Visual Attention in Deaf Humans: A Neuroplasticity Perspective

Abstract

The loss of one sensory modality prompts central compensatory mechanisms that increase the performance of the intact spared modalities. This chapter, by focusing on the consequences of auditory deprivation, provides evidence of cortical plasticity and cross-modal compensation that occur after sensory deprivation. So far, auditory deprivation is the only sensory modality offering the opportunity to study both cross-modal compensation during deafness (especially visual compensation through sign language and lip reading), and cross-modal reorganization accompanying the recovery of hearing functions after auditory rehabilitation by a cochlear implant (CI). We first develop the anatomical evidence for multimodal networks, in animal models and in humans, showing that sensory signals from different modalities can interact at several levels of auditory processing, from the thalamus to the primary auditory areas. Secondarily we develop the functional consequences of cross-modal reorganization in humans, deafened from birth (congenital deafness) or after normal language development (postlingual deafness). These two cases differ in terms of early brain maturation and show distinct patterns of reorganization induced by the sensory loss and differ in terms of adaptation to auditory rehabilitation. In both cases, duration of auditory deprivation negatively impacts CI outcome, though by different mechanisms, whereas audiovisual interactions tend to improve speech understanding. Today, one crucial issue is to narrow down the large variability of rehabilitation performances in developing and adult CI users, by emphasizing beneficial brain plasticity using behavioral training both before and after cochlear implantation.