Investigating Individual Differences in Speech Motor Skills in Neurotypical Speakers and Persons With Disordered Speech

Brain Mechanisms Underlying Neurotypical and Disordered Speech

This study aims to understand how people use different types of feedback to control their speech. When an individual speaks, the brain relies on several systems at the same time, such as sensory systems that monitor an individuals own voice and the movements of their speech muscles, and a motor system that builds and reads out learned motor patterns. The investigators are studying how these systems work together and how they differ across individuals.

Investigators will test 90 adults between 18 and 50 years old, including people who stutter, people with dyslexia, and people with typical speech and reading development. Participants will complete several short speech tasks in which the sounds they hear or the movements of their jaw or larynx are briefly changed. These responses will be used to measure each person's speech motor skills and to estimate the settings of a computer model called "SimpleDIVA," which simulates how the brain controls speech.

Participants will also complete an MRI scan so investigators can measure the structure and connectivity of different brain regions. These measures will help investigators understand how individual differences in the brain relate to the speech motor control skills we observe. Participants will also complete sessions with noninvasive brain stimulation (transcranial current stimulation, or tCS) to examine how stimulation of specific areas of the brain affects responses during the speech tasks.

The knowledge gained from this study will help researchers understand why speech motor skills vary across people and how differences in neural function may contribute to conditions such as stuttering and dyslexia.

Study Overview

• Status: Not yet recruiting
• Conditions: Dyslexia; Healthy Participants; Stuttering, Developmental
• Intervention / Treatment: Behavioral: Unpredictable auditory feedback perturbation: 2 behavioral sessions; Behavioral: Unpredictable auditory feedback perturbation during tCS: 3 behavioral sessions; Behavioral: Sustained F1 auditory feedback perturbation; Behavioral: Sustained F0 auditory feedback perturbation; Behavioral: Reflexive somatosensory perturbation; Other: Anodal tCS targeting pSTG and vSSC; Other: Sham tCS targeting pSTG or vSSC; Other: Anodal tCS targeting left or right vPMC; Other: Sham tCS targeting left vPMC or right vPMC

• Study Type: Interventional
• Enrollment (Estimated): 90
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: Frank H Guenther, Ph.D.; Phone Number: 617-353-5765; Email: guenther@bu.edu
• Study Contact Backup: Name: Barbara G Holland, M.A.; Phone Number: 617-353-6181; Email: bobbieh@bu.edu

Study Locations

• United States
  • Massachusetts
    • Boston, Massachusetts, United States, 02215
      • Boston University
      • Contact: Frank H Guenther, Ph.D.; Phone Number: 617-353-5765; Email: guenther@bu.edu
      • Principal Investigator: Frank H Guenther, Ph.D.
      • Sub-Investigator: Alfonso Nieto-Castanon, Ph.D.
      • Sub-Investigator: Jason Tourville, Ph.D.
      • Sub-Investigator: Alyssa R. Boucher, Ph.D.
      • Sub-Investigator: Caroline J Brinkert, M.S.
      • Sub-Investigator: Tyler K Perrachione, Ph.D.

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult
• Accepts Healthy Volunteers: Yes

Description

Inclusion Criteria:

• Native speakers of American English
• Adults age 18-50
• Age-appropriate cognitive and receptive vocabulary skills
• Age-appropriate hearing
• Adults with dyslexia will have a history of dyslexia or report of ongoing reading difficulties that will be confirmed at the first screening visit
• Adults who stutter will have a history of stuttering that will be confirmed at the first screening visit

Exclusion Criteria:

• History of neurological disorder, including a history of seizures
• Major brain injury, brain surgery, or stroke
• Orthodontia or atypical oral structure (e.g., cleft palate) that interferes with speech
• Fluency disorder (except those in the persons who stutter cohort), apraxia of speech, or dysarthria
• Language or reading disorder (except those in persons with dyslexia cohort)
• Standardized score below 80 on the Kaufman Brief Intelligence Test
• Standardized score below 1 standard deviation on the NIH Toolbox Picture Vocabulary Test
• Pregnancy
• Severe claustrophobia
• Presence of magnetically or mechanically active implant, or other ferromagnetic material embedded in any part of the body
• Significant scalp lesions that would prevent transcranial direct stimulation

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Basic Science
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: Single

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: pSTG and vSSC tCS Targeting; Participants in Arm 1 will complete all behavioral, MRI, and tCS study procedures. During the tCS portion of the study, they will receive anodal transcranial current stimulation (tCS) targeting two brain regions: posterior superior temporal gyrus (pSTG) in one stimulation session and ventral somatosensory cortex (vSSC) in another. In a third session, they will complete the same speech task while receiving sham stimulation targeting either pSTG or vSSC. All participants in this arm will also complete speech motor control tasks involving unpredictable auditory perturbations, sustained auditory perturbations, and somatosensory perturbations, as well as one MRI session.	Behavioral: Unpredictable auditory feedback perturbation: 2 behavioral sessions; Participants in Arms 1 and 2 will repeat consonant/vowel/consonant (/CVC/) words containing the vowel "eh" between two consonants that they hear over headphones. As they speak, vocal output from the participant will be transduced via a microphone and then played back to the participant over headphones at an undetectable delay. On a subset of (perturbed) trials, F0 or F1 in the auditory feedback presented to the participant will be shifted relative to their vocal output. On the remaining (baseline) trials, auditory feedback will be unaltered. During each behavioral session, participants will complete 80 unperturbed trials, 40 trials that involve an F0 perturbation, and 40 trials that involve an F1 perturbation.; Behavioral: Unpredictable auditory feedback perturbation during tCS: 3 behavioral sessions; Participants in Arms 1 and 2 will repeat /CVC/ words containing the vowel "eh" between two consonants that they hear over headphones. As they speak, vocal output from the participant will be transduced via a microphone and then played back to the participant over headphones at an undetectable delay. On a subset of (perturbed) trials, F0 or F1 in the auditory feedback presented to the participant will be shifted relative to their vocal output. On the remaining (baseline) trials, auditory feedback will be unaltered. During each session, participants will complete 50 unperturbed trials, 50 trials that involve an F0 perturbation, and 50 trials that involve an F1 perturbation.; Behavioral: Sustained F1 auditory feedback perturbation; Participants in Arms 1 and 2 will repeat /CVC/ words containing the vowel "eh" between two consonants that they hear over headphones. As they speak, vocal output from the participant will be transduced via a microphone and then played back to the participant over headphones at an undetectable delay. Over the course of each protocol, the first formant (F1) in the auditory feedback presented to the participant will be shifted relative to their vocal output. Trials will be organized in four phases: an initial baseline phase in which auditory feedback is unaltered, a ramp phase over which the formant of auditory feedback is gradually shifted to a maximum level, a hold phase in which the feedback shift is held at its maximum level, and then an after-effect phase in which feedback returns to normal. Four trials will be performed in each phase.; Behavioral: Sustained F0 auditory feedback perturbation; Participants in Arm 1 and 2 will repeat /CVC/ words containing the vowel "eh" between two consonants that they hear over headphones. As they speak, vocal output from the participant will be transduced via a microphone and then played back to the participant over headphones at an undetectable delay. As they speak the fundamental frequency (F0) in the auditory feedback presented to the participant will be shifted relative to their vocal output. Trials will be organized in four phases: an initial baseline phase in which auditory feedback is unaltered, a ramp phase over which the formant of auditory feedback is gradually shifted to a maximum level, a hold phase in which the feedback shift is held at its maximum level, and then an after-effect phase in which feedback returns to normal.; Behavioral: Reflexive somatosensory perturbation; Participants in Arms 1 and 2 will repeat /CVC/ words containing the vowel "eh" between two consonants that they hear over headphones. While they speak, speech-shaped masking noise will be presented to participants at 85 dB. On a subset of trials (word productions), movements of the jaw will be perturbed (restricted) by the rapid inflation of a balloon placed between the upper and lower teeth shortly after voice onset. On another subset of trials, the position of the larynx will be perturbed by the rapid inflation of a balloon placed against the laryngeal prominence. During the remaining (unperturbed) trials, both balloons will remain deflated.; Other: Anodal tCS targeting pSTG and vSSC; Participants in Arm 1 will receive continuous anodal tCS targeting posterior superior temporal gyrus (pSTG) during a 20-minute reflexive auditory feedback task during one session and stimulation targeting ventral somatosensory cortex (vSSC) during the same task in another session. The tCS stimulation will ramp up to its maximum value (2 milliamperes) over the first 30 s of the session and will be maintained at that level throughout the remainder of the session.; Other: Sham tCS targeting pSTG or vSSC; Participants in Arm 1 will receive Sham tCS stimulation targeting the pSTG or vSSC during a 20-minute reflexive auditory feedback task. During the minute prior to training onset, the tCS stimulator will ramp up to 2 milliamperes and then back down to 0 for the remainder of the session.
Experimental: Left and Right vPMC tCS Targeting; Participants in Arm 2 will complete all behavioral, MRI, and tCS study procedures. During the tCS portion of the study, they will receive anodal transcranial current stimulation (tCS) targeting left ventral premotor cortex (vPMC) in one stimulation session and right vPMC in another. In a third session, they will complete the same speech task while receiving sham stimulation targeting either the left or right vPMC. All participants in this arm will also complete speech motor control tasks involving unpredictable auditory perturbations, sustained auditory perturbations, and somatosensory perturbations, as well as one MRI session.	Behavioral: Unpredictable auditory feedback perturbation: 2 behavioral sessions; Participants in Arms 1 and 2 will repeat consonant/vowel/consonant (/CVC/) words containing the vowel "eh" between two consonants that they hear over headphones. As they speak, vocal output from the participant will be transduced via a microphone and then played back to the participant over headphones at an undetectable delay. On a subset of (perturbed) trials, F0 or F1 in the auditory feedback presented to the participant will be shifted relative to their vocal output. On the remaining (baseline) trials, auditory feedback will be unaltered. During each behavioral session, participants will complete 80 unperturbed trials, 40 trials that involve an F0 perturbation, and 40 trials that involve an F1 perturbation.; Behavioral: Unpredictable auditory feedback perturbation during tCS: 3 behavioral sessions; Participants in Arms 1 and 2 will repeat /CVC/ words containing the vowel "eh" between two consonants that they hear over headphones. As they speak, vocal output from the participant will be transduced via a microphone and then played back to the participant over headphones at an undetectable delay. On a subset of (perturbed) trials, F0 or F1 in the auditory feedback presented to the participant will be shifted relative to their vocal output. On the remaining (baseline) trials, auditory feedback will be unaltered. During each session, participants will complete 50 unperturbed trials, 50 trials that involve an F0 perturbation, and 50 trials that involve an F1 perturbation.; Behavioral: Sustained F1 auditory feedback perturbation; Participants in Arms 1 and 2 will repeat /CVC/ words containing the vowel "eh" between two consonants that they hear over headphones. As they speak, vocal output from the participant will be transduced via a microphone and then played back to the participant over headphones at an undetectable delay. Over the course of each protocol, the first formant (F1) in the auditory feedback presented to the participant will be shifted relative to their vocal output. Trials will be organized in four phases: an initial baseline phase in which auditory feedback is unaltered, a ramp phase over which the formant of auditory feedback is gradually shifted to a maximum level, a hold phase in which the feedback shift is held at its maximum level, and then an after-effect phase in which feedback returns to normal. Four trials will be performed in each phase.; Behavioral: Sustained F0 auditory feedback perturbation; Participants in Arm 1 and 2 will repeat /CVC/ words containing the vowel "eh" between two consonants that they hear over headphones. As they speak, vocal output from the participant will be transduced via a microphone and then played back to the participant over headphones at an undetectable delay. As they speak the fundamental frequency (F0) in the auditory feedback presented to the participant will be shifted relative to their vocal output. Trials will be organized in four phases: an initial baseline phase in which auditory feedback is unaltered, a ramp phase over which the formant of auditory feedback is gradually shifted to a maximum level, a hold phase in which the feedback shift is held at its maximum level, and then an after-effect phase in which feedback returns to normal.; Behavioral: Reflexive somatosensory perturbation; Participants in Arms 1 and 2 will repeat /CVC/ words containing the vowel "eh" between two consonants that they hear over headphones. While they speak, speech-shaped masking noise will be presented to participants at 85 dB. On a subset of trials (word productions), movements of the jaw will be perturbed (restricted) by the rapid inflation of a balloon placed between the upper and lower teeth shortly after voice onset. On another subset of trials, the position of the larynx will be perturbed by the rapid inflation of a balloon placed against the laryngeal prominence. During the remaining (unperturbed) trials, both balloons will remain deflated.; Other: Anodal tCS targeting left or right vPMC; Participants in Arm 2 will receive continuous anodal tCS targeting left ventral premotor cortex (vPMC) during a 20-minute reflexive auditory feedback task during one session and stimulation targeting right vPMC during the same task in another session. The tCS stimulation will ramp up to its maximum value (2 milliamperes) over the first 30 s of the session and will be maintained at that level throughout the remainder of the session.; Other: Sham tCS targeting left vPMC or right vPMC; Participants in Arm 1 will receive Sham tCS stimulation targeting left or right vPMC during a 20-minute reflexive auditory feedback task. During the minute prior to training onset, the tCS stimulator will ramp up to 2 milliamperes and then back down to 0 for the remainder of the session.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Reflexive compensatory response	The amount of compensation to induced F0 and F1 perturbations will be calculated by finding the maximum deviation of the perturbed variable (F0 or F1) from baseline, dividing it by the perturbation size, and then averaging that across all trials of that perturbation.	Day 1 and Day 2
Adaptive compensatory response	The adaptive compensatory response to persistent F0 and F1 perturbations will be calculated by subtracting the mean F0/F1 from the baseline phase from the mean during the after-effect phase, then dividing by the perturbation size to obtain percent adaptation.	Day 1 and Day 2

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Stuttering Severity	The composite score of the Stuttering Severity Instrument, 4th Edition, and the frequency of stuttering-like dysfluencies will be used to identify correlations between stuttering severity and other outcome measures in persons who stutter.	Baseline
Dyslexia Severity	A mean composite score from subtests of the Test of Word Reading Efficiency and the Woodcock Reading Mastery Test will be used to identify correlations between dyslexia severity and other outcome measures in persons with dyslexia.	Baseline
Verbal and Nonverbal Intelligence	The composite score from the Kaufman Brief Intelligence Test for each participant will be used to identify correlations between intelligence and other outcome measures.	Baseline
Receptive Vocabulary	The score from the Picture Vocabulary Test (PVT) from the NIH Toolbox for each participant will be used to identify correlations between receptive vocabulary and other outcome measures.	Baseline
Brain region volume	Volume (mm^3) will be extracted for subcortical regions of interest (ROIs). ROIs will be delineated and volume measures extracted using FreeSurfer's standard structural MRI processing pipeline.	Day 2
Brain region area	Area (mm^2) will be extracted for cortical regions of interest (ROIs). ROIs will be delineated and area measures extracted using FreeSurfer's standard structural MRI processing pipeline.	Day 2
Brain region cortical thickness	Cortical thickness (mm) will be extracted for cortical regions of interest (ROIs). ROIs will be delineated and cortical thickness extracted using FreeSurfer's standard structural MRI processing pipeline.	Day 2
Brain region cortical gyrification	Local gyrification index (a unitless measure of the ratio of pial surface and external surface in an area) will be extracted for cortical regions of interest (ROIs). ROIs will be delineated and cortical thickness extracted using FreeSurfer's standard structural MRI processing pipeline.	Day 2
Brain region functional connectivity	Functional connectivity between pairs of brain ROIs will be estimated from resting state functional MRI using the CONN functional connectivity toolbox.	Day 2
Brain region structural connectivity	Structural connectivity between pairs of brain ROIs will be estimated from diffusion-weighted MRI using components of the FSL Diffusion Toolbox and the MRtrix software package.	Day 2

Collaborators and Investigators

• Sponsor: Boston University Charles River Campus
• Collaborators: National Institute on Deafness and Other Communication Disorders (NIDCD)
• Investigators: Principal Investigator: Frank H Guenther, Ph.D., Boston University

Study record dates

Study Major Dates

• Study Start (Estimated): April 1, 2026
• Primary Completion (Estimated): March 1, 2030
• Study Completion (Estimated): March 1, 2030

Study Registration Dates

• First Submitted: December 12, 2025
• First Submitted That Met QC Criteria: March 3, 2026
• First Posted (Actual): March 10, 2026

Study Record Updates

• Last Update Posted (Actual): March 12, 2026
• Last Update Submitted That Met QC Criteria: March 10, 2026
• Last Verified: March 1, 2026

More Information

Terms related to this study

• Keywords: Magnetic Resonance Imaging; Dyslexia; Speech Disorders; Speech Motor Learning; Neurocomputational Modeling; Stuttering Developmental
• Additional Relevant MeSH Terms: Specific Learning Disorder; Neurologic Manifestations; Nervous System Diseases; Mental Disorders; Neurobehavioral Manifestations; Neurodevelopmental Disorders; Communication Disorders; Language Disorders; Learning Disabilities; Pathological Conditions, Signs and Symptoms; Signs and Symptoms; Speech Disorders; Dyslexia; Stuttering
• Other Study ID Numbers: Guenther_8013; R01DC022014-01 (U.S. NIH Grant/Contract)

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: YES

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No