Prosodic Pitch Perception in Right Premotor Cortex: A Transcranial Magnetic Stimulation Study
Poster No:
1044
Submission Type:
Abstract Submission
Authors:
Daniela Sammler1, Gesa Hartwigsen2
Institutions:
1Max Planck Institute for Empirical Aesthetics, Frankfurt am Main, Hesse, 2Leipzig University, Leipzig, Saxony
First Author:
Co-Author:
Introduction:
Speech perception is believed to recruit (pre)motor cortex (PMC) in the left dorsal auditory stream (Liebenthal & Möttönen, 2018). Articulator-specific involvement of left PMC has been found for the perception of phonemes (D'Ausilio et al., 2009) and lexical tones (Liang et al., 2023). However, PMC's role for prosody-the melody of speech-still lacks investigation. Motor control of prosodic pitch contours is anchored in the right (and left) PMC (Dichter et al., 2018). This kindles questions of hemispheric lateralization, reminiscent of auditory asymmetries (Zatorre et al., 2002). Moreover, the role of PMC in supporting either perceptual or response-related processes is still a matter of debate (Hickok, 2010). The present study used repetitive transcranial magnetic stimulation (rTMS) and behavioral drift diffusion modelling to (i) assess the causal role of right PMC in prosodic pitch categorization, compared to left PMC and a non-prosodic pitch control task (speaker gender categorization), and to (ii) disentangle the weighting of perceptual vs. response-related biases in PMC contributions.
Methods:
In two separate sessions, 24 listeners (M ± SD = 27 ± 3.4 years) categorized prosodic pitch contours (question vs. statement) and speaker gender (male vs. female) of monosyllabic words while receiving neuronavigated inhibitory or sham rTMS of left or right PMC (MNI: ±45, 5, 40 mm, based on Sammler et al., 2015) using co-registered individual T1-weighted images. A 5-pulse train of 10 Hz rTMS at an intensity of 100% individual resting motor threshold was delivered in each trial, time-locked to word onset, using a focal figure-of-eight-shaped coil (CB-60, 7.5 cm outer diameter) connected to a MagPro X100 stimulator. Sham rTMS was delivered by a second coil placed in a 90° angle over the first coil. The order of sessions (left/right PMC) and blocks (prosody/gender task, sham/effective rTMS) was counterbalanced across subjects (Fig 1A).
Single trial response times and accuracies were analyzed with the drift diffusion model (DDM; Ratcliff, 1978; fast-dm: Voss & Voss, 2007) to decompose latent processes that lead to a decision. Parameters v (drift rate; rate of evidence accumulation), a (threshold separation; indicating response biases), and t0 (non-decision time; decision-independent time for stimulus encoding and button press) were compared between tasks (prosody/gender), stimulation (effective/sham), and hemispheres (left/right) using rmANOVAs. Multiple regressions were used to predict ∆v (effective–sham) in both tasks from individual ratings of (i) perceptual focus on prosodic contour, (ii) on mean pitch, (iii) amount of subvocal rehearsal, and (iv) stimulated hemisphere, controlled for (v) years of musical training and (vi) perceived task difficulty.
Single trial response times and accuracies were analyzed with the drift diffusion model (DDM; Ratcliff, 1978; fast-dm: Voss & Voss, 2007) to decompose latent processes that lead to a decision. Parameters v (drift rate; rate of evidence accumulation), a (threshold separation; indicating response biases), and t0 (non-decision time; decision-independent time for stimulus encoding and button press) were compared between tasks (prosody/gender), stimulation (effective/sham), and hemispheres (left/right) using rmANOVAs. Multiple regressions were used to predict ∆v (effective–sham) in both tasks from individual ratings of (i) perceptual focus on prosodic contour, (ii) on mean pitch, (iii) amount of subvocal rehearsal, and (iv) stimulated hemisphere, controlled for (v) years of musical training and (vi) perceived task difficulty.
Results:
Drift rate v in the prosody task dropped after effective compared to sham stimulation of right (but not left) PMC, and more strongly in participants who were biased to focus on the prosodic contours (Fig 1B). No such effects were found for parameters a and t0 or the categorization of speaker gender. Neither amount of subvocal rehearsal, nor years of musical training or perceived task difficulty influenced ∆v.
Conclusions:
The combined findings extend the modulatory role of PMC in speech perception from phonemes and tones to speech prosody. In particular, the results highlight the causal role of right PMC in pitch contour categorization, in line with auditory cortical asymmetries (Zatorre et al., 2002). The absence of rTMS effects on parameter a denoting response biases, and the stronger modulation of performance in case of a stronger perceptual bias towards pitch contour suggests a role of PMC in perceptual rather than solely response-related processes. Future studies should investigate the time-course of PMC involvement during prosody processing using chronometric protocols to substantiate this conclusion.
Brain Stimulation:
TMS 2
Language:
Speech Perception 1
Motor Behavior:
Mirror System
Keywords:
Cognition
Cortex
Hemispheric Specialization
Language
Motor
Perception
Transcranial Magnetic Stimulation (TMS)
Other - Prosody
1|2Indicates the priority used for review
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