Left and Right Hemisphere Contributions to Speech Perception

Study Overview
=================
Brief Summary
-----------------
Left and right temporal brain areas are thought to contribute to speech perception, but the division of labor between left and right hemisphere regions is still unclear. Here we use transcranial magnetic stimulation (TMS) to stimulate left and right temporal foci and a vertex control site to temporarily disrupt activation at the stimulation site, using a virtual lesion approach to test the effect of stimulation site on a series of speech perception tasks. This portion of the project is basic research. However, since TMS is viewed as an intervention, studies involving TMS in this grant are considered clinical trials.

Detailed Description
-----------------
This study uses TMS to temporarily disrupt neural activity in the left and right temporal cortex and examine the effect of this disruption on speech perception tasks. Vertex stimulation is included as a control condition against which left and right superior temporal stimulation effects are compared. Adult participants first undergo structural MRI and a speech localizer using functional MRI to identify speech-sensitive voxels in the left and right temporal cortex. These regions are set by-participant as the foci for stimulation. Stimulation site is blocked, and typically distributed across sessions. 10 Hz pulse trains of 2.5 sec each are delivered to the stimulation site, with an auditory stimulus arriving either immediately after the last pulse (Exps 2 and 6) or, for longer sentence level stimuli (Exp 3), during the pulse train. Behavioral measures include accuracy and reaction times to rate phonetic stimuli (Exp 2), detect the presence of a probe word in the preceding sentence (Exp 3), or categorize stimuli by phonetic contrast and talker (Exp 6).

Official Title
-----------------
The Role of Frontal and Temporal Brain Areas in the Perception of Phonetic Category Structure

Conditions
-----------------
Neural Bases of Speech Perception

Intervention / Treatment
-----------------
* Device: Transcranial Magnetic Stimulation


Participation Criteria
=================
Eligibility Criteria
-----------------
Inclusion Criteria: Monolingual native speaker of English No history of neurological impairments or disease Free of speech and language disorders (per self-report, and confirmed by short language battery described by Fidler, Vance, & Plante, 2011) Pure-tone thresholds of 30 decibels or better in both ears (no worse than mild hearing loss), with no more than 15 dB between-ear difference. Right-handed, as confirmed by Oldfield Handedness Inventory Exclusion Criteria: Any condition where TMS would be contraindicated according to the most recent guidelines, including, but not limited to: History of seizure or epilepsy Metal in the skull Use of legal or illicit drugs that can potentially reduce the threshold for seizure. As examples, we list some exclusionary drugs in each of the following categories. This is not an exhaustive list of the exclusionary drugs. We consult with faculty in the University of Connecticut College of Pharmacy to check for seizure risk with other drugs that participants report. Antidepressants including Imipramine, amitriptyline, sertraline, venlafaxine, buproprion Antipsychotics including Chlorpromazine, clozapine, haloperidol, aripiprazole Antivirals including foscarnet, ganciclovir Antiparasitics including chloroquine, mefloquine (antiparasitics) Antibiotics including penicillin, ampicillin Immunosuppressants including cyclosporin Anticholinergenics Antihistimines (including over-the-counter drugs like Claritin & Benadryl) Sympathomimetics (including Sudafed, Ritalin). Illegal drugs such as methamphetamines, cocaine, MDMA, ketamine. Diagnosis of a psychiatric disorder (per self-report) Pregnancy

Ages Eligible for Study
-----------------
Minimum Age: 18 Years

Sexes Eligible for Study
-----------------
All

Accepts Healthy Volunteers
-----------------
Accepts Healthy Volunteers

Study Plan
=================
How is the study designed?
-----------------

Design Details

Primary Purpose: Basic Science
Allocation: Randomized
Intervention Model: Crossover Assignment
Interventional Model Description: Participants will receive blocks of stimulation at the left temporal lobe, right temporal lobe, and vertex, with the order of stimulation counterbalanced across participants (a crossover design). All analysis is within-subject. Participants in each arm will hear different types of speech stimuli, which allows for the assessment of the effect of stimulation at different stimulation sites on processing that specific aspect of the speech signal.
Masking: Single


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: Experiment 2. Phonetic precision disrupted by TMS<br>Experiment 2 tests the influence of temporary disruption of activity within the left or right temporal cortex on the speed and precision of phonetic decisions compared to vertex stimulation. Participants will receive stimulation at all three sites (left temporal, right temporal, vertex, with order of stimulation counterbalanced across participants). Immediately following stimulation pulses, participants will perform a visual analog scale (VAS) phonetic rating task on tokens from the four continua, embedded in speech-shaped noise. To control for the possibility that TMS leads to a generalized deficit in categorization, a control task will involve categorization of visual objects on a morphed dog to cat object continuum. (We expect this task to be unaffected by TMS). The variables of interest are the steepness of the categorization curve, mean reaction time to all items on the continuum, and the difference in reaction time for boundary vs. endpoint tokens. | Device: Transcranial Magnetic Stimulation<br>* TMS will be delivered in 10 Hz pulses for 2.5 seconds, with behavioral measures of speech perception and object categorization immediately following each pulse. TMS at this schedule is thought to temporarily disrupt activity at the stimulation site.<br>|
| Experimental: Experiment 3. Phonetic ambiguity in continuous speech<br>Experiment 3 is designed to test whether left vs. right temporal lobe stimulation selectively disrupts processing of naturally-occurring phonetic ambiguity as compared to vertex stimulation (control). Participants will receive stimulation at all three sites (left temporal, right temporal, vertex, with order of stimulation counterbalanced across participants). Stimuli will be nonsense sentences produced clearly or in a casual register. By-sentence phonetic ambiguity is estimated by the proximity of each token to other vowels belonging to different categories. Sentences will be embedded in speech-shaped noise to increase difficulty. Participants will listen to each sentence, then respond whether a visually-presented probe word appeared in the sentence (BRASS?). Dependent variables are accuracy and reaction time on this probe verification task. | Device: Transcranial Magnetic Stimulation<br>* TMS will be delivered in 10 Hz pulses for 2.5 seconds, with behavioral measures of speech perception and object categorization immediately following each pulse. TMS at this schedule is thought to temporarily disrupt activity at the stimulation site.<br>|
| Experimental: Experiment 6: Disruption of talker-specific phonetic learning using TMS.<br>Experiment 6 is designed to test whether disruption of activity in left or right temporal regions (vs. vertex control) using TMS interferes with talker-specific learning. Participants will receive stimulation at all three sites (left temporal, right temporal, vertex, with order of stimulation counterbalanced across participants). The study uses a training paradigm where one talker's speech is manipulated to always have relatively short voice onset times (VOTs) for voiceless stops (e.g., /k/ in coal) and another to have relatively long VOTs. Immediately after stimulation, listeners will undergo a training trial where they identify sounds as mapping to Talker 1 or Talker 2's voice, and to the word (e.g. gain vs. cane). At test, listeners hear two VOT variants and are asked which is more typical of that talker's speech. The dependent variable is the accuracy of reporting which variant is typical of the talker. | Device: Transcranial Magnetic Stimulation<br>* TMS will be delivered in 10 Hz pulses for 2.5 seconds, with behavioral measures of speech perception and object categorization immediately following each pulse. TMS at this schedule is thought to temporarily disrupt activity at the stimulation site.<br>|

What is the study measuring?
-----------------
Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Categorization accuracy | Participants categorize items which vary along a perceptual continuum. Steepness of the categorization curve is extracted to estimate categorization accuracy. | Immediately following the stimulation pulses (within one second of the final pulse). | 
| Two-alternative forced choice accuracy | Participants are given two options and asked to indicate which item they heard in the previous signal. Accuracy in making this decision is a primary outcome measure. | Immediately following the stimulation pulses (within one second of the final pulse). | 
| Two-alternative forced choice reaction time | Participants are given two options and asked to indicate which item they heard in the previous signal. Reaction time to make this decision is a primary outcome measure. | Immediately following the stimulation pulses (within one second of the final pulse). | 

 Terms related to the study
=================
Keywords Provided by Centre Hospitalier Valida
-----------------
Speech perception, Left temporal lobe, Right temporal lobe