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Kaoru Amano, Toshimasa Takahashi, Tsunehiro Takeda, Isamu Motoyoshi; Neural responses involved in adaptation-induced blindness. Journal of Vision 2011;11(11):184. doi: 10.1167/11.11.184.
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Neural correlates of visual awareness have been studied using displays such as binocular rivalry and motion-induced blindness, in which the perception of a target is replaced by that of a competing stimulus. Recently Motoyoshi and Hayakawa (2010) reported a novel illusion that adaptation to dynamic stimuli can make a gradually-presented target totally invisible without any competing stimuli (adaptation-induced blindness). Here, we recorded magnetoencephalography (MEG) responses during this illusion to determine the neural correlates of awareness for such a competition-free target. The adapting stimulus was a circular patch of drifting grating presented at the upper-left visual field with an eccentricity of 12.5 deg. The test grating was a static grating presented within a Gaussian temporal window that peaked at 1 s after the adaptor offset with a standard deviation of 250 ms. After the initial 30-s adaptation, the sequence of adapting gratings for 5 s and the test grating for 2 s was repeatedly shown. The test gratings appeared either at the adapted location (adapted condition) or at the non-adapted location (non-adapted condition), or did not appear at all (no image condition). The observers fixated on a small black dot at the center of the screen, and were instructed to judge whether they perceived the test grating or not. The MEG responses to the test grating were recorded using 440 ch whole-head MEG system (PQ2440R: Yokogawa, Japan), and beamformer analysis was conducted. We discovered that while the observers perceived nothing on a uniform background in the adapted condition, the invisible test grating produced a significant decrease in alpha and an increase in gamma response around hMT+. The results are consistent with an additional fMRI experiment showing the hMT+ response evoked by the invisible test, and reveal cortical activities that do not prompt perceptual awareness even without any competing inputs.
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