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Qiming Han, Jianrong Jia, Huan Luo; Enhanced Alpha-mediated inhibition on target when it is crowded by flankers. Journal of Vision 2018;18(10):248. doi: 10.1167/18.10.248.
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Crowding is known as a perceptual phenomenon where the identification of objects presented far away from the fovea is impaired by the presence of neighboring flankers. Previous psychophysical and brain imaging studies have suggested that the crowding effect reflects top-down influence (e.g., insufficiency of attention resolution at the target) or a bottom-up process (e.g., originating from early visual processing). To examine the associated spatiotemporal neural processing underlying crowding effect, a key challenge is to dissociate the brain response for the target and flankers and monitor their respective neural activations as well as their interactions. In the present EEG study, subjects were asked to discriminate the orientation of a grating target presented on the peripheral visual field. The grating target was presented with grating flankers, and the intensity of crowding effect was manipulated by adjusting the orientation difference between the target and flanker gratings ("high-crowding" and "low-crowding"). Next, we employed a temporal response function (TRF) approach to dissociate the neuronal response that specifically tracks the target and flankers from the same EEG signals. Eye movement was monitored to ensure that subject fixated at the central fixation point. Preliminary data (N=6) demonstrates significant difference in crowding effect in behavioral performance between the high- and the low-crowding conditions. Furthermore, target for the high-crowding condition showed stronger alpha-band (~ 10 Hz) response in the latency of 300-400 ms than that for low-crowding condition, indicating an enhanced inhibition on the target. In sum, the observed association between the crowding effect and the late inhibitory alpha-band oscillation supports the view that crowding effect is attributed to attention-related top-down modulations.
Meeting abstract presented at VSS 2018
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