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Accepted: 16 March 2023 / Published online: 31 March 2023
© The Psychonomic Society, Inc. 2023
Abstract
The programming of rapid eye movements or "saccades" involves a large collection of neural substrates. The subcortical oculomotor center - the superior colliculus (SC) - contains a topographical motor map that encodes saccade vectors. Using a visual distractor task, the present study examined a classic model of the SC motor map, which assumes a symmetrical representation of the upper visual field (UVF) and lower visual field (LVF). Visual distractors are known to attract or repel the saccade trajectory, depending on their angular distance from the target. In the present study, the distractor (if presented) was placed at a location that mirrored the target in the opposite visual field (upper or lower). The symmetrical SC model predicts equivalent directional deviations for saccades into the UVF and LVF. The results, however, showed that the directional deviations evoked by visual distractors were much stronger for saccades directed to the LVF. We argue that this observation is consistent with the recent neurophysiological finding that the LVF is relatively under-represented, as compared to the UVF, in the SC and possibly in other oculomotor centers. We conclude the paper with a suggested revision to the SC model.
Keywords Eye Movements · Mechanisms · Motor control · Inhibition
(ProQuest: ... denotes formulae omitted.)
Introduction
Humans make two to three rapid eye movements or "saccades" while awake (Rayner, 1998). Saccades are either voluntarily controlled or triggered by salient external events (i.e., oculomotor capture; Theeuwes et al., 1998). Saccades quickly shift gaze from one place to another so the brain can effectively sample information from the environment despite a tiny fovea on the retina. The control of saccades involves a collection of neural substrates (for an overview, see Munoz et al., 2007; Schall, 1997), including but not limited to the frontal eye fields (FEFs; for a review, see Schall, 1997), the lateral intraparietal cortices (LIP; for a review, see Glimcher, 2001), the basal ganglia (for a review, see Hikosaka et al., 2006), and the superior colliculus (SC; e.g., Robinson, 1972; for a review, see White & Munoz, 2011).
The SC has a layered structure. The superficial layers process external visual input, the deep layers process multisensory...