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A simple psychophysical procedure separates sensory and cognitive components of impairments of speech prosody perception after right-hemisphere stroke
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Poster E36 in Poster Session E, Thursday, October 26, 10:15 am - 12:00 pm CEST, Espace Vieux-Port
Aynaz ADLZARRABI1, Jean-Julien AUCOUTURIER1, Lionel NACCACHE2, Emmanuel PONSOT3, Marie VILLAIN2; 1Université de Franche-Comté, SUPMICROTECH, CNRS, FEMTO-ST Institute, Besançon France, 2Institut du Cerveau et de la Moelle Epinière (ICM), Paris, France, 3Science & Technologue of Music & Science (STMS), IRCAM/CNRS/Sorbonne Université, Paris, France
Introduction After a right hemisphere stroke, more than half of the patients present a communication disorder such as aprosodia, the impossibility to produce or comprehend speech prosody. Despite its social-cognitive implications for patients, aprosodia following stroke has received scant attention: first, existing assessment tools based on simple perceptive tasks are insufficiently sensitive; second, we lack a mechanistic understanding of why patients perform poorly on such tasks and therefore practical therapeutic targets for rehabilitation. In this report, we introduce a psychophysical procedure which, by combining systematic digital manipulations of speech stimuli and reverse-correlation analysis, allows estimating the internal sensory representations that subtend how individual patients perceive speech prosody. We compare its validity to the existing gold standard for diagnosing aprosodia (Montreal Evaluation of Communication; MEC). Methods Participants N=22 brain stroke survivors (male:17; M=57 yo), and N=12 age-matched controls (male: 6; M=59 yo) participated in the study. All patients had a history of supratentorial right-hemisphere ischaemic stroke dating less than 1y, were first-language French speakers, and had no deficits of language comprehension or major hearing impairment. Procedure: We recorded a 500-ms utterance of the French word « vraiment » (« really »), and generated random prosodic variations by dividing it into six successive segments and randomly manipulating the pitch of each segment. We then presented participants with 150 successive pairs of manipulated utterances (« really/really? ») asking them to judge, within each pair, which sounded most interrogative. Patient responses were then fitted with a 2-stage psychophysical model, consisting, first, of a prosodic template (or “internal representation”) to which sound stimuli are compared and, second, of a level of “internal noise” which controls how consistently this representation is applied to incoming stimuli. Results In the control group, internal representations of interrogative prosody exhibited a typical final-rise contour, with a marked increase of pitch at the end of the second syllable. In contrast, patients’ internal representations had lower amplitude, more variable shape across individuals, and were applied with higher levels of internal noise (M=+2.40, Mann-Whitley’s U(-0.83)=628, p<0.001). Within the patient group, larger internal noise values were associated with more severe scores on the MEC prosody comprehension scale (R2 = 0.263, t(20)=-2.66, p=.015). Second, both atypical representations and internal noise had good symptom specificity, as neither correlated with the MEC score for prosody repetition (representation: R2: 0.00, p=.94; noise: R2=0.039, p=.38). Finally, both measures had good sensitivity, as they allowed separating patients above the pathological cut-off (9/12) on the MEC prosody comprehension scale (N=11/22) from controls (N=12), both in terms of typicality of representation (M=-0.14, U(0.9)=7, p<.001) and internal noise (M=0.85, U(-0.68)= 71, p<.015). Conclusion. The representation+noise model paints a simple yet potent portrait of the variety of sensory/cognitive mechanisms that can explain impairments of prosody processing after stroke. By separating these different profiles of pathology, it is our hope that the method will provide more effective and individualized therapeutic targets for the rehabilitation of individuals with impaired speech prosody perception than existing measures.
Topic Areas: Prosody, Disorders: Acquired