The Effect of Perceptually Challenging Conditions on Speech and Sign Language Perception.

Language is often processed in perceptually challenging conditions. Although the neural correlates of speech processing in such conditions have been well studied, this is not the case for sign language. Thus, it is unknown whether the neural mechanisms involved in this process are comparable across language modalities. One reason for the lack of studies in sign language might be attributed to the difficulties in adapting perceptual manipulations from the context of speech to sign language. In the present study, we aim to address the gap in the literature by investigating whether the neural correlates for processing language presented in perceptually challenging conditions are similar across the visual and auditory modalities, using manipulations of background noise and spectral degradation that are comparable between languages and a within-subject design. We recruited 22 hearing signers who did a perceptual attention task while in an MRI scanner, in which the signal is either clear, presented in background noise, or spectrally degraded. Overall, our results suggest that language processing in perceptually challenging conditions relies primarily on modality-specific mechanisms rather than a shared, modality-independent neural system. Whereas speech processing appeared relatively robust to perceptual degradation, sign language recruited additional visual indicating modality-dependent compensatory strategies. These findings refine current neurobiological models of language by demonstrating that perceptual challenge interacts fundamentally with language modality.