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Biomedical subjects

M F Dorman

Publications and source records attributed to M F Dorman.

At least 19 recordsLinked to original sources
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↗
PubMed1987

Vowel intelligibility in the absence of the acoustic reflex: performance-intensity characteristics.

Performance-intensity functions were defined for ten synthetic vowels whose durations (50 ms) were shorter than the time necessary for the acoustic reflex to alter the transmission characteristics of the middle ear. Recognition accuracy for ten listeners with normal auditory function was asymptotic from 72 to 90 dB and then fell linearly to 108 dB. Thus, at SPLs greater than approximately 90 dB, the auditory encoding of vowels is altered by the absence of the acoustic reflex.

Adult↗
PubMed1987

Effects of spectral flattening on vowel identification.

The identification of front vowels was studied in normal-hearing listeners using stimuli whose spectra had been altered to approximate the spectrum of vowels processed by auditory filters similar to those that might accompany sensorineural hearing loss. In the first experiment, front vowels were identified with greater than 95% accuracy when the first formant was specified in a normal manner and the higher frequency formants were represented by a broad, flat spectral plateau ranging from approximately 1600 to 3500 Hz. In the second experiment, the bandwidth of the first formant was systematically widened for stimuli with already flattened higher frequency formants. Normal vowel identification was preserved until the first formant was widened to six times its normal bandwidth. These results may account for the coexistence of abnormal vowel masking patterns (indicating flattened auditory spectra) and normal vowel recognition.

Auditory Perception↗
PubMed1985

Influence of the first formant on the recognition of voiced stop consonants by hearing-impaired listeners.

In order to examine first formant masking effects in hearing-impaired listeners, bay, day, and gay were synthesized with and without a first formant. The signals were presented at several levels. Removal of the first formant did not improve intelligibility at levels above, at, or below the point of maximum intelligibility. These results and others converge to suggest that masking spread from the first formant is not a significant factor in the identification of voiced stop consonants by listeners with sloping, mild-to-moderate hearing loss.

Aged↗
PubMed1985

Phonetic identification by elderly normal and hearing-impaired listeners.

Young normal-hearing listeners, elderly normal-hearing listeners, and elderly hearing-impaired listeners were tested on a variety of phonetic identification tasks. Where identity was cued by stimulus duration, the elderly hearing-impaired listeners evidenced normal identification functions. On a task in which there were multiple cues to vowel identity, performance was also normal. On a/b d g/identification task in which the starting frequency of the second formant was varied, performance was abnormal for both the elderly hearing-impaired listeners and the elderly normal-hearing listeners. We conclude that errors in phonetic identification among elderly hearing-impaired listeners with mild to moderate, sloping hearing impairment do not stem from abnormalities in processing stimulus duration. The results with the /b d g/continuum suggest that one factor underlying errors may be an inability to base identification on dynamic spectral information when relatively static information, which is normally characteristic of a phonetic segment, is unavailable.

Adult↗
PubMed1979

Some experiments on the sound of silence in phonetic perception.

The results of several experiments demonstrate that silence is an important cue for the perception of stop-consonant and affricate manner. In some circumstances, silence is necessary; in others, it is sufficient. But silence is not the only cue to these manners. There are other cues that are more or less equivalent in their perceptual effects, though they are quite different acoustically. Finally, silence is effective as a cue when it separates utterances produced by male and female speakers. These findings are taken to imply that, in these instances, perception is constrained as if by some abstract conception of what vocal tracts do when they make linguistically significant gestures.

Cues↗