Shortening and prolongation of saccade latencies following microsaccades

Martin Rolfs, Jochen Laubrock

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DOI 10.1007/s00221-005-0148-1

When the eyes fixate at a point in a visual scene, small saccades rapidly shift the image on the retina. The effect of these microsaccades on the latency of sub- sequent large-scale saccades may be twofold. First, microsaccades are associated with an enhancement of visual perception. Their occurrence during saccade tar- get perception could, thus, decrease saccade latencies. Second, microsaccades are likely to indicate activity in fixation-related oculomotor neurons. These represent competitors to saccade-related cells in the interplay of gaze holding and shifting. Consequently, an increase in saccade latencies would be expected after microsaccades. Here, we present evidence for both aspects of micro- saccadic impact on saccade latency. In a delayed re- sponse task, participants made saccades to visible or memorized targets. First, microsaccade occurrence up to 50 ms before target disappearance correlated with 18 ms (or 8%) faster saccades to memorized targets. Second, if microsaccades occurred shortly (i.e., <150 ms) before a saccade was required, mean saccadic reaction time in visual and memory trials was increased by about 40 ms (or 16%). Hence, microsaccades can have opposite consequences for saccade latencies, pointing at a differ- ential role of these fixational eye movements in the preparation of saccade motor programs.



Experimental Brain Research