Neural signatures of auditory statistics: a window into auditory computations and their interactions with other modalities

The auditory system processes information at high temporal resolutions, extracting fine-grained details from complex sounds. However, this ability comes at a cost as the acoustic information often exceeds memory storage capacity. To keep track of sound changes occurring over several seconds, the auditory system abstracts local features into compact representations (summary statistics). This thesis addresses three questions: (i) whether it is possible to distinguish from neural activity the processing of local features or summary statistics; (ii) whether the brain is endowed with distinct structures for computations based on local features or summary statistics; (iii) whether these basic computations are affected by other sensory modalities. First, we designed a protocol for the EEG. Participants were exposed to streams comprising triplets of synthetic sound excerpts. Two sounds were identical, while the third could vary for its local features or summary statistics. We presented sounds of different durations to manipulate the similarity of statistics measured from the repeated and novel sounds. Results showed that local details and summary statistics are processed automatically and encoded by different neural oscillatory profiles. Second, we collected MEG data with the same protocol and performed source reconstruction of the evoked response to the novel sounds. This analysis revealed functional cortical specializations and hemispheric asymmetries for the processing of computations occurring at high or low temporal resolutions. Third, we tested three groups of individuals, congenitally (CB), late- onset blinds (LB), and sighted controls (SC) in two behavioral experiments. One benefitted from the processing of local features, the other from summary statistics. CB performed as SC in both tasks, showing that both computations can develop independently from vision. Conversely, LB’s performance was impaired when relying xv on local features, with no alterations in summary statistics processing. These findings suggest an audiovisual interplay selectively for processing auditory details, which emerges only in late development. Overall, these findings demonstrate that the auditory system utilizes distinct neural processes and dedicated brain structures to encode local features and summary statistics of sound and emphasize the role of visual experience in the processing of local features. By unraveling these fundamental aspects of auditory perception, this thesis expands our knowledge in the context of auditory cognition and its complex interplay with other sensory modalities.