Distinct functional levels of human voice processing in the auditory cortex

Abstract

Voice signaling is integral to human communication, and a cortical voice area seemed to support the discrimination of voices from other auditory objects. This large cortical voice area in the auditory cortex (AC) was suggested to process voices selectively, but its functional differentiation remained elusive. We used neuroimaging while humans processed voices and nonvoice sounds, and artificial sounds that mimicked certain voice sound features. First and surprisingly, specific auditory cortical voice processing beyond basic acoustic sound analyses is only supported by a very small portion of the originally described voice area in higher-order AC located centrally in superior Te3. Second, besides this core voice processing area, large parts of the remaining voice area in low- and higher-order AC only accessorily process voices and might primarily pick up nonspecific psychoacoustic differences between voices and nonvoices. Third, a specific subfield of low-order AC seems to specifically decode acoustic sound features that are relevant but not exclusive for voice detection. Taken together, the previously defined voice area might have been overestimated since cortical support for human voice processing seems rather restricted. Cortical voice processing also seems to be functionally more diverse and embedded in broader functional principles of the human auditory system.

Evidence for a Spoken Word Lexicon in the Auditory Ventral Stream

“…Our data not only present compelling evidence for the existence of an auditory lexicon—they also place its location in the anterior STG where it is ideally suited to interface with semantic representations located further anteriorly in the temporal lobe ( Lambon Ralph et al, 2017 ; Ueno et al, 2011 ), thereby completing the mapping of speech sounds to meaning. Furthermore, this anterior STG location is consistent with prior studies demonstrating other familiar auditory objects ( Griffiths & Warren, 2004 ), such as human voices ( Belin et al, 2000 ; Bodin et al, 2021 ; Staib & Frühholz, 2023 ) or musical instruments ( Leaver & Rauschecker, 2010 ). Moreover, such a simple-to-complex progression in selectivity from simple perceptual features over lexical representations to semantic representations in the anteroventral auditory processing stream along the STC is a direct counterpart of the ventral visual stream in the inferior temporal cortex ( Damera et al, 2020 ; Kravitz et al, 2013 ), revealing convergent processing strategies across speech modalities.…”

Evidence for a Spoken Word Lexicon in the Auditory Ventral Stream

“…Our data do not only present compelling evidence for the existence of an auditory lexicon – they additionally place its location in the anterior STG where it is ideally suited to interface with semantic representations located further anteriorly in the temporal lobe 16,55 , thereby completing the mapping of speech sounds to meaning. Furthermore, this anterior STG location is consistent with prior studies demonstrating other familiar “auditory objects” 56 such as human voices 57–59 or musical instruments 60 . Moreover, such a simple-to-complex progression in selectivity from simple perceptual features over lexical representations to semantic representations in the anteroventral auditory processing stream along the superior temporal cortex is a direct counterpart of the ventral visual stream in the inferior temporal cortex 9,14 , revealing convergent processing strategies across speech modalities.…”

Cortical-striatal brain network distinguishes deepfake from real speaker identity

“…When reversing the contrast to find higher brain activity during the deepfake compared with the natural identity task, we found significant activity in bilateral primary and higher-order AC. This activity was located within the general voice-sensitive cortex from posterior to anterior AC suggesting the contribution of the AC to different levels of voice decoding ranging from sensory-acoustic to higher-level processing 49 .The AC activity did not survive an interaction analysis and the AC classified both identity and speech sound classes with high accuracy. The decoding of voice information in the AC is thus rather independent of the task, but seems to be crucial for deepfake sound processing.…”

“…Contrast images for each condition were then taken to a random-effects, group-level analysis to investigate the neural processing for natural and synthetic sounds during the identity and speech task. Consistent with previous studies reporting voice-sensitive response in the bilateral temporal lobe 29 , 49 , 66 , 70 integrated into a broader brain network 52 , 66 , 71 , 72 , we conducted the contrast analysis at the level of the whole brain.…”

“…We ran LMMs to statistically test interactions and main effects of the fMRI matching task. For LMMs we used the lme4 package (version 1.1-26, 49 ). We conducted the model reduction approach to find the best fitting model structure for both random and fixed effects.…”