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Kyle Mathewson, Christopher Prudhomme, Monica Fabiani, Diane Beck, Gabriele Gratton, Alejandro Lleras; Controlling the timing of oscillations in neural activity and consciousness with rhythmic visual stimulation. Journal of Vision 2010;10(7):1396. doi: 10.1167/10.7.1396.
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© ARVO (1962-2015); The Authors (2016-present)
What is the underlying nature of conscious awareness? William James observed introspectively that consciousness, “… does not appear to itself chopped into bits…A ‘river’ or a ‘stream’ are the metaphors by which it is most naturally described.” (James, 1890). Since this time, however, evidence has accumulated supporting an alternative, discrete nature of perception (Efron 1970; VanRullen & Koch 2003). Recently, we have found evidence that perception fluctuates on a fine temporal scale, as a function of the phase of ongoing neural oscillations. Visual targets presented in the peak of ongoing 10 Hz neural oscillations (alpha rhythm) are visible, while identical stimuli presented in the trough are less likely to reach consciousness (Mathewson et al., 2009). Furthermore, we have shown that rhythmic visual stimulation at similar frequencies can control the timing of oscillations in consciousness (Mathewson et al., in press). Here we show that it is possible to control ongoing neural oscillations with this rhythmic visual stimulation, thus eliciting predictable concomitant oscillations in brain activity and consciousness. After the offset of periodic visual stimulation, masked visual targets were presented at multiple lags, sampling various phases with respect to the induced oscillations. Targets presented in phase with the preceding rhythmic stimulation were more likely to be detected than those out of phase. This induced oscillation in visual sensitivity was strongly correlated with an induced oscillation in the EEG. These effects were markedly smaller for randomly spaced preceding stimulation. These data provide the first evidence of a causal link between ongoing neural oscillations and fine grained temporal variations in consciousness, and reveal a method to experimentally control these discrete perceptual snapshots.
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