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Rapid auditory and linguistic processing requires the left planum temporale
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Poster E79 in Poster Session E, Thursday, October 26, 10:15 am - 12:00 pm CEST, Espace Vieux-Port
Kelly Martin1, Andrew DeMarco1, Peter Turkeltaub1,2; 1Georgetown University Department of Neurology, 2MedStar National Rehabilitation Hospital
After bilateral acoustic processing, speech and language processing is left-lateralized. The reason for this remains an open question. One prominent hypothesis (Asymmetric Sampling in Time) proposes different biases in the left and right hemispheres for processing auditory information in short (25ms) versus long (250ms) temporal windows, respectively. Here we investigated this hypothesis in a sample of adults with left hemisphere stroke (LHS) with respect to both auditory and linguistic processing. We first asked: Do adults with LHS perform worse on rapid auditory judgments than healthy controls, and is there a certain lesion location that predicts worse performance on these judgments? Fifty LHS participants (18 female, 20 African American, ages ranging 39.4-81.4 years with a mean of 60.0 years, time since stroke ranging from 0.12-16.7 years with a mean of 3.9 years) and 61 healthy controls (34 female, 20 African American, ages ranging 30.7-83.8 years with a mean of 61.0 years) performed a frequency-modulated (FM) sweeps judgment task involving short (25ms) and long (250ms) sweeps. Mean accuracies for each participant were calculated across all short-sweep and long-sweep trials respectively. Performance was significantly lower for patients than controls, and for short sweeps than long sweeps. We then performed support vector regression lesion-symptom mapping (SVR-LSM) using manually traced lesions warped to MNI space. Lesion volume was included as a covariate in the behavioral measures and voxelwise lesion data, and maps were thresholded using continuous family-wise error correction based on permutation analyses. The SVR-LSM results revealed that a stroke to the planum temporale (PT) predicted worse performance on short sweeps, controlling for performance on long sweeps. We then asked: Do adults with a stroke to the PT perform worse on linguistic judgments that rely on these short time windows? We separated patients into subgroups of “PT lesion” or “No PT lesion,” and examined their performance on a categorical phoneme identification (CP ID) task in which they identified a phoneme as either /ba/ or /da/. Importantly, the spectrograms for /ba/ versus /da/ differ in the initial 25ms segment of the second formant. We examined two measures of CP ID accuracy: categorization slope, measured as the steepness of the transition between the two mid-point stimuli, and end-point accuracies, measured as the difference between the accuracies on the two end-point stimuli (i.e., the most “/ba/-like” and the most “/da/-like” stimuli). To calculate categorization slope, we first sigmoid-fit each participant’s raw response data using a nonlinear least squares approach. Controls performed significantly better than LHS participants on both measures of CP ID accuracy. Additionally, the PT lesion group performed significantly worse than the No PT lesion group on correctly identifying the end-point stimuli. An SVR-LSM analysis revealed that worse performance on both measures of CP ID proficiency related to strokes to the PT. We conclude that the left PT is an essential region for processing auditory information in short temporal windows, and it may also be an essential transfer point in auditory-to-linguistic processing.
Topic Areas: Speech Perception, Phonology