Visual working memory of jungle crows (Corvus macrorhynchos) in operant delayed matching-to-sample

We examined the capacity of visual working memory in three male jungle crows using an operant delayed matching-to-sample procedure. In the delayed matching-to-sample, each trial started with the presentation of a sample stimulus, followed by the presentation of comparison stimuli after a delay interval. The choice of the matching comparison was rewarded. Jungle crows showed a steady decline in proportion correct with increasing delay interval. The proportion correct was higher when the sample stimulus was the same in the preceding trial, suggesting that proactive interference prevented the birds from retrieving the memory successfully. The analysis of response time revealed that response time was faster in correct than incorrect trials when the matching performance was acquired. Furthermore, response time linearly increased as the delay interval increased. Response time may reflect the processing of scanning memory as well as the level of confidence in their choice when retrieving.