Fixational saccades alter the gap effect

Abstract

The reaction times of saccadic eye movements have been studied extensively as a probe for cognitive behavior controlled by large-scale cortical and subcortical neural networks. Recent studies have shown that the reaction times of targeting saccades toward peripheral visual stimuli are prolonged by fixational saccades, the largest miniature eye movements including microsaccades. We have shown previously that the frequency of fixational saccades is decreased by volitional action preparation controlled internally during the antisaccade paradigm (look away from a stimulus). Instead, here we examined whether fixational saccade modulation induced externally by sensory events could also account for targeting saccade facilitation by the same sensory events. When targeting saccades were facilitated by prior fixation stimulus disappearance (gap effect), fixational saccade occurrence was reduced, which could theoretically facilitate targeting saccades. However, such reduction was followed immediately by the rebound of fixational saccade occurrence in some subjects, which could eliminate potential benefits from the previous fixational saccade reduction. These results do not mean that fixational saccades were unrelated to the gap effect because they indeed altered that effect by delaying targeting saccade initiation on trials without the fixation gap more strongly than trials with it. Such changes might be attributed to the disruption of volitional saccade preparation because the frequency of fixational saccades observed in this study was associated with the ability of volitional control over antisaccade behavior. These results suggest that fixational saccades alter the gap effect on targeting saccade reaction times, presumably by disrupting volitional saccade commands.

Gap Effect Abnormalities during a Visually Guided Pro-Saccade Task in Children with Attention Deficit Hyperactivity Disorder

“…We designed this model to provide the simplest possible explanation for the saccade abnormalities observed in ADHD. Recently Watanabe et al suggested that fixation saccades alter the gap effect, presumably by disrupting volitional saccade preparation [ 60 ]. However, an important limitation of this model is that it does not take into account execution signals for saccades, which may also be dysfunctional in ADHD.…”

Ocular drift reflects volitional action preparation

“…We have shown previously that individual differences in fixational saccades are correlated with those in antisaccade performance (Watanabe, Matsuo, Zha, MacAskill, & Kobayashi, ; Watanabe et al., ). Here, we extended the previous findings and identified relationships between antisaccade performance and ocular drift across subjects along with the other fixational eye movements.…”

Microsaccade direction reflects the economic value of potential saccade goals and predicts saccade choice

“…Presumably, this is because early, high activity at the rostral pole is more likely to surpass threshold, and later, low activity is less likely to surpass threshold. It is unclear from this account why some subjects showed a rebound in microsaccade frequency in the middle of the warning period, although such rebounds have been reported previously (Watanabe et al 2014). Others have suggested that (micro)saccade production is controlled, in part, by an oscillatory rhythm, and stimuli onsets or offsets can reset this oscillator (Hafed and Ignashchenkova 2013).…”

“…Other subjects displayed a decrease in microsaccade frequency that remained low throughout the remainder of the warning period. This variability may result, in part, from differences in subjects (Watanabe et al 2014), species (Martinez-Conde et al 2009), and warning-period durations, used here across species. Consistently, microsaccade frequency was lowest at the end of the respective warning periods, just before target presentation, suggesting that expected saccade timing influenced microsaccade generation (Hafed et al 2011;Pastukhov and Braun 2010).…”

“…Microsaccades benefit the performance of high-acuity tasks (Ko et al 2010;Poletti et al 2013;Rucci et al 2007). Visual perception can be altered before microsaccades, and perceptual/motor responses are suppressed after microsaccades (Hafed 2011(Hafed , 2013Hafed and Krauzlis 2010;Herrington et al 2009;Watanabe et al 2014). In turn, their production is not entirely random, as microsaccade occurrence, direction, and timing have been correlated to the appearance of sensory stimuli, attentional processes, and the degree of active fixation (Engbert and Kliegl 2003;Hafed and Clark 2002;Hafed et al 2011;Rolfs et al 2008;Watanabe et al 2013).…”