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Phonetic categorization and adaptation is impaired in adults with acquired lesions to the left hemisphere.

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Poster E75 in Poster Session E, Thursday, October 26, 10:15 am - 12:00 pm CEST, Espace Vieux-Port

Hellmuth Obrig1,5, Annika Werwach1,2, Frank Regenbrecht1, Eva Mosig1, Merav Ahissar6, Claudia Männel1,3,4; 1Clinic for Cognitive Neurology, Medical Faculty, University Leipzig, Germany, 2Max Planck School of Cognition, Leipzig, 3Department of Audiology and Phoniatrics, Charité–Universitätsmedizin Berlin, Germany, 4Department of Neuropsychology, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, 5Department of Neurology, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, 6ELSC Center for Brain Research, The Hebrew University Jerusalem, Israel

Introduction: Categorical phoneme-perception is a cornerstone of language competence. Tuning into a given phonetic inventory starts in infancy and allows listeners to categorize the manifold acoustic realizations of a phoneme to successfully ‘map sound to meaning’. Phonetic boundaries are relevant for minimal pair differentiation (e.g., /dad/↔/bad/) and acquisition of written language, however, boundaries can be rapidly modulated, allowing for example for speaker adaptation. In the selective adaptation paradigm (1), repeated exposure to ‘prototypical’ phoneme-exemplars shifts the judgment on a continuum between, for example, /b/↔/d/ towards the prototype. More generally, repeated exposure to identical stimuli increases sensitivity to change detection, such as the frequency of tones. This adaptation process is called perceptual anchoring (2). Both, selective phoneme adaptation and perceptual anchoring have been proposed to be impaired in developmental dyslexia (2, 3). However, to our knowledge, data on individuals with an acquired lesion to the auditory/language-cortices are missing. The current project hence studies participants with unilateral left- or right-hemispheric lesions (including primary/ secondary auditory cortices) and age-matched neurotypical controls on selective phoneme adaptation and perceptual anchoring. Methods: The speech adaptation paradigm (1) required forced choice on the perception of /ba/ versus /da/ for 20 exemplars on a morphed continuum (/ba/↔/da/) (4). So far, we have included 10 participants with a left-hemispheric lesion (including primary/secondary auditory cortex) and 10 age-matched neurotypical controls. The task was administered monaurally (left/right ear); the other ear was masked with noise (dichotic presentation). Linear-mixed-model (LMM) analyses targeted participants’ categorical speech perception (consistency of syllable identification) and speech adaptation (phonetic-boundary shift after adaptation to prototypical exemplars). For lesion effects and lateralization, the model included group (lesion/neurotypical) and presentation side (right/left-ear). Additionally, all participants completed a tone-discrimination task with/without perceptual anchor, requiring judgement on frequency differences between tone-pairs. For the anchor condition (first tone constant across trials) the just-noted-difference is expected to be smaller compared to the no-anchor-condition (first tone variable). Results: LMMs revealed lower speech adaptation to continuum endpoints in left-hemisphere-lesioned participants compared to controls (F(1,18)=5.22, p=.035, ηp2=0.22), in particular for right-ear-presentation (t(51.2)=3.20, p=.002). Overall categorical perception was also impaired in the patient group (F(1,18.47)=11.41, p=.003, ηp2=0.38). Preliminary analyses of the tone-discrimination task, confirm the smaller just-noted-difference for the anchor condition, however, differences between groups and right/left ear presentation were not significant. Discussion: We demonstrate that not only categorical phoneme perception but also speech-adaptation is altered after lesions to the left-hemispheric auditory/language cortices. The lateralization of the effect (right-ear-dominance) and the unaltered anchor-effect for frequency discrimination point to a language-related impairment. This is currently corroborated by increasing the sample size to the pre-registered n=16 and including participants with corresponding right-hemispheric lesions (n=7 at time of submission). Additional correlations with participants’ patholinguistic profiles will address the relevance of deficits in perceptual anchoring and selective speech adaptation for speech comprehension in people with aphasia. Citations: (1) Eimas & Corbit, Cognitive Psychol 4:99-109 (1973). (2) Ahissar, et al. Nat Neurosci 9:1558-1564 (2006). (3) Ozernov-Palchik et al., J Exp Psychol General 151:1556-1572 (2022). (4) Stephens & Holt, Speech Commun 53:877-888 (2011).

Topic Areas: Speech Perception, Phonology

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