Speech-Driven Spectrotemporal Receptive Fields Beyond the Auditory Cortex

• Published in: Hearing research Vol. 408; p. 108307
• Main Authors: Venezia, Jonathan H., Richards, Virginia M., Hickok, Gregory
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.09.2021
• Subjects: Acoustic Stimulation; Auditory Cortex - diagnostic imaging; Brain Mapping; Fmri; Humans; Magnetic Resonance Imaging; Pitch; Premotor; Spectrotemporal modulations; Speech; Speech Intelligibility; Speech Perception; STRF; Premotor; Pitch; Speech Intelligibility; STRF; Spectrotemporal modulations; Fmri
• ISSN: 0378-5955; 1878-5891; 1878-5891
• DOI: 10.1016/j.heares.2021.108307

•Speech-driven spectrotemporal receptive fields (STRFs) are estimated using fMRI with spectrotemporal modulation filtering of continuous speech (“Auditory Bubbles”).•A multivariate analysis of cross-subject STRF alignment is developed to maintain sensitivity to small clusters of STRFs outside traditional auditory cortex.•Left dorsal speech-premotor cortex (dPM) and bilateral calcarine sulcus (calcS) respond to acoustic speech features associated with speech intelligibility and vocal pitch, but left inferior frontal gyrus (IFG) responds only to features associated with intelligibility.•dPM and calcS are maximally functionally connected with early auditory cortex; IFG is maximally connected with superior temporal gyrus/sulcus and middle temporal gyrus.•STRFs in dPM predict activation on trials for which speech is rated as unintelligible by listeners, a hallmark auditory profile; thus we posit that dPM is capable of processing speech in an ‘auditory mode’. We recently developed a method to estimate speech-driven spectrotemporal receptive fields (STRFs) using fMRI. The method uses spectrotemporal modulation filtering, a form of acoustic distortion that renders speech sometimes intelligible and sometimes unintelligible. Using this method, we found significant STRF responses only in classic auditory regions throughout the superior temporal lobes. However, our analysis was not optimized to detect small clusters of STRFs as might be expected in non-auditory regions. Here, we re-analyze our data using a more sensitive multivariate statistical test for cross-subject alignment of STRFs, and we identify STRF responses in non-auditory regions including the left dorsal premotor cortex (dPM), left inferior frontal gyrus (IFG), and bilateral calcarine sulcus (calcS). All three regions responded more to intelligible than unintelligible speech, but left dPM and calcS responded significantly to vocal pitch and demonstrated strong functional connectivity with early auditory regions. Left dPM's STRF generated the best predictions of activation on trials rated as unintelligible by listeners, a hallmark auditory profile. IFG, on the other hand, responded almost exclusively to intelligible speech and was functionally connected with classic speech-language regions in the superior temporal sulcus and middle temporal gyrus. IFG's STRF was also (weakly) able to predict activation on unintelligible trials, suggesting the presence of a partial ‘acoustic trace’ in the region. We conclude that left dPM is part of the human dorsal laryngeal motor cortex, a region previously shown to be capable of operating in an ‘auditory mode’ to encode vocal pitch. Further, given previous observations that IFG is involved in syntactic working memory and/or processing of linear order, we conclude that IFG is part of a higher-order speech circuit that exerts a top-down influence on processing of speech acoustics. Finally, because calcS is modulated by emotion, we speculate that changes in the quality of vocal pitch may have contributed to its response.