Abstract
Previous studies have shown that face stimuli elicit extremely fast and involuntary saccadic responses toward them, relative to other categories of visual stimuli. In the present study, we further investigated to what extent face stimuli influence the programming and execution of saccades examining their amplitude. We performed two experiments using a saccadic choice task: two images (one with a face, one with a vehicle) were simultaneously displayed in the left and right visual fields of participants who had to initiate a saccade toward the image (Experiment 1) or toward a cross in the image (Experiment 2) containing a target stimulus (a face or a vehicle). Results revealed shorter saccades toward vehicle than face targets, even if participants were explicitly asked to perform their saccades toward a specific location (Experiment 2). Furthermore, error saccades had smaller amplitude than correct saccades. Further analyses showed that error saccades were interrupted in mid-flight to initiate a concurrently-programmed corrective saccade. Overall, these data suggest that the content of visual stimuli can influence the programming of saccade amplitude, and that efficient online correction of saccades can be performed during the saccadic choice task.
Highlights
Faces are very salient visual stimuli for humans and our visual system has developed efficient mechanisms to preferentially detect and process them
Results revealed that participants made significantly more error saccades when the target stimulus was a vehicle than when it was a face
ANOVAs with Target Stimulus (Face, Vehicle) and Saccade Accuracy (Correct, Error) as within-subject factors were performed on mean saccadic reaction times (SRTs) of the first saccade and saccade amplitude
Summary
Faces are very salient visual stimuli for humans and our visual system has developed efficient mechanisms to preferentially detect and process them. Participants have to perform a saccade as fast as possible toward the target stimulus (e.g., a face[3,12,13,14,15]) This task requires multiple processes (i.e. simultaneous processing of two images, a categorical decision, programming and execution of an eye movement toward the target), it has been shown that human observers are able to initiate accurate saccadic responses toward a face with extremely short latencies of just 100–110 ms[3]. Further studies using the same saccadic choice task revealed that the bias for face stimuli persists even if they are presented at large eccentricities (up to 80°)[13] or if stimuli are filtered so that only coarse, low-spatial frequency information remains in the stimulus[14] Overall, these eye-tracking data suggest that faces contain specific information that influences the programming of saccades by triggering extremely fast and automatic orienting responses toward them. It is for example possible that a saccade program toward a face stimulus interferes more strongly with a concurrently programmed saccade toward a vehicle than the other way around
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