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Harold Greene, James Brown; Effects of Simulated Scotomas on Pre-saccadic Fixation Durations. Journal of Vision 2015;15(12):208. doi: 10.1167/15.12.208.
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© 2017 Association for Research in Vision and Ophthalmology.
Altitudinal scotomas from visual cortex injuries are rare, and upper visual field (UpVF) scotomas are rarer than lower visual field (LoVF) scotomas. Simulation of scotomas provides insight on adaptive behavior in defective visual fields. For example, fixation durations increase in the presence of simulated peripheral-surround scotomas. While useful, peripheral-surround scotomas do not address functional specialization in specific visual field areas. Electrophysiological and functional data suggest that processing of visual information below fixation (i.e., LoVF) is typically superior to processing of information above fixation (i.e., UpVF). An exception is the case of the saccadic system, where an UpVF bias is evident for pre-saccadic fixation durations (PSFDs) in visual search tasks. PSFDs are briefer when the ensuing saccade is directed upwards. Generally, the LoVF is biased towards global/sensory detection processing near the body, and the upper visual field is biased towards local/saccadic checking of distant objects. Here we examined how an UpVF/LoVF scotoma affects PSFDs. The superiority of LoVF processing suggests a LoVF scotoma may indiscriminately prolong PSFDs. However, given the specialization of the UpVF in saccadic behavior, a LoVF scotoma may be expected to prolong PSFDs only for downward-bound saccades. Eye movements were monitored as observers engaged in visual search with either no scotoma (N=12), an UpVF scotoma (N=12), or a LoVF scotoma (N=12). Scotomas blocked the entire UpVF or LoVF, 2 deg from the current fixation point. PSFDs associated with saccades directed within 90 deg visual field bins were compared. Contrast analyses revealed a vertical field asymmetry for each task, such that PSFDs were briefer for saccades directed upwards than downwards. Importantly, while the UpVF scotoma prolonged PSFDs only for upward-bound saccades, the LoVF scotoma prolonged PSFDs for both upward- and downward-bound saccades. The results demonstrate the importance of LoVF processing, even in a saccadic task.
Meeting abstract presented at VSS 2015
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