Rapid Visual Processing of Picture Stimuli by Pigeons in an RSVP Task

Three experiments that were carried out in series with 5 pigeons used novel training methods to investigate the rapid visual processing of picture stimuli by pigeons. On each trial, a sequence containing 1 of 2 bird pictures (the target) and nontarget bird pictures (the distractors) was presented. After the termination of the last item in the sequence, the pigeons were required to choose 1 of 2 colored squares corresponding to the target presented in the preceding sequence. The pigeons learned the task with 2-item lists (1 target and 1 distractor) in Experiment1 and with 3-item lists (1 target and 2 distractors) in Experiment 2. The pigeons showed better performance when the target appeared last in the sequence (a recency effect) and poorer performance the shorter the item duration. In Experiment 3, the pigeons were tested with 3-item lists, but on half the trials 2 distractors were replaced with blanks; for example, a target-distractor-distractor trial became a target-blank-blank trial and performances on these trials were compared. When the item duration was 80 ms or greater, omission of the distractors did not have an effect of increasing performance, suggesting that the recency effect was determined by simple passage of time. With the item durations less than 80 ms, the distractors interfered with memory of the target. When the distractors were omitted, performance remained slightly above chance even at the shortest, 17-ms, item duration. These findings indicate that pigeons are equipped with visual mechanisms that enable them to process visual stimuli rapidly.