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Olga Savina, Andre Bergeron, Daniel Guitton; A visual target in the blind hemifield of hemidecorticate patients reduces latency and improves accuracy of antisaccades. Journal of Vision 2008;8(6):929. doi: 10.1167/8.6.929.
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It is thought that the phenomenon of blindsight in hemidecorticate patients requires the superior colliculus (SC), which appears viable after a hemispherectomy. Using a task that maximally solicits the SC, we investigated whether an unseen target in the blind hemifield can alter the timing/amplitude of an ongoing antisaccade in a hemidecorticate patient. Each trial began with a central fixation point that was extinguished, followed by a brief (86ms) light spot (cue) in the seeing hemifield. The patient was required to make a saccade away from the cue to its mirror location (antisaccade). The cue was presented either alone, or was accompanied by a flashed probe (86ms) at the cue's mirror location in the blind hemifield. The probe was presented simultaneously with the cue, or after random delays of 86ms, 136ms, or 186ms. We found that for delays of 86ms and greater there was a significant reduction in the latencies of antisaccades. A reduction in the error of the antisaccade was found, which was most pronounced at delays of 136ms and 186ms. At these delays the error was reduced by half relative to the no-probe condition. A recent study showed a correlation between behavioral choice and an ipsi-lesional neural activity in the SC of monkeys' with V1 lesions (Yoshida et al., 2007). Thus, our findings suggest that the presentation of a light stimulus at the goal position, after a cue has already been presented, increases neuronal activity in the ipsi-lesional SC which adds to preparatory motor activity and drives the firing frequency over the threshold necessary for saccade generation to the probe position.
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