Fixation-related saccadic inhibition in free viewing in response to stimulus saliency

Abstract

Microsaccades that occur during fixation were studied extensively in response to transient stimuli, showing a typical inhibition (Oculomotor Inhibition, OMI), and a later release with a latency that depends on stimulus saliency, attention, and expectations. Here, we investigated the hypothesis that in free viewing every saccade provides a new transient stimulation that should result in a stimulus-dependent OMI like a flashed presentation during fixation. Participants (N = 16) freely inspected static displays of randomly oriented Gabor texture images, with varied contrast and spatial frequency (SF) for periods of 10 s each. Eye tracking recordings were divided into epochs triggered by saccade landing (> 1 dva), and microsaccade latency relative to fixation onset was computed (msRT). We found that the msRT in free viewing was shorter for more salient stimuli (higher contrast or lower SF), as previously found for flashed stimuli. It increased with saccade size and decreased across successive saccades, but only for higher contrast, suggesting contrast-dependent repetition enhancement in free viewing. Our results indicate that visual stimulus-dependent inhibition of microsaccades also applies to free viewing. These findings are in agreement with the similarity found between event-related and fixation-related potentials and open the way for studies combining both approaches to study natural vision.

Face familiarity revealed by fixational eye movements and fixation-related potentials in free viewing

“…Whereas stimulus saliency, such as high contrast, is known to shorten the inhibition 17 , prolonged inhibition was found in response to deviants 18 . Although most studies used flashed stimuli, we have recently found similar inhibitory patterns in free viewing in response to stimulus saliency 19 .…”

“…In our recent paper, fixation-related OMI was measured for low-level stimuli in free viewing 19 . We found a resembling effect for OMI across saccades in the form of shortening of the OMI by repetition priming.…”

“…BC has a range of 0–1, where values greater than ~ 0.555 (the value for the uniform distribution) indicate bimodal or multimodal data distributions 49 . Eye tracking epochs were extracted, triggered by saccade (> 1 dva ) landing time, as in our previous study 19 , in a range of − 0.2 s to 0.8 s relative to the fixation onset with some overlap between epochs. This was taken into consideration when computing the microsaccade Reaction Time (msRT).…”

Face Familiarity Revealed by Fixational Eye Movements and Fixation-Related Potentials in Free Viewing

“…Whereas stimulus saliency, such as high contrast, is known to shorten the inhibition (Bonneh, Adini, & Polat, 2015), prolonged inhibition was found in response to deviants (Valsecchi, Betta, & Turatto, 2007). Although most studies used flashed stimuli, we have recently found similar inhibitory patterns in free viewing in response to stimulus saliency (Kadosh & Bonneh, 2022a).…”

“…In our recent paper, fixation-related OMI was measured for low-level stimuli in free viewing (Kadosh & Bonneh, 2022a). We found a resembling effect for OMI across saccades in the form of shortening of the OMI by repetition priming.…”