Left and Right Hemisphere Contributions to Speech Perception

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.

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).

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