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Title: Multi-level reorganization in the temporal dynamics of sound processing in early blind people
Authors: Siddharth Talwar1, Stefania Mattioni2, Eléonore Giraudet1, Roberta P. Calce1, Francesca M. Barbero1, Olivier Collignon1,3 Affiliation: 1 Institute for research in Psychology (IPSY) & Neuroscience (IoNS), Louvain Bionics, University of Louvain (UCLouvain), Louvain, Belgium 2 Department of Experimental Psychology; UGent, Gent, Belgium 3 HES-SO Valais-Wallis, School of Health Sciences; The Sense Innovation and Research Center, Lausanne and Sion, Switzerland
Early blindness triggers reorganization in the brain networks that code for sound processing. However, how visual deprivation impacts the temporal dynamics of different stages of auditory discrimination (acoustic to categorical coding) remains mostly unexplored. We characterized the time course of brain activity using electroencephalography (EEG) while congenitally blind and sighted individuals listened to 1-second-long sounds belonging to eight categories. Multivariate decoding analyses revealed enhanced sound decoding in the brain of the blind compared to sighted from 200 to 1200 ms after sound onset. Furthermore, the classifier weights transformed and projected on the sensors were enhanced in the blinds with the topography evolving along a frontal-posterior axis as the sound unfolded in time. To investigate which stages of sound processing were enhanced in the blind, we used representational similarity analysis (RSA) with different models of sound representation: (i) the Modulation Transfer Function (MTF) to simulate early stages of acoustic processing, (ii) layers of a deep neural network (YAMNET), (iii) a high-level model based on the categorical membership of sounds. RSA with MTF displayed no differences between the two populations, while correlations with the DNN layers showed distinctions at 200 ms specifically in layers representing intermediate acoustic processing. While categorical representation of sounds emerged at 250 ms in both populations, only blinds showed an enhanced categorical representation peaking at 550 ms. These results suggest that early blindness triggers a multi-level reorganization in brain networks coding for sounds, with enhanced intermediate-level acoustic discrimination earlier in time, followed by an increased categorical coding later.