Pupillary dilations in response control across contexts

Pupil dilation is a sensitive marker of motor processing and is influenced by task demands. Previous studies have shown that pupil dilation increases with response complexity and is more pronounced when a response must be executed rather than inhibited. However, it is not clear whether more nuanced adjustments are made in relation to the context of the action. To address this issue, we performed two experiments. In Experiment 1, participants heard a “ready” tone followed by a “go” tone and responded with either a single key press (simple response) or a sequence of four presses (complex response). In Experiment 2, intermingled with go trials, no-go trials (50% no-go tone, instead of the go tone) were presented. The same participants were asked to withhold the response following the go signal. We found that increased response complexity in go trials led to greater pupil dilation. This effect was also observed in the go/no-go task, in both go and no-go trials. However, in the go/no-go task, the differences were reduced. These findings indicate that pupil size is associated with the complexity of the response and that this association is modulated by the specific context. This study supports the view that action generation is characterized by a continuous and nuanced interplay between the somatic and autonomic nervous systems.