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Modeling Sign Language Production in Light of Neurological Impairment
Poster Session B, Friday, September 12, 4:30 - 6:00 pm, Field House
Anna Noelle Boyer1, David Corina1; 1University of California, Davis
Conduction aphasia resulting from a traumatic brain injury typically presents with deficiencies in linguistic production. Patients with spoken language conduction aphasia have fluent speech production with good auditory comprehension, but show a disproportionate inability to repeat, with frequent phonemic errors in production. These patterns are typically explained as resulting from damage to the interface between separate linguistic sensory and motor systems. However, there are no known cases which examine how a person who uses a visual-modality language may be affected by this disorder. We present a unique case study of a 59-year-old native Deaf ASL signer “D.K.” with bilateral lesions in the right and left temporal-parietal lobes. She shows well-preserved ASL comprehension, but with formational errors in sign production and fingerspelling, and significant disruption in the repetition of signs and non-sign manual actions. In the case of DK, we present evidence that the observed sign language and manual errors implicate impairment of somatosensory feedback in hierarchical motor plans underlying sign production. Specifically, at the broadest-level, we posit that an arm-based ballistic gesture is guided by a specification for a body or spatial target configuration (i.e. a postural target, see Corina 2021). Proprioceptive knowledge in the superior-parietal regions is a robust signal that drives the execution of location-specified path movements. Superimposed upon this broad movement is a finer-grained somatosensory-based specification for handshape configuration. In the present case, the loss of somatosensory knowledge of the fingers, thumb positions, and palms leaves D.K. vulnerable to phonetic formational errors. This could reflect an underspecified forward model of handshape information and/or impairment in the evaluation of error signals between the intended target handshape and her actual production. The compositional nature of signed languages may expose the interactions between somatosensory and proprioceptive signals in skilled manual actions. This case study is unique, and is, to our knowledge, the first description of a conduction-like aphasia in a signed language user. Corina, D. P. (2021). Articulatory postures and forward models in American Sign Language: Linguistic and neuroscience evidence. FEAST. Formal and Experimental Advances in Sign language Theory, 4, 61-73.
Topic Areas: Signed Language and Gesture, Multisensory or Sensorimotor Integration