Limited cross-modal activation to visual language in the auditory cortices of hearing-impaired children

What predicts spoken language outcomes in hearing-impaired children has been insufficiently understood, particularly with respect to cross-modal neural activation and sign language input. This study assessed neural activation in the auditory cortices of Czech-learning preschoolers with cochlear implants (CI), hearing aids (HA), and normal-hearing (NH) controls. The children were exposed to auditory speech, visual silent speech, and sign language, while hemodynamic activity was recorded using fNIRS. In response to auditory speech, CI children had weaker cortical activation than both NH and HA children. Rather surprisingly, sign language yielded reliable activation in the right auditory cortex of normal-hearing children, arguably reflecting the processing of the regular, relatively slow, sign language rhythm patterns. Visual silent speech failed to elicit reliable hemodynamic activation in hearing-impaired children, but yielded a non-significant trend in CI children left-laterally. Inverted hemodynamic responses were observed for silent speech in HA and NH children, possibly indicating auditory suppression during speech imagery. Experience with sign language modulated auditory speech processing: CI children with prior sign language input exhibited reliable cortical activation to auditory speech (unlike CI children without sign language input), suggesting a scaffolding effect of early experience with sign language on the development of spoken language. The findings advance the current understanding of how auditory and visual language processing develop in children with hearing loss, and highlight the cross-modal contributions of sensory experience and early language exposure.