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Biomedical subjects

M Dorman

Publications and source records attributed to M Dorman.

13 recordsLinked to original sources
PubMed2000

The effect of reduced dynamic range on speech understanding: implications for patients with cochlear implants.

OBJECTIVE: To determine the effect of reduced dynamic range on speech understanding when the speech signals are processed in a manner similar to a 6-channel cochlear implant speech processor. DESIGN: Signals were processed in a manner similar to a 6-channel cochlear implant processor and output as a sum of sine waves with frequencies equal to the center frequencies of the analysis filters. The amplitudes of the sine waves were compressed in a systematic fashion to simulate the effect of reduced dynamic range. The compressed signals were presented to 10 normal-hearing listeners for identification. RESULTS: There was a significant effect of compression for all test materials. The effect of the compression on speech understanding was different for the three test materials (vowels, consonants, and sentences). Vowel recognition was affected the most by the compression, and consonant recognition was affected the least by the compression. Feature analysis indicated that the reception of place information was affected the most. Sentence recognition was moderately affected by the compression. CONCLUSIONS: Dynamic range should affect the speech perception abilities of cochlear implant users. Our results suggest that a relatively wide dynamic range is needed for a high level of vowel recognition and a relatively small dynamic range is sufficient to maintain consonant recognition. We infer from this outcome that, if other factors were held equal, an implant patient with a small dynamic range could achieve moderately high scores on tests of consonant recognition but poor performance on vowel recognition, and that it is more likely for an implant patient with a large dynamic range to obtain high scores on vowel recognition than for an implant patient with a small dynamic range.

Cochlear Implants↗
PubMed2000

Palmoplantar keratoderma (Voerner) with composite keratohyalin granules: studies on keratinization parameters and ultrastructures.

A case of the Voerner type palmoplantar keratoderma was studied for abnormalities of keratinization parameters. An enzyme and materials used to build the marginal band or cellular envelope of the cornified cell were all abnormally expressed; i.e. transglutaminase I (TGK), loricrin, and involucrin were abnormally immunostained. In the normal controls, their expression was limited to the upper epidermis, mainly in the granular layer. In the lesional skin, they were detected from the suprabasal layer to the lower horny layer. Filaggrin, the protein of the keratohyalin granule, was also expressed more widely than in controls. Ultrastructural abnormalities included a significantly higher frequency of composite keratohyalin granules than controls, early formation of a marginal band in the midepidermis, and, most remarkably, the clumping of tonofilaments causing vacuolization of the cytoplasm of affected keratinocytes.

Adult↗
PubMed2000

Speech recognition by normal-hearing and cochlear implant listeners as a function of intensity resolution.

The importance of intensity resolution in terms of the number of intensity steps needed for speech recognition was assessed for normal-hearing and cochlear implant listeners. In experiment 1, the channel amplitudes extracted from a six-channel continuous interleaved sampling (CIS) processor were quantized into 2, 4, 8, 16, or 32 steps. Consonant recognition was assessed for five cochlear implant listeners, using the Med-El/CIS-link device, as a function of the number of steps in the electrical dynamic range. Results showed that eight steps within the dynamic range are sufficient for reaching asymptotic performance in consonant recognition. These results suggest that amplitude resolution is not a major factor in determining consonant identification. In experiment 2, the relationship between spectral resolution (number of channels) and intensity resolution (number of steps) in normal-hearing listeners was investigated. Speech was filtered through 4-20 frequency bands, synthesized as a linear combination of sine waves with amplitudes extracted from the envelopes of the bandpassed waveforms, and then quantized into 2-32 levels to produce stimuli with varying degrees of intensity resolution. Results showed that the number of steps needed to achieve asymptotic performance was a function of the number of channels and the speech material used. For vowels, asymptotic performance was obtained with four steps, while for consonants, eight steps were needed for most channel conditions, consistent with our findings in experiment 1. For sentences processed though 4 channels, 16 steps were needed to reach asymptotic performance, while for sentences processed through 16 channels, 4 steps were needed. The results with normal-hearing listeners on sentence recognition point to an inverse relationship between spectral resolution and intensity resolution. When spectral resolution is poor (i.e., a small number of channels is available) a relatively fine intensity resolution is needed to achieve high levels of understanding. Conversely, when the intensity resolution is poor, a high degree of spectral resolution is needed to achieve asymptotic performance. The results of this study, taken together with previous findings on the effect of reduced dynamic range, suggest that the performance of cochlear implant subjects is primarily limited by the small number (four to six) of channels received, and not by the small number of intensity steps or reduced dynamic range.

Acoustic Stimulation↗
PubMed2000

The effect of parametric variations of cochlear implant processors on speech understanding.

This study investigated the effect of five speech processing parameters, currently employed in cochlear implant processors, on speech understanding. Experiment 1 examined speech recognition as a function of stimulation rate in six Med-E1/CIS-Link cochlear implant listeners. Results showed that higher stimulation rates (2100 pulses/s) produced a significantly higher performance on word and consonant recognition than lower stimulation rates (<800 pulses/s). The effect of stimulation rate on consonant recognition was highly dependent on the vowel context. The largest benefit was noted for consonants in the /uCu/ and /iCi/ contexts, while the smallest benefit was noted for consonants in the /aCa/ context. This finding suggests that the /aCa/ consonant test, which is widely used today, is not sensitive enough to parametric variations of implant processors. Experiment 2 examined vowel and consonant recognition as a function of pulse width for low-rate (400 and 800 pps) implementations of the CIS strategy. For the 400-pps condition, wider pulse widths (208 micros/phase) produced significantly higher performance on consonant recognition than shorter pulse widths (40 micros/phase). Experiments 3-5 examined vowel and consonant recognition as a function of the filter overlap in the analysis filters, shape of the amplitude mapping function, and signal bandwidth. Results showed that the amount of filter overlap (ranging from -20 to -60 dB/oct) and the signal bandwidth (ranging from 6.7 to 9.9 kHz) had no effect on phoneme recognition. The shape of the amplitude mapping functions (ranging from strongly compressive to weakly compressive) had only a minor effect on performance, with the lowest performance obtained for nearly linear mapping functions. Of the five speech processing parameters examined in this study, the pulse rate and the pulse width had the largest (positive) effect on speech recognition. For a fixed pulse width, higher rates (2100 pps) of stimulation provided a significantly better performance on word recognition than lower rates (<800 pps) of stimulation. High performance was also achieved by jointly varying the pulse rate and pulse width. The above results indicate that audiologists can optimize the implant listener's performance either by increasing the pulse rate or by jointly varying the pulse rate and pulse width.

Adult↗
PubMed1999

On the number of channels needed to understand speech.

Recent studies have shown that high levels of speech understanding could be achieved when the speech spectrum was divided into four channels and then reconstructed as a sum of four noise bands or sine waves with frequencies equal to the center frequencies of the channels. In these studies speech understanding was assessed using sentences produced by a single male talker. The aim of experiment 1 was to assess the number of channels necessary for a high level of speech understanding when sentences were produced by multiple talkers. In experiment 1, sentences produced by 135 different talkers were processed through n (2 < or = n < or = 16) number of channels, synthesized as a sum of n sine waves with frequencies equal to the center frequencies of the filters, and presented to normal-hearing listeners for identification. A minimum of five channels was needed to achieve a high level (90%) of speech understanding. Asymptotic performance was achieved with eight channels, at least for the speech material used in this study. The outcome of experiment 1 demonstrated that the number of channels needed to reach asymptotic performance varies as a function of the recognition task and/or need for listeners to attend to fine phonetic detail. In experiment 2, sentences were processed through 6 and 16 channels and quantized into a small number of steps. The purpose of this experiment was to investigate whether listeners use across-channel differences in amplitude to code frequency information, particularly when speech is processed through a small number of channels. For sentences processed through six channels there was a significant reduction in speech understanding when the spectral amplitudes were quantized into a small number (< 8) of steps. High levels (92%) of speech understanding were maintained for sentences processed through 16 channels and quantized into only 2 steps. The findings of experiment 2 suggest an inverse relationship between the importance of spectral amplitude resolution (number of steps) and spectral resolution (number of channels).

Acoustic Stimulation↗
PubMed1995

Automatic recognition of syllable-final nasals preceded by /epsilon/.

In this paper, it is shown how an automatic recognition algorithm, based on hidden Markov models (HMM), can benefit by properly utilizing findings from perceptual experiments on nasals. Perceptual studies on nasal consonants have shown that both nasal murmurs and formant transitions are important in the identification of place of articulation. Thus both acoustic segments bordering the nasal release were incorporated into this HMM-based system. A 7% improvement in alveolar recognition was obtained by explicitly modeling the vowel-nasal transition segments. Further overall improvement (6%) was realized by making the HMM recognizer "focus" more on the vowel-nasal transition segments bordering the nasal release, and less on the nasal murmur and vowel portion of the /epsilon m/ and /epsilon n/ syllables. An overall average [m]-[n] recognition of 95% was obtained when testing this technique on 60 speakers outside the training set.

Humans↗
PubMed1989

Consonant recognition as a function of the number of channels of stimulation by patients who use the Symbion cochlear implant.

The intelligibility of a 16-item consonant set was assessed for 10 patients who use the Symbion four-channel cochlear implant. The patients were selected on the basis of "good" speech recognition scores. For each patient, consonant intelligibility was assessed when his/her processor was configured to pass from one to four channels of information. The results suggest, most generally, that two channels, one low frequency and one high frequency, provide most of the information about consonant identity.

Adult↗
PubMed1988

Stimulus factors influencing the identification of voiced stop consonants by normal-hearing and hearing-impaired adults.

The effects of mild-to-moderate hearing impairment on the perceptual importance of three acoustic correlates of stop consonant place of articulation were examined. Normal-hearing and hearing-impaired adults identified a stimulus set comprising all possible combinations of the levels of three factors: formant transition type (three levels), spectral tilt type (three levels), and abruptness of frequency change (two levels). The levels of these factors correspond to those appropriate for /b/, /d/, and /g/ in the /ae/ environment. Normal-hearing subjects responded primarily in accord with the place of articulation specified by the formant transitions. Hearing-impaired subjects showed less-than-normal reliance on formant transitions and greater-than-normal reliance on spectral tilt and abruptness of frequency change. These results suggest that hearing impairment affects the perceptual importance of cues to stop consonant identity, increasing the importance of information provided by both temporal characteristics and gross spectral shape and decreasing the importance of information provided by the formant transitions.

Adult↗
PubMed1986

Influence of the acoustic reflex on vowel recognition.

Computer synthesized vowels of 50- and 300-ms duration were presented to normal-hearing listeners at a moderate and high sound pressure level (SPL). Presentation at the high SPL resulted in poor recognition accuracy for vowels of a duration (50 ms) shorter than the latency of the acoustic stapedial reflex. Presentation level had no effect on recognition accuracy for vowels of sufficient duration (300 ms) to elicit the reflex. The poor recognition accuracy for the brief, high intensity vowels was significantly improved when the reflex was preactivated. These results demonstrate the importance of the acoustic reflex in extending the dynamic range of the auditory system for speech recognition.

Air Pressure↗
PubMed1986

Assessing the family environment of schizophrenic patients with multiple hospital admissions.

The authors compared the responses on the Family Environment Scale of 12 schizophrenic inpatients who had been hospitalized more than three times in the previous 12 months and a control group of 12 similarly diagnosed inpatients who had been admitted less frequently. Responses of the patients' families were also computed. Patients who were admitted more often reported greater family conflict and less freedom to express emotions. Family responses revealed significantly more incongruity among family members of the more frequently hospitalized patients than among those of the control group. The authors suggest that studies be conducted to determine if the data obtained by the scale are analogous to data on expressed emotion obtained by the more complex Camberwell Family Interview; if so, the Family Environment Scale could be an alternative to the Camberwell Family Interview in studies of schizophrenic patients and their families.

Adolescent↗
PubMed1985

Children's perception of sibilants: the relation between articulation and perceptual development.

When synthetic fricative noises from an [s] continuum are followed by [a] and [u], adult listeners perceive fewer instances of in the context of the rounded vowel [u] (Mann & Repp, 1980). This perceptual context effect presumably reflects adjustment for certain coarticulatory effects and implies tacit knowledge of coarticulation and its consequences. To clarify the role of articulatory experience in the ontogeny of such knowledge and the consequent perceptual adjustment, the present study examined the effect of rounded and unrounded vowels on the perception of [s] and by adults, 5-, and 7-year-old children who produce and [s] and 7-year-old children who misarticulate these phonemes. All three groups of children showed a context effect equivalent to that of adults and independent of age and articulation ability. Therefore, productive mastery of [s] and is not critically responsible for perception of the [s] distinction, nor for perceptual sensitivity to the consequences of sibilant-vowel coarticulation.

Adolescent↗
PubMedDate not supplied

Genetic engineering of structural protein polymers.

Genetic and protein engineering are components of a new polymer chemistry that provide the tools for producing macromolecular polyamide copolymers of diversity and precision far beyond the current capabilities of synthetic polymer chemistry. The genetic machinery allows molecular control of chemical and physical chain properties. Nature utilizes this control to formulate protein polymers into materials with extraordinary mechanical properties, such as the strength and toughness of silk and the elasticity and resilience of mammalian elastin. The properties of these materials have been attributed to the presence of short repeating oligopeptide sequences contained in the proteins, fibroin, and elastin. We have produced homoblock protein polymers consisting exclusively of silk-like crystalline blocks and elastin-like flexible blocks. We have demonstrated that each homoblock polymer as produced by microbial fermentation exhibits measurable properties of crystallinity and elasticity. Additionally, we have produced alternating block copolymers of various amounts of silk-like and elastin-like blocks, ranging from a ratio of 1:4 to 2:1, respectively. The crystallinity of each copolymer varies with the amount of crystalline block interruptions. The production of fiber materials with custom-engineered mechanical properties is a potential outcome of this technology.

Amino Acid Sequence↗