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Olga Savina, Daniel Guitton; The different effects of a visual target in the blind hemifield of hemidecorticate patients on the latency of antisaccades. Journal of Vision 2009;9(8):379. doi: 10.1167/9.8.379.
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It is thought that the phenomenon of blindsight in hemidecorticate patients requires the superior colliculus (SC) (Leh et al. 2006). Using a task that maximally solicits the SC, we investigate whether an unseen visual probe stimulus in the blind hemifield can alter the timing of an ongoing antisaccade in a hemidecorticate patient.
Each trial began with a central fixation point, followed by a brief presentation of a visual stimulus (cue) in the seeing hemifield. A cue was presented alone (86ms), or was accompanied by a probe (86ms) in the blind hemifield at a location different from the mirror location of the cue. The probe was presented simultaneously with the cue, or after a random delay of 86ms, 136ms, or 186ms with respect to cue onset. The patient was required to make a saccade away from the cue to its mirror location (antisaccade). We found that in all of the conditions the latency of the antisaccade was positively correlated with the distance in collicular coordinates between the probe's location and the mirror location of the cue; specifically, as the distance increased so did the SRT. Furthermore, delaying the probe after the offset of the cue significantly reduced the latencies of the antisaccades compared to the condition where the cue and the probe were presented simultaneously.
These findings suggest that presenting the probe in the blind hemifield, after a cue has already been presented to the seeing hemifield, increases cue-driven neuronal activity in the ipsi-lesional SC and drives it over the threshold for antisaccade initiation, resulting in a faster antisaccade to the intended location in the blind hemifield. However, the degree of increase in neuronal activity depends on the distance on the SC map between the cue-driven and probe-driven activity loci.
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