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Retroactive interference in discrimination learning.

In stage 1 of this experiment pigeons were trained to discriminate between two levels of noise or two colors by pecking on one of two disks. In stage 2 the discriminative stimuli were not presented, but pecking on the disks was rewarded on a random schedule. The second procedure caused the pigeons to forget the discrimination they had learned.

Acoustic Stimulation

Temporal correlates of discrimination learning.

The relationship between human temporal behavior and learning was investigated by means of an experimental design which measured temporal behavior using the methods of reproduction and production as possible correlates for a complex-form of discrimination-reversal learning. The results indicated that the method of reproduction is a temporal correlate of original learning and that the method of production is a temporal correlate of reversal learning. The theoretical explanations proposed for these results employed the mechanisms of conditioning, extinction, and stimulus generalization, the intervening variables of excitation and inhibition and the Pavlovian levels of behavioral organization of the first and second signalling systems.

Adult

The effects of hippocampal-area parahippocampalis lesions on discrimination learning in the pigeon.

Three experiments examined the behavioural effects of bilateral ablation of the avian hippocampus-area parahippocampalis (Hp-APH), a region which is considered to be the homologue of the mammalian hippocampal formation. Pigeons with lesions of the Hp-APH were impaired in learning the reversal (but not the acquisition) of a position (left/right) discrimination (Expt. 1). In contrast, lesion birds were unimpaired relative to controls in both the acquisition and reversal of a visual (pattern) discrimination (Expt. 2) in terms of errors to criterion; there was evidence, however, that the pattern of responding differed between groups during reversal. Finally, Hp-APH pigeons were impaired in the acquisition of a conditional discrimination (Expt. 3). The results are compared with the effects of hippocampal ablation in mammals, and their implications for a behavioural homology between the avian Hp-APH and the mammalian hippocampal formation are considered.

Animals

A configural analysis for feature-negative discrimination learning.

In 4 experiments, rats were initially trained with an A+ AXo discrimination in which Stimulus A by itself signaled the delivery of food, A+, whereas the simultaneous presentation of A and X was followed by nothing, AXo. In each experiment X was then paired with food prior to a test phase in which A and X were again presented for a discrimination. The discrimination was of the form A+ AXo in Experiments 1 and 2, whereas it was of the form X+ AXo for Experiments 3 and 4. In all 4 experiments the test discrimination was acquired more rapidly than a control discrimination. The results are interpreted in terms of the original A+ AXo discrimination resulting in the growth of an association between a representation of the entire AX compound and the effects of nonreinforcement.

Animals

Olfactory discrimination learning is blocked by leupeptin, a thiol protease inhibitor.

Rats were trained on successive two-odor discriminations with the cues randomly located in an 8-arm radial maze. After several days of training using different odor pairs, the thiol protease inhibitor leupeptin was infused into the ventricles and testing continued. Leupeptin caused a pronounced, dose-dependent and reversible deficit in performance in this task. Previous studies have shown that these drug concentrations do not influence spontaneous activity, feeding and drinking, or the acquisition and retention of avoidance conditioning. The results are interpreted as supporting the hypothesis that a calcium-sensitive proteinase is involved in certain forms of memory that require modification of telencephalic circuitries.

Animals