A comparison of the short-term memory performances of pigeons and jackdaws

Abstract

Two experiments employed a delayed conditional discrimination procedure in which half the trials began with the presentation of food and half with no food; following a retention interval, subjects were presented with a choice between red and green keys, a response to one of which was reinforced according to whether the trial had started with food or no food. In Experiment 1, after 38 training sessions during which the retention interval was gradually increased, pigeons performed at a moderate level with intervals of 5 to 7.5 sec. A final test produced a steep forgetting function for food trials, but not for no-food trials; performance was unaffected by the duration of the intertrial interval (10 or 40 sec). Experiment 2 used the delayed conditional discrimination procedure to compare short-term memory in jackdaws (Corvus monedulus) with that in pigeons. Although the performance of the jackdaws was below that of the pigeons at the start of training, they showed more rapid learning over long delays, and, in the final test, a shallower forgetting function for food trials than that shown by pigeons. The results suggested superior short-term memory in jackdaws, which may help to explain the better performance of corvids in general when compared with that of pigeons in certain complex learning tasks.It is widely agreed that proficient performance by an animal on certain complex learning tasks involves the employment of a win-stay/lose-shift strategy (Levine, 1959; for a recent review, see Macphail, 1982). In other words, the behavior of the animal comes under the control of the most recent trial and is relatively free from the influence of events preceding that trial. Some of the strongest evidence for the important role of this strategy comes from studies that have found positive transfer from training on a serial-reversal task to the acquisition oflearning-set performance, a result first obtained in primates (Schrier, 1974;Schusterman, 1962Schusterman, , 1964Warren, 1966). In a comparable study using birds, Kamil, Jones, Pietrewicz, and Mauldin (1977) first trained a group of blue jays on a serial-reversal task involving a single pair of objects and then transferred them to an object-discrimination learning set. This group displayed much more rapid acquisition of learning-set performance than a control group initially trained on a single discrimination problem. The differences between the groups were most marked on problems in which animals made an error on the first trial; this provides strong support for the suggestion that the control animals needed to acquire the "lose-shift" part of the strategy in order to perform well.If good learning-set performance depends on the use of transient memories of what happened on the previous trial, then the interval between trials should be a critical factor. Confirmation of this prediction has been obtained in experiments that have found a large impairment of per-

Rats exhibit asymmetrical retention functions for hedonic and nonhedonic samples in many-to-one symbolic delayed matching to sample

“…Rats rapidly acquired the SDMTS task with food and nofood samples to a high level of accuracy. During the initial retention test, rats exhibited faster forgetting of the food sample than of the no-food sample, a result that replicates previous findings reported in pigeons (Colwill, 1984;Grant, 1991;Grant & Kelly, 2001;Sherburne & Zentall, 1993a, 1993bWilson & Boakes, 1985;Zentall et al, 1995), jackdaws (Wilson & Boakes, 1985), and rats (Santi et al, 2011). One explanation of the asymmetric retention of food/nofood samples that has been ruled out in pigeons has also been ruled out in rats: According to this hypothesis, animals confuse the novel retention interval with the no-food sample when the stimulus conditions during the no-food sample are identical to those that occur during the retention interval.…”

“…Presence/absence samples of nonhedonic visual stimuli (e.g., red hue vs. the absence of a red hue) also exhibit a retention asymmetry similar to that initially reported for hedonic food and nofood samples (Grant, 1991;Sherburne & Zentall, 1993a, 1993bWixted, 1993). A single-code/default strategy was initially proposed as an explanation of this effect (Colwill, 1984;Wilson & Boakes, 1985). According to this hypothesis, pigeons only code the presence (e.g., food) sample in memory, and respond to the comparison stimulus associated with the absence (e.g., no food) sample by default when the code for the presence sample is absent from memory.…”

“…2). However, when the samples consist of the occurrence and nonoccurrence of food, pigeons (Colwill, 1984;Wilson & Boakes, 1985) and jackdaws (Wilson & Boakes, 1985) exhibit markedly asymmetrical retention functions. As the retention interval increases, accuracy rapidly decreases to below-chance levels for trials initiated by a food sample (brief access to grain), but it remains very high for trials initiated by a no-food sample (an equivalent period of hopper illumination or darkness).…”

“…With the exception of a study by Wilson and Boakes (1985), in which jackdaws were also studied, all of the published experiments on presence/absence retention functions and changes in these functions as a result of an MTO mapping have been conducted in pigeons. Recently, we demonstrated that rats also exhibit asymmetric retention functions for food and no-food samples (Santi, Simmons, & Mischler, 2011).…”

Concept Learning in Animals

“…This unique pattern of results has been interpreted as evidence that pigeons have developed a single-code/default coding strategy (Colwill, 1984;Grant, 1991;Wilson & Boakes, 1985); that is, on present-sample trials, choice of the comparison associated with the present sample occurs whenever there is a representation of that sample in memory; otherwise, choice of the alternative comparison occurs by default. Thus, on present-sample trials, as the delays increase in duration, memory of the present sample is gradually lost and there is an increasing tendency to respond to the alternative comparison, by default.…”