Tuesday, May 01, 2007

An interesting effect of Cochlear Implants - better than normal audiovisual integration

Rouger et al. show that deaf people have superior lip-reading abilities and superior audiovisual integration compared with those with normal hearing and that they maintain superior lip-reading performance even after cochlear implantation.

From Shannon's review of this work:
Cochlear implants are sensory prostheses that restore hearing to deafened individuals by electric stimulation of the remaining auditory nerve. Contemporary cochlear implants generally use 16–22 electrodes placed along the tonotopic axis of the cochlea. Each electrode is designed to stimulate a discrete neural region and thereby present a coarse representation of the frequency-specific neural activation in a normal cochlea. However, within each region of stimulated neurons, the fine spectro-temporal structure of neural activation/response is quite different from that of the normal ear. Despite these differences, modern cochlear implants provide high levels of speech understanding, with most recipients capable of telephone conversation.
from Rouger et al.'s abstract:
... recovery goes through long-term adaptative processes to build coherent percepts from the coarse information delivered by the implant.... we analyzed the longitudinal postimplantation evolution of word recognition in a large sample of cochlear implant (CI) users in unisensory (visual or auditory) and bisensory (visuoauditory) conditions. We found that, despite considerable recovery of auditory performance during the first year postimplantation, CI patients maintain a much higher level of word recognition in speechreading conditions compared with normally hearing subjects, even several years after implantation. Consequently, we show that CI users present higher visuoauditory performance when compared with normally hearing subjects with similar auditory stimuli. This better performance is not only due to greater speechreading performance, but, most importantly, also due to a greater capacity to integrate visual input with the distorted speech signal. Our results suggest that these behavioral changes in CI users might be mediated by a reorganization of the cortical network involved in speech recognition that favors a more specific involvement of visual areas. Furthermore, they provide crucial indications to guide the rehabilitation of CI patients by using visually oriented therapeutic strategies.

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