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The Journal of Neuroscience, October 15, 2008, 28(42):10517-10530; doi:10.1523/JNEUROSCI.1973-08.2008

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Behavioral/Systems/Cognitive
Striate Cortical Lesions Affect Deliberate Decision and Control of Saccade: Implication for Blindsight

Masatoshi Yoshida,^1,2 Kana Takaura,^1,2 Rikako Kato,^1,3 Takuro Ikeda,^1,3 and Tadashi Isa^1,2,3

¹Laboratory of Behavioral Development, Department of Developmental Physiology, National Institute for Physiological Sciences, National Institutes of Natural Sciences, Okazaki 444-8585, Japan, ²School of Life Science, the Graduate University for Advanced Studies, Hayama 204-0193, Japan, and ³Core Research for Evolutional Science and Technology, Japan Science and Technology Agency, Kawaguchi 332-0012, Japan

Correspondence should be addressed to Tadashi Isa, Laboratory of Behavioral Development, Department of Developmental Physiology, National Institute for Physiological Sciences, National Institutes of Natural Sciences, Myodaiji-cho, Okazaki City, Aichi Prefecture 444-8585, Japan. Email: tisa{at}nips.ac.jp

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.

Key words: residual vision; superior colliculus; monkey; decision; macaque; oculomotor

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Received May 31, 2008; revised July 17, 2008; accepted Aug. 27, 2008.

Correspondence should be addressed to Tadashi Isa, Laboratory of Behavioral Development, Department of Developmental Physiology, National Institute for Physiological Sciences, National Institutes of Natural Sciences, Myodaiji-cho, Okazaki City, Aichi Prefecture 444-8585, Japan. Email: tisa{at}nips.ac.jp

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