Impact of conscious awareness on pupillary response to faces

Abstract

Pupillary response reflects not only ambient light changes but also top-down factors. Nevertheless, it remains inconclusive whether the conscious awareness modulates the pupillary response. We investigated pupillary responses to faces under different conscious conditions using continuous flash suppression (CFS). In Experiment 1 and 2, we used a breaking-CFS procedure in which participants had to detect the face from suppression. Results showed that the pupil constricted more to upright faces than to inverted faces before the face was detected, suggesting that pupillary responses reflect face processing entering consciousness. In Experiment 3 and 4, we used a fixed duration-CFS procedure with both objective performance and subjective reports. Different pupillary responses were observed only when the participant was aware of the face. These findings imply that the conscious awareness is critical for modulating autonomic neural circuits of the pupillary function. The corresponding pupillary responses may reflect dynamic processes underlying conscious awareness.