Theme 4: Functional roles of microsaccades

Visual fixation is accompanied by miniature eye movements called fixational eye movements (FEMs). Three types of FEMs (drift, tremor, and microsaccades) can be distinguished (Rolfs, 2009). Yet, the functional role of microsaccades was questioned in early studies: several groups provided evidence that microsaccades are nothing but oculomotor noise, as argue by Collewijn & Kowler, (2008). In contrast, Ko, Poletti & Rucci, (2010) replicated the “threading a needle” task in a highly controlled virtual environment and observed that the frequency of occurrence of the smallest microsaccades significantly increased near the completion of the task, while they were rare during threading or fixation. Such potential noise-enhanced properties of microsaccades were recently modeled using a basic model of retinal photoreceptors (Zozor, Amblard & Duchene, 2009). The terminology noise-enhanced denotes the ability of systems to enhance their performances in the presence of noise. Since microsaccades generate rapid fluctuations in the retinal image, Zozor et al. (2009) suggested that these visual transients might be helpful in terms of spatial information processing.

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