Effects of a task-relevant response on pupil size.

Abstract

ABSTRACTThis experiment examined the effects on pupil size of the relevance of an overt response to a cognitive task. Sixteen Ss were assigned to two experimental groups. In one group Ss were required to judge the pitch equality of tones and, subsequently, indicate their decision by pressing or not pressing a telegraph key. In the other group Ss were required to make the pitch‐discriminations, but the key press response was unrelated to the preceding cognitive task. Continuous photographs of each S's pupil were taken during the experiment. Results showed that a small amount of pupillary dilation occurred during the discrimination task in the group where the key press was irrelevant to the pitch‐discrimination. In the group where S's behavior indicated task fulfillment, however, a significantly greater increase in pupil size occurred, the amount of dilation being larger when task completion was indicated by the key press response than when fulfillment was indicated by no key press. The findings were discussed in terms of arousal associated with apprehension about evaluation, and muscle tension from anticipation of making the overt response.