Covert and overt orienting to gaze direction cues and the effects of fixation offset.

Abstract

We examined covert and overt orienting in response to non-predictive gaze direction cues and investigated whether the subcortical superior colliculus (SC) plays a role in this type of orienting. Participants viewed a centrally presented gazing schematic face and responded to targets appearing at gazed-at or non-gazed-at locations either by making a keypress response while maintaining central fixation or by making an eye movement to the target. For both response conditions, the fixation stimulus (the gazing face) either remained on the screen or was extinguished at the time of target presentation, a manipulation known to engage and disengage the SC. Results revealed that participants making manual responses oriented covertly to the gazed-at location regardless of the fixation condition, and that participants making eye movements oriented overtly only if the fixation stimulus remained on the screen. Overt gaze-triggered orienting was not enhanced relative to covert orienting, and the fixation offset effect was not reduced for averted gaze cues relative to straight gaze cues. These findings suggest that gaze direction cues do not activate or predisengage the oculomotor system, and thus that orienting to gaze direction does not engage the SC. This is consistent with the view that gaze-triggered orienting is a unique form of reflexive orienting that depends crucially on cortical processes.