Conscious processing of auditory regularities induces a pupil dilation.

Pupil dilation is a reliable marker of conscious mental effort. In healthy volunteers, consciously detected violations of global auditory patterns triggered pupil dilation, whether participants actively counted or passively listened. This effect appeared at both group and individual levels. Unreported violations of global patterns, and local violations that do not require conscious awareness, produced no pupil dilation. The results were replicated with phonemes. Pupil dilation appears to be a somatic marker of conscious access in the auditory modality, offering a way to probe conscious processing without interrupting a person's stream of thought.

Study at a glance

Abstract

Pupil dilation has been reliably identified as a physiological marker of consciously reportable mental effort. This classical finding raises the question of whether or not pupil dilation could be a specific somatic signature of conscious processing. In order to explore this possibility, we engaged healthy volunteers in the 'local global' auditory paradigm we previously designed to disentangle conscious from non-conscious processing of novelty. We discovered that consciously reported violations of global (inter-trials) regularity were associated with a pupil dilation effect both in an active counting task and in a passive attentive task. This pupil dilation effect was detectable both at the group-level and at the individual level. In contrast, unreported violations of this global regularity, as well as unreported violations of local (intra-trial) regularity that do not require conscious access, were not associated with a pupil dilation effect. We replicated these findings in a phonemic version of the 'local global'. Taken together these results strongly suggest that pupil dilation is a somatic marker of conscious access in the auditory modality, and that it could therefore be used to easily probe conscious processing at the individual level without interfering with participant's stream of consciousness by questioning him/her.