Environmental Sound Perception in Patients with Cochlear Implants Compared with That in Patients with Auditory Nerve Diseases (Auditory Neuropathy) and Cortical Deafness

Abstract

The mechanism for perception of environmental sounds is considered to be different from the cognitive mechanism of language. The environmental sound perception of cochlear implantees appears to be good but not perfect. However, its underlying mechanism is not yet known. The aim of this study was to investigate perception of environmental sounds in postlingually deaf patients with cochlear implants compared with that in patients with central auditory disorders. Seventeen postlingual patients with cochlear implants, 6 patients with auditory nerve disease (auditory neuropathy), and 10 patients with cortical deafness were selected for the comparison. A tape-recorded environmental sound perception test of 24 environmental sounds, which was developed by the authors in 1987, was used. This test is divided into two categories: the category of vocalization includes human voice as well as animal and bird sounds, and the category of non-voice sounds includes sounds of nature and musical instruments, as well as sounds from man-made sources. The test procedure consists of two steps. The fi rst step (open set) is only to listen and to identify each sound either orally or in writing. The second step (closed set) is to listen and chooses a picture card matching test form among four different pictures. The percentages of correctly identifi ed environmental sounds in postlingually deaf patients with cochlear implants was markedly higher than that in patients with cortical deafness, but was similar to that in patients with auditory nerve disease (auditory neuropathy), in both the closed and open sets. Our study revealed that the perception of environmental sounds in postlingual patients with cochlear implants was not good in the open set but markedly better in the closed set. This result is similar to those for auditory nerve disease patients but completely different from those for cortical deafness patients. The ability of patients with cochlear implants to perceive environmental sounds is similar to that of patients with auditory nerve disease, perhaps because information carried by the cochlear nerve is similarly degraded.