Abstract
Previous studies have observed different onset times for the neural markers of conscious perception. This variability could be attributed to procedural differences between studies. Here we show that the onset times for the markers of conscious visual perception can strongly vary even within a single study. A heterogeneous stimulus set was presented at threshold contrast. Trials with and without conscious perception were contrasted on 100 balanced subsets of the data. Importantly, the 100 subsets with heterogeneous stimuli did not differ in stimulus content, but only with regard to specific trials used. This approach enabled us to study general markers of conscious visual perception independent of stimulus content, characterize their onset and its variability within one study. N200 and P300 were the two reliable markers of conscious visual perception common to all perceived stimuli and absent for all non-perceived stimuli. The estimated mean onset latency for both markers was shortly after 200 ms. However, the onset latency of these markers was associated with considerable variability depending on which subsets of the data were considered. We show that it is first and foremost the amplitude fluctuation in the condition without conscious perception that explains the observed variability in onset latencies of the markers of conscious visual perception.
Highlights
How long does it take from the moment when a stimulus is presented in the environment until the conscious experience of the stimulus starts to arise? Despite the decades-long quest for the neural correlates of consciousness (NCC) it is not known at what time after stimulus onset they occur
To exclude any possible confounds with latency variance and to demonstrate more convincingly the relevance of the amplitude parameter for the observed variability in general markers of NCC (gmNCC) onset times, the above analysis was repeated by first averaging single trials and extracting peak amplitude
The first goal of the present experiment was to find general markers of NCC, that is – markers that distinguish consciously perceived trials of a heterogenous visual stimulus set from the non-perceived trials
Summary
How long does it take from the moment when a stimulus is presented in the environment until the conscious experience of the stimulus starts to arise? Despite the decades-long quest for the neural correlates of consciousness (NCC) it is not known at what time after stimulus onset they occur. Still others have found very early correlates for conscious perception (Pins and Ffytche, 2003; Aru and Bachmann, 2009). One reason for these discrepancies may be that the contrastive method typically used to identify NCC is sensitive regarding the actual NCC and unravels neural processes that precede or follow conscious perception (Overgaard, 2004; Bachmann, 2009; Aru et al, 2012; de Graaf et al, 2012). Depending on how visual awareness is manipulated and assessed within
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