Subjects (Table I)

Eight adults (four females and four males) participated in the study. They received a HiRes90K® cochlear implant from Advanced Bionics Corporation at the Edouard Herriot University Hospital of Lyon (France). All subjects were implanted by the same surgeon and had a full electrode insertion. Subjects were full-time users of their cochlear implant. They ranged in age from 16 to 74 years. The known aetiology of subjects’ deafness included perinatal asphyxia (N = 1), stroke (N = 2), and hereditary origin (N = 1). The mean duration of profound bilateral deafness prior implantation was eight years. Two groups of subjects were defined according to their duration of deafness: subjects with less than seven years of deafness are in group 1, while group 2 is constituted of subjects with more than seven years of deafness length. Their degree of hearing loss varied as shown by their pre-operative audiogram. Subjects 1, 3, 4, and 5 had better hearing with less than 100 dB HL audiometric thresholds for 500, 1000, 2000 and 4000 Hz tones (group 1) and the audiometric thresholds for Subjects 2, 6, 7, and 8 were above 100 dB HL for each frequency (group 2). A Chi-square test showed that groups for duration of deafness and audiogram are unrelated (p > 0.05). Since EABR wave latencies have been found to change during the first months of implant use (Gordon et al., 2003, 2006), all subjects had at least three months of cochlear implant experience at the time of the study. Subjects were separated according to their duration of implant use: subjects who had used their implant for less than five months were in group 1; subjects with more than five months of implant use were in group 2. As it is clearly shown in Table 1, subjects with longer duration of implant use were evenly distributed in groups used for analysis about deafness duration, audiometric performance, and M levels. A Chi-square test also showed that these latter groups are unrelated to the groups made according to the duration of implant use (p > 0.05). Even if duration of implant use could be a confounding variable in the present study, it was then assumed that its potential effect would fade away. Subjects had a maximum duration of implant use of two years and the mean duration across subjects was nine months. The subjects’ benefit from their cochlear implant was variable as revealed by the percentage of correctly perceived phonemes at three months of cochlear implant use. Lafon lists (Lists of three-phoneme words, Lafon, 1985) were presented in an open set format in quiet at 65 dB HL in a sound field. Table I summarises this information for each subject. Subjects were fully informed about the experimental procedures in accordance with the decision of the local ethical committee. They signed a consent form prior to participation.

Table I. Demographic information on subjects: aetiology and onset of deafness, age at test, duration of deafness prior to implantation and groups, audiogram groups, duration of cochlear implant use and group, and speech perception scores.