Early and Late ERP Correlates of Conscivousness- A Direct Comparison Between Visual and Auditory Modalities

Abstract

The majority of previous research on neural correlates of consciousness (NCC) have used the visual system as a model. However, to what extent reported findings generalize to other sensory modalities has not been comprehensively investigated. To fill this gap we directly compared visual and auditory NCCs by testing the same group of participants with two analogous procedures. Participants were presented with near-threshold visual and auditory stimuli followed by a detection task and Perceptual Awareness Scale (PAS). On the behavioral level, as expected from visual awareness studies, PAS ratings were highly correlated with accuracy in the detection task. Analysis of EEG data revealed that analogous ERP components-early visual or auditory awareness negativity (VAN and AAN) were related to perceptual awareness, but regarding late positivity (LP), it was related to perceptual awareness only in the visual modality. Further, we found that VAN and visual LP exhibited shorter latencies than respective auditory components suggesting earlier access of visual stimuli to consciousness, compared to auditory ones. Finally, neither estimated perceptual thresholds nor amplitudes and latencies of the awareness-related ERPs components were correlated between modalities, suggesting a lack of a close link between visual and auditory perceptual mechanisms. Therefore, the observed differences between visual and auditory modalities indicate the investigated NCC are rather modality-specific, and thus that neither of the proposed measures track consciousness independently to the content-related processing.

Keywords: auditory awareness negativity; awareness; late positivity; perception; visual awareness negativity.

FIGURE 1

Schematic presentation of experimental trials included in visual and auditory procedures.

FIGURE 2

(A) Distribution of PAS ratings in the auditory and visual procedures (for critical, control and catch trials). (B) The relationship between the detection task accuracy and PAS ratings for each procedure (for critical, control and catch trials). Red dotted lines represent the 50% chance level. (C) c (response bias) and d’ (sensitivity) values obtained in the detection task. The lower and upper hinges of the boxplots correspond to the 25% and 75% quartiles; the thick horizontal line indicates the median. Whiskers extend to the lowest/largest value and the dots represent the individual values of participants.

FIGURE 3

(A) Mean response bias (c) and (B) mean sensitivity (d’) depending on the PAS ratings and sensory modality. Error bars represent SEs. Significance level: ***p < 0.001, **p < 0.01, *p < 0.05.

FIGURE 4

(A) Mean detection task accuracy and (B) mean PAS rating depending on the modality. Error bars represent SEs. Significance level: ^ns p > 0.05. Red dotted lines represent the 50% chance level in detection task accuracy.

FIGURE 5

Scalp topographies from critical trials divided by procedures (i.e., modalities) and PAS ratings. Colors represent amplitudes from −1.5 to +1.5 μV.

FIGURE 6

ERP waveforms from critical trials divided by PAS ratings for (A) auditory and (B) visual procedures, and divided by detection task accuracy for (C) auditory and (D) visual procedures. (E) Topoplots in selected time‐windows and electrodes chosen for statistical analyses (highlighted in white) for each component: AAN component was measured at C1, C3, C5, FC3, CP3, C2, C4, C6, FC4, CP4; VAN at PO7, PO8, O2, O1, PO3, PO4 channels; LP in auditory and in visual procedures at Cz, FCz, C1, C2, FC1, FC2 channels. Colored ribbons indicate 95% CI. The gray vertical area represents the time window selected for analysis of each component: AAN: 210–330 ms, VAN: 180–350 ms, LP audio: 300–500 ms, LP visual: 250–450 ms. Timepoint “0 ms” indicates the moment of the stimuli presentation. Topoplots' colors represent amplitudes from −1 to +2 μV.

FIGURE 7

(A) Mean early components amplitudes depending on the sensory modality and accuracy in the detection task. (B) Mean early components amplitudes depending on the modality and PAS ratings. (C) Mean late components amplitudes depending on the sensory modality and accuracy in the detection task. (D) Mean late components amplitudes depending on the sensory modality and PAS ratings. Error bars represent SEs, asterisks indicate significance levels: ***p < 0.001, **p < 0.01, *p < 0.05, ^ns p > 0.05.

FIGURE 8

Mean latency of early (A) and late (B) components depending on the sensory modality. The latency is presented with respect to the target stimulus onset. Error bars represent SEs; asterisks indicate significance levels: ***p < 0.001, **p < 0.01, *p < 0.05, ^ns p > 0.05.