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Repetition blindness (RB) is a visual deficit, wherein observers fail to perceive the second occurrence of a repeated item in a rapid serial visual presentation stream. Chen and Yeh (Psychon Bull Rev 15:404–408, 2008) recently observed a reduction of the RB effect when the repeated items were accompanied by two sounds. The current study further manipulated the pitch of the two sounds (same versus different) in order to examine whether this cross-modal facilitation effect is caused by the multisensory enhancement of the visual event by sound, or multisensory Gestalt (perceptual grouping) of a new representation formed by combining the visual and auditory inputs. The results showed robust facilitatory effects of sound on RB regardless of the pitch of the sounds (Experiment 1), despite an effort to further increase the difference in pitch (Experiment 2). Experiment 3 revealed a close link between participants’ awareness of pitch and the effect of pitch on the RB effect. We conclude that the facilitatory effect of sound on RB results from multisensory enhancement of the perception of visual events by auditory signals.

We report several studies on the effects of removing the medial premotor cortex (supplementary motor area) in monkeys. The removal of this area alone does not cause either paralysis or akinesia. However, the animals were poor at performing a simple learned task in which they had to carry out an arbitrary action: they were taught to raise their arm in order to obtain food in a foodwell below. They were impaired whether they worked in the light or the dark. They were impaired when they had to perform the movements at their own pace, but much less impaired when a tone paced performance. Monkeys with lesions in the anterior cingulate cortex were as impaired as monkeys with medial premotor lesions at performing this task at their own pace. However, monkeys with lateral premotor lesions were less impaired. We conclude that the medial premotor areas play a crucial role in the performance of learned movements when there is no external stimulus to prompt performance.

Monkeys with medial premotor cortex (MPC) lesions are impaired on a simple learned task that requires them to raise their arm at their own pace. However, they can succeed on this task if they are given tones to guide performance. In the externally paced task the tones could aid performance in several ways. They tell the animal when to act (trigger), they remind the animal that food is available and so motivate (predictor), and they remind the animal of what to do (instruction). Monkeys with MPC lesions can respond quickly to visual cues (experiment 1), and they can respond as well as normal monkeys when there is no immediate trigger (experiment 2). They are also quick to relearn a task in which external cues tell them what to do (experiment 5). However, they are poor at selecting between movements on a simple motor sequence task (experiment 3), and they are poor at changing between two movements (experiment 4). On these tasks there were cues to act as triggers and predictors, but there were no external instructions. We conclude that the reason why animals with MPC lesions perform better with external cues is that these cues act as instructions. The cues prompt retrieval of the appropriate action. This is true whether the task requires the animal to perform one action (experiments 1 and 2) or to select between actions (experiments 3 and 4).