A number of psychologists have suggested that episodic memory is a uniquely human phenomenon and, until recently, there was little evidence that animals could recall a unique past experience and respond appropriately. Experiments on food-caching memory in scrub jays question this assumption. On the basis of a single caching episode, scrub jays can remember when and where they cached a variety of foods that differ in the rate at which they degrade, in a way that is inexplicable by relative familiarity. They can update their memory of the contents of a cache depending on whether or not they have emptied the cache site, and can also remember where another bird has hidden caches, suggesting that they encode rich representations of the caching event. They make temporal generalizations about when perishable items should degrade and also remember the relative time since caching when the same food is cached in distinct sites at different times. These results show that jays form integrated memories for the location, content and time of caching. This memory capability fulfils Tulving's behavioural criteria for episodic memory and is thus termed 'episodic-like'. We suggest that several features of episodic memory may not be unique to humans.
Preexposure to two compound flavors (AX and BX) typically enhances their discriminability: An aversion conditioned to AXwill generalize less to BX,especially if the preexposure regime has involved altemated presentations ofAX and BX rather than presenting all AX trials before BX trials (or vice versa). One possible explanation ofthis finding is that altemating preexposure establishes inhibitory associations between the two unique features A and B, thus counteracting the generalization produced by excitatory associations between X and A and between X and B, which might result in either the retrieval of B on a conditioning trial to AX, or the retrieval of A on a test trial to BX.Three experiments on flavor aversion conditioning in rats tested these predictions. Experiment 1 suggested that the more important of these excitatory associations was that which allowed X to retrieve A on the test trial to BX. Experiment 2 suggested that the more important inhibitory association was that which allowed B to inhibit the representation of A on this test trial. Experiment 3 provided direct evidence of the role of this inhibitory B-IA association.Discrimination between two or more complex stimuli is often enhanced by prior exposure to one or more ofthem (see Hall, 1991, for a review). Such perceptualleaming effects have been weil established in flavor aversion conditioning, where discrimination between compound flavors such as mixtures of sucrose-Iemon and saline-lemon is enhanced by exposure to one or both ofthese flavors prior to conditioning an aversion to one and testing generalization to the other (see, e.g., Bennett, Wills, Wells, & Mackintosh, 1994;Mackintosh, Kaye, & Bennett, 1991;Symonds & Hall, 1995). Mackintosh et al. (1991) showed that this perceptua1 learning effect was dependent on the use of compound flavors sharing an element or feature in common. If an aversion was conditioned to saline alone, it did not generalize strongly to sucrose, and prior exposure to saline and sucrose did nothing to reduce the generalization that did occur. This is hardly surprising. According to one popular account, generalization between two stimuli occurs to the extent that they share elements in common (Estes, 1950). Ifwe represent two compound stimuli sharing elements in common as AX and BX, where A and Bare the elements unique to each stimulus, and X are those common to both, then conditioning to AX will generalize to BX because some of that conditioning accrues to the X elements shared by BX. There is, moreover, a very simple reason why preexposure to two compound stimuli, AX and BX, should reduce generalization between them (McLaren, Kaye, & Mackintosh, 1989). One of the best established consequences of preexposure to a stimulus that sub sequently serves as the conditional stimulus (CS) in a conditioning experiment is a retardation of subsequent conditioning to that stimulus-the phenomenon of latent inhibition (Lubow, 1989). But preexposure to both AX and BX will ensure twice as much preexposure to X as to A and B. It seems pr...
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