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The Journal of Neuroscience, April 11, 2007, 27(15):4120-4131; doi:10.1523/JNEUROSCI.4912-06.2007

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Behavioral/Systems/Cognitive
Early Cross-Modal Interactions in Auditory and Visual Cortex Underlie a Sound-Induced Visual Illusion

Jyoti Mishra,¹ Antigona Martinez,^2,3 Terrence J. Sejnowski,^1,4 and Steven A. Hillyard²

¹Division of Biological Sciences and ²Department of Neurosciences, University of California, San Diego, La Jolla, California 92093, ³Nathan S. Kline Institute for Psychiatric Research, Orangeburg, New York 10962, and ⁴Howard Hughes Medical Institute, Computational Neurobiology Laboratory, Salk Institute, La Jolla, California 92037

Correspondence should be addressed to Steven A. Hillyard, University of California, San Diego, Department of Neurosciences 0608, 9500 Gilman Drive, La Jolla, CA 92093-0608. Email: shillyard{at}ucsd.edu

When a single flash of light is presented interposed between two brief auditory stimuli separated by 60–100 ms, subjects typically report perceiving two flashes (Shams et al., 2000, 2002). We investigated the timing and localization of the cortical processes that underlie this illusory flash effect in 34 subjects by means of 64-channel recordings of event-related potentials (ERPs). A difference ERP calculated to isolate neural activity associated with the illusory second flash revealed an early modulation of visual cortex activity at 30–60 ms after the second sound, which was larger in amplitude in subjects who saw the illusory flash more frequently. These subjects also showed this early modulation in response to other combinations of auditory and visual stimuli, thus pointing to consistent individual differences in the neural connectivity that underlies cross-modal integration. The overall pattern of cortical activity associated with the cross-modally induced illusory flash, however, differed markedly from that evoked by a real second flash. A trial-by-trial analysis showed that short-latency ERP activity localized to auditory cortex and polymodal cortex of the temporal lobe, concurrent with gamma bursts in visual cortex, were associated with perception of the double-flash illusion. These results provide evidence that perception of the illusory second flash is based on a very rapid dynamic interplay between auditory and visual cortical areas that is triggered by the second sound.

Key words: ERPs; auditory cortex; visual cortex; illusory flash; cross-modal interaction; source analysis

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Received Nov. 12, 2006; revised Feb. 28, 2007; accepted March 8, 2007.

Correspondence should be addressed to Steven A. Hillyard, University of California, San Diego, Department of Neurosciences 0608, 9500 Gilman Drive, La Jolla, CA 92093-0608. Email: shillyard{at}ucsd.edu

This article has been cited by other articles:

				O. Collignon, M. Davare, A. G. De Volder, C. Poirier, E. Olivier, and C. Veraart Time-course of Posterior Parietal and Occipital Cortex Contribution to Sound Localization J. Cogn. Neurosci., August 1, 2008; 20(8): 1454 - 1463. [Abstract] [Full Text] [PDF]

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