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Niko Busch; Attention-induced lateralization of EEG alpha-oscillations subserves a psychophysical contrast-gain effect.. Journal of Vision 2014;14(10):625. doi: https://doi.org/10.1167/14.10.625.
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© ARVO (1962-2015); The Authors (2016-present)
The brain is never resting; spontaneous neuronal activity is ever-present even in the absence of external stimulation. How does this spontaneous brain activity interact with the processing of visual information? Spontaneous electrophysiological oscillations in the alpha frequency-band (812 Hz) just before stimulus onset have been shown to impair detection of an upcoming stimulus. Moreover, voluntary shifts of covert attention induce lateralization of alpha power: power increases in the cortical hemisphere ipsilateral to the attended location and decreases in the contralateral hemisphere, indicating suppression of distracting information in the unattended hemifield. In this study, we investigated the psychophysical mechanism underlying this effect in an orientation discrimination task using Gabor patches of different contrast levels in combination with an attentional cueing procedure. Compared to a neutral condition, attentional cueing improved discrimination of the Gabor targets, and this effect was best described by a contrast gain effect. Moreover, cueing induced the expected lateralization of alpha-band power in the time interval between cue and target onset when power was averaged across trials. However, the degree and direction of pre-target single-trial lateralization was highly variable across trials. On some trials, pre-target lateralization was even reversed, indicating attentional shifts directed away from the cued location. We found that this single-trial lateralization was predictive of task performance on cued trials: strong lateralization towards the cued location resulted in best performance. Modeling of the resulting psychometric functions revealed that this improvement was characterized by a contrast gain effect that paralleled the effect found in the comparison of cued vs. neutral trials. Thus, the psychophysical effect of attention-induced alpha-band lateralization is best described as a net increase in visual sensitivity, similar to an actual change in physical stimulus contrast.
Meeting abstract presented at VSS 2014
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