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Stefan Van der Stigchel, Tanja C.W. Nijboer, Douwe D.P. Bergsma, Mathias Abegg, Jason J.S. Barton; The global effect induced by “blind” distractors in visual hemifield defects. Journal of Vision 2009;9(8):404. doi: https://doi.org/10.1167/9.8.404.
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© ARVO (1962-2015); The Authors (2016-present)
Visual information in blind regions may still be processed in patients with hemifield defects after cerebral lesions (“blindsight”). Recently, we tested the hypothesis that, in the absence of retinogeniculostriate processing, residual retinotectal processing may still be detected as modifications of saccades to seen targets by irrelevant distractors in the blind hemifield (Van der Stigchel et al., 2008). Patients with hemifield defects were presented with distractors in both the blind and intact visual field and participants were instructed to make eye movements to targets in the intact field. Eye movements were recorded to determine if blind-field distractors caused deviation in saccadic trajectories. In one of these experiments, two patients were tested with the target and the distractor closely aligned. Both patients showed saccades that deviated toward the blind-field distractor (i.e. global effect). This finding might be a typical phenomenon in patients with hemifield defects. Here we present four new cases in which we tested with the same paradigm whether a distractor presented in the blind visual field induces a global effect when target and distractor are closely aligned. Results showed that the blind-field distractor did not cause a deviation in saccadic trajectories in two of the four patients, although the distractor in the intact field caused a consistent global effect. Interestingly, in the two patients in whom an effect of a blind-field distractor was observed, the direction of the deviation was different from the previous study as eye movements deviated away from the blind-field distractor. Whereas this study again confirms that distractor effects on saccadic trajectories can occur in some patients with damage to the retinogeniculostriate visual pathway but preserved retinotectal projections, it reveals that the direction of this effect differs between patients, reflecting differences in oculomotor inhibition of blind-field distractors.
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