Three experiments compared the performance of pigeons and corvids when they were given the opportunity to transfer the relational rule underlying matching or oddity discriminations to new sets of stimuli. In the first, pigeons and jackdaws were initially trained either on a matching or on a non-relational conditional discrimination and then transferred to a new matching discrimination. In the second, pigeons and jays were trained on a series of three matching (or oddity) discriminations with three different pairs of colours and finally tested, either with the same or the reversed rule, on matching or oddity to line orientations. In the third, pigeons and rooks were trained to perform one response when two coloured panels were the same and a different response when the two colours were different and then transferred, either with the same or the reversed rule, to a new set of colour stimuli. All three experiments produced the same result: no evidence of transfer of the relational rule by pigeons, but substantial and significant transfer by corvids.
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-
Three experiments examined the extent to which pigeons trained on a matching or oddity discrimination with one pair of colours showed transfer when tested on a new matching or oddity discrimination with a new pair of colours. Experiment 1 examined the effects of key spacing and a delay procedure and replicated previous reports that in the transfer stage subjects given the same kind of problem (Non-shift condition) in general learn more rapidly than those given the opposite problem (Shift condition). However, this difference appeared only when pigeons given matching in both training and transfer stages were compared to those shifted from oddity to matching; it did not appear in birds transferred to oddity. Transfer was not significantly affected by key spacing or by the delay. Experiments 2 and 3 examined transfer from a non-relational conditional discrimination based on one set of colours to a subsequent matching or oddity task based on two new colours. Both a comparison between the results of Experiment 1 and 2 and the corresponding within-experiment comparison from Experiment 3 showed that transfer from conditional training to matching was as great as from prior training on matching, while prior training on oddity produced negative transfer on shift to matching. It was suggested that this negative transfer occurs because pigeons trained on oddity have not learned to override an initial bias towards the odd stimulus in an array. Whatever the correct explanation; the present results provide no support for the claim that pigeons solve matching or oddity discriminations relationally.
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