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Human visual cortex responds to invisible chromatic flicker

Abstract

When two isoluminant colors alternate at frequencies of 25 Hz or higher, observers perceive only one fused color. Chromatic flicker beyond the fusion frequency induces flicker adaptation in human observers and stimulates monkey V1 neurons. Here we use functional magnetic resonance imaging (fMRI) to show that many human visual cortical areas, with the exception of VO, can distinguish between fused chromatic flicker and its matched nonflickering control. This result supports the existence of significant intracortical temporal filtering of high-frequency chromatic information. The result also suggests that a considerable difference in cortical activation in many visual cortical areas does not necessarily lead to different conscious experiences.

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Figure 1: Illustrations of chromatic flicker stimuli and cortical visual areas.
Figure 2: fMRI responses to 5- and 30-Hz flicker in different visual areas.
Figure 3: BOLD response as a function of flicker temporal frequency and contrast.
Figure 4: Distribution of fMRI responses to 5- and 30-Hz flicker in different visual areas.

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Acknowledgements

We thank F. Fang for technical assistance, D. MacLeod for comments on an early version of the manuscript, and P. Costello and R. Shannon for their help with the manuscript. This research was supported by the James S. McDonnell foundation, the US National Institutes of Health (EY-015261-01), the 973 program (2005CB522800) and the Knowledge Innovation Project of the Chinese Academy of Sciences. The 3T scanner at the University of Minnesota is supported by Biotechnology Research Resource (BTRR) grant P41 008079 and by the Mental Illness and Neuroscience Discovery (MIND) Institute.

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Correspondence to Sheng He.

Supplementary information

Supplementary Fig. 1

BOLD response as a function of flicker temporal frequency and contrast. (PDF 87 kb)

Supplementary Table 1

Talairach coordinates of ROIs (hV4 and VO). (PDF 59 kb)

Supplementary Table 2

Behavioral results in the 4AFC stimulus discrimination task. (PDF 61 kb)

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Jiang, Y., Zhou, K. & He, S. Human visual cortex responds to invisible chromatic flicker. Nat Neurosci 10, 657–662 (2007). https://doi.org/10.1038/nn1879

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