Abstract
The content of conscious perception is known to correlate with steady-state responses (SSRs), yet their causal relationship remains unclear. Can we manipulate conscious perception by directly interfering with SSRs through transcranial alternating current stimulation (tACS)? Here, we directly addressed this question in three experiments involving binocular rivalry and continuous flash suppression (CFS). Specifically, while participants (N=24) viewed either binocular rivalry or tried to detect stimuli masked by CFS, we applied sham or real tACS across parieto-occipital cortex at either the same or a different frequency and phase as an SSR eliciting flicker stimulus. We found that tACS did not differentially affect conscious perception in the forms of predominance, CFS detection accuracy, reaction time, or metacognitive sensitivity, confirmed by Bayesian statistics. We conclude that tACS application at frequencies of stimulus-induced SSRs does not have perceptual effects and that SSRs may be epiphenomenal to conscious perception.
Highlights
Can we manipulate conscious perception by directly interfering with steady-state responses (SSRs) through transcranial alternating current stimulation? Here, we directly addressed this question in three experiments involving binocular rivalry and continuous flash suppression (CFS)
Considering the above, one account for the absence of perceptual effects of transcranial alternating current stimulation (tACS) in the present study could be that the SSRs amplitude was too large to be significantly modulated by tACS
In the case of fMRI evidence pointing towards the role of the parietal cortex in bistability, such a causal role was supported by use of transcranial magnetic stimulation (Carmel et al, 2010; Kanai et al, 2010, 2011; Zarektskaya et al, 2010, 2013; Wood & Schauer et al, in prep)
Summary
When participants are presented with a flickering visual stimulus, the firing rate of neurons in the early visual cortex synchronises to the frequency of the stimulus flicker and its harmonics (Regan, 1989; Herrmann, 2001; Pastor et al, 2003; Norcia et al, 2015, Vialatte et al, 2010) These oscillatory brain responses can be recorded non-invasively by electroencephalography (EEG) and are known as steady-state responses (SSRs). While they can correlate with conscious perception, and have been used to decode these (Brown & Norcia, 1997; Tononi, et al, 1998), it is unknown if they are causally involved in determining the content of conscious perception, or merely correlate with it If they are epiphenomenal, they behave like a shadow does in relation to the object that cast it: while any change to the object leads to a change in the shadow, this relationship is purely unidirectional. The question is : can conscious perception be modulated by interfering with SSRs?
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