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Rakesh Nanjappa, Robert M McPeek; Superior colliculus activity represents future saccade goals during visual search. Journal of Vision 2020;20(11):1454. doi: https://doi.org/10.1167/jov.20.11.1454.
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While searching for a target object in a scene, we move our eyes in a series of fixations and saccades to collect information incrementally. This requires the oculomotor system to make a series of decisions concerning where to saccade next. Previous studies suggest that this decision process can evolve dynamically, with a future saccade being planned in parallel with the current movement, rather than as a strictly serial process wherein the system chooses the goal of the next saccade only during the preceding fixation.
We examined single-unit neural activity in the macaque superior colliculus (SC) related to planning sequences of saccades in a self-paced visual search task. In each trial, an array of multiple targets and distractors (distinguished by color) was presented. One of the targets was randomly selected as the stimulus which would provide a reward when fixated, and monkeys were trained to sequentially fixate different stimuli in the array until they obtained the reward.
We found that monkeys more often made saccades to targets than to distractors, and that SC activity was higher for saccades made into the receptive field (RF) than elsewhere. Interestingly, SC activity was greater before and during a saccade out of the RF when a future movement would subsequently be made to the current RF stimulus. This enhanced activity suggests that SC selection of the target for a future saccade can occur during planning and execution of the current saccade. The magnitude of this enhancement depended on how soon the eye landed on the RF location after the current saccade, with a larger modulation when the RF location became the saccade goal sooner rather than later. These findings indicate that in a self-paced visual search task, the oculomotor system dynamically plans future saccades, and that SC activity represents this process.
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