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Abstract:
Spot pursuit is thought to require attention, yet pursuit of larger targets does not. Interestingly, catch-up saccades are also more frequent during spot pursuit. Thus it is possible that the saccadic system, which itself is attentive, might confer the attentive properties to pursuit, while small-object pursuit itself is also inattentive. Alternatively, spot pursuit may require attention because the saccadic system is contributing to pursuit velocity in addition to triggering catch-up saccades. Here we test this by adapting the saccadic system and seeing if the adaptation transfers to pursuit. During adaptation, observers fixated a central spot and generated saccades to a flashed 10° eccentric target. While the saccade was in progress, the target was displaced 3° towards the fixation point. An EyeLink 1000 recorded eye movements at 1000 Hz, and provided gaze contingent target displacement. Saccade adaptation proceeded for 100 trials, following which saccade amplitude was significantly shortened. Following adaptation, observers pursued a spot stimulus (0.5°) or a large concentric ring of 8 spots (6° diameter) that moved from the center of the screen at a constant velocity of 10°/sec. We found that steady-state eye velocity in the adapted saccade direction was significantly reduced following saccade adaptation but only for spot pursuit – eye velocity during pursuit of the large target was not affected. The results are evidence that saccadic adaptation transfers to spot but not large object pursuit, and suggest that sub-saccadic signals contribute to smooth eye velocity during pursuit of a small spot.
