Immediate preparatory influences on microsaccades before saccade onset to endogenously vs. exogenously defined targets S Ohl1, S Brandt1, R Kliegl2 |
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1Charité Universitätsmedizin Berlin, Germany |
| During fixation, small-amplitude eye movements are observed. So called microsaccades can be influenced by bottom-up and top-down processes and they are thought to share many aspects of large saccades, just on a smaller amplitude-scale. In the present experiment, we study whether preparatory processes modulate microsaccade statistics (e.g., rate and amplitude) before execution of a response saccade. To this end, we examined microsaccades before saccades to targets defined by an endogenous vs. exogenous cue in a blocked design. We observed a strong preparatory influence on microsaccade statistics in terms of a higher microsaccade rate before endogenously as compared to exogenously defined targets. This effect was further substantiated by an additional influence of target eccentricity. The modulation of microsaccade rate as a function of the preparatory set can be explained by a model of microsaccade generation, which is based on two assumptions. First, microsaccades are generated in the center of a saccadic motor map, while increasingly distant sites from the center code for increasingly large saccades. Second, attending a location in the visual scene increases activity at the corresponding site in the saccadic motor map. Thus, our study provides important insights into the implementation of immediate preparatory processes on microsaccade generation. |
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