Sounds and behavioral relevance modulate oculomotor responses toward images rendered invisible by continuous flash suppression

Abstract

People can act on visual stimuli without being aware of them. This thesis examined how different forms of behavioral relevance and sounds shape oculomotor responses to unseen images. We used continuous flash suppression to render images invisible and tracked observers’ eye movements during stimulus presentation. Across three studies, we presented different types of behaviorally relevant images, including objects, human body parts, emotional facial expressions, and socially relevant faces. In two studies, we paired images with sounds to test whether auditory modulation of eye movements depends on visual awareness. For each study, we verified the absence of visual awareness of the images using objective measures (chance performance in image localization and categorization tasks) and subjective measures (reports of zero image visibility). Eye tracking data from trials with successful suppression revealed distinct gaze patterns. We found that sound-enhanced threat-related objects (Study 1), sound-enhanced neutral faces (Study 2), fearful faces (Study 2) and socially relevant out-group faces (Study 3) significantly biased observers’ eye movements when they remain unseen. Notably, auditory modulation of eye movements is not contingent on visual awareness of the stimulus but may depend on stimulus type. Together, these findings suggest that oculomotor responses can be guided by behaviorally relevant visual information even without visual awareness, and that such responses can be further enhanced crossmodally.