Sensory modality defines the relation between EEG Lempel-Ziv diversity and meaningfulness of a stimulus

Abstract

Diversity of brain activity is a robust neural correlate of the global states of consciousness. It has been recently proposed that diversity measures specifically reflect richness and differentiation of conscious experience. In line, previous studies found that perception of meaningful visual stimuli, causing richer and more differentiated experiences, caused greater brain signal diversity than perception of meaningless stimuli. To investigate whether this relation is consistent across sensory modalities we used naturalistic visual and auditory stimuli (movies and audiobooks) and presented them to participants in three versions varying in the amount of meaning (original, scrambled, and noise) while recording EEG signals. We report three main findings. First, greater meaningfulness of the visual stimulus was related with higher Lempel-Ziv diversity of EEG signals, but a reverse effect was found in the auditory modality. Second, visual perception was related with generally higher EEG diversity than auditory perception. Third and relatedly, perception of meaningful visual stimuli resulted in higher, while perception of auditory stimuli in lower EEG diversity in comparison to the resting-state. In conclusion, brain signal diversity depends on the stimulated sensory modality, and thus is not a generic index of the richness and differentiation of conscious experience.