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Johannes J. Fahrenfort, Steven H. S. Scholte, Victor A. F. Lamme; Masking interrupts feedback processing. Journal of Vision 2005;5(8):963. doi: https://doi.org/10.1167/5.8.963.
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© ARVO (1962-2015); The Authors (2016-present)
In masking, a stimulus is rendered invisible through the presentation of a second stimulus shortly after the first. Although numerous accounts for masking have been given, an unequivocal explanation for this phenomenon remains elusive. However, neurophysiological studies from recent years indicate that visual perception depends strongly on cortico-cortical feedback connections from higher to lower tier visual areas. In macaque monkeys it has been shown that masking derives its effectiveness from interrupting these feedback processes. In this experiment, we used fMRI and EEG measurements to determine what happens in human visual cortex during detection of a texture defined square under masked and non-masked conditions. EEG derivatives that are typically associated with early feedback processing turn out to be absent in the masked condition. Moreover, preliminary fMRI results suggest that the masked stimulus still evokes activation of visual cortex, with higher visual areas being activated more strongly than lower areas. This indicates that feed-forward processing is preserved, even when subject performance is close to chance. From these results we conclude that in humans, as in macaques, masking derives its effectiveness from interrupting feedback projections.
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