Representation Strength in Pigeon Short-Term Memory: Effect of Delay Training

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Animal Learning and Behavior





An attempt was made to manipulate the strength of internal stimulus representations by ex- posing pigeons to brief delays between sample offset and comparison onset in a delayed conditional discrimination. In Experiment 1, pigeons were first trained on delayed conditional discrimination with either short (0.5-sec) delays or no delays. When delays were increased by 2.0 sec, birds trained with a delay performed at a higher level than did birds trained with no delays. In Experiment 2, subjects were first trained on a delayed simplediscrimination. Following a circle stimulus, responses to a white key were reinforced; however, following a dot stimulus, responses to the white key were not reinforced. The pigeons were then trained on a delayed conditional discrimination involving hue samples and line-orientation comparisons with differential outcomes. Choice ofvertical following redyielded food; choice of horizontalfollowinggreen yielded no food. Mixed delayswere then introducedtobirdsin Group Delay, whereas birds inthe control group received overtraining. When tested on a delayed simple discrimination with hue stimuli (red and green initialstimuli followed by white responsestimulus), pigeons inGroupDelaytended to perform at a higher level than did birds in the control group (i.e., although the birds in both groups responded more following red than following green, birds in Group Delay did this to a greater extent than did birds in the control group). Thus, experience with delays appears to strengthen stimulus representations established during training.