Abstract
Human faces capture attention more than other visual stimuli. Normal observers notice changes in faces more rapidly than changes to other visual objects and brain damaged patients suffering from visual neglect show sensitivity to faces in their neglected hemifield. Here we investigated whether such face specific biases rely on automatic (involuntary) or voluntary orienting responses. To this end, we used an anti-saccade paradigm, which requires the ability to inhibit a reflexive automatic response and to generate a voluntary saccade to the opposite direction of the target. To control for potential low-level confounds in the eye-movement data, we manipulated the high-level visual properties of the stimuli while normalizing their low-level visual properties.
Stimuli consisted of faces and cars (normalized for amplitude and contrast spectra), as well as noise patterns generated by randomizing the phase-spectrum of the normalized face and car images. We recorded the eye movements of 20 participants while performing either pro- or anti-saccades to a face, car or noise pattern randomly presented to the left or right of a fixation point. For each trial, a symbolic cue randomly instructed the observer to generate either a pro-saccade or an anti-saccade.
We report a significant increase in anti-saccade error rates for faces compared to cars and noise patterns, as well as faster pro-saccades to faces and cars in comparison to noise patterns. Moreover, the fixation duration after the first saccade was much shorter for pro-saccades to faces compared to other stimuli, suggesting a more efficient processing for faces. These results indicate that human faces generate a stronger involuntary orienting response than other visual objects in line with an automatic processing for faces. Importantly, this involuntary processing cannot be accounted for by low-level visual factors.
This work was supported by the Economic and Social Research Council and the Medical Research Council (RES-060-25-0010).