The pupillary response as an indicator of arousal and cognition

Psychological research on the pupillary response since 1960 has focused on an arousal interpretation and a cognitive interpretation. Experiment 1 was an attempt to manipulate some arousal factors while controlling the cognitive demands of the task. Pupil size was cinematographically recorded while subjects who had different degrees of reported fear of snakes listened to passages describing imagined interactions with a snake in different proximities. There was also a set of control passages that made no mention of snakes but were otherwise semantically and syntactically identical to the aversive passages. The pupillary response showed no influence of the arousal manipulations, but rating and behavioral data indicated that the arousal variables had been effective. The cognitive demands of the task were clearly indicated by the pupillary response. In Experiment 2 two types of tasks were used: one that employed both arousal (incentive) and cognitive factors and another that had an arousal manipulation (threat of shock) but no explicit cognitive demands. The pupil response was recorded as well as heart rate, skin conductance, and EMG. The pupillary response showed an effect of the arousal manipulations only when cognitive demands were minimal. The results of both experiments are consistent with the view that cognitive demands take priority over arousal factors in affecting the pupillary response. Heart rate did show arousal effects that were not preempted by cognitive demands.