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

Official title

Brain Mechanisms Underlying Neurotypical and Disordered Speech

Overview

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.

Interventions

• 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 (baselin
• 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
• 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:
• 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 b
• 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 t
• 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 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 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.
• 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.

Primary outcome measures

• Reflexive compensatory response [Time frame: Day 1 and Day 2]
• Adaptive compensatory response [Time frame: Day 1 and Day 2]

Secondary outcome measures (10)

• Stuttering Severity [Time frame: Baseline]
• Dyslexia Severity [Time frame: Baseline]
• Verbal and Nonverbal Intelligence [Time frame: Baseline]
• Receptive Vocabulary [Time frame: Baseline]
• Brain region volume [Time frame: Day 2]
• Brain region area [Time frame: Day 2]
• Brain region cortical thickness [Time frame: Day 2]
• Brain region cortical gyrification [Time frame: Day 2]
• Brain region functional connectivity [Time frame: Day 2]
• Brain region structural connectivity [Time frame: Day 2]

Eligibility criteria

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

Criteria are shown verbatim from the registry (in English). Final eligibility is always assessed by the study center.

Healthy volunteers: Yes

Study design

Allocation

Randomized

Model

Parallel assignment

Masking

Single blind

Primary purpose

Basic science

Study locations

United States · 2 centers

• Boston University Charles River Campus — Boston
• Boston University — Boston

Identifiers

NCT: NCT07459803 · Guenther_8013 · R01DC022014-01

Primary sources (government registries)

• ClinicalTrials.gov (US NIH)

View this study on ClinicalTrials.gov ↗