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John-Dylan Haynes, Jon Driver, Geraint Rees; Human cortical activations related to visual metacontrast masking. Journal of Vision 2004;4(8):45. doi: https://doi.org/10.1167/4.8.45.
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Metacontrast masking is a type of backward masking that occurs when a target is followed by a non-overlapping mask which shares a contour. We investigated responses of human visual cortex to novel metacontrast stimuli that maximised surface area of the target, while minimising mask size. Target-mask asynchrony and attention towards or away specific quadrants were manipulated orthogonally. Brain activations were characterised using functional MRI. Retinotopically mapped visual areas showed responses that varied in a qualitatively similar way to the psychophysically measured metacontrast masking function against SOA. While activations in V1 showed little attentional modulation, those in V2 and higher areas were strongly modulated by attention. Activations for both attended and unattended stimuli were related to the psychophysical masking function. Quantitatively, area V4 showed the closest match between fMRI response and the behavioural masking function against SOA. Strong and reliable fMRI responses that closely paralleled psychophysical performance were also identified in temporoparietal cortex, basal ganglia and prefrontal cortex. These results suggest that metacontrast masking modulates conscious perception and neural responses in humans not only in a retinotopically-specific manner within posterior visual cortex, but also in areas of prefrontal and parietal cortex.
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