Journal
JOURNAL OF NEUROSCIENCE
Volume 28, Issue 42, Pages 10517-10530Publisher
SOC NEUROSCIENCE
DOI: 10.1523/JNEUROSCI.1973-08.2008
Keywords
residual vision; superior colliculus; monkey; decision; macaque; oculomotor
Categories
Funding
- Ministry of Education, Culture, Sports, Science, and Technology of Japan [18500317, 18019038]
- Core Research for Evolutional Science and Technology
- Japan Science and Technology Agency
- Grants-in-Aid for Scientific Research [18019038, 18500317] Funding Source: KAKEN
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Monkeys with unilateral lesions of the primary visual cortex (V1) can make saccades to visual stimuli in their contralateral (affected) hemifield, but their sensitivity to luminance contrast is reduced. We examined whether the effects of V1 lesions were restricted to vision or included later stages of visual-oculomotor processing. Monkeys with unilateral V1 lesions were tested with a visually guided saccade task with stimuli in various spatial positions and of various luminance contrasts. Saccades to the stimuli in the affected hemifield were compared with those to the near-threshold stimuli in the normal hemifield so that the performances of localization were similar. Scatter in the end points of saccades to the affected hemifield was much larger than that of saccades to the near-threshold stimuli in the normal hemifield. Additional analysis revealed that this was because the initial directional error was not as sufficiently compensated as it was in the normal hemifield. The distribution of saccadic reaction times in the affected hemifield tended to be narrow. We modeled the distribution of saccadic reaction times by a modified diffusion model and obtained evidence that the decision threshold for initiation of saccades to the affected hemifield was lower than that for saccades to the normal hemifield. These results suggest that the geniculostriate pathway is crucial for on-line compensatory mechanisms of saccadic control and for decision processes. We propose that these results reflect deficits in deliberate control of visual-oculomotor processing after V1 lesions, which may parallel loss of visual awareness in human blindsight patients.
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