ISCA Workshop on Plasticity in Speech Perception (PSP2005)

Senate House, London, UK
June 15-17, 2005

Plasticity in Speech Perception: Lessons from Cochlear Implants

Stuart Rosen

University College London, UK

Cochlear implants, which replace damaged inner ear transduction mechanisms with direct electrical stimulation of residual auditory nerve fibres, have progressed over the last 30 years from laboratory curiosities to standard clinical application in many thousands of users. They also provide an interesting testing ground, with important practical implications, for exploring the nature and limits of plasticity in the human speech perceptual system.

For post-lingually deafened adults, implanted late in life, the primary focus of plasticity-related questions relates to adaptation to unusual representations of speech signals already well known to users. Of particular interest is the typical upward shift in spectral representation caused by incomplete electrode insertions into the higher turns of the cochlea where low frequencies are represented. Although a serious impediment to accurate perception initially, it appears that such shifts can be adapted to quite quickly. Studies concerning the speed and extent of adaptation, and ways to optimise the process, will be reviewed.

Quite different questions arise in connection with implanted children with little or no auditory experience of speech. One striking finding is that earlier implantation appears to lead to better outcomes for speech and language, even for children under 3 years old. Results from relevant studies will be discussed in the light of the notion of a critical period for language development, and what kinds of biological and environmental factors limit eventual performance.

Bibliographic reference.  Rosen, Stuart (2005): "Plasticity in speech perception: lessons from cochlear implants", In PSP2005, 201 (abstract).