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Biomedical subjects

M F Dorman

Publications and source records attributed to M F Dorman.

At least 37 records · Page 2Linked to original sources
PubMed1996

Improving consonant intelligibility for Ineraid patients fit with continuous interleaved sampling (CIS) processors by enhancing contrast among channel outputs.

OBJECTIVE: In Experiment 1 the objective was to determine whether patients who have been implanted with the Ineraid electrode array perform better on tests of consonant identification when signals are processed through a continuous interleaved sampling (CIS) processor than when signals are processed through an analogue (Ineraid) processor. In Experiment 2 the objective was to determine, for patients using the CIS strategy, whether identification accuracy for stop consonant place of articulation could be improved by enhancing differences in the patterns of the signal processor channel outputs. DESIGN: In Experiment 1, 16 consonants were presented in VCV format for identification. In Experiment 1 the CIS patients evidence difficulty in identifying /p t k/. Therefore, in Experiment 2 the voiceless stop consonants were presented in two stimulus conditions. In one, the stimuli were unfiltered. In the other, the stimuli were individually filtered so as to enhance the differences in channel outputs for /p/, /t/, and /k/. RESULTS: In Experiment 1 the patients performed better with CIS processors than with analogue processors. In Experiment 2 the "enhanced" stimuli were identified with better accuracy than were the unfiltered stimuli. CONCLUSIONS: We confirm that Ineraid patients achieve higher scores on tests of consonant identification when using a CIS processor than when using an analogue processor. Errors in identification of stop consonant place of articulation, when using a CIS processor, are due to the similarity in the patterns of the processor's channel outputs. By showing that consonant intelligibility can be improved by filtering, we show that we have not reached the limit of speech understanding that can be supported by the population of neural elements remaining in our patients' auditory systems.

Adult↗
PubMed1996

Frequency discrimination and speech recognition by patients who use the Ineraid and continuous interleaved sampling cochlear-implant signal processors.

Patients who use the Ineraid cochlear implant were tested in four experiments with materials which assessed frequency discrimination and speech understanding. In each experiment both frequency discrimination and speech recognition varied among patients. Correlations between the two measures were significant and ranged from 0.60 to 0.83. Most generally, frequency discrimination was better in the frequency domain of F1 than in the domain of F2. In experiment 5, both the Ineraid signal processing strategy and a continuous interleaved sampling (CIS) strategy were implemented for a single patient. The CIS strategy improved frequency discrimination in the domain of F2 and improved speech understanding.

Adult↗
PubMed1996

Relative spectral change and formant transitions as cues to labial and alveolar place of articulation.

The perceptual salience of relative spectral change [Lahiri et al., J. Acoust. Soc. Am. 76, 391-404 (1984)] and formant transitions as cues to labial and alveolar/dental place of articulation was assessed in a conflicting cue paradigm. The prototype stimuli were produced by two English speakers. The stimuli with conflicting cues to place of articulation were created by altering the spectra of the signals so that the change in spectral energy from signal onset to voicing onset specified one place of articulation while the formant transitions specified the other place of articulation. Listeners' identification of these stimuli was determined principally by the information from formant transitions. This outcome provides no support for the view that the relative spectral change is a significant perceptual cue to stop consonant place of articulation.

Humans↗
PubMed1994

The pitch of electrically presented sinusoids.

A patient who uses the Ineraid cochlear implant, and who has hearing thresholds less than 50 dB HL for frequencies under 500 Hz in his nonimplanted ear, was asked to match the pitch of low-frequency signals presented to his two ears. The patient produced pitch matches, for frequencies of 125, 200, and 300 Hz presented to his most apical electrode, that were slightly higher than the reference frequency. When signals of fixed frequency were presented to electrodes located in successively more basal cochlear locations, pitch increased in an orderly fashion--an average of 57 Hz (range = 31-87 Hz) for each change in electrode location.

Auditory Threshold↗
PubMed1993

Loudness balance between acoustic and electric stimulation by a patient with a multichannel cochlear implant.

Estimates of loudness balance were obtained for acoustically and electrically presented 250 Hz sine signals from a patient who uses the Ineraid multichannel cochlear implant. Acoustic and electric loudness matching was possible because the patient evidenced a 25 dB HL threshold at 250 Hz in his nonimplanted ear. The level of the electrical stimulus in microamperes required for a balance of loudness grew linearly with equal increments in decibels for the acoustic stimulus. These data, in concert with the very limited data from previous studies, provide a rationale for using a logarithmic transformation of acoustic to electric intensity in signal processors for cochlear implants.

Acoustic Stimulation↗
PubMed1992

Long-term measures of electrode impedance and auditory thresholds for the Ineraid cochlear implant.

Measures of electrode impedance and of detection thresholds for electrical stimuli were extracted from the records of patients implanted with the Ineraid cochlear prosthesis. An analysis of impedance measures, obtained at 1, 12, 24, and 36 months after surgery, demonstrated (a) a significant decrease in impedance over the first year for electrodes that carried current and (b) significant increases in impedance at 24 and 36 months for electrodes that did not carry current. An analysis of detection thresholds, obtained at the same times as the impedance measures, demonstrated that averaged thresholds for the current-carrying electrodes varied no more than 0.5 dB over the 3-year period. These results support the conclusion that stimulation with the Ineraid device does not produce deleterious changes in the electrodes or in the target neural tissue.

Acoustic Impedance Tests↗
PubMed1991

Vowel and consonant recognition with the aid of a multichannel cochlear implant.

In this report we review the vowel and consonant recognition ability of patients who use a multichannel cochlear implant and who achieve relatively good word identification scores. The results suggest that vowel recognition is accomplished by good resolution of the frequency of the first formant (F1) combined with poor resolution of the frequency of the second formant (F2). The results also suggest that consonant recognition is accomplished (1) by using information from the amplitude envelope, including periodicity/aperiodicity, as cues to manner and voicing, (2) by using F1 as an aid to the identification of manner and voicing, and (3) by using information from cochlear place of stimulation to provide a very crude indication of the shape of the frequency spectrum above 1 kHz.

Adult↗
PubMed1991

Telephone use by patients fitted with the Ineraid cochlear implant.

A survey of telephone use by 66 patients fitted with the Ineraid cochlear prosthesis revealed that 51% initiate telephone calls (most calls are to family or friends) and that 66% answer the telephone. Of the patients who answer the telephone, 49% indicated that they could identify the gender and/or age of the caller most of the time, 27% could identify a familiar caller most of the time, and 48% indicated that they could understand a conversation most of the time if speaking to a familiar speaker about a familiar topic. Understanding dropped rapidly as the speaker and topic became unfamiliar.

Cochlear Implants↗
PubMed1991

Informational masking and auditory attention.

Informational masking is broadly defined as a degradation of auditory detection or discrimination of a signal embedded in a context of other similar sounds; it is not related to energetic masking caused by physical interactions between signal and masker. In this paper, we report a systematic release from informational masking of a target tone in a nine-tone rapid auditory sequence as the target is increasingly isolated in frequency or intensity from the remaining sequence components. Improved target-tone frequency difference limens as isolation increases are interpreted as a reflection of increasingly focused auditory attention. The change from diffuse to highly focused attention is gradual over the frequency and intensity ranges examined, with each 1-dB increment in target intensity relative to the remaining components producing performance improvements equivalent to those produced by a 2% increase in frequency isolation. The results are modeled as bands of attention in the frequency and intensity domains. For attention directed by frequency isolation, there is a strong correspondence with auditory filters predicted by the power spectrum model of masking. These data also support the existence of an attention band of intensity, with a bandwidth of about 5-7 dB at the moderate levels used in this experiment.

Adult↗
PubMed1990

Pitch scaling and speech understanding by patients who use the Ineraid cochlear implant.

Pitch scaling was assessed for 10 normal-hearing listeners and 8 patients who use the Ineraid multichannel cochlear implant. For two patients who were excellent users of the prosthesis, pitch increased over a wide range of frequencies (100 Hz to 2333-3000 Hz). For three patients who were above average users of the prosthesis, pitch increased with frequency over a smaller range (100 Hz to 1200-2300 Hz). For three patients who demonstrated poor word recognition ability, pitch increased with frequency over a very small range (100 Hz to 600-1000 Hz). These results suggest that differences in speech understanding among patients who use the Ineraid may be accounted for, in part, by the range of pitch available through the implant.

Acoustics↗
PubMed1990

Longitudinal changes in word recognition by patients who use the Ineraid cochlear implant.

The time course for reacquisition of spondee word recognition was examined for 27 patients who use the Ineraid cochlear implant. At 1 month postfitting, test scores ranged from 0 to 84% correct. The median score was 10% correct. At 22 to 28 months postfitting, the scores ranged from 0 to 100% correct. The median score was 56% correct. The rate of improvement in spondee recognition varied greatly within the sample. Most patients continued to extract new information from the electrically evoked representation of the speech signal over a period of a year or more.

Cochlear Implants↗
PubMed1990

Acoustic cues for consonant identification by patients who use the Ineraid cochlear implant.

Ten patients who use the Ineraid cochlear implant were tested on a consonant identification task. The stimuli were 16 consonants in the "aCa" environment. The patients who scored greater than 60 percent correct were found to have high feature information scores for amplitude envelope features and for features requiring the detection of high-frequency energy. The patients who scored less than 60 percent correct exhibited lower scores for all features of the signal. The difference in performance between the two groups of patients may be due, at least in part, to differences in the detection or resolution of high-frequency components in the speech signal.

Adult↗
PubMed1989

Identification of synthetic vowels by patients using the Symbion multichannel cochlear implant.

In this report we describe the vowel identification ability of eight patients who scored above 70% correct on a test of spondee word identification. The stimuli were 12 synthetic vowels in "bVt" format. The vowels differed in the frequency of F1, F2, and F3. The mean identification accuracy was 60% correct. Front vowels and dipthongs, (3), and (u) were relatively well identified. The vowels in "but," "bought," and "bout," which were characterized by high F1s and low F2s were not well identified. The results are consistent with a model of recognition in which F1 is specified, with relatively good accuracy, by a rate code and in which extreme values of F2 are specified by a rate/place code.

Adolescent↗
PubMed1989

Word recognition by 50 patients fitted with the Symbion multichannel cochlear implant.

We describe the word recognition ability of 50 patients who use the multichannel cochlear implant manufactured by Symbion, Inc. The median scores for open set tests involving auditory stimulation alone were: 14% correct (range 0 to 60) for monosyllabic words, 44% correct (range 0 to 100) for spondees, and 45% correct (range 0 to 100) for words in the Everyday CID Sentences. In the visual stimulation condition of the Everyday CID Sentences, the median score was 64% correct (range 0 to 100). In the visual plus auditory stimulation condition, the median score was 99% correct (range 46 to 100). These results demonstrate that relatively good speech understanding can be achieved using a cochlear implant which employs only a few channels of stimulation and which simultaneously activates monopolar electrodes.

Acoustic Stimulation↗
PubMed1988

Auditory/phonetic categorization with the Symbion multichannel cochlear implant.

The phonetic identification ability of an individual (SS) who exhibits the best, or equal to the best, speech understanding of patients using the Symbion four-channel cochlear implant is described. It has been found that SS: (1) can use aspects of signal duration to form categories that are isomorphic with the phonetic categories established by listeners with normal auditory function; (2) can combine temporal and spectral cues in a normal fashion to form categories; (3) can use aspects of fricative noises to form categories that correspond to normal phonetic categories; (4) uses information from both F1 and higher formants in vowel identification; and (5) appears to identify stop consonant place of articulation on the basis of information provided by the center frequency of the burst and by the abruptness of frequency change following signal onset. SS has difficulty identifying stop consonants from the information provided by formant transitions and cannot differentially identify signals that have identical F1's and relatively low-frequency F2's. SS's performance suggests that simple speech processing strategies (filtering of the signal into four bands) and monopolar electrode design are viable options in the design of cochlear prostheses.

Adult↗
PubMed1987

Minimum spectral contrast for vowel identification by normal-hearing and hearing-impaired listeners.

To determine the minimum difference in amplitude between spectral peaks and troughs sufficient for vowel identification by normal-hearing and hearing-impaired listeners, four vowel-like complex sounds were created by summing the first 30 harmonics of a 100-Hz tone. The amplitudes of all harmonics were equal, except for two consecutive harmonics located at each of three "formant" locations. The amplitudes of these harmonics were equal and ranged from 1-8 dB more than the remaining components. Normal-hearing listeners achieved greater than 75% accuracy when peak-to-trough differences were 1-2 dB. Normal-hearing listeners who were tested in a noise background sufficient to raise their thresholds to the level of a flat, moderate hearing loss needed a 4-dB difference for identification. Listeners with a moderate, flat hearing loss required a 6- to 7-dB difference for identification. The results suggest, for normal-hearing listeners, that the peak-to-trough amplitude difference required for identification of this set of vowels is very near the threshold for detection of a change in the amplitude spectrum of a complex signal. Hearing-impaired listeners may have difficulty using closely spaced formants for vowel identification due to abnormal smoothing of the internal representation of the spectrum by broadened auditory filters.

Adult↗