Humans can experience aftereffects from oriented stimuli that are not consciously perceived, suggesting that such stimuli receive cortical processing. Determining the physiological substrate of such effects has proven elusive owing to the low spatial resolution of conventional human neuroimaging techniques compared to the size of orientation columns in visual cortex. Here we show that even at conventional resolutions it is possible to use fMRI to obtain a direct measure of orientation-selective processing in V1. We found that many parts of V1 show subtle but reproducible biases to oriented stimuli, and that we could accumulate this information across the whole of V1 using multivariate pattern recognition. Using this information, we could then successfully predict which one of two oriented stimuli a participant was viewing, even when masking rendered that stimulus invisible. Our findings show that conventional fMRI can be used to reveal feature-selective processing in human cortex, even for invisible stimuli.
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We thank K. Friston and J. Driver for comments on the manuscript. The Wellcome Trust funded this work.
The authors declare no competing financial interests.
Simulation of expected orientation bias. (PDF 104 kb)
Spatial distribution of orientation biases of voxels entering into the discriminant analysis. (PDF 246 kb)
Analysis of radial and tangential contributions to orientation bias in V1. (GIF 75 kb)
Details of pattern classification for experiment 1. (PDF 181 kb)
Comparison of prediction using conventional and pattern signals. (PDF 90 kb)
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Haynes, J., Rees, G. Predicting the orientation of invisible stimuli from activity in human primary visual cortex. Nat Neurosci 8, 686–691 (2005). https://doi.org/10.1038/nn1445
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