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Isabelle Bareither, Arno Villringer, Niko Busch; Opposite neural responses for visual stimuli above and below perceptual threshold. Journal of Vision 2012;12(9):654. doi: 10.1167/12.9.654.
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© ARVO (1962-2015); The Authors (2016-present)
Visual events come at an enormous range of intensities - from the faint light in the dark to the blinding light of the midday sun. How does the visual system respond to stimuli of such different intensities? A number of experiments have reported weaker, but similar brain responses for stimuli of strong intensity that were made invisible by masking. However, it is currently unknown whether the visual system responds in a similar fashion to stimuli that are invisible due to their low contrast. Somatosensory stimuli of low intensity cause a deactivation of somatosensory cortex rather than just a weak activation as has been demonstrated using fMRI. These so called subliminal visual stimuli therefore elicit a response that is opposite from conscious, supraliminal stimuli. The deactivation in response to subliminal stimuli has been interpreted as a focal inhibition mechanism that protects the cortex against spurious activation due to noise. In visual cortical areas, functional activation is related to reduced alpha-band (8-14 Hz) power while deactivation is related to elevated alpha power. In the present study, we tested the hypothesis that – as in the somatosensory system – low-intensity stimuli result in neuronal inhibition as indicated by alpha power increase while high-contrast stimuli result in alpha power decrease. We investigated EEG responses to subliminal and supraliminal visual stimuli after estimating each participant’s detection threshold. Stimuli consisted of peripherally presented small circular patches displayed on a background consisting of a random white noise pattern. We demonstrate that low- and high-intensity stimuli indeed induce opposite effects in the alpha-band: while supraliminal stimuli induce a decrease in alpha-band power, subliminal visual stimuli induce an increase in alpha-band power. This indicates that the visual system uses an inhibitory mechanism to counter spurious activation that is unlikely to be caused by real events in the world.
Meeting abstract presented at VSS 2012
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