mental time travel
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psychology Psychology is the scientific study of mind and behavior. Psychology includes the study of conscious and unconscious phenomena, including feelings and thoughts. It is an academic discipline of immense scope, crossing the boundaries betwe ...
, mental time travel is the capacity to mentally reconstruct personal events from the past (
episodic memory Episodic memory is the memory of everyday events (such as times, location geography, associated emotions, and other contextual information) that can be explicitly stated or conjured. It is the collection of past personal experiences that occurred ...
) as well as to imagine possible scenarios in the
future The future is the time after the past and present. Its arrival is considered inevitable due to the existence of time and the laws of physics. Due to the apparent nature of reality and the unavoidability of the future, everything that currently ...
(episodic foresight / episodic future thinking). The term was coined by Thomas Suddendorf and Michael Corballis, building on
Endel Tulving Endel Tulving (born May 26, 1927) is an Estonian-born Canadian experimental psychologist and cognitive neuroscientist. In his research on human memory he proposed the distinction between semantic and episodic memory. Tulving is a professor emerit ...
's work on
episodic memory Episodic memory is the memory of everyday events (such as times, location geography, associated emotions, and other contextual information) that can be explicitly stated or conjured. It is the collection of past personal experiences that occurred ...
(Tulving proposed the alternative term chronesthesia ). Mental time travel has been studied by
psychologists A psychologist is a professional who practices psychology and studies mental states, perceptual, cognitive, emotional, and social processes and behavior. Their work often involves the experimentation, observation, and interpretation of how indi ...
, cognitive neuroscientists, philosophers and in a variety of other academic disciplines. Major areas of interest include the nature of the relationship between
memory Memory is the faculty of the mind by which data or information is encoded, stored, and retrieved when needed. It is the retention of information over time for the purpose of influencing future action. If past events could not be remembered, ...
and foresight, the
evolution Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...
of the ability (including whether it is uniquely human or shared with other animals), its development in young children, its underlying brain mechanisms, as well as its potential links to
consciousness Consciousness, at its simplest, is sentience and awareness of internal and external existence. However, the lack of definitions has led to millennia of analyses, explanations and debates by philosophers, theologians, linguisticians, and scien ...
, the
self The self is an individual as the object of that individual’s own reflective consciousness. Since the ''self'' is a reference by a subject to the same subject, this reference is necessarily subjective. The sense of having a self—or ''selfhood ...
, and
free will Free will is the capacity of agents to choose between different possible courses of action unimpeded. Free will is closely linked to the concepts of moral responsibility, praise, culpability, sin, and other judgements which apply only to actio ...
.


Overview, terminology, and relationship to other cognitive capacities

Declarative memory Explicit memory (or declarative memory) is one of the two main types of long-term human memory, the other of which is implicit memory. Explicit memory is the conscious, intentional recollection of factual information, previous experiences, and con ...
refers to the capacity to store and retrieve information that can be explicitly expressed, and consists of both facts or knowledge about the world (
semantic memory Semantic memory refers to general world knowledge that humans have accumulated throughout their lives. This general knowledge (word meanings, concepts, facts, and ideas) is intertwined in experience and dependent on culture. We can learn about n ...
) and autobiographical details about one's own experiences (
episodic memory Episodic memory is the memory of everyday events (such as times, location geography, associated emotions, and other contextual information) that can be explicitly stated or conjured. It is the collection of past personal experiences that occurred ...
). Tulving (1985) originally suggested that episodic memory involved a kind of ‘autonoetic’ (‘self-knowing’) consciousness that required the first-person subjective experience of previously lived events, whereas
semantic memory Semantic memory refers to general world knowledge that humans have accumulated throughout their lives. This general knowledge (word meanings, concepts, facts, and ideas) is intertwined in experience and dependent on culture. We can learn about n ...
is associated with ‘noetic’ (knowing) consciousness but does not require such mental simulation. It has become increasingly clear that both semantic and episodic memory are integral for thinking about the future. Mental time travel, however, specifically refers to the ‘autonoetic’ systems, and thus selectively comprises episodic memory and episodic foresight. The close link between episodic memory and episodic foresight has been established with evidence of their shared developmental trajectory, similar impairment profiles in
neuropsychiatric Neuropsychiatry or Organic Psychiatry is a branch of medicine that deals with psychiatry as it relates to neurology, in an effort to understand and attribute behavior to the interaction of neurobiology and social psychology factors. Within neurop ...
disease and in brain damage, phenomenological analyses, and with
neuroimaging Neuroimaging is the use of quantitative (computational) techniques to study the structure and function of the central nervous system, developed as an objective way of scientifically studying the healthy human brain in a non-invasive manner. Incre ...
. Mental time travel may be one of several processes enabled by a general scenario building or construction system in the brain. This general capacity to generate and reflect on mental scenarios has been compared to a theatre in the mind that depends on the working together of a host of components. Investigations have been conducted into diverse aspects of mental time travel, including individual differences relating to
personality Personality is the characteristic sets of behaviors, cognitions, and emotional patterns that are formed from biological and environmental factors, and which change over time. While there is no generally agreed-upon definition of personality, mos ...
, its instantiation in
artificial intelligence Artificial intelligence (AI) is intelligence—perceiving, synthesizing, and inferring information—demonstrated by machines, as opposed to intelligence displayed by animals and humans. Example tasks in which this is done include speech re ...
systems, and its relationship with
theory of mind In psychology, theory of mind refers to the capacity to understand other people by ascribing mental states to them (that is, surmising what is happening in their mind). This includes the knowledge that others' mental states may be different fro ...
and
mind-wandering Mind-wandering is a broad term with no currently universal definition. According to McMillan, Kaufmann and Singer (2013) mind-wandering consists of 3 different subtypes: positive constructive daydreaming, guilty fear of failure, and poor attention ...
. The study of mental time travel in general terms is also related to – but distinct from – the study of the way individuals differ in terms of their
future orientation In psychology and related fields, future orientation is broadly defined as the extent to which an individual thinks about the future, anticipates future consequences, and plans ahead before acting. Across development, future orientation is particul ...
, time perspective, and temporal self-continuity.


Brain regions involved

Various
neuroimaging Neuroimaging is the use of quantitative (computational) techniques to study the structure and function of the central nervous system, developed as an objective way of scientifically studying the healthy human brain in a non-invasive manner. Incre ...
studies have elucidated the
brain A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a v ...
systems underlying the capacity for mental time travel in adults. Early
fMRI Functional magnetic resonance imaging or functional MRI (fMRI) measures brain activity by detecting changes associated with blood flow. This technique relies on the fact that cerebral blood flow and neuronal activation are coupled. When an area o ...
studies on the topic revealed a number of close correspondences between remembering past experiences and imagining future experiences in brain activity.


fMRI mapping of brain regions

Addis et al. conducted an
fMRI Functional magnetic resonance imaging or functional MRI (fMRI) measures brain activity by detecting changes associated with blood flow. This technique relies on the fact that cerebral blood flow and neuronal activation are coupled. When an area o ...
study to examine neural regions mediating construction and elaboration of past and future events. The elaboration phase, unlike the construction phase, has overlap in the cortical areas comprising the autobiographical memory retrieval network. In this study, it was also found that the left hippocampus and the right middle
occipital The occipital bone () is a cranial dermal bone and the main bone of the occiput (back and lower part of the skull). It is trapezoidal in shape and curved on itself like a shallow dish. The occipital bone overlies the occipital lobes of the cereb ...
gyrus In neuroanatomy, a gyrus (pl. gyri) is a ridge on the cerebral cortex. It is generally surrounded by one or more sulci (depressions or furrows; sg. ''sulcus''). Gyri and sulci create the folded appearance of the brain in humans and other ma ...
were significantly activated during past and future event construction, while the right hippocampus was significantly deactivated during past event construction. It was only activated during the creation of future events. Episodic future thinking involves multiple component processes: retrieval and integration of relevant information from memory, processing of subjective time, and self-referential processing. D'Argembeau et al.'s study found that the ventral
medial prefrontal cortex In mammalian brain anatomy, the prefrontal cortex (PFC) covers the front part of the frontal lobe of the cerebral cortex. The PFC contains the Brodmann areas BA8, BA9, BA10, BA11, BA12, BA13, BA14, BA24, BA25, BA32, BA44, BA45, BA4 ...
and
posterior cingulate The posterior cingulate cortex (PCC) is the caudal part of the cingulate cortex, located posterior to the anterior cingulate cortex. This is the upper part of the " limbic lobe". The cingulate cortex is made up of an area around the midline of th ...
cortex are the most activated areas when imagining future events that are relevant to one's personal goals than to unrelated ones. This shows that these brain regions play a role in personal goal processing, which is a critical feature of episodic future thinking.


Brain regions involved in the 'what' and 'where' of an event

Cabeza et al. conducted a
positron emission tomography Positron emission tomography (PET) is a functional imaging technique that uses radioactive substances known as radiotracers to visualize and measure changes in Metabolism, metabolic processes, and in other physiological activities including bl ...
(PET) scan study on a group of human test subjects to identify the brain regions involved in temporal memory, which is based on a linear progression of events. Since 'recollecting a past episode involves remembering not only what happened but also when it happened', PET scans were used to find the areas of the brain that were activated when trying to remember a certain word in a sequence. The results show that temporal-order memory of past events involves the frontal and posterior brain regions and item retrieval shows neural activity in the medial temporal and basal fore brain regions.


Evolution and human uniqueness

The ability to travel mentally in time – especially into the future – has been highlighted as a potential prime mover in
human evolution Human evolution is the evolutionary process within the history of primates that led to the emergence of ''Homo sapiens'' as a distinct species of the hominid family, which includes the great apes. This process involved the gradual development of ...
, enabling humans to prepare, plan and shape the future to their advantage. However, the question of whether or to what extent animals other than human beings can engage in mental time travel has remained controversial. One proposal, the Bischof-Köhler hypothesis, posits that non-human animals cannot act upon drive states they do not currently possess, for example seeking out water while currently fully quenched. Other proposals suggest that different species may have some capacities, but are limited because of shortcomings in a range of component capacities of mental scenario building and imagination. A number of studies have claimed to have demonstrated mental time travel in animals including, most notably, various
great apes The Hominidae (), whose members are known as the great apes or hominids (), are a taxonomic family of primates that includes eight extant species in four genera: '' Pongo'' (the Bornean, Sumatran and Tapanuli orangutan); ''Gorilla'' (the east ...
, crows, ravens, and
western scrub jay Western scrub jay has been split into the following species: * California scrub jay, ''Aphelocoma californica'' * Woodhouse's scrub jay, ''Aphelocoma woodhouseii'' The island scrub jay The island scrub jay (''Aphelocoma insularis''), also known ...
s, but these have been subjected to a number of criticisms and simpler alternative explanations have been proposed for the results. This debate is ongoing. If mental time travel is unique to humans, then it must have emerged over the last 6 million years since the line leading to modern humans split from the line leading to modern
chimpanzees The chimpanzee (''Pan troglodytes''), also known as simply the chimp, is a species of great ape native to the forest and savannah of tropical Africa. It has four confirmed subspecies and a fifth proposed subspecies. When its close relative the ...
. Perhaps the first hard evidence for the evolution of mental time travel in humans comes in the form of
Acheulean Acheulean (; also Acheulian and Mode II), from the French ''acheuléen'' after the type site of Saint-Acheul, is an archaeological industry of stone tool manufacture characterized by the distinctive oval and pear-shaped "hand axes" associated ...
bifacial handaxes associated with
Homo erectus ''Homo erectus'' (; meaning "upright man") is an extinct species of archaic human from the Pleistocene, with its earliest occurrence about 2 million years ago. Several human species, such as '' H. heidelbergensis'' and '' H. antecessor' ...
. Acheulean tools are complex and appear to have required advanced planning to create. There is also evidence that they were often crafted in one location and then taken elsewhere for repeated use. A number of important adaptive functions have been identified that rely to some degree on the capacity to remember the past and imagine the future. These functions include predicting future emotional reactions (
affective forecasting Affective forecasting (also known as hedonic forecasting, or the hedonic forecasting mechanism) is the prediction of one's affect (emotional state) in the future. As a process that influences preferences, decisions, and behavior, affective foreca ...
), deliberate practice,
intertemporal choice Intertemporal choice is the process by which people make decisions about what and how much to do at various points in time, when choices at one time influence the possibilities available at other points in time. These choices are influenced by the ...
,
navigation Navigation is a field of study that focuses on the process of monitoring and controlling the movement of a craft or vehicle from one place to another.Bowditch, 2003:799. The field of navigation includes four general categories: land navigation, ...
,
prospective memory Prospective memory is a form of memory that involves remembering to perform a planned action or recall a planned intention at some future point in time.McDaniel, M. A., & Einstein, G. O. (2007). ''Prospective memory: An overview and synthesis of an ...
,
counterfactual thinking Counterfactual thinking is a concept in psychology that involves the human tendency to create possible alternatives to life events that have already occurred; something that is contrary to what actually happened. Counterfactual thinking is, as it ...
, and
planning Planning is the process of thinking regarding the activities required to achieve a desired goal. Planning is based on foresight, the fundamental capacity for mental time travel. The evolution of forethought, the capacity to think ahead, is consi ...
.


Episodic-like memory and planning for the future in great apes

Osvath et al. conducted a study on apes to show that they have the ability of foresight. The study consisted of testing for self-control,
associative learning Learning is the process of acquiring new understanding, knowledge, behaviors, skills, values, attitudes, and preferences. The ability to learn is possessed by humans, animals, and some machines; there is also evidence for some kind of l ...
, and envisioning in chimpanzees and orangutans through a series of experiments. Critics questioned whether these animals truly exhibited mental time travel, or whether it was associative learning that caused them to behave as they did. The Bischof-Kohler hypothesis says that animals cannot anticipate future needs, and this study by Osvath tried to disprove the hypothesis. The scientists showed that when the apes were presented with a food item in conjunction with a utensil that could be used to actually eat that particular food, these animals chose the utensil instead of food. They anticipated a future need for the utensil that overcame the current want for just a food reward. This is an example of mental time travel in animals. It was not a result of associative learning, that they actually chose the utensil instead of the food reward, since the scientists ran another experiment to account for that. Other examples, such as food caching by birds, may be examples of mental time travel in non-humans. Even survival instinct by certain animals such as elephants, in response to imminent danger, could involve mental time travel mechanisms. Another study to show that great apes have the ability of foresight was conducted by Martin-Ordas G. et al. These scientists were able to show that "apes remember in an integrated fashion what, where and when" a particular event had happened. Two experiments were conducted in this study, the first being an investigation of the content of the memories of apes i.e. could these animals remember when and where two types of food they were shown before are hidden. The second experiment explored the structure of the memories. It was found that the apes' memories were formed in an integrated what–where–when structure. All these findings suggest that it is not instinctive or learning predispositions that made the animals behave the way they did, but rather that they have the ability to mentally time travel. However, comparative psychologists are divided about this conclusion.


Episodic-like memory in western scrub-jays

In their study to show that birds exhibit episodic-like memory, Clayton et al. used 3 behavioral criteria: content, structure, and flexibility, to decide whether the food caching habits of these birds were evidence of their ability to recall the past and plan for the future. Content involved remembering what happened based on a specific past experience. Structure required the formation of a 'what-where-when' representation of the event. Finally, flexibility was used to see how well the information could be organized and re-organized, based on facts and experiences. Mental time travel involves the use of both episodic future thinking and semantic knowledge. This study also contradicts the Bischof-Kohler hypothesis by showing that some animals may mentally time travel into the future or back to the past. However this interpretation has remained controversial.


Development in children

Studies into the development of mental time travel in
infancy An infant or baby is the very young offspring of human beings. ''Infant'' (from the Latin word ''infans'', meaning 'unable to speak' or 'speechless') is a formal or specialised synonym for the common term ''baby''. The terms may also be used to ...
suggest that the involved component processes come online piece by piece. Most of the required psychological subcomponents appear to be available by approximately age four. This includes the fundamental capacity to prepare for two
mutually exclusive In logic and probability theory, two events (or propositions) are mutually exclusive or disjoint if they cannot both occur at the same time. A clear example is the set of outcomes of a single coin toss, which can result in either heads or tails ...
possible future events, which appears to develop between the ages of 3 and 5. Two and three-year-old children can report some information about upcoming events, and by ages four and five, children can talk more clearly about future situations. However, there is concern that children may understand more than they can articulate, and that they may say things without fully understanding. Thus, researchers have tried to examine future-oriented action. A carefully controlled study found that four-year-olds could already remember a specific problem they saw in a different room sufficiently enough to prepare for its future solution. These results suggest that children by the end of the
preschool A preschool, also known as nursery school, pre-primary school, or play school or creche, is an educational establishment or learning space offering early childhood education to children before they begin compulsory education at primary school ...
years have developed some fundamental capacity for foresight, capacities that continue to develop throughout
childhood A child (plural, : children) is a human being between the stages of childbirth, birth and puberty, or between the Development of the human body, developmental period of infancy and puberty. The legal definition of ''child'' generally refers ...
and
adolescence Adolescence () is a transitional stage of physical and psychological development that generally occurs during the period from puberty to adulthood (typically corresponding to the age of majority). Adolescence is usually associated with the t ...
.


Measurement

Studies of mental time travel require the
measurement Measurement is the quantification of attributes of an object or event, which can be used to compare with other objects or events. In other words, measurement is a process of determining how large or small a physical quantity is as compared ...
of both
episodic memory Episodic memory is the memory of everyday events (such as times, location geography, associated emotions, and other contextual information) that can be explicitly stated or conjured. It is the collection of past personal experiences that occurred ...
and episodic foresight.


Episodic memory

Episodic memory is typically measured in human adults by asking people to report or describe past events that they had experienced. Many studies provide participants with information at one point in the study and then assess their memory for this information at a later point in the study. The advantage of these studies is that they allow the accuracy of recall to be assessed. However, Cheke and Clayton found that such different measurements of memory do not mutually correspond enough and may therefore capture different facets of memory. A more general limitation with studies in this field is that they fail to capture people's actual memories for real-life events, just like in other studied animals. Many studies focus on asking people to recall episodes from their own lives. Some of them attempt to verify the accuracy of recall by comparing participants’ memories to those of family, friends or relatives who experienced the same event, or in some cases by comparing peoples’ memories of an event to public information about the event. However it is not always easy to verify the accuracy of recall, so many measures of episodic memory do not do this, focusing instead on aspects of people's verbal descriptions of their memories. Three commonly used measures that do not verify the accuracy of people's memories are as follows: 1) Dritschel et al. adapted the Controlled Oral Word Association Test to assess the fluency with which people recall personal autobiographical episodes in specific given time periods (e.g., last week, last year, last 5 years, etc.) in a specific time limit (e.g., 1 min). 2) Baddeley and Wilson used a 4-point scale with which to rate participants’ memories as (3) specific, (2) intermediate, (1) general, and (0) nil, based on the level of the detail provided in their description. 3) Levine and colleagues designed the Autobiographical Interview to distinguish between episodic and semantic components of episodic memories based on participants’ verbal descriptions.


Episodic foresight

Miloyan and McFarlane performed a systematic review of episodic foresight measurement instruments used in human adults and found that most of these measures were adapted from measures of episodic memory. 1) The measure by Dritschel et al. based on the Controlled Oral Word Association Test was adapted by MacLeod and colleagues to assess episodic foresight. 2) Williams et al. adapted the 4-point scale from Baddeley and Wilson to assess episodic foresight. 3) The Autobiographical Interview by Levine and colleagues which was designed to distinguish the episodic and semantic components of episodic memories was adapted by Addis and colleagues to measure episodic foresight. The authors of the systematic review noted that a limitation of all such episodic foresight measures is that they do not compare people's simulation of future events to objective preparatory behaviors or to the actual occurrence of future events. Thus, none of the available measures verify the accuracy or relevance of people's imaginings. This is in contrast to studies of episodic foresight in children and animals that require participants to demonstrate episodic foresight with behaviors to compensate for their lack of verbal ability.


See also

*
Episodic memory Episodic memory is the memory of everyday events (such as times, location geography, associated emotions, and other contextual information) that can be explicitly stated or conjured. It is the collection of past personal experiences that occurred ...
*
Foresight (psychology) Foresight is the ability to predict, or the action of predicting, what will happen or what is needed in the future. Studies suggest that much of human daily thought is directed towards potential future events. Because of this and its role in human ...
*
Semantic memory Semantic memory refers to general world knowledge that humans have accumulated throughout their lives. This general knowledge (word meanings, concepts, facts, and ideas) is intertwined in experience and dependent on culture. We can learn about n ...
*
Prospective memory Prospective memory is a form of memory that involves remembering to perform a planned action or recall a planned intention at some future point in time.McDaniel, M. A., & Einstein, G. O. (2007). ''Prospective memory: An overview and synthesis of an ...
*
Prospection In psychology, prospection is the generation and evaluation of mental representations of possible futures. The term therefore captures a wide array of future-oriented psychological phenomena, including the prediction of future emotion (affective fo ...
*
Time perception The study of time perception or chronoception is a field within psychology, cognitive linguistics and neuroscience that refers to the subjective experience, or sense, of time, which is measured by someone's own perception of the duration of the ind ...
*
Intertemporal choice Intertemporal choice is the process by which people make decisions about what and how much to do at various points in time, when choices at one time influence the possibilities available at other points in time. These choices are influenced by the ...
*
Practice (learning method) Practice is the act of rehearsing a behaviour repeatedly, to help learn and eventually master a skill. The word derives from the Greek "πρακτική" (''praktike''), feminine of "πρακτικός" (''praktikos''), "fit for or concerned with ...
*
Affective forecasting Affective forecasting (also known as hedonic forecasting, or the hedonic forecasting mechanism) is the prediction of one's affect (emotional state) in the future. As a process that influences preferences, decisions, and behavior, affective foreca ...
*
Predictive coding In neuroscience, predictive coding (also known as predictive processing) is a theory of brain function which postulates that the brain is constantly generating and updating a "mental model" of the environment. According to the theory, such a ment ...
*
Free energy principle The free energy principle is a mathematical principle in biophysics and cognitive science that provides a formal account of the representational capacities of physical systems: that is, why things that exist look as if they track properties of the ...


References

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