Strategies of Simultaneous Discrimination Learning in the Pigeon

In Experiment I pigeons were trained on a simultaneous discrimination between red and orange. After they had overcome their position habits and mastered the problem they were presented on occasional test trials with two red or with two orange stimuli. On those test trials when both stimuli were positives the birds tended to peck always to one key; this key was the preferred key during the position habit phase of acquisition. On trials with two negative stimuli the birds chose the other key. These results suggest that the pigeons use the presence of the S− on their preferred side as a cue for pecking to the other side. Experiment II investigated the role of the S+. Transfer tests involving the introduction of a neutral stimulus suggested that pigeons vary in the extent to which they rely upon the S+. Some birds showed no preference for the S+ over the neutral stimulus. However, when required to learn a discrimination between the old S+ and the neutral stimulus, birds given the old S+ as the positive learned more rapidly than those given the neutral stimulus as the positive.

Patterns of Behavior of Hippocampal Lesioned Rats in an Exploratory Motivated Situation

10 rats with bilateral dorsal hippocampal lesions and 16 control rats were pretrained in an unbaited T maze and then trained on a position habit reinforced by the opportunity for exploration. In comparison with the control Ss the hippocampal lesioned rats during pretraining perseverated more, made more maze-unit entries after some exposure, ran more slowly initially, and were less distracted by environmental change. During choice training the hippocampal lesioned rats perseverated more than control Ss and ran faster over days on forced trials. The results are consistent with a response inhibition interpretation of hippocampal function and emphasize the importance of pretraining and changes over time in interpreting the effects of hippocampal lesions.