Cross-modal reorganization and speech perception in cochlear implant users

Abstract

Recent work suggests that once the auditory cortex of deaf persons has been reorganized by cross-modal plasticity, it can no longer respond to signals from a cochlear implant (CI) installed subsequently. To further examine this issue, we compared the evoked potentials involved in the processing of visual stimuli between CI users and hearing controls. The stimuli were concentric circles replaced by a different overlapping shape, inducing a shape transformation, known to activate the ventral visual pathway in human adults. All CI users had their device implanted for >1 year, but obtained different levels of auditory performance following training to establish language comprehension. Seven of the 13 patients showed good capacities for speech recognition with the CI (good performers) while the six others demonstrated poor speech recognition abilities (poor performers). The evoked potentials of all patients showed larger amplitudes, with different distributions of scalp activations between the two groups. The poor performers exhibited broader, anteriorly distributed, high P2 amplitudes over the cortex whereas the good performers showed significantly higher P2 amplitudes over visual occipital areas. These results suggest the existence of a profound cross-modal reorganization in the poor performers and an intramodal reorganization in the good performers. We interpret these data on the basis of enhanced audiovisual coupling as the key to a long-term functional improvement in speech discrimination in CI users.

Evolution of non-speech sound memory in postlingual deafness: Implications for cochlear implant rehabilitation

“…Good CI performers rely more on fronto-parietal regions dedicated to attentional and high level strategies (e.g. phonologic assembly and semantic associations) (Lazard et al, 2010;Lee, Truy, et al, 2007;Mortensen et al, 2006), reproducing sounds through audio-visual and articulatory processes (Hickok & Poeppel, 2007), and on occipital regions performing audio-visual associations (Doucet, Bergeron, Lassonde, Ferron, & Lepore, 2006;Mortensen et al, 2006). In contrast, poor CI users perform a more global identification, tapping into stored, presumably distorted, acoustic representations, and trying to match them with the new auditory information, i.e.…”

Altered Cortical Activity in Prelingually Deafened Cochlear Implant Users Following Long Periods of Auditory Deprivation

“…Postoperative results in terms of speech perception tend to be much poorer in prelingually deaf adults when they received their cochlear implant after a long duration of deafness (Teoh et al 2004;Klop et al 2007). These poor performances might be explained by a hampered development of the auditory pathway and cross-modal changes during the period of auditory deprivation (Doucet et al 2006;Lee et al 2007;Kral and O'Donoghue 2010;Kral and Sharma 2012).…”

Electrophysiological evidence for altered visual, but not auditory, selective attention in adolescent cochlear implant users

“…Presumably, early implantation in the children tested here precludes deafness-induced cross-modal plasticity as an explanation for the visual N1 effects. Moreover, increased recruitment of the auditory cortex to process visual information is typically associated with decrements in CI speech perception abilities [37][38], which is not a characteristic of our sample. Thus, the current results suggest that differences in visual processing between CI users and NH children are due, at least in part, to changes in selective attention, driven by the demand to adapt to the environment with impaired hearing.…”