Automatic and attentive processing of sounds in cochlear implant patients - electrophysiological evidence

Processing auditory scenes requires the automatic detection of unexpected acoustic irregularities which allows to reorient the attentional focus for further in-depth analysis. Even if cochlea implants (CI) may partly restore hearing capabilities in patients suffering from profound peripheral deafness, CI users complain about difficulties in identifying novel and unexpected acoustic events. To assess whether this impairment is attributable to preattentive auditory deficits, impaired automatic orienting to novel events and/or to deficits in attentional processing we recorded event-related potentials (ERPs) in an auditory novelty oddball paradigm.

ERPs were obtained in 7 postlingually deafened CI patients and their age-matched controls in passive and active listening conditions. Subjects had to press a button for infrequent novel sounds but not for frequent standard sounds in the active condition.

In the active condition patients and controls did not differ with regard to hit-rates and reaction times. ERPs to novel stimuli in the active condition were characterized by enhanced N2b and P3b components that did not differ between groups. By contrast, the P3a component to novel sounds in the passive condition, an index of automatic orienting of attention, was greatly attenuated in the CI users.

CI-users are impaired in the preattentive registration of novel auditory events while attentive processing of a designated auditory stream appears intact.