Place-pitch sensitivity and its relation to consonant recognition by cochlear implant listeners using the MPEAK and SPEAK speech processing strategies

Two related studies investigated the relationship between place-pitch sensi tivity and consonant recognition in cochlear implant listeners using the Nu cleus MPEAK and SPEAK speech processing strategies. Average place-pitch sen sitivity across the electrode array was evaluated as a function of electrod e separation, using a psychophysical electrode pitch-ranking task. Consonan t recognition was assessed by analyzing error matrices obtained with a stan dard consonant confusion procedure to obtain relative transmitted informati on (RTI) measures for three features: stimulus (RTI stim), envelope (RTIenv ([plc])), and place-of-articulation (RTIplc([env])). The first experiment e valuated consonant recognition performance with MPEAK and SPEAK in the same subjects. Subjects were experienced users of the MPEAK strategy who used t he SPEAK strategy on a daily basis for one month and were tested with both processors. It was hypothesized that subjects with good place-pitch sensiti vity would demonstrate better consonant place-cue perception with SPEAK tha n with MPEAK, by virtue of their ability to make use of SPEAK's enhanced re presentation of spectral speech cues. Surprisingly, all but one subject dem onstrated poor consonant place-cue performance with both MPEAK and SPEAK ev en though most subjects demonstrated good or excellent place-pitch sensitiv ity. Consistent with this, no systematic relationship between place-pitch s ensitivity and consonant place-cue performance was observed. Subjects' poor place-cue perception with SPEAK was subsequently attributed to the relativ ely short period of experience that they were given with the SPEAK strategy . The second study reexamined the relationship between place-pitch sensitiv ity and consonant recognition in a group of experienced SPEAK users. For th ese subjects, a positive relationship was observed between place-pitch sens itivity and consonant place-cue performance, supporting the hypothesis that good place-pitch sensitivity facilitates subjects' use of spectral cues to consonant identity. A strong, linear relationship was also observed betwee n measures of envelope- and place-cue extraction, with place-cue performanc e increasing as a constant proportion (similar to 0.8) of envelope-cue perf ormance. To the extent that the envelope-cue measure reflects subjects' abi lities to resolve amplitude fluctuations in the speech envelope, this findi ng suggests that both envelope- and place-cue perception depend strongly on subjects' envelope-processing abilities. Related to this, the data suggest that good place-cue perception depends both on envelope-processing abiliti es and place-pitch sensitivity, and that either factor may limit place-cue perception in a given cochlear implant listener. Data from both experiments indicate that subjects with small electric dynamic ranges (<8 dB for 125-H z, 205-mu s/ph pulse trains) are more likely to demonstrate poor electrode pitch-ranking skills and poor consonant recognition performance than subjec ts with larger electric dynamic ranges. (C) 2000 Acoustical Society of Amer ica. [S0001-4966(00)01403-X].