Electrode ranking of ‘‘place pitch’’ and speech recognition in electrical hearing

Abstract

The ability to distinguish electrical stimulation of different electrodes on the basis of "pitch or sharpness" was evaluated with an electrode ranking procedure in 14 individual users of the Nucleus cochlear implant. Prior to the electrode ranking test, absolute thresholds and maximum comfortable loudness levels were measured, and loudness balancing was accomplished across all usable electrodes. Performance on the electrode ranking task was defined in terms of d' per mm of distance between comparison electrodes. Large individual differences were found among cochlear-implant users. In subjects with good to excellent place-pitch sensitivity, the electrode ranking task was limited by a ceiling effect; however, in those with poor to moderate sensitivity d'/mm was relatively constant with spatial separation between electrodes. Place pitch was typically ordered from apical to basal electrodes, i.e., basal electrodes were judged to be higher in pitch than more apical electrodes. However, instances of reversals in place-pitch ordering were seen on some electrodes in some subjects. Instances were also seen of better electrode ranking in the apical half of the electrode array than in the basal half, and vice-versa. Analyses of the electrode ranking functions in terms of d' per stimulus indicated that, in some subjects, perfect performance was reached with as little as 0.75 mm between comparison electrodes, the minimum possible. In other subjects, perfect performance was not reached until the spatial separation between comparison electrodes was over 13 mm, more than three quarters of the entire length of the electrode array. Ten of the subjects also participated in a closed-set recognition task of intervocalic consonants. Although the maximum transmitted information for place of consonant articulation (which is based primarily on spectral speech cues) was only 34%, correlations between place-pitch sensitivity and transmitted speech information were as high as 0.71. This was surprising considering the excellent place-pitch sensitivity exhibited by some of the subjects, and may reflect limitations of the Nucleus speech coding strategy for representing spectrally coded speech information. The two prelingual subjects performed notably poorer on the speech task than the postlingual subjects, even though one of the prelingual subjects demonstrated very good place-pitch sensitivity.

Music Perception with Cochlear Implants: A Review

“…Several publications have confirmed that the pitch perceived generally increases when a constant-rate pulse train is presented on one electrode at a time, and the position of the active electrode is moved from an apical to a more basal location in the cochlea (Tong and Clark, 1985;Townshend et al, 1987;McDermott and McKay, 1994;Nelson et al, 1995;Zwolan et al, 1997).…”

The resolution of complex spectral patterns by cochlear implant and normal-hearing listeners

“…Psychophysical studies which have investigated the ability to discriminate between stimulation on different electrodes also indicate that the perception of spectral cues is a performance-limiting factor in CI speech perception ͑Collins et al Donaldson and Nelson, 2000;Henry et al, 2000;Nelson et al, 1995;Throckmorton andCollins, 1999͒. Henry et al ͑2000͒ showed a correlation between speech perception and electrode discrimination in the frequency regions below approximately 2.7 kHz when the stimuli in the electrode discrimination task were presented with randomly varying levels, but no correlation between the two measures in the frequency regions above 2.7 kHz, indicating that fine spectral discrimination may be relatively more important in the vowel-formant regions than in the high-frequency regions, where the cues are mostly broadband.…”

Cochlear Implant Stimulation Rates and Speech Perception

“…In addition, the tonotopicity seen in the CI is not perfect in all subjects. Some subjects cannot discriminate between the pitches across different electrodes and/or a more basal electrode may sound lower in pitch than a more apical one (so called pitch reversal) (Busby et al, 1994;Cohen et al, 1996;Nelson et al, 1995;Donaldson and Nelson, 2000). Spatial separation between electrodes has also been found to affect CI users' pitch perception ability.…”

“…Spatial separation between electrodes has also been found to affect CI users' pitch perception ability. Increased separation improved pitch ranking performance of CI subjects (Nelson et al, 1995;Tong and Clark, 1985). In addition, most CI listeners cannot make full use of the spectral information available through their implants.…”