Poster B59, Tuesday, August 20, 2019, 3:15 – 5:00 pm, Restaurant Hall
Bilateral Opercular Syndrome and Speech Perception
Grant Walker1, Ryan Stokes1, Patrick Rollo2, Nitin Tandon2, Gregory Hickok1;1University of California, Irvine, 2University of Texas at Houston
Different theories have posited a range of responsibilities for the motor system in the perception of speech: from motor representations being the critical loci for perception, to the motor system merely providing support for disambiguation in noisy situations. Proponents of the motor system’s prominent contributions point to studies showing that TMS of lip and tongue primary motor areas induces effector-specific perceptual discrimination errors and response delays. Proponents of a limited, supplementary role for the motor system point to instances of humans and non-humans performing speech perception tasks normally despite disruption or lack of speech motor representations. Preserved perceptual abilities in cases of motor disruption caused by unilateral, left-hemisphere stroke leave open the possibility that contralateral homologous systems might be compensating for the deficit. We had the rare opportunity to analyze structural MRI and a comprehensive speech perception task battery in two cases with a bilateral opercular syndrome with sparing of temporal cortex. Although the opercular syndromes occurred in the context of different etiologies (Case 1: epilepsy, Case 2: brain hemorrhages from multiple cavernous malformations), both participants underwent resection of left frontal operculum (by another neurosurgeon, not in the authorship), and after a period during which speech production recovered, a right-sided resection resulted in the loss of voluntary control of speech effectors and permanent mutism. Lesions were segmented from T1-weighted MRI. Participants’ receptive language abilities were assessed at the phoneme, word, and sentence levels. Verbal short-term memory was also evaluated. Lesion reconstruction revealed damage in bilateral opercula in both cases. Case 1 had larger resections in homologous frontal regions, whereas Case 2’s right-sided lesions extended posteriorly from the inferior precentral region destroying frontal-parietal white matter. Both participants performed within or near normal limits on the word recognition, word-to-picture matching tasks, and word-pair discrimination task, even when resolution of subtle phonemic cues was required. Case 1 had difficulty with discrimination of nonwords and synthesized speech in noise, likely stemming from a phonological short-term/working memory deficit. Both participants showed sensitivity to mismatched audiovisual speech signals and were able to comprehend simple sentences. Case 2 was also able to comprehend syntactically complex sentences showing largely preserved receptive language abilities. Case 1 had difficulty with complex syntax and limited immediate recall span, consistent with a working memory deficit. Bilateral damage to the motor speech system had little effect on the ability to recognize speech. Such damage can impair phonological short-term memory and produce an agrammatic-type comprehension pattern. Audiovisual speech integration is not necessarily impaired, nor is speech-in-noise perception necessarily profoundly affected. These results contribute to the evidence against a critical role of the motor system for perception of speech. Special consideration of task demands on verbal short-term/working memory is recommended to disambiguate performance declines that are unrelated to residual speech perception abilities.
Themes: Perception: Speech Perception and Audiovisual Integration, Disorders: Acquired
Method: Behavioral