A Spatial Map of Onset and Sustained Responses to Speech in the Human Superior Temporal Gyrus

Abstract

To derive meaning from speech, we must extract multiple dimensions of concurrent information from incoming speech signals. That is, equally important to processing phonetic features is the detection of acoustic cues that give structure and context to the information we hear. How the brain organizes this information is unknown. Using data-driven computational methods on high-density intracranial recordings from 27 human participants, we reveal the functional distinction of neural responses to speech in the posterior superior temporal gyrus according to either onset or sustained response profiles. Though similar response types have been observed throughout the auditory system, we found novel evidence for a major spatial parcellation in which a distinct caudal zone detects acoustic onsets and a rostral-surround zone shows sustained, relatively delayed responses to ongoing speech stimuli. While posterior onset and anterior sustained responses are used substantially during natural speech perception, they are not limited to speech stimuli and are seen even for reversed or spectrally rotated speech. Single-electrode encoding of phonetic features in each zone depended upon whether the sound occurred at sentence onset, suggesting joint encoding of phonetic features and their temporal context. Onset responses in the caudal zone could accurately decode sentence and phrase onset boundaries, providing a potentially important internal mechanism for detecting temporal landmarks in speech and other natural sounds. These findings suggest that onset and sustained responses not only define the basic spatial organization of high-order auditory cortex but also have direct implications for how speech information is parsed in the cortex. VIDEO ABSTRACT.

Rapid Transformation from Auditory to Linguistic Representations of Continuous Speech

“…The presence of analogous peaks in the TRFs to both acoustic representations might indicate that they jointly arise from a single, more complex underlying neural response type, reflecting both onset and continuous acoustic properties [48]. On the other hand, spatially, the two response peaks to acoustic onsets were localized posterior to the corresponding acoustic envelope peaks ( d = 8 mm, p = .002; d = 10 mm, p < .001), which might instead indicate that the two responses stem from partially distinct neural populations [49]. …”

Cross-modal Suppression of Auditory Association Cortex by Visual Speech as a Mechanism for Audiovisual Speech Perception

“…To understand this observation, we constructed a neural model ( Figure 5). The neural model incorporated the conceptual model principles of suppression/enhancement by visual speech and the experimental observation that the pSTG contains populations of neurons that are partially selective for specific phonemes, resulting in reduced but non-zero responses for non-preferred phonemes (Hamilton et al, 2018;Mesgarani et al, 2014).…”

“…This would lead to a predominance of suppression if pSTG electrodes recorded the total response summed across a combination of many suppressed populations and a few enhanced populations. Using smaller recording electrodes could allow for recording individual populations, separating those that show suppression from those that showed enhancement (Hamilton et al, 2018;Mesgarani et al, 2014).…”

Estimating and interpreting nonlinear receptive fields of sensory responses with deep neural network models

“…All five patients had depth electrodes (stereotactic EEG) with coverage of Heschl's gyrus (HG) and STG ( Fig 1A). While HG and the STG are functionally heterogenous and each contain multiple auditory fields (43)(44)(45)(46)(47), HG includes the primary auditory cortex, while the STG is considered mostly a nonprimary auditory cortical area (48). The patients listened to stories spoken by four speakers (two females) with a total duration of 30 minutes.…”