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Sara Simpson, Mathias Abegg, Jason JS Barton; Short Term Adaptation of Visual Search Strategies in Simulated Hemianopia. Journal of Vision 2010;10(7):1127. doi: 10.1167/10.7.1127.
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Objective: In this study we isolated the effects of strategic adaptation of healthy individuals to a simulated homonymous hemianopia (sHH) and studied the time course of early changes in search task performance. Background: Patients with homonymous visual field defects from occipital stroke are known to have impaired visual search performance both clinically and experimentally. Rehabilitation training is often used to improve on such deficits. If improvement occurs it is not clear as to whether it is due to strategic adaptation or recovery through neural plasticity. Moreover, it is not clear how rapidly adaptation occurs. Design/Methods: We used a video eyetracker with a gaze-contingent display to simulate hemianopia. 10 healthy subjects performed a letter search task under conditions of normal viewing, right sHH and left sHH, with 25 trials per condition. We measured search performance in terms of both speed and accuracy, assessed the effect of viewing condition and, to reveal adaptation effects, assessed the time course within a given viewing condition. Results: Visual search was slower and less accurate in the sHH than normal viewing conditions. Search performance was comparable in left and right sHH. In the normal viewing condition subjects showed task-learning improvements in search speed over the first 6 trials, and then maintained a steady asymptotic performance. After the onset of sHH, subjects showed early improvements in search speed that continued over all the 25 trials. This hemianopic adaptation was larger in magnitude than the task-learning displayed in the normal viewing condition. Conclusions/Relevance: Our results indicate that an early and rapid strategic adaptation of visual search to hemianopic limitations on vision occurs in the first few minutes after the onset of visual field deficits. Such strategic shifts may account for the alterations in search behaviour seen in pathologic hemianopia, and may need to be taken into account when evaluating the effects of rehabilitation.
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