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Keeping track of time: evidence for episodic-like memory in great apes Gema Martin- Ordas Daniel Haun Fernando Colmenares Josep Call. Emily & Geoff. Clayton et al.
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Keeping track of time: evidence for episodic-like memory in great apesGema Martin-Ordas Daniel Haun Fernando ColmenaresJosep Call Emily & Geoff
Clayton et al. • Clayton and colleagues have shown that scrub jays flexibly integrate memories for the what, where, and when of an event. (other bird and mammal species have also been shown to have this type of memory) • Weakness in Clayton’s experimental approach: it does not measure memory for unique experiences because they require training. • Clayton et al argued that the training was to allow subjects to acquire semantic information that is applicable to different events in a flexible way. • Clayton et al conclusion: Searching for recovery is controlled by semantic information (perishablility of the cached food items) but also by episodic-like recall
Zentall et al. (2001) • Zentall et al. have suggested that in order to study episodic memory, the test should be unexpected because the episodic information should be encoded automatically; that is, episodic memory experiments should be based on trial-unique learning. • The trial-unique learning paradigm has been successfully implemented in rodents and birds.
Tulving (1972) • The capability to recall the what, where and when of an eventfulfilsTulving’s behavioral criteria for episodic memory, and is referred to as episodic-like memory rather than episodic memory because it does not assess subjective experiences that accompany conscious recollection in humans.
Suddendorf and Busby (2003) • S & B argued that one could know what, where, and when something happened (e.g., know when you were born) without actually being able to remember the event. • Personal memories not always accurate • Therefore, remembering a personal past event does not necessarily involve remembering the when and the where of the past event (you don’t remember it, you just know it.)
Eacott et al. (2005) • Alternative approach: challenged the main role of the “when” component in episodic-like memory. They argue that human episodic memory is poor in recalling the timing of an event and, therefore, “when” serves exclusively as a marker to distinguish an event from another event. Hence, they proposed that episodic-like memory in animals should involve the recall of what, where and which instead.
Experiment 1: Content of Memories Goal: to see if subjects can remember when and where 2 types of food were hidden • 3 baiting places: • Place 1: Favorite, perishable treat (frozen juice) • Place 2: Less preferred, non-perishable (grape) • Place 3: Empty
Experiment 1 • After the treats were hidden, subjects allowed to choose 1 item (1 place) after either 5 minutes or 1 hour (the retention interval) • After 1 hour, the frozen juice melted and became unobtainable • If apes can remember when and where food was hidden, they should choose juice after 5m trials but not choose juice after 1 hour
Experiment 1 - Methods • 2 bonobos, 7 chimpanzees, 3 orangutans • 4 males, 8 females all ages 6-31 years • Subjects all familiar with participating in tests • 36 different opaque containers and two plastic platforms (70cm x 35cm) • One platform had holes drilled in it covered in netting, allowing melted juice to seep through
Experiment 1 - Procedure • Experimenter and subject sat facing each other on either side of a Plexiglass barrier • E showed subject the reward(s) and placed them under containers
Memory ability pre-test • In the pre-test, they tested subjects’ general long-term memory. • Subjects had to remember location of a reward placed under 1 of 3 cups after 2 min, 1 hr, 2 hr, and 24 hr RI’s (time between baiting and choosing) • Subjects went through 12 trials (3 per condition) each
Pre-test results • Overall apes remembered the location of the food after each retention interval above chance levels, and there was no change in performance across ages
Food preference test • Done to establish the apes’ preference for 2 food items • Apes had no previous experience with the frozen juice they used • Subjects given 2 food choices at a time (different combos of banana, grape, frozen juice) Locations balanced, only 1 choice allowed • They did this until each subject chose a given treat at least 5 out of 6 trials.
What-where-when memory test • 3 possible baiting choices – frozen juice, less preferred food, empty • Subjects presented with 5 min and 1 hour trials • 5 min trials: both items available • 1 hr trials: only less preferred available • Counterbalanced order of trials, apes received total of three 12-trial rounds • Different opaque containers used
What-where-when results • Subjects chose the frozen juice significantly more often after the 5-min interval than after the 1-hr interval • 4 out of 12 subjects chose the frozen juice significantly more often than the grape after the short RI, and chose the grape after the long RI • Subjects almost never chose the empty container which suggests their choice of the less-desired food after a delay were not due to memory lapses
What-where-when results • Age showed no effect for general long-term memory in pre-test, but for the www-memory test subjects younger than 7 and older than 18 years old showed a much lower performance than adolescents and young adults
Experiment 1 Discussion • Subjects’ performance can only be explained by the recall of the what, where, and when food items were hidden • Purely behavioral criteria: results provide evidence for episodic-like memory in great apes
Experiment 1 Discussion • Age effect in www-memory test • No age effect in long term memory pre-test • During pre-test, subjects’ recall of the location of food after 24h was as good as that after a 2min delay • Interestingly, human memory studies have reported the same: an inverted U-shaped curve as a function of age for episodic memory, and no age effect for long-term memory
Experiment 2: Memory Structure Two possible memory structures: • What-Where-When 2. Where-What-When Subjects: The five apes that were “successful” (could distinguish between episodes) in Experiment 1 • Two chimps, two bonobos, one orangutan Where What When What Where When
Exp. 2: Procedure • Two platforms, each with three opaque cups, set up in two different cages • At t=0, E enters first cage and baits one cup with frozen juice (best treat), a second cup with a grape, and leaves a third container empty • At t=1h, E enters other cage and does the same thing • Two conditions: ape chooses cup on 5-min-ago platform first and 1-hr-ago platform second, or vice versa • Each subject performs under each condition three times (six trials total)
Exp. 2: Results • Subjects selected cup with frozen juice (favored treat) significantly more from recently baited table compared to table baited first • Temporal information DOES affect apes’ choices • Subject had to remember a baiting event in terms of time (when) and location (where) of certain treat (what)
Exp. 2: Discussion • Where-what-when structure does not support these results • “What” (e.g. grape) would have simultaneously triggered recollection of both platforms (where) and both baiting events (when), making the observed results impossible • What-where-when model structure supports findings • “Where” (the platform) triggers memory of the treats’ natures and the time that the baiting event happened • Episodes can be differentiated in an integrated fashion Where What When What Where When
General Discussion How might apes process temporal info? • Measuring elapsed time using circadian timers or strength of memory • Coding of specific time of occurrence • Friedman (1993,2004) found no evidence of this in humans • Forgetting (process of elimination using lack of memory as a cue) • But, pre-test showed that apes’ memory was accurate for at least 24 hours • Familiarity • But, apes were exposed to both platforms for same amount of time
General Discussion • Effects of age • Inverted U-shaped distribution of memory development (though sample size was quite small) • Similar to that of humans • Species might have comparable information encoding and storage mechanisms • Similar to development of mirror self-recognition in chimps • Should be subjected to more rigorous future studies
Future Studies • Do great apes project a stronger sense of episodic memory behaviorally when the task invokes stronger emotions? • Would great apes perform similarly in a task like this one but with extended retention intervals? (e.g., 1 hour and 5 hours) • What about a non-food-related task?
