Psychological emerged that episodic memory and cognitive time
Posted On May 27, 2019
Psychological research over the years has
investigated episodic memory and mental time travel across a variety of
species. Episodic memory refers to memory for personal episodes, which can be
located to a specific time and place (Tulving, 1972, 1983, 1984). The notion of
episodic memory has been linked to self conscious (autonetic consciousness) and
cognitive time travel was initially perceived as being a trait unique to humans
(Tulving, 1983, 1984, 1985). According to the mental time travel hypothesis
animals live in the present and are incapable of episodic recall of specific
past life events and they can’t contemplate incidents that might occur in
long-term future (Suddendorf and Corballis, 1997). Research evidence, however,
has emerged that episodic memory and cognitive time travel may not be exclusive
to humans and other species such as Western Scrub Jays, Rats and Apes appear to
possess episodic memory meaning they are capable of planning for future states.
Episodic memory and cognitive
time travel requires a concept of time (Roberts, 2005). Human beings have a
strong concept of time as they can remember what, when and where they did
something. They are retrospective and prospective as they can use their
knowledge of previous experiences (retrospective) to plan for future states and
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Early evidence challenging the
idea that episodic memory is unique to humans comes from pecking behaviour in
pigeons (Olton, 1984). Pigeons were trained to match a red or green sample
stimulus with a memory interval between sample and matching test. When pigeons
were presented with a central key that is green for a few seconds, they then
had to spend 10 seconds in the dark after which they had to choose between the
green and red keys and they choose the matching green key, significantly more
often than chance level of 50% showing memory for the sample stimulus (Grant,
1978). Such behaviour was claimed to be characteristic of episodic memory as
the pigeons can only remember the correct responses by travelling back in time
to the start of the trial and remembering the stimulus presented.
Although Oltons study seems to
suggest animals may not be cognitively stuck in time a limitation of Olton’s
study is that other feasible explanations for such findings. The pigeon could
have memory of the green sample stimulus, however, no memory of the sample
having occurred in the past. The memory of green is the strongest available to
the pigeon at testing, irrespective of their concept of time. On this basis it
is argued that animals do not have an acquired temporal framework of time and
aren’t capable of mental time travel (Roberts, 2002).
Evidence has, however, emerged
to suggest non-human animals are sensitive to time.
Laboratory studies have provide
evidence for time tracking in animals. For instance, garden warblers were
placed in an apparatus, which contained a central living room with four feeding
rooms around it, and during different periods of the day they had food
available in different rooms (Biebach, Gordijn and Krebs 1989). Room one
contained food from 0600 to 0900, whereas, feeding rooms 2,3,4 contained food
between 0900 to 1200, 1200 and 1500, 1500 and 1800 respectively. They could fly
to these rooms at these times open a feeder and eat for 20 seconds, however,
they had to return the living room for 280 seconds before they could visit a
feeding room again. 5 birds learned to go to appropriate room at the
appropriate time of day to obtain food.
It’s, however, possible that
garden warblers sampled rooms until they found the one that yielded reward. To
test this possibility test days were run in which all four contained food
throughout the day. Nonetheless birds continued to go to the room containing
food during each time period in training.
Whilst there is evidence to
demonstrate that animals are sensitive to time, it has been argued the
behaviours they have elicited in such studies do not require a concept of time
as a dimension of the past, present and future. Food seeking behaviours in a
particular day and place as well as tracking of short intervals have been
attributed to circadian oscillators and changes in their internal state (Roberts,
2002). Circadian cues act as occasion setters as they don’t directly elicit
behaviour but tell the animal the occasion has arisen for a conditioned
stimulus to be followed by a particular unconditioned stimulus. Circadian cues
may indicate the time at which food will be found at a given place and phase
state oscillators act as retrieval cues arousing memory of placed food
Much of the early evidence,
therefore, suggests non-human animals are incapable of cognitive time travel
and don’t possess episodic memory. They may be sensitive to time; however, on
the basis of such evidence they don’t appear to have a concept of time. It’s
circadian oscillators that drive such behaviours. Essentially such behaviours
fail to demonstrate a concept of time, thereby, suggesting that the behaviours,
which animals are demonstrating, are not characteristic of episodic memory (Roberts,
Whilst a lot of the early
evidence seems to suggest that animals are insensitive to time, therefore,
meaning they don’t possess episodic memory a crucial turning point in
psychological research concerning episodic memory and mental time travel in non
human animals comes from a series of studies which look at caching behaviour in
Western Scrub Jays. (Clayton and Dickinson, 1998). Their studies provide
concrete evidence for episodic memory and mental time travel whilst falsifying
other possible explanations such as relative familiarity and forgetting through
The ability of animals to cache
food for recovery is likely to be based on prospective and retrospective
cognition. In the case of Western Scrub Jays it has been claimed that it would
be advantageous for them to remember not only where the food was cached but
also if it was perishable and how long ago the cache was made (Clayton et al, 1998).
Episodic memory can only be assessed by the original definition of episodic
memory that involves receiving and storing information about temporally spatial
relations amongst those events. This involves information about when an event
occurred, what happened and where, therefore, constituting a strong concept of
time (Clayton et al,1998).
This has been illustrated by
allowing western scrub jays to cache and recover perishable wax worms and
non-perishable peanuts. Scrub jays learnt to prefer the worm over the peanuts
when the wax worms were fresh but the preference was reversed when the worms
decayed. This suggests Scrub Jays are sensitive to the food type (what), the
location in the tray(where) and when(time of caching and recovery). For some
scrub jays the worms decayed after a long retention interval, whereas, for
other birds they were replenished with fresh wax worms. A what- where- when
memory for a caching episode would allow the jay to recover the perishable food
before it became unpalatable (content) and their decisions in such situations
highlights such components are integrated and can be updated and generalized
over situations (Flexibility) (De Kort, Dickinson and Clayton 2005).
Alternative explanations to
explicit temporal encoding such as such as relative familiarity and forgetting
have been provided to explain caching behaviour in Western Scrub Jays. They
have been ruled out through experimental manipulations (De Kort et al, 2005).
The relative familiarity hypothesis
claimed that relative familiarity could provide temporal conditional cues for
knowledge of perishability of caches. For instance birds may have learned to
search for worms when tray cues were relatively familiar after one day but
avoid doing so when cues were relatively unfamiliar after five days. Relative
familiarity was removed by allowing jays to cache two different food items
either side of a single tray at different times. Nonetheless the birds searched
for wax worms when they were cached on previous morning but for nuts if wax
worms were cached five days earlier. This rules out the relative familiarity
hypothesis, as their recovery patterns are the same despite a lack of retrieval
cues (De Kort et al, 2005).
On the other hand, the
forgetting hypothesis suggests birds quite simply forget the location of
degrading worms. Older memories are said to be less vivid, therefore, if worms
did not degrade with time since caching, time dependent forgetting should be
accompanied by a loss in accuracy of locating different food caches. Observing
cache recovery behaviour of a second group of jays whose perishable caches did
not degrade. Birds, however, didn’t show any loss in accuracy of locating
caches after 5 days as they were after 4 hours (De Kort et al, 2005).
Furthermore scrub jays in a
degrade and ripen group show considerable differences in caching behaviour.
Such differences suggest that forgetting isn’t occurring because if it was then
differences wouldn’t be observed and the ripen group wouldn’t be searching for
wax worms after a long retention interval which have ripened, therefore, they
are in fact remembering their caches (De Kort et al, 2005).
however, of Clayton and Dickinson’s studies is that the what component of an
episodic memory should be per se novel (Dere et al, 2006). This means that it
should represent new information that involves consolidation of information
such as physical characteristics of a novel object as opposed to just
presenting two types of highly familiar food in which the features had been
learned before testing.
Other research in different species such as rats
also provide a detailed representation of what- where- when memory (Crystal et
al, 2010). When a modified version of a standard radial maze was used in rats
they had to take part in a study phase, retention interval and test phase.
During the study phase four locations were randomly selected to provide food.
Two locations contained standard chow flavoured food. The other two locations
had distinctive grape flavoured food and distinctive raspberry flavoured food.
Following eating the rat was removed from the maze for a retention interval
that was either short (1 hour) or long (6 hours). The locations had grape and
raspberry replenished after a long retention interval but not after a short
interval. A temporal component was required to revisit locations about to
replenish and reduce tendency at other times. Rats showed evidence for what-
when- where memory as they revisited grape and raspberry locations at a higher
rate when locations were not about to replenish. This could only be
accomplished if they remembered locations that recently had a distinctive flaw
and temporal information about study and test phase. Rats also reduced visits
to devalued flavours whilst continuing to visit the location with non-devalued
flavour (Crystal et al, 2010).
Episodic memory may also benefit animals in
terms of social interactions .For example when Pinyon Jays observed a dominant
member of their own social group had been defeated by an unknown jay from
another group they behaved submissively during their first encounter with the
foreign jay (Dere et al, 2006).
It has been suggested that species probably
possess other sophisticated mechanisms that track regularities and guide future
directed behaviour. The most evolved species such as apes demonstrate a
capacity for mirror self-recognition like humans share a similar brain aspect
to humans in order to possess this trait, whereas, Gibbons don’t (Suddendorf et
al, 2010). This suggests an evolution ladder for episodic memory and mental
time travel in non-human animals.
To conclude although the idea of episodic memory
and mental time travel was initially disputed in non human animals, robust
evidence concerning western scrub jays and rats has emerged which meets the
criteria for episodic-like memory. From an evolutionary perspective it appears
that episodic like memory may be providing a survival advantage by enhancing
food caching and recovery as well as benefiting animals in terms of social
interactions. Future research, however, needs to identify more precisely the
neural regions involved in episodic memory and mental time travel in non-human
animals. Most importantly other possible sophisticated mechanisms tracking
regularities and guiding future directed behaviour in less evolved species need
to be identified.