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ORIGINAL RESEARCH article

Front. Integr. Neurosci.
Volume 18 - 2024 | doi: 10.3389/fnint.2024.1427149

Onset timing of letter processing in auditory and visual sensory cortices

Provisionally accepted
Tommi Raij Tommi Raij 1*Fa-Hsuan Lin Fa-Hsuan Lin 2Benjamin Letham Benjamin Letham 1Kaisu Lankinen Kaisu Lankinen 3Tapsya Nayak Tapsya Nayak 3Thomas Witzel Thomas Witzel 4Matti Hämäläinen Matti Hämäläinen 5Jyrki Ahveninen Jyrki Ahveninen 1
  • 1 Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, United States
  • 2 University of Toronto, Toronto, Ontario, Canada
  • 3 MGH/MIT/HMS Athinoula A. Martinos Center for Biomedical Imaging, Boston, United States
  • 4 Harvard-MIT Division of Health Sciences and Technology, Cambridge, MA, United States
  • 5 Aalto University, Otakaari, Ostrobothnia, Finland

The final, formatted version of the article will be published soon.

    Here, we report onset latencies for multisensory processing of letters in the primary auditory and visual sensory cortices. Healthy adults were presented with 300-ms visual and/or auditory letters (uppercase Roman alphabet and the corresponding auditory letter names in English). Magnetoencephalography (MEG) evoked response generators were extracted from the auditory and visual sensory cortices for both within-modality and cross-sensory activations; these locations were mainly consistent with functional magnetic resonance imaging (fMRI) results in the same subjects. In the primary auditory cortices (Heschl's gyri) activity to auditory stimuli commenced at 25 ms and to visual stimuli at 65 ms (median values). In the primary visual cortex (Calcarine fissure) the activations started at 48 ms to visual and at 62 ms to auditory stimuli. This timing pattern suggests that the origins of the cross-sensory activations may be in the primary sensory cortices of the opposite modality, with conduction delays (from one sensory cortex to another) of 17 -37 ms. Audiovisual interactions for letters started at 125 ms in the auditory and at 133 ms in the visual cortex (60 -71 ms after inputs from both modalities converged). Multivariate pattern analysis suggested similar latency differences between the sensory cortices. Combined with our earlier findings for simpler stimuli (noise bursts and checkerboards), these results suggest that primary sensory cortices participate in early cross-modal and interaction processes similarly for different stimulus materials, but previously learned audiovisual associations and stimulus complexity may delay the start of the audiovisual interaction stage.

    Keywords: Audiovisual interaction, cross-modal, Language, MEG, multisensory

    Received: 03 May 2024; Accepted: 29 Oct 2024.

    Copyright: © 2024 Raij, Lin, Letham, Lankinen, Nayak, Witzel, Hämäläinen and Ahveninen. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

    * Correspondence: Tommi Raij, Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, 02129, Massachusetts, United States

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