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Niko Busch, Rufin VanRullen; Pre-Stimulus EEG Oscillations Reveal Periodic Sampling Of Visual Attention. Journal of Vision 2010;10(7):219. doi: 10.1167/10.7.219.
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© ARVO (1962-2015); The Authors (2016-present)
Our senses are constantly confronted with an excess of information. One mechanism that limits this input to a manageable amount is selective attention. An important effect of sustained attention is the facilitation of perception through enhanced contrast sensitivity. While the term ‘sustained’ suggests that this facilitative effect endures continuously as long as something is attended, we present electrophysiological evidence that perception at attended locations is actually modulated periodically.
Subjects had to detect brief flashes of light that were presented peripherally at the individual contrast threshold such that subjects detected approximately half of the flashes (hits) and entirely missed the other half (misses). Additionally, a central cue instructed subjects where to focus their attention, so that stimuli could be presented either at the attended or the unattended location. EEG was recorded concurrently.
As expected, the contrast threshold was lower for attended than for unattended stimuli. Analysis of the EEG data revealed that event-related potentials (ERPs) were of much larger amplitude for hits than for misses. Moreover, the single-trial amplitude of the ERP was correlated with the single-trial phase of spontaneous EEG oscillations in the theta (∼7Hz) frequency-band just before stimulus onset. In fact, the single-trial phase in this time-frequency range was significantly predictive of detection performance for attended stimuli - but not for unattended ones.
Spontaneous EEG oscillations correspond to ongoing periodic fluctuations of the local electrical field and the excitability of neuronal populations. The present results extend our recent finding that visual detection performance fluctuates over time along with the phase of such oscillations in the theta (4-8Hz) and alpha (8-13Hz) range. By demonstrating that this effect exists only for attended stimuli, the data suggest that sustained attention in fact operates in a periodic fashion.
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