P. J. Blamey

Psychophysical studies for two multiple-channel cochlear implant patients.

Psychophysical studies were conducted on two multiple-channel cochlear implant patients to examine the nature of the hearing sensations produced by electrical stimulation of auditory nerve fibers using electrodes at different sites in the scala tympani (one electrode at a time). Both time-invariant stimuli, whose parameter values did not vary in time, and time-varying stimuli, specified by a linear variation in parameter values, were used. A sharpness ranking study using time-invariant signals suggested that the hearing sensations produced by different electrodes varied from dull to sharp in an apical to basal direction in the scala tympani. A categorization study showed that the hearing sensations produced by two adjacent electrodes (1.5 mm apart) were rarely confused for a restricted range of time-invariant pulse rates. Discriminability studies by a same-different procedure for stimuli with pulse rate below 250 pps showed: (1) relative difference limens of 6% to 12% for time-invariant pulse rates, and 9% and 13% for time-varying pulse rates; (2) stimuli with time-varying electrode position differing in the direction of electrode trajectory were readily discriminated; and (3) the discrimination of time-varying pulse rates deteriorated with decreases in the duration of the variation, while the discriminability of single-electrode trajectories was the same for the three durations: 25, 50, and 100 ms. A speech processing strategy was also proposed on the bases of these results.

Vowel and consonant recognition of cochlear implant patients using formant-estimating speech processors

Vowel and consonant confusion matrices were collected in the hearing alone (H), lipreading alone (L), and hearing plus lipreading (HL) conditions for 28 patients participating in the clinical trial of the multiple-channel cochlear implant. All patients were profound-to-totally deaf and hearing refers to the presentation of auditory information via the implant. The average scores were 49% for vowels and 37% for consonants in the H condition and the HL scores were significantly higher than the L scores. Information transmission and multidimensional scaling analyses showed that different speech features were conveyed at different levels in the H and L conditions. In the HL condition, the visual and auditory signals provided independent information sources for each feature. For vowels, the auditory signal was the major source of duration information, while the visual signal was the major source of first and second formant frequency information. The implant provided information about the amplitude envelope of the speech and the estimated frequency of the main spectral peak between 800 and 4000 Hz, which was useful for consonant recognition. A speech processor that coded the estimated frequency and amplitude of an additional peak between 300 and 1000 Hz was shown to increase the vowel and consonant recognition in the H condition by improving the transmission of first formant and voicing information.

A clinical report on receptive vocabulary skills in cochlear implant users

Objective The aim was to measure the rate of vocabulary acquisition for cochlear implant users and compare the pre- and postoperative rates with published data for other groups with normal or impaired hearing. The hypothesis was that the postoperative rate would be greater than the preoperative rate. Design The Peabody Picture Vocabulary Test (PPVT) was administered to 32 children, adolescents, and prelinguistically deafened adults implanted with the 22-electrode cochlear implant. Age at implantation ranged from 2 yr 6 mo to 20 yr and implant use ranged from 6 mo to 7 yr 8 mo. Results The group mean postoperative performance at various postoperative intervals was significantly higher than mean preoperative performance. Single-subject data indicated statistically significant gains over time on this test for 13 of the subjects. The mean postoperative rate of vocabulary acquisition of 1.06 times the rate for normally hearing children was significantly greater than the mean preoperative rate of 0.43. Conclusions These rates of improvement were in accord with previous reports on smaller numbers of implant users, but could not be attributed unambiguously to use of the implant because no control group was used for this clinical work. Variables such as age at implantation, duration of profound deafness, communication mode, and speech perception skill failed to significantly predict rate of improvement on the PPVT.

A clinical report on speech production of cochlear implant users

Objective The aim was to assess articulation and speech intelligibility over time in a group of cochlear implant users implanted at 8 yr or over. The hypothesis was that the postoperative speech production performance would be greater than the preoperative performance. Design A test of intelligibility using sentences and an articulation test measuring non-imitative elicited speech were administered to 11 and 10 subjects, respectively, who were implanted with the 22-elec-trode cochlear implant. Nine subjects received both tests. Age at implantation ranged from 8 yr to 20 yr and implant use ranged from 1 yr to 4 yr 5 mo. Results For both the intelligibility and articulation tests roughly half of the subjects showed significant improvements over time and group mean postoperative performance significantly exceeded preoperative performance. Improvements occurred for front, middle, and back consonants; for stops, fricatives, and glides and for voiceless and voiced consonants. Conclusions Despite being deprived of acoustic speech information for many childhood years, roughly half of the patients assessed showed significant gains in speech intelligibility and articulation postimplantation. The lack of a control group of non-implanted patients means that we cannot separate out the influence of the implant on speech production from other influences such as training and tactile-kinaesthetic feedback.

Results for two children using a multiple-electrode intracochlear implant

Assessments in speech perception, speech production, and language skills were conducted on two children, 5 and 10 years old at the time of surgery, using the Nucleus multiple-electrode cochlear implant. Data were collected pre- and post-operatively to measure changes in performance over time. For closed-set speech perception tests in the audition alone condition, post-operative performance was generally better than pre-operative performance and performance improved post-operatively for both patients. In closed-set vowel and consonant identification and open-set sentence perception for the older patient, post-operative improvements from the vision alone to the auditory-visual condition were recorded and performance improved post-operatively in both conditions. In all measures of speech production for both patients, post-operative scores were higher than pre-operative scores and performance improved post-operatively. In language skills, post-operative scores were higher than pre-operative scores and scores improved post-operatively in all measures for both patients.

Results in children using the 22‐electrode cochlear implant

This is an abstract of a paper presented at the 9th National Conference of the Audiological Society of Australia , Thredbo, NSW , 26- 29 April 1990.The Cochlear Implant Clinic, The Royal Victorian Eye and Ear Hospital, 32 Gisborne Street, East Melbourne, Victoria 3052, Australia Five children (aged 6.0 to 14.8 years) out of a group of nine implanted with the 22‐electrode cochlear implant (Cochlear Pty. Ltd.) have achieved substantial open‐set speech recognition scores for monosyllabic word (30% to 72% for phonemes) and sentence (26% to 74% for words in sentences) tests using hearing without lipreading. Four of these five children were implanted during preadolescence and the fifth, who had a progressive loss, was implanted during adolescence. The remaining children who did not demonstrate open‐set recognition were implanted during adolescence after a long duration of profound deafness. Post‐operative performance on closed‐set speech perception tests was better than preoperative performance for the group of five children with open‐set recognition. Improvements in speech and language assessments were also noted for these children. The results are discus...

The effects of electrode position and stimulus period on the hearing sensations in a multiple‐channel cochlear implant patient

The first study involved the categorization of sensations produced by decreasing and increasing electrical stimulus period (SP) trajectories as “Questions” or “Statements” (corresponding to rising or falling pitch). Separate studies were conducted with the 300 ms SP trajectories superimposed on: (i) individual electrodes with no variation in electrode position (EP), and (ii) electrode trajectories shifting in succession from one electrode to another in the basal or apical direction. Statistical tests showed that the slopes of the linearized categorization functions were significantly different from zero, and there was no significant difference between the individual electrode and the electrode trajectory results. The second study investigated the perceptual dissimilarities of nine periodic stimuli by the method of triadic comparisons. The 300‐ms stimuli were the nine possible combinations of three electrodes, spaced 3‐ram apart, at three SPs (4, 8, 12 ms). A two‐dimensional solution by nonmetric multi‐di...

Perceptual dissimilarity and discrimination studies using two‐electrode stimulation with a multiple‐channel cochlear implant patient

The stimuli used in the two studies were trains of biphasic current pulses delivered to pairs of the ten electrodes implanted in the patients scala tympani. The first study investigated the perceptual dissimilarities of ten two‐electrode stimuli by the method of triadic comparisons. Electrode separations from 1.5–10.5 mm were used. A nonmetric multi‐dimensional scaling analysis of the data obtained showed a two‐dimensional solution to be appropriate with dimensions corresponding to the position of: (i) the more basal electrode, and (ii) the more apical electrode of the combinations. In the second study, pulse period discrimination was assessed for a set of two‐electrode combinations in a same‐different task. Electrode separations from 3–9 mm were used. Analysis using nonparametric indices of discriminability and response bias showed that the discrimination improved with increasing electrode separation, and for constant separation discrimination was better for more apical combinations.

Pitch and loudness studies on a multipie‐channel cochlear implant patient

Electrical stimuli, 300 ms in duration, were delivered to individual electrodes in the following two modes: (i) a single pulse per period (SPP), and (ii) multiple pulses occurring in the first half of each period (MPP), keeping the total charge delivered during the 300 ms constant. In the first study, subjective loudness as a function of current level and stimulus period were measured by magnitude estimation. For SPP, loudness was a power function of current level with exponent greater than 10. MPP was always louder than SPP with a greater difference at lower current levels. The variation of loudness with stimulus period was greater for SPP than MPP. In the second study, stimuli with periods between 1 and 12 ms were used. Ratio estimation with a fixed reference indicated pitch ratios varying over 1.5 to 2.0 decades for both modes. In the third study, a 2I‐2AFC paradigm measured stimulus period difference limens in the range 2.0%–3.3% for a 10 ms period and 3.6%–5.8% for 5 ms. MPP limens were 0.5%–1.0% low...

Speech perception with cochlear implants and tactile aids

Three related areas in our research are speech perception in noise, consonant recognition, and multimodal speech perception. Perception of speech in four‐speaker babble was evaluated with a multiple channel cochlear implant presenting first‐ and second‐formant information. In quiet, scores were 80% for vowels, 48% for consonants, and 51% for sentences. The signal‐to‐noise ratios required to reduce scores to 75% of the value in quiet were 8 dB for vowels, 12 dB for consonants, and 14 dB for sentences. Detailed consonant studies showed that amplitude information contributed directly to the recognition of voicing and manner of articulation and influenced the perception of other cues. In addition to auditory cues, lipreading is commonly used with implants and other aids. A probabilistic model of feature recognition describes the combination of auditory plus visual information well. The combined effect of tactile information is overestimated by the model for minimally trained subjects. The model may clarify issues in the training of hearing‐impaired children, as well as the design of speech processing aids.Three related areas in our research are speech perception in noise, consonant recognition, and multimodal speech perception. Perception of speech in four‐speaker babble was evaluated with a multiple channel cochlear implant presenting first‐ and second‐formant information. In quiet, scores were 80% for vowels, 48% for consonants, and 51% for sentences. The signal‐to‐noise ratios required to reduce scores to 75% of the value in quiet were 8 dB for vowels, 12 dB for consonants, and 14 dB for sentences. Detailed consonant studies showed that amplitude information contributed directly to the recognition of voicing and manner of articulation and influenced the perception of other cues. In addition to auditory cues, lipreading is commonly used with implants and other aids. A probabilistic model of feature recognition describes the combination of auditory plus visual information well. The combined effect of tactile information is overestimated by the model for minimally trained subjects. The model may clarify is...