REPRESENTATION STRENGTH IN PIGEON SHORT-TERM-MEMORY - EFFECT OF DELAYTRAINING

An attempt was made to manipulate the strength of internal stimulus re presentations by exposing pigeons to brief delays between sample offse t and comparison onset in a delayed conditional discrimination. In Exp eriment 1, pigeons were first trained on delayed conditional discrimin ation with either short (0.5-sec) delays or no delays. When delays wer e increased by 2.0 sec, birds trained with a delay performed at a high er level than did birds trained with no delays. In Experiment 2, subje cts were first trained on a delayed simple discrimination. Following a circle stimulus, responses to a white key were reinforced; however, f ollowing a dot stimulus, responses to the white key were not reinforce d. The pigeons were then trained on a delayed conditional discriminati on involving hue samples and line-orientation comparisons with differe ntial outcomes. Choice of vertical following red yielded food; choice of horizontal following green yielded no food. Mixed delays were then introduced to birds in Group Delay, whereas birds in the control group received overtraining. When tested on a delayed simple discrimination with hue stimuli (red and green initial stimuli followed by white res ponse stimulus), pigeons in Group Delay tended 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 cont rol group). Thus, experience with delays appears to strengthen stimulu s representations established during training.