Abstract
Selective spatial attention enhances task performance at restricted regions within the visual field. The magnitude of this effect depends on the level of attentional load, which determines the efficiency of distractor rejection. Mechanisms of attentional load include perceptual selection and/or cognitive control involving working memory. Recent studies have provided evidence that microsaccades are influenced by spatial attention. Therefore, microsaccade activities may be exploited to help understand the dynamic control of selective attention under different load levels. However, previous reports in humans on the effect of attentional load on microsaccades are inconsistent, and it is not clear to what extent these results and the dynamic changes of microsaccade activities are similar in monkeys. We trained monkeys to perform a color detection task in which the perceptual load was manipulated by task difficulty with limited involvement of working memory. Our results indicate that during the task with high perceptual load, the rate and amplitude of microsaccades immediately before the target color change were significantly suppressed. We also found that the occurrence of microsaccades before the monkeys’ detection response deteriorated their performance, especially in the hard task. We propose that the activity of microsaccades might be an efficacious indicator of the perceptual load.
Highlights
Duing gaze fixation, our eyes are not still but often perform small and involuntary movements
We found that the microsaccade rate immediately before the target color change was significantly suppressed while the perceptual load increased
Errors resulting from fixation break were early release and late release
Summary
Our eyes are not still but often perform small and involuntary movements. Pastukhov and Braun[9] used visual recognition tasks that required either a low attentional load (reporting color) or a high attentional load (reporting letter shape) They found a lower microsaccade rate and better microsaccade directional congruency associated with higher attentional load. Siegenthaler et al.[27] required the human subjects to mentally count forward (low load) or backward (high load) in a mental arithmetic task and showed that the microsaccade rate decreased and the microsaccade amplitude increased, corresponding to higher working memory load. Hicheur et al.[24] employed a forced choice-task paradigm in which participants had to judge the orientation of a titled stimulus embedded in static or dynamic backgrounds They found significantly higher microsaccade rate when participants were engaged in the execution of the discrimination task (high load) compared to that when they did not need to make response (low load). Clarification is needed of the dynamic link between the perceptual load and microsaccades, which in turn would offer a unique window probing the attentional load
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