Action-based distractor effects on the manual response times of chimpanzees during discrimination tasks

Two chimpanzees performed visual search and simple discrimination tasks in which manual pointing to the target stimulus was required. To clarify the action-based interference effects of the distractors, response time data were analyzed on the basis of the relationship among the positions of the target, distractors, and hand. In both tasks, clear action-based interference effects were observed. Firstly, distractors along the path of the manual response to the target caused greater interference (the response-path effect). Secondly, when distractors were located ipsilateral to the responding hand, response times were longer (the ipsilateral effect). These results are consistent with previous studies on selective reaching in humans, and they suggest that manual responses in chimpanzees are controlled by action-centered attention as is the case for humans.