are we going to do about it. When considering the future, the conditional may also be important—if it rains, then X will happen; if it does not we may enjoy Y. To a large extent, then, the stuff of mental time travel is also the stuff of language ( Corballis & Suddendorf 2007 ).

Language allows personal episodes and plans to be shared, enhancing the ability to plan and construct viable futures. To do so, though, requires ways of representing the elements of episodes: people; objects; actions; qualities; times of occurrence; and so forth. Language may well have begun as pantomime, with the use of bodily gestures to mimic events ( Donald 1991 ), with gestures becoming conventionalized, and thus more arbitrary and less representational, in the interests of greater economy and efficiency. According to this scenario, vocal gestures gradually replaced manual ones as the dominant mode ( Corballis 2003 ; Rizzolatti & Sinigalglia 2007 ), although most people still gesture manually as they speak.

The recounting of mental time travel places a considerable and, perhaps, uniquely human burden on communication, since there must be ways of referring to different points in time—past, present and future—and to locations other than that of the present. Different cultures have solved these problems in different ways. Many languages use tense as a way of modifying verbs to indicate the time of an episode, and to make other temporal distinctions, such as that between continuous action and completed action. Some languages, such as Chinese, have no tenses, but indicate time through other means, such as adverbs or aspect markers ( Lin 2005 ). The language spoken by the Pirahã, a tribe of some 200 people in Brazil, has only a very primitive way of talking about relative time, in the form of two tense-like morphemes, which seem to indicate simply whether an event is in the present or not, and Pirahã are said to live largely in the present ( Everett 2005 ).

Reference to space may have a basis in hippocampal function; as noted earlier, current theories suggest that the hippocampus provides the mechanism for the retrieval of memories based on spatial cues. It has also been suggested that, in humans, the hippocampus may encompass temporal coding, perhaps through analogy with space; thus, most prepositions referring to time are borrowed from those referring to space. In English, for example, words such as at , about , around , between , among , along , across , opposite , against , from , to and through are fundamentally spatial, but are also employed to refer to time, although a few, such as since or until , apply only to the time dimension ( O'Keefe 1996 ). It has been suggested that the hippocampus may have undergone modification in human evolution, such that the right hippocampus is responsible for the retrieval of spatial information, and the left for temporal (episodic or autobiographical) information ( Burgess et al . 2002 ). It remains unclear whether the left hippocampal specialization is a consequence of left hemispheric specialization for language, or of the incorporation of time into human consciousness of past and future, but either way it reinforces the link between language and mental time travel.

The most striking parallel between language and mental time travel has to do with generativity. We generate episodes from basic vocabularies of events, just as we generate sentences to describe them. It is the properties of generativity and recursiveness that, perhaps, most clearly single out language as a uniquely human capacity ( Hauser et al . 2002 ). The rules governing the generation of sentences about episodes must depend partly on the way in which the episodes themselves are constructed, but added rules are required by the constraints of the communication medium itself. Speech, for example, requires that the account of an event that is structured in space–time be linearized, or reduced to a temporal sequence of events. Sign languages allow more freedom to incorporate spatial as well as temporal structure, but still require conventions. For example, in American sign language, the time at which an event occurred is indicated spatially, with the continuum of past to future running from behind the body to the front of the body.

Of course, language is not wholly dependent on mental time travel. We can talk freely about semantic knowledge without reference to events in time, as typically required by the education industry—and, indeed, this very paper. However, it is mental time travel that forced communication to incorporate the time dimension, and to deal with reference to elements of the world, and combinations of those elements, that are not immediately available to the senses. It is these factors, we suggest, that were in large part responsible for the development of grammars. Given the variety of ways in which grammars are constructed, such as the different ways in which time is marked in different languages, we suspect that grammar is not so much a product of some innately determined universal grammar ( Chomsky 1988 ; O'Keefe 1996 ) as it is a product of culture and human ingenuity, constrained by brain structure ( Christiansen & Chater 2008 ). Through language, then, we see not just language itself, but also the structure of human thought, and how it is composed of basic elements including ‘events, states, things, substances, places and goals’ ( Pinker 2007 )—and times. Moreover, the generativity of language reflects the generativity of the underlying thought processes themselves.

5. Evolutionary considerations

Instinct, learning and memory are adaptations that enhance the fitness of animals, and shape their futures. Episodic memory is a form of memory, possibly unique to humans, that further allows the fine-tuning of behaviour, based on specific episodes in the past. It allows us to imagine future episodes, make specific plans and compare different scenarios. Language, we suspect, coevolved with mental time travel to allow the sharing of episodic information, sometimes to the point that we confuse events that have actually happened in our lives with those told to us by others, or even with those gleaned from fictional accounts.

Mental time travel and grammatical language probably evolved during the Pleistocene (Suddendorf & Corballis 1997 , 2007 ; Corballis 2003 ). Survival pressures brought about by changes in climate and the replacement of a forested environment by the more exposed savannah necessitated greater social cohesion, more detailed future planning and more effective communication. Brain size increased dramatically in the genus Homo during the Pleistocene, reaching a peak with the large-brained Neanderthals and precursors to modern humans perhaps 500 000 years ago. It has been suggested that the emergence of the genus Homo was also accompanied by a prolongation of the period of development from infancy to adulthood, and that an extra stage, known as childhood, was inserted into the sequence of developmental stages ( Locke & Bogin 2006 ). Childhood lasts from age 2.5 to approximately age 7, roughly the period during which both mental time travel and grammatical language develop.

There can be little doubt that flexible foresight became a key human survival strategy ( Suddendorf 2006 ) and that humans have taken the quest for securing future survival to a new level. Consider, for example, Norway's construction of a ‘doomsday’ seed bank designed to withstand global catastrophes to protect all known varieties of the world's crop. Yet, in spite of our strong reliance on foresight, humans are notoriously fallible with our predictions. For example, we display systematic errors in predicting the affective consequences of future action. Gilbert & Wilson (2007) recently reviewed these biases and concluded that several characteristics of mental simulation are the main contributors to these pervasive errors. Simulations tend to be unrepresentative, since they are often based on the most recent or most salient aspects of episodic memory, rather than on the most representative sampling. They often tend to reflect the gist of an event but fail to represent many details, and they often fail to take into account different future contexts in which events occur. The systematic biases in misapprehending how we will feel when a future event becomes the here and now is an essential problem for anyone in pursuit of happiness, and Gilbert (2006) offered the following simple solution to the dilemma: ask someone else who is or has been where we project ourselves as going. Their advice, on average, will be a far better guide to what it will be like than one's own biased simulations. This resonates with our proposal that one adaptive function of language may be to allow us to improve our mental time travel by drawing on the descriptions others can offer of what the future may hold. Undoubtedly, language allows us to learn from other individuals' experiences as no other animal can.

Whether this also leads to greater happiness remains debatable. Unlike, perhaps, psychologists, evolution does not care for our happiness and errors in affective forecasting are only errors if they negatively affect survival and reproduction. As with reconstruction of past events, it is not accuracy per se but the fitness consequences of foresight that matter. Systematic biases and errors may thus, in fact, serve adaptive purposes. For example, humans generally tend to expect more positive events than is rational to expect, and this optimism bias has specific neural correlates ( Sharot et al . 2007 ). Although we may often be wrong with our optimism, this positive mental stance may have profound selective advantages over a more realistic (and possibly bleak) perspective. Foresight, fallible and biased as it often may be, must have made a net positive contribution to fitness. Indeed, it is arguably our most formidable weapon. The price we might have had to pay for this are unique psychological stresses and disorders (e.g. Brune 2006 makes the case for obsessive–compulsive disorder).

In this review, we proposed that human language evolved in the first instance for the sharing of mental time travel. After reviewing the growing neuroscientific evidence linking episodic memory and episodic foresight, we discussed data from non-human animals. On current evidence, mental time travel, as with language, appears to reflect something uniquely human. This is not to say, however, that language and mental time travel are drawing on the same neurocognitive machinery. Language and mental time travel are clearly dissociable in modern humans. The total collapse of our faculty for mental time travel leaves a linguistically sophisticated person such as Clive Wearing trapped in the present and unable to conduct his life without the extensive support of others who can look ahead.

Acknowledgments

The writing of this manuscript was supported in part by an Australian Research Council Discovery Grant (DP0770113) to T.S.

One contribution of 18 to a Theme Issue ‘Predictions in the brain: using our past to prepare for the future’.

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Time Travel Mater

Travel Back in Time to the Start of Radiator Springs with Mater

Time Travel Mater [3] is the 11th short in the Cars Toons series , which was first aired on June 5, 2012 on Disney Channel. It was officially premiered ten days later, on June 15 at the Disneyland Resort in Blue Sky Cellar at Disney California Adventure park to celebrate the opening of Cars Land , and first aired on ABC the next day. [4]  It was included on the DVD and Blu-ray of Pixar Short Films Collection Volume 2 . The episode features Mater telling a story according to which he time traveled, back to the beginnings of Radiator Springs , thus reusing part of the abandoned concept of the unmade Tall Tale Backwards to the Forwards . Stanley, the founder of Radiator Springs, appears alive in this episode when Mater time travels. It is the third production of Pixar Canada . [5] The music is composed by Mark Watters. [6]

• 2.1 Additional Voices
• 5 References

Lightning McQueen and Mater are in front of the Courthouse when Lizzie drives by. She says good morning to Lightning and Mater in a rude way, but she says it in a nice way to the statue of Stanley . Lightning McQueen asks Mater how Lizzie and Stanley met. Mater replies by telling one of his stories, which "all started last week."

The story starts with him putting up a new town sign with a clock on it. The sign falls on Mater, and the clock ends up on his "nose." Mater sneezes, and then disappears.

He ends up inside the Tail Light Caverns. He exits the caverns to go tell everyone back in town. However, when he does, he can't find the town, but he does see a car at a nearby spring. When Mater gets closer to the car, he discovers that it's Stanley! Stanley asks Mater if he needs a radiator cap. When Mater says no, Stanley leaves to go to California in search of customers. Mater realizes that if Stanley didn't stay, there wouldn't be a Radiator Springs in the future! So, he goes to the present, gets Lightning, and they both go back to the past, where Mater removes Lightning's radiator cap and calls out to Stanley, saying that there's a car that needs a radiator cap (Lightning). So, Stanley gives Lightning a new radiator cap. Two cars that also need radiator caps enter the scene, and Stanley leads them to the spring, where the cars get a "drink." Mater suggests that Stanley build a town right next to "this here radiator spring." Stanley likes the idea, and even comes up with a name for the town right then and there: Radiator Springs . While Stanley was planning how to build the town, Mater and Lightning travel to the future to speed things up a bit.

Mater and Lightning then travel to 1927. Stanley shows them the town. Then, Stanley takes note of a Model T (which turns out to be Lizzie) that arrives in town. Lizzie breaks down, so Mater helps her out. Lizzie sees Lightning and appears to be falling in love with him, and Mater realizes that if Lizzie falls in love with Lightning, then she won't fall in love with Stanley, and then Stanley will leave town, and there'd be no Radiator Springs! But then Lizzie asks Lightning to get out of the way, revealing that she had her eye on Stanley, not Lightning, as Mater thought. Lightning introduces Lizzie and Stanley. Stanley took Lizzie to his spring so that she could get a drink. Then he took her to get a new radiator cap. Then, Lightning and Mater leave.

They reappear in Radiator Springs at the time that Lizzie and Stanley get married. After getting married, they went honeymooning at Comfy Caverns. Then, Mater and Lightning leave, and Mater finishes his story.

Lightning says that there's no such thing as time travel, but then Lizzie comes and thanks Lightning for introducing her and Stanley. Mater says, "And that's how you make history."

• Larry the Cable Guy : Mater
• Keith Ferguson : Lightning McQueen
• John Michael Higgins : Stanley
• Katherine Helmond : Lizzie

Additional Voices [ ]

• Jess Harnell
• James Kevin Ward
• The first and, so far, only Cars Toons: Mater's Tall Tales episode with Lizzie in it, and actually the first time she played a role as a secondary tritagonist.
• The first episode without any pitties and without Mia and Tia in it. This may be due to the fact that being modernized cars, they weren't even built (born) yet.
• The first episode not to have Mater say something similar to his line: "Don't you remember? You was there too!"
• The first episode with Lightning McQueen in his World Grand Prix paint job. It is also the first time it has shown McQueen's hood open, showing his motor.
• Tail Light Caverns, Stanley's early settlement, and Comfy Caverns, all places which had never been seen before, are sets that come from Cars Land . Their appearance in the short enables to establish them as canon, and perhaps to promote the attraction.
• This is the second Cars Toons: Mater's Tall Tales episode that has Mater's story in black and white. The first one is Mater Private Eye . However, in this episode, it's not Mater's whole story that's in black and white. After Mater drives out of the Tail Light Caverns, everything was in sepia tones (a common color tone used in "flashback" sequences). When he and McQueen time travel to when Stanley's early settlement was made, everything was in black and white. When Mater and McQueen time travel to when Lizzie and Stanley get married, the entire color scheme is a homage to the two color Technicolor processes that were used in movies from 1917 to 1936.
• The alternating color schemes used in this story seem to be an homage to how photographs of each particular time period looked. This gave each era that Mater visits its own unique visual identity. It was likely implemented to avoid confusion.
• When Mater puts the sign with the clock up, it then leans towards him and falls on him. This is a reference to the first film when he tries to put his sign upright, but it leans to the other side; and in Cars 2 when he puts the Leaning Tower of Pisa upright, but it then leans to the other side.
• Also, the clock on Mater's "nose" is a reference to  Cars 2 when the lemons planted a bomb on his "nose."
• The story of Radiator Springs seen in Time Travel Mater was used before the movie Cars . [7]
• Mater's "Whoa!" when he notices he's in the Tail Light Caverns is the same sound he makes when he sees the moon in  Moon Mater .
• The scream that Mater makes when he sees that there would be no town in the future if Stanley doesn't stay is the same scream he makes when he is fighting the I-Screamer in  Monster Truck Mater .
• The episode may be a homage to Back to the Future . This may be because Mater goes really fast to travel through time and he warps into the past with an electrical reaction.
• This short is on the Pixar Short Films Collection Volume 2 DVD and Blu-Ray.

Gallery [ ]

References [ ]

• ↑ Disney Channel program on Zap2it.com
• ↑ 'Pixar Shorts Volume 2' List of Included Shorts Announced
• ↑ Cars Official Website (see screenshot )
• ↑ Travel Back in Time with Mater – ‘ Time Travel Mater ’ to Premiere June 15 at Disney California Adventure Park and June 16 on ABC
• ↑ 2011 BC Film and TV Productions
• ↑ Mark Watters's profile on ASCAP's official website
• 1 Inside Out 2

HYPOTHESIS AND THEORY article

Language, memory, and mental time travel: an evolutionary perspective.

• School of Psychology, Faculty of Science, University of Auckland, Auckland, New Zealand

Language could not exist without memory, in all its forms: working memory for sequential production and understanding, implicit memory for grammatical rules, semantic memory for knowledge, and episodic memory for communicating personal experience. Episodic memory is part of a more general capacity for mental travel both forward and backward in time, and extending even into fantasy and stories. I argue that the generativity of mental time travel underlies the generativity of language itself, and could be the basis of what Chomsky calls I-language, or universal grammar (UG), a capacity for recursive thought independent of communicative language itself. Whereas Chomsky proposed that I-language evolved in a single step well after the emergence of Homo sapiens , I suggest that generative imagination, extended in space and time, has a long evolutionary history, and that it was the capacity to share internal thoughts, rather than the nature of the thoughts themselves, that more clearly distinguishes humans from other species.

Introduction

Memory, in all its forms, is critical to language. Because language is sequential, we need short-term memory (working memory) as a moving window of consciousness if we are to integrate over time to make sense of sentences, and indeed stories. Long-term memory is itself divided into several components, each also serving a necessary function in linguistic communication. First is the distinction between unconscious and conscious memory. The rules of language are in large part overlearned and unconscious, and even linguists have not completely articulated how those rules work. They operate largely automatically; we know intuitively how to construct a sentence, but do not really know how we do it. Conscious memory is sometimes also referred to as declarative memory, or memory that can be declared. If part of memory is declarative memory, so part of language is memorial declaration.

Conscious memory can, in turn, be divided into semantic memory, or basic knowledge, and episodic memory, which is memory for personal episodes. Broadly speaking, semantic memory is a combined internal dictionary and encyclopedia, while episodic memory is an internal diary that records personal experiences ( Tulving, 1972 ). Language draws on both. Semantic memory includes the large data bank of the tens of thousands of words that we use to express our thoughts, as well as providing kinds of knowledge that we can and do talk about—the political situation, the history of Ireland, differential calculus. It is episodic memory, though, that gives language many of its most distinctive properties.

Episodic memory is part of the more general capacity for mental time travel , a term probably first used by Tulving (1985) and elaborated by ( Suddendorf and Corballis, 1997 , 2007 ) We can travel mentally into a personal future as well as a personal past, and even create purely fictional events that need have no reference to specific time (“Once upon a time”). These are constructive acts—even episodic memory itself is better regarded as a construction than as a replay, and not always accurate. As Neisser (2008) put it, “Remembering is not like playing back a tape or looking at a picture; it is more like telling a story” (p. 88). Mental time travel is in turn founded on the understanding of space and time, with events encoded according to what happened, where it happened, and when it happened (the www criterion; Suddendorf and Corballis, 2007 ). I argue in this article that mental time travel provides the basis for the generative and creative aspects of language, allowing us to communicate about past and future, and indeed tell stories that need have no basis in reality.

Language, whether spoken or signed, can then be considered a device by which we share our mental travels—as Dor (2015) put it, it allows “the instruction of imagination.” Indeed, the recursive, generative nature of language may itself derive, not from the structure of language itself, but from the structure of the imaginative thoughts that underlie it.

Mental Time Travel and Universal Grammar

This view has some connection to the approach to language known as the Minimalist Program ( Chomsky, 1995 , 2015 ), but it also differs in important ways. A central tenet of the Minimalist Program is that language is structured by universal grammar (UG), which is common to all peoples. UG is the primary component of I-language , where the “I” is taken to suggest “internal,” “individual,” and “intensional.” Its main property is merge , a recursive operation that allows elements to be combined, and the mergers themselves to be merged, in a progressive fashion to build structures of any desired degree of complexity. The notion of UG has been criticized on the grounds that the 6,000 or so languages of the world have diverse grammars, and do not seem to conform to an overriding grammatical structure, forcing one commentary to conclude that “the emperor of UG has no clothes” ( Evans and Levinson, 2009 ).

In his preface to the most recent edition of The Minimalist Program , though, Chomsky (2015) makes clear his view that UG is fundamentally a property, not of communicative language itself, but rather of thought, and is only incidental to communication. He writes: “It is a familiar fact ( sic ) that the complexity and variety of language appears to be localized overwhelmingly—and perhaps completely—in externalization (p. xi),” where “externalization” refers to the formation of specific languages from the underlying I-language. By extricating UG from communicative language itself, Chomsky appears to have sidestepped the problem of linguistic diversity. He also suggests that UG arose in a narrow window of time, shortly before the exodus of our species from Africa 50,000 to 80,000 years ago—a view endorsed by a number of anthropologists (e.g., Hoffecker, 2007 ; Tattersall, 2012 ). Chomsky (2010) even suggests that the emergence of the operation merge occurred in a single individual whom he whimsically names “Prometheus.”

By reducing the essence of UG to the single operation of merge, Berwick and Chomsky (2016) claim also to have overcome the seemingly intractable problem of how a faculty as complex as language could have evolved in a single step, in defiance of Darwinian evolution. As they put it, “… narrowly focusing the phenotype in this way greatly eases the explanatory burden for evolutionary theory—we simply don’t have as much to explain, reducing the Darwinian paradox” (p. 11). They go on to write, though, that “Any residue of principles of language not reducible to Merge will have to be accounted for by some other evolutionary processes—one that we are unlikely to learn much about, at least by presently understood methods …” (p. 71); and they insist that “there is no room in this picture for any precursor to language” (p. 71).

My suggestion here, though, is that the recursive, generative nature of language may reside, not in a specialized I-language or UG, but in mental time travel itself, or more generally in our capacity to entertain thoughts not tied to the present. Such thoughts are the essence of imagination, defined by the Merriam-Webster Dictionary as “the act or power of forming a mental image of something not present to the senses or never before wholly perceived in reality.” Imaginative thoughts carry the generativity and recursiveness exemplified in our reconstructions of the past, in mental anticipations of the future, and perhaps most commonly in the fabrication of stories ( McBride, 2014 ; Boyd, 2009 ). In providing the means to communicate such events, language requires the property of displacement , the capacity to refer to the non-present ( Hockett, 1960 ), and arguably the most important driver of its evolution. Again, though, this capacity may reside not in language itself, but rather in the imaginative construction of mental events.

Uniquely Human?

Tulving (2002) view on the emergence of episodic memory echoes Chomsky’s account of the late arrival of UG itself:

Many nonhuman animals, especially mammals and birds, possess well-developed knowledge-of-the-world (declarative, or semantic, memory) systems and are capable of acquiring vast amounts of flexibly expressible information. Early humans were like these animals, but at some point in human evolution, possibly rather recently, episodic memory emerged as an “embellishment” of the semantic memory system (p. 7).

By extension, mental time travel has also been attributed uniquely to humans and denied to all other species ( Suddendorf and Corballis, 1997 , 2007 ).

More recently, I have argued that, on the contrary, the origins of mental time travel may go far back in evolution ( Corballis, 2013 ; but see also Suddendorf, 2013 ). This change of opinion is based partly on behavioral evidence for mental time travel in a diverse range of species, including great apes ( Martin-Ordas et al., 2010 ; Beran et al., 2012 ; Janmaat et al., 2014 ), meadow voles ( Ferkin et al., 2008 ), rats ( Wilson et al., 2013 ), ravens ( Kabadayi and Osvath, 2017 ), scrub jays ( Clayton et al., 2003 ), and even cuttlefish ( Jozet-Alves et al., 2013 ). In one recent study, rats remembered many different episodes over intervals of up to 45 min without any evidence of decline in performance ( Panoz-Brown et al., 2016 ).

Role of the Hippocampus

Evidence also comes from neuroscience, much of it focused on the hippocampus, and on parallels between human and animal hippocampal function. In humans, the hippocampus plays a critical role in declarative memory, including episodic memory and its extension to episodic future thinking. People with destruction of the hippocampus show striking difficulties in recalling past events or imaging future ones ( Tulving, 2002 ; Wearing, 2005 ; Corkin, 2013 ), as well as in imagining fictitious scenes ( Hassabis et al., 2007 )—although impairment of the ability to imagine personal past or future events has also been linked to damage of the ventromedial prefrontal cortex ( Bertossi et al., 2016 ).

Brain imaging confirms the role of the hippocampus when people are asked to recall previous episodes or to imagine future ones ( Addis et al., 2011 ; Martin et al., 2011 ). Again, though, areas other than the hippocampus are also active, including the angular gyrus, the medial frontal cortex, and the posterior cingulate ( Rugg and Vilberg, 2013 ; Karapanagiotidis et al., 2017 ). The particular role of the hippocampus may lie in what has been termed scene construction ( Maguire et al., 2016 ), the drawing together of dispersed information for autonoetic inspection. McCormick et al. (2018) suggest that hippocampal function goes beyond mental time travel to mind-wandering more generally, and lies at “the heart of mental life” (p. 2745).

In the rat, the hippocampus is well known to play a role in spatial location. So-called “place cells” record the animal’s location in space, creating a “cognitive map” ( O’Keefe and Nadel, 1978 )—or a kind of internal GPS system. The population of active cells shifts as the animal moves around, recording a trajectory. It has become clear, though, that the activity of place cells is not restricted to the present, but can convey information about past trajectories or even trajectories that it did not take, perhaps representing future plans or simply exploratory movements. Such trajectories have been described as “replays,” although in many cases they might be better described as preplays or mental explorations not specifically located in time. Reviewing the evidence, Moser et al. (2015) write that:

“the replay phenomenon may support ‘mental time travel’ … through the spatial map, both forward and backward in time (p. 6).”

Hippocampal activity, in conjunction with the neighboring entorhinal cortex, is also tagged in other memory-like ways. Place cells respond not only to specific locations, but also to nonspatial features of past events, such as odors ( Igarashi et al., 2014 ), touch sensations, and the timing of events. Similar associations seem to be tagged to place cells in the human hippocampus. In one study, human patients about to undergo surgery had electrodes implanted in cells in the medial temporal lobe, in an attempt to locate the source of epileptic seizures. They were given the task of navigating a virtual town on a computer screen and delivering items to one of the stores in town. They were then asked to recall only the items and not the location to which they were delivered. The act of recall, though, activated place cells corresponding to that location, effectively mirroring the replay of place-cell activity in the rat brain ( Miller et al., 2013 ). In a similar study using subdural electrodes, Vaz et al. (2019) found that oscillatory activity between the medial temporal lobe and the temporal associative cortex were coupled when people retrieved memories of associated items.

The spatial function of the hippocampus is modulated by activity in the neighboring entorhinal cortex. So-called grid cells in the medial entorhinal cortex code locations corresponding to spatial features such as spatial scale and orientation, and other cells code shape and color, proximity to borders, and direction in which the head is facing ( Diehl et al., 2017 ). These cells operate in a modular fashion, creating an enormous number of combinations reflecting the possible spatial contexts in which an animal may find itself. Moser et al. (2015) liken this to “an alphabet in which all words of a language can be generated by combining only 30 letters or less” (p. 11). This is suggestive of the generativity of language itself.

Recordings from the rat hippocampus also reveal what has been termed “time cells,” which respond in a coordinated fashion to code the relative times in which events have occurred in the past. The pattern itself changes over time as the temporal context changes ( Eichenbaum, 2017 ). This can be observed experientially in our own memories of when things happened, gradually losing immediacy and detail, both spatial and temporal. The hippocampal coding of space, time and context in both humans and animals suggest that episodic mental travel may long predate human evolution.

The coding of episodic memories can be specified in time rather than space, and need not be visual. We might mentally replay a memory of a concert, but the ordering of individual pieces is not marked by different locations. A similar phenomenon has been reported in rats, based on their fine discrimination of different odors. Panoz-Brown et al. (2018) presented rats with sequences of specific odors in different contexts. Later, when presented with one given context, they were able to select the second from the last odor in the sequence as distinct from a different odor from the sequence, while given a different context they were able to select the fourth from the last odor in the sequence. The number of odors in the sequences varied from trial to trial, making it impossible to specify the required odor when it occurred. The animals must have held the entire sequence in memory and replayed it in order to select the required odor. Performance was well above chance even after the lapse of an hour between presentation and test and was little affected by interference. Performance dropped significantly with chemical suppression of hippocampal activity. These properties imply robust hippocampal-dependent episodic memory for sequences of events defined by the order in which they occurred and not by locations within sequences, although the retrieval of the sequences themselves depended on spatial context.

The evidence for mental time travels in nonhuman animal raises the question of whether they are conscious. To Tulving, episodic memories are what he called autonoetic , or part of personal consciousness, and the same might be said of mental time travel more generally. If such travels are not exclusive to humans, contrary to what Tulving believed, can we conclude that animals too are conscious of their mental time travels? The commonality between what we know of the role of the hippocampus through electrophysiology in animals and through brain imaging, and indeed through cases of implanted electrodes in humans, seems to give little reason to doubt that in both cases the experience is conscious. Nevertheless, this is likely to remain a contentious issue.

The role of the hippocampus is not restricted to episodic information, but includes semantic information as well—indeed the replay of the past and prediction of the future is probably always a mix of the episodic and the semantic ( Klein, 2013 ). Duff and Brown-Schmidt (2012) review evidence from studies of hippocampal amnesia that the hippocampus is critical to language itself, in binding information from different sources and supplying a flexibility of operation. Piai et al. (2016) add evidence from recording of hippocampal theta during sentence processing, and suggest that the hippocampus should be considered part of the language network, a conclusion endorsed by Covington and Duff (2016) . Individuals with large-scale destruction of the hippocampus can retain the basic ability to speak, but loss of episodic memory, and of mental time travel more generally, severely restricts communicative content ( Wearing, 2005 ; Corkin, 2013 ), and word learning becomes sparse and slow ( Warren and Duff, 2019 ). The hippocampus not only contributes to the generative and integrative aspects of language, but also provides for displacement, the power of language to refer to events removed from the present in time and space.

Expansions of Scale

A good deal of human language has to do with events or material far displaced from the present; we can tell of events from childhood, experiences in far-away places, or plans for a distant future. This suggests that mental time travel itself may have expanded in scale beyond that evident in other species, and indeed this expansion may have partly driven the evolution of language itself–although such a claim may well simply reflect what has been called the “human superiority complex” ( Villa and Roebroeks, 2014 , p. 1). Many animals and birds do appear to have extensive understanding of space. Dolins et al. (2014) assessed the ability of humans and chimpanzees to learn complex virtual environments and navigate through them, and found chimpanzees generally on the same level as children, and one chimpanzee (Panzee) was more accurate than human adults. Nevertheless, it is likely that the capacity for mental excursions probably expanded in both time and space, and indeed content, over the past six million years or so with the emergence of the hominins, and especially the genus Homo . Humans probably have more extensive memories, plans, and fantasies than do rats and chimpanzees.

In human evolution, a critical period for such an expansion, and indeed for the pressure to communicate about it, was probably the Pleistocene, dating from some 2.8 million to 12,000 years ago, when our forebears adapted to a post-arboreal existence, with an emergent hunter-gatherer pattern. This resulted in long delays between the acquisition and the use of tools, as well as geographical distance between the sources of raw material for tools and killing or butchering sites ( Gärdenfors and Osvath, 2010 ). The hunter-gatherer lifestyle involved frequent shifts of camp as resources were depleted, forcing the group to move on to another more abundant region—a pattern still evident in present-day hunter-gatherers ( Venkataraman et al., 2017 ).

Migrations increased in scale during the Pleistocene, adding further to the demands of space, time, memory, and planning, and brain size also tripled during this era ( Klein, 2009 ). The dispersals of early Homo from Africa reached the Loess Plateau in China by 2.1 million years ago ( Zhu et al., 2018 ), and other widespread regions in Europe and Asia in the previous millennium ( Kappelman, 2018 ). Later waves of migration of Homo sapiens out of Africa began from about 120,000 years ago ( Timmermann and Friedrich, 2016 ), eventually inhabiting most of the globe. Of course, humans are not entirely alone in undertaking large-scale migrations. Birds, whales, wildebeest, and even butterflies migrate vast distances, but these are largely seasonal (as are some human migrations, especially of the wealthy) and based on instinct rather than planning. The Clark’s nutcracker is said to cache some 33,000 seeds in around 7,000 locations every fall and relies on spatial memory to recover them over the winter ( Kamil and Balda, 1985 ). Evidence from scrub jays, moreover, suggests that caching behavior involves mental time travel both forward and backward in time ( Clayton et al., 2003 ). Even so, the human ability to recapture the past and imagine the future, at least with respect to time and flexibility, probably exceeds that of any other living animal.

Perhaps the ultimate stretch is the ability to imagine events outside of the lifespan, although this is a matter of semantic rather than episodic time travel—or what Klein et al. (2010) call known time as distinct from lived time . Historical records have allowed us to create stories and movies reconstructing events long in the past, and even to imagine ourselves as spectators. Physicists have even dared to envisage the origins of the universe. We also imagine life after death. Pettitt (2018) notes that even chimpanzees follow certain mortuary behaviors on finding a dead conspecific, including staying by the body for many hours, giving alarm calls, and showing signs of grief, as though aware of the permanence of death. The parallels with observation of human reactions to death, he suggests, “are striking” (p. 6). In humans, this is further transformed into burial and rituals associated with it, and in the modern world most of these rituals seem to have to do with “transforming the deceased into some form of afterlife” (p. 6). Evidence for the deliberate disposal of corpses, implying a sense of one’s own mortality, has been dated from around 600,000 to 300,000 years ago ( Egeland et al., 2018 ).

Communication

These expansions in time and space no doubt added to the pressure to communicate, so that experiences not restricted to the immediate environment could be shared, and indeed make up much of what we call culture. Communication of our internal thoughts is what Chomsky (2015) called externalization . Again, the critical period of its development was probably the Pleistocene. Beginning with the hunter-gatherer phase, and extending to more complex modes of existence through the development of farming and manufacture, life depended increasingly on cooperation and the sharing of experience, plans, and mental exploration leading to stories. The main requirement for communicating internal mental events, though, was a signaling device capable of matching the generativity and complexity of experience itself. Most animals have only a limited range of systems permitting intentional output. Neurophysiology increasingly reveals the complexity of the rat’s excursions in time and space, but the animal has no obvious way to convey those excursions to others. Songbirds are something of an exception, with often complex songs, but these seem adapted to sexual or identification signaling rather than to the sharing of memories or plans. They appear not well adapted to communicating about events.

Even non-human primates have very limited vocal repertoires, dedicated for the most past to instinctive or emotional calls. Seyfarth and Cheney (2018) identify different baboon calls signaling identity, social rank, kin and various social interactions, and go so far as to suggest that the sequences of calls between different individuals constitutes a system that is “ discrete, combinatorial, and rule-governed ” (p. 28, their italics), with the implication that it may be a precursor to grammatical language itself. But as Godfrey Smith (2018) points out, the combinatorial structure is evident in the interweaving of calls between individuals, and not in individual calls themselves.

The problem of communication is largely one of production rather than reception. The understanding of spoken words can actually be quite high in nonhuman animals. Border collies have been shown to respond to verbal requests to select a particular object from an otherwise uninhabited room and returns it to a given location. One border collie called Rico has a receptive vocabulary of over 200 items ( Kaminski et al., 2004 ), while another is said to respond to the names of 1,022 objects ( Pilley and Reid, 2011 ). Kanzi, a bonobo, appears able to respond appropriately to simple spoken requests, such as “Could you carry the television outdoors?” or “Could you put the pine needles in the refrigerator?” ( Savage-Rumbaugh et al., 1998 ).

None of these species, though, can speak. A fundamental problem is that most mammals and apes, with the exception of humans, have at best limited voluntary control over voicing. Chimpanzees seem to have some ability to modify emotional calls (e.g., Slocombe and Zuberbühler, 2005 ) but little evident capacity to produce or learn anything like spoken words, either in number or complexity. According to Petkov and Jarvis (2012) , only parrots approach humans as “high vocal learners,” with songbirds not far behind, while nonhuman primates are merely “limited vocal learners.” The origins of communicative language may lie in the production of visual signals, rather than vocal ones ( Corballis, 2017 ).

Chimpanzees and bonobos trained to use lexigrams to refer to objects and actions are able to use these, along with gestures, to make requests and even to comment on past and future events, or on other individuals ( Lyn et al., 2011 ). In one study, the chimpanzee Panzee, who uses a keyboard containing 256 lexigrams, watched an experimenter hide objects in the woods outside her enclosure. After imposed delays of up to 16 h, she interacted with a person who did not know that an object had been hidden, pointed to the lexigram representing the object, pointed outdoors, and led the person to where the object was hidden, continually pointing as she went ( Menzel, 1999 ). There were 34 such trials, with different objects and locations. Panzee, therefore, seems capable not only of mental time travel, but also of displacement in her ability to communicate.

Chimpanzees in the wild gesture prolifically to each other, in an intentional fashion. Byrne et al. (2017) report evidence for repertoires of at least 66 natural gestures in the chimpanzee, 68 in bonobos, 102 in gorillas, and 64 in orangutans, considerably larger than repertoires of vocal calls. Many of those observed in the wild are common to the different species, suggesting that they are based on phylogeny rather than social learning, but they are also greatly augmented in the case of apes trained to use gestures or lexigrams. The gorilla Koko, for example, is said to use and understand over 1,000 signs ( Patterson and Gordon, 2001 ).

Gestures are also more obviously intentional than are vocal calls, and are in that sense language-like, but they are more deictic than referential ( Byrne et al., 2017 ), and occur in short sequences of seldom more than one or two, with no evidence of syntactic structure.

The ability to generate complex sequences probably emerged in human evolution with pressure to communicate about more complex events or plans. Given our ape physiognomy, a natural way to communicate mental time travels would be through pantomime, and apes do seem capable of limited pantomime. Russon and Andrews (2001) identified 18 different pantomimes produced by orangutans in a forest-living enclave in Indonesia, 14 addressed to humans and four to fellow orangutans. These included mimed offers of fruit, enacting a haircut, and requests to have their stomachs scratched by scratching their own stomachs and then offering a stick to the prospective scratcher. A chimpanzee in the wild watched her daughter trying to use a stone to crack a nut and then enacted the operation to show her how to do it properly ( Boesch, 1993 ). Tanner and Perlman (2017) also note that gorillas combine gestures in sequence creatively and interactively, although this seems to have more to do with play and personal display than with propositional communication, and may be the origin of music and dance rather than of language itself. Nevertheless, it seems likely that language did emerge from primate gestures rather than vocal calls. Based on studies of gestural communication in apes, Tomasello ( 2008 , p. 55) refers to gestures as “the original font from which the richness and complexities of human communication and language have flowed.”

But it was probably during the Pleistocene, with the so-called “cognitive niche” ( Pinker, 2010 ) as an adaptation to the more dangerous and uncertain environment, that gesture, perhaps originally as pantomime, emerged as a powerful way to share episodic events, whether past, future, or simply invented. Donald (1991) referred to the “mimetic culture” of the early Pleistocene. Pantomime involves whole-body action to represent events, but the essence of an event in space and time could be relayed more economically just using gestures of the hands and arms, which were freed from any involvement in locomotion with the advent of bipedalism. Gestural language may well have developed to resemble modern sign languages invented by deaf communities. Emerging sign languages typically begin with pantomime, but signs are then conventionalized so that many no longer provide a pictorial indication of what they stand for ( Burling, 1999 ). Conventionalization may be at the cost of transparency but leads to greater efficiency. On an evolutionary scale, speech itself may be the end product of a conventionalization process that began with pantomime, as our forebears gained great intentional control over voicing.

Nevertheless, bodily gesture remains an integral accompaniment to speech, even in the blind ( Iverson and Goldin-Meadow, 1998 ). They can improve the speaker’s lexical access and fluency ( Rauscher et al., 1996 ), and even reduce the speaker’s working memory load ( Goldin-Meadow et al., 2001 ; Wagner et al., 2004 ). Some have gone so far as to suggest that manual gestures were in equal partnership with vocalization throughout the evolution of language (e.g., Kendon, 2011 ; McNeill, 2012 ), but the evidence from primates suggests that manual gestures preceded vocalization in the evolution of intentional communication ( Corballis, 2014 ). It remains something of an open question when speech evolved to the level of articulation evident in Homo sapiens . It is possible, even likely, that the one of our closest forebears, the Neanderthals, were capable of speech ( Dediu and Levinson, 2013 ), but their articulation was probably relatively more restricted through non-optimal development of the vocal tract ( Gokhman et al., 2019 ).

Conclusions

The main thesis of this article is that imagination, initially in the form of mental travels in time and space, provide the recursive and generative properties underlying language itself. These mental travels are extensions of episodic memory and make up much of what we call imagination. Unlike Chomsky’s concept of I-language, imagination probably has a long evolutionary history, as is becoming evident from behavioral studies in a wide variety species, along with work on the role of the hippocampus and related structures in rodents. Communicative language is then the externalization of imagination, and different languages use different conventions to express the products of imagination. This approach differs from that of Chomsky and colleagues also in that both imagination and its externalization have a strong evolutionary basis in spatial understanding and bodily movement, whereas I-language is regarded as abstract and symbolic, creating what is known as the problem of grounding ( Harnad, 1990 ). How can a person relate abstract symbols to events in the real world?

In the view adopted here, symbolic representation arises in the process of externalization, rather than in innate symbolic dispositions. Internal representations of objects, actions and events are for the most part similar across different peoples (corresponding to the “universal” of UG), but the symbols to represent them differ markedly. Some 6,000 languages exist in the world, each more or less incomprehensible to almost every other. As suggested earlier, those symbols probably begin as iconic, or pantomimic, but become increasingly arbitrary and abstract in the process of conventionalization. This process increases efficiency, but may also be driven by exclusiveness, acting as a barricade to outsiders. Language operates in part as a secret code. Sign languages are more transparent, but even they conventionalize differently. Nevertheless, it is also becoming clear that many speech sounds are non-arbitrary, and show similar associations across language groups ( Blasi et al., 2016 ).

The symbols that arise in the process of externalization themselves become part of our semantic memories; we can imagine the word “dog” as easily as we can imagine the animal with which it is associated. We can play with words just as we play with toys. The use of abstract symbols may well have influenced cognition itself. Mathematics may be an extreme example, in which abstraction has developed to the point that a single symbol, say x or y, can stand for variables of wide reference. But the invention of abstract symbols was not the outcome of some singular event in our evolutionary past, but was the product of gradual evolution, perhaps leading to increased powers of reasoning and discourse.

Given that words themselves have become part of memory, the emergence of language may well have expanded our capacity for mental time travels, and perhaps especially for the imaginative extensions into fiction and storytelling. The capacity to communicate our mental excursions vastly exceeds that required for personal experience alone. To accommodate the information added through communication, including not only speech, but also the vast repertoire of information through books, films, television, and so forth, storage capacity itself must surely have expanded. The link between language and memory might, therefore, be considered bidirectional.

From the Bible to Chomsky, the emergence of language has been regarded as a singular event, bestowed uniquely on our own species. The concept of time, too, is also widely viewed as uniquely human. Donald (1991) , for example, wrote that “The lives of apes are lived entirely in the present” (p. 149), and much earlier Kohler (1927) , based on his studies of problem solving in chimpanzees, wrote that “the time in which chimpanzees live is limited in past and future” (p. 272). The poet Robert Browning, in his 1885 poem “A Grammarian’s Funeral,” prophetically wrote:

“He said, What’s time? Leave Now for dogs and apes

Man has Forever!”

Contrary to these commonly held views, the experience of past and future probably goes far back in the evolution of animals that move, and need to know where they are, where they have been, and where they might go next—along with what happened or might happen there. The sharing of this information, though, probably evolved later, as our forebears were forced for survival into their cognitive niche.

One-hundred and sixty years after the publication of Darwin’s (1859) Origin of Species , it is time to work toward an evolutionarily plausible understanding of how the human mind evolved.

Data Availability

All datasets analyzed for this study are included in the manuscript and the supplementary files.

Author Contributions

The author confirms being the sole contributor of this work and has approved it for publication.

Conflict of Interest Statement

The author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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Keywords: displacement, evolution, externalization, gesture, imagination, memory, mental time travel, universal grammar

Citation: Corballis MC (2019) Language, Memory, and Mental Time Travel: An Evolutionary Perspective. Front. Hum. Neurosci. 13:217. doi: 10.3389/fnhum.2019.00217

Received: 21 February 2019; Accepted: 14 June 2019; Published: 04 July 2019.

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*Correspondence: Michael C. Corballis, [email protected]

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‘Mental Time Travel’: Remembering the Past, Imagining the Future, and the Particularity of Events

• Published: 26 April 2014
• Volume 5 , pages 333–350, ( 2014 )

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The present paper offers a philosophical discussion of phenomena which in the empirical literature have recently been subsumed under the concept of ‘mental time travel’. More precisely, the paper considers differences and similarities between two cases of ‘mental time travel’, recollective memories (‘R-memories’) of past events on the one hand, and sensory imaginations (‘S-imaginations’) of future events on the other. It develops and defends the claim that, because a subject who R-remembers a past event is experientially aware of a past particular event, while a subject who S-imagines a future event could not possibly be experientially aware of a future particular event, R-memories of past events and S-imaginations of future events are ultimately mental occurrences of two different kinds.

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Self-Referential Memory and Mental Time Travel

Mental Time Travel

Hidden Duration: Time-Lag in the World and Mind

Suddendorf and Corballis ( 2007 ) 299. Published in the same year, Schacter et al. ( 2007 ) offer another very useful review of research on ‘mental time travel’ up to 2007.

For recent empirical work on relevant neurophysiological issues see e.g. Addis et al. ( 2007 ), Schacter et al. ( 2008 ), and Viard et al. ( 2011 ).

For recent work on relevant developmental themes see e.g. Perner et al. ( 2010 ).

For example, it has been suggested that people who suffer from amnesia—that is, people whose ‘mental time travel’ into the past is impaired—also have serious difficulties with engaging in ‘mental time travel’ in the other direction, i.e., with imagining the future (see e.g. Klein and Loftus ( 2002 )). Similarly, people who suffer from depression have a tendency to remember the past in over-general ways, and it has been suggested that they might be imagining the future in over-general ways also (see e.g. Williams et al. ( 1996 )).

See e.g. Suddendorf and Corballis ( 1997 ) and Suddendorf and Corballis ( 2007 ) who argue that ‘mental time travel’ is unique to humans; however, Corballis ( 2013a ) now argues for the opposing view, while Suddendorf ( 2013 ), in a reply to Corballis ( 2013a ), continues to defend their earlier joint position and insists that ‘on current evidence, it still appears that human mental time travel is profoundly special’ (151). Corballis ( 2013b ) responds in turn, concluding that ‘from a Darwinian perspective, it might sometimes be more prudent to assume differences in degree rather than kind as the default position, and seek evidence that this is not the case’ (152). The debate is clearly ongoing.

Matthen ( 2010 ) 8f.

Byrne ( 2010 ) 25.

Martin ( 2002 ) 403.

As far as recollective memories of past events and sensory imaginations of future events are concerned, one might try to capture this similarity with the help of the suggestion that both recollective memories of past events and sensory imaginations of future events ‘concern the self’s experiences in subjective space and time’ (Tulving ( 1993 ) 67). Tulving refers to mental states which display this characteristic as cases of ‘autonoetic consciousness’, and one might accordingly hold that both recollective memories of past events and sensory imaginations of future events are, when considered in isolation and from the experiencing subject’s own point of view, similar because they are both cases of ‘autonoetic consciousness’. For example, some such suggestion has recently been made by Szpunar ( 2010 ). (Thanks to the editor for suggesting that a reference to Tulving’s and Szpunar’s work might be relevant in the present context.)

For relevant empirical work see e.g. Addis et al. ( 2007 ).

Without awaiting any such further discussion, an opponent might object immediately that the Main Argument could not possibly be defended successfully because neither the Memory-Claim nor the Imagination-Claim could possibly be true. As far as the Memory-Claim is concerned, the opponent might suggest that ‘when recollecting a past event I am not experiencing the event, I am experiencing […] a recollection (a re-experience or mental simulation of reliving this event). So remembering [a past event does not] involve [any] experiential awareness [of the relevant past event]’ (referee’s report), and thus the Memory-Claim must be false. - Clearly, this is one possible view which one might take on memory in general and R-memory more specifically; however, it is not the only possible view. Quite on the contrary, at least at first sight it might seem possible to endorse the alternative view that when, for example, Anna recollectively remembers yesterday night’s dinner, she is in some way experientially aware of yesterday night’s dinner. Thus, I think the Memory-Claim does at least deserve a fair hearing, and I therefore hope the opponent is willing to suspend judgement on the tenability of the Memory-Claim until Section  4 below, where I will offer a more detailed discussion of that claim. (A further, even more detailed (paper-length) discussion of the Memory-Claim is offered in the Debus ( 2008 ).) We might hope that our opponent is prepared to grant us this much; nevertheless, the opponent might then move on to point out that the Imagination-Claim could not possibly be true, and that the Main Argument is therefore bound to fail regardless of the present concession. The opponent might suggest that the Imagination-Claim seems to presuppose that a future event could not possibly be a particular event. But then, ‘[w]hether a future event can be a particular event or not depends on how we individuate the event’ (referee’s report), and it might well be possible to individuate future events in such a way that future events can be thought of as particular events.—In response to the present objection, we should grant immediately that the individuation of future events is of great importance in the present context. However, even if it was possible to individuate future events in such a way that they should count as particulars, as the opponent holds it is possible to do, this by itself would not entail that the Imagination-Claim is false. For the Imagination-Claim talks of a subject’s experiential awareness of future events, and it holds that a subject could not possibly be experientially aware of a future particular event. Even if it was possible to individuate future events in such a way that they should count as particulars, it might still be impossible to be experientially aware of such future particular events. Thus, while the present suggestion rightly brings out the importance of the individuation of events for our discussion, we should wait with an assessment of the Imagination-Claim until the end of the next section, in which the Imagination-Claim will be discussed in greater detail. (Thanks to an anonymous referee for prompting the present set of comments.)

However, an opponent might hold that in some sense, we can and should say that Jo is aware that Bill is approaching, even though it is Bob who is coming towards her. And indeed, everybody will all agree that, in the situation as described, Jo (wrongly) takes the person coming towards her to be Bill; we might also say that Jo has a visual experience as of Bill approaching (even though it actually is Bob). However, the suggestion that we should say that Jo is aware that Bill is approaching (even though it is Bob who is coming towards her) does strike me as idiomatically problematic. Indeed, I think it would be idiomatically inappropriate to say this, because I take it that the verb ‘to be aware of’ is, in this respect, used in ways which are analogous to our usage of the verb ‘to know’: We might be very happy to say that Jo believes that Bill is coming towards her, but we certainly would not want to say that Jo knows that Bill is coming towards her (given that it is Bob who is); analogously, while we might be happy to say that Jo ‘takes it’ that Bill is coming towards her, we would not want to say that Jo is aware that Bill is coming towards her. This observation in turn does seem to give us reason to accept that the verb ‘to be aware of’ is factive , just as the verb ‘to know’ is. (Thanks to the editor for prompting the present comment.)

Davidson develops the view in his classic paper on ‘Events as Particulars’ (Davidson ( 1980a )). For a survey of alternative views, cf. Simons ( 2003 ). More generally, as Simons ( 2003 ) 357 points out, ‘philosophical discussion of the ontological category of events is relatively young. […] Most philosophically mooted categories are old, but events come to full prominence only in the twentieth century.’—I think it will be important to keep the category of events firmly on the list of core ontological and wider philosophical concerns during the twenty-first century, because it seems an important concept in various areas of contemporary philosophical interest. In any case, the argument presently under consideration clearly does rely on one particular (and in my view accurate) conception of what events are.

More precisely, we have meanwhile seen that we have good reason to accept the Memory-Claim and the Imagination-Claim, and I had so far assumed that the third premise of the Main Argument is uncontroversial. However, an opponent might hold that being experientially aware of a particular event and being experientially aware of a general type of event are not, as the third premise of the Main Argument has it, two different kinds of mental states, but are ultimately mental states of the same kind which just happen to be directed at different kinds of objects. Hence, so the opponent concludes, the third premise of the Main Argument is false.—In response, we might point out that at least at first sight, it seems plausible to assume that being experientially aware of a particular event and being experientially aware of a general type of event are two different kinds of mental states precisely because, as the opponent emphasizes, the two kinds of mental states have different kinds of objects. It seems plausible to assume that what kind a mental state is of is in part determined by what kind of object it is directed at. Indeed, it seems that anybody who wants to insist in the face of this intuitive idea that ‘ultimately’, mental states which have objects of different kinds nevertheless are mental states of the same kind, as our present opponent wants to do, will have to offer an explanation as to why relevant differences should be disregarded rather than taken into account. Thus, it seems plausible to conclude that as long as the opponent has not provivded any such reasons, we can continue to endorse the third premise of the Main Argument. (Thanks to the editor for prompting the present set of comments.)

Classic points of reference for this suggestion are Block ( 1980 ) and Shoemaker ( 1975 ). For an interesting more recent development of relevant ideas see also Shoemaker ( 2007 ).

This thought does, for example, motivate Davidson ( 1980b ) to develop his non-reductive materialist (or, in his own terminology, ‘anomalous monist’) account of mental events—see especially the introductory paragraphs of the relevant paper (Davidson ( 1980b ) 207).

Suddendorf and Corballis ( 2007 ) 299, my emphasis.

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Dorothea Debus

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Debus, D. ‘Mental Time Travel’: Remembering the Past, Imagining the Future, and the Particularity of Events. Rev.Phil.Psych. 5 , 333–350 (2014). https://doi.org/10.1007/s13164-014-0182-7

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Published : 26 April 2014

Issue Date : September 2014

DOI : https://doi.org/10.1007/s13164-014-0182-7

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