Prospective memory in the formation of learning sets by rhesus monkeys (Macaca mulatta)

In conventional discrimination learning-set formation, it is possible that rhesus monkeys (Macaca mulatta) learn to lay down prospective memories by anticipating the next trial and deciding in advance what choice will be made. To test this hypothesis, the authors administered discrimination problems with 24-hr intertrial intervals, predicting that these long intervals would disrupt or prevent the putative anticipation of the next trial. Confirming their expectation, the authors found no indication of learning-set formation under these conditions.     

Rats acquire spatial learning sets

This experiment was designed to examine the development of a spatial learning set in rats and some of the variables influencing the retention of individual problems. The apparatus was a plus maze. At the beginning of each test, the rat was put on two arms, each in a different place. Food was present in one of the arms, but not in the other. The rat was then given a choice between these two places; the correct response was to return to the place that previously contained food (win-stay, lose-shift, response-reinforcement contingency). Fifty different two-choice spatial discriminations were given, each in a different location. At the end of testing, the mean percentage of correct responding for the first choice between the two places was 83%. Control procedures showed that the discriminative stimuli were distal, extramaze spatial stimuli. Variations of the procedure examined the influence of proactive interference and temporal delay on the memory for each discrimination. These results demonstrate that rats can develop a spatial learning set and provide new information about the characteristics of the memory underlying learning sets.     

Deficits in visual learning produced by posterior temporal lesions in cats

Eight cats with lesions in the posterior temporal (PT) cortex, seven cats with lesions in the basolateral amygdala (BLA), and eight intact controls were observed on eight tests of visual discrimination learning and of spontaneous responses to salient visual stimuli. The effects of the two lesions were somewhat dissociable. The PT lesions were accompanied by a severe deficit in pattern discrimination learning but no loss in visual tracking or orientation to the silhouette of a threatening cat. The BLA lesions produced a milder and less consistent loss in pattern discrimination but serious defects in tracking and reponse to the cat silhouette. Both operated groups performed well on the visual cliff. The deficit from PT lesions appeared independent of damage to the geniculocortical system. The parallel of symptoms from PT lesions in cats and inferotemporal lesions in monkeys is discussed.