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The Journal of Neuroscience, August 23, 2006, 26(34):8804-8809; doi:10.1523/JNEUROSCI.1765-06.2006

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Brief Communications
Toward a Common Circle: Interhemispheric Contextual Modulation in Human Early Visual Areas

Hiroshi Ban,^1,2 Hiroki Yamamoto,¹ Masaki Fukunaga,^3,4 Asuka Nakagoshi,⁵ Masahiro Umeda,⁴ Chuzo Tanaka,^4,5 and Yoshimichi Ejima⁶

¹Department of Cognitive and Behavioral Science, Graduate School of Human and Environmental Studies, Kyoto University, Kyoto 606-8501, Japan, ²The Japan Society for the Promotion of Science, Tokyo 102-8472, Japan, ³Laboratory of Functional Molecular Imaging, National Institutes of Health, Bethesda, Maryland 20892-1065, ⁴Faculty of Medical Informatics and ⁵Neurosurgery, Meiji University of Oriental Medicine, Kyoto 629-0392, Japan, and ⁶Kyoto Institute of Technology, Kyoto 606-8585, Japan

Correspondence should be addressed to Hiroshi Ban, Department of Cognitive and Behavioral Science, Graduate School of Human and Environmental Studies, Kyoto University, Yoshida-Nihonmatsu-Cho, Sakyo-Ku, Kyoto City, Kyoto 606-8501, Japan. Email: ban{at}cv.jinkan.kyoto-u.ac.jp

Humans can readily and effortlessly perceive a rich, stable, and unified visual world from a complex visual scene. Yet our internal representation of a visual object appears to be sparse and fragmented. How and where in the brain are such fragmented representations organized into a whole percept? Recent studies have accumulated evidence that some global feature integration is mediated at the early stage of visual processing. However, the spatial operating range of the integration still remains unclear. The present human functional magnetic resonance imaging study provides support that the global integration process in early visual areas, including even the primary visual area V1, is mediated beyond the separated projection of visual hemifields from right and left sides of the fixation to the visual cortex of the contralateral cerebral hemisphere. Retinotopic neural responses corresponding to a visual target were significantly enhanced when another target was simultaneously presented at the point-symmetrical position in the nonassociated visual field quadrant. The result makes a convincing case that the contextual effects involve feedback from higher areas, because there are no direct callosal connections that allow such interhemispheric contextual modulation. This enhancement from the ipsilateral hemifield may help rapid position-and-size-invariant detection of a circular pattern, which may be special among visual structures because of its ubiquity in natural scenes. Early visual areas as well as higher ones may play a more essential role in perceiving the unity of the real world than previously thought.

Key words: visual cortex; retinotopy; contextual modulation; interhemispheric integration; object/shape perception; fMRI

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Received April 25, 2006; revised July 15, 2006; accepted July 17, 2006.

Correspondence should be addressed to Hiroshi Ban, Department of Cognitive and Behavioral Science, Graduate School of Human and Environmental Studies, Kyoto University, Yoshida-Nihonmatsu-Cho, Sakyo-Ku, Kyoto City, Kyoto 606-8501, Japan. Email: ban{at}cv.jinkan.kyoto-u.ac.jp

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