[Acoustic memory of the speech evoked by a 22-channel cochlear implant]

Immediate recall of serial 6 digits was examined in order to clarify whether the electrical information heard via a 22-channel cochlear implant can give rise to normal acoustic memory or not. Serial 6 digits were generated randomly using the digits 1 through 6. Following results were obtained in 2 patients with the implant prosthesis. 1) There was a normal primary effect, i.e., good performance of recall at the first or two digits, and also a normal recency effect, i.e., an increased probability of recall at the last one or two digits. 2) There was a normal suffix effect or attenuation of the recency effect when the digits were followed by an another irrelevant speech suffix, the "8". 3) The suffix effect, however, was not observed when the digits were followed by a non-speech noise suffix. Thus, in noise suffix mode, probability of recall was increased at the last one or two digits as similarly with in no suffix mode. The primary effect, the recency effect and the suffix effect are already regarded as the characteristic items of acoustic memory produced in subjects with normal hearing ability. Therefore, it was suggested that a speech perception with a 22-channel cochlear implant prosthesis can produce an normal acoustic memory, and that there is a similarity of neurophysiological functions between natural audition and electrical audition. Moreover, it was demonstrated that the patients with the cochlear implant can distinguish between speech and noise.