Maureen Hannley

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.

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.

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.

Susceptibility to intraspeech spread of masking in listeners with sensorineural hearing loss

Previous research with speechlike signals has suggested that upward spread of masking from the first formant (F 1) may interfere with the identification of place of articulation information signaled by changes in the upper formants. This suggestion was tested by presenting two-formant stop consonant--vowel syllables varying along a/ba--/da/--/ga/ continuum to hearing-impaired listeners grouped according to etiological basis of the disorder. The syllables were presented monaurally at 80 dB and 100 dB SPL when formant amplitudes were equal and when F 1 amplitude was reduced by 6, 12, and 18 dB. Noise-on-tone masking patterns were also generated using narrow bands of noise at 80 and 100 dB SPL to assess the extent of upward spread of masking. Upward spread of masking could be demonstrated in both speech and nonspeech tasks, irrespective of the subjects age, audiometric configuration, or etiology of hearing impairment. Attenuation of F 1 had different effects on phonetic identification in different subject groups: While listeners with noise-induced hearing loss showed substantial improvement in identifying place of articulation, upward spread of masking did not consistently account for poor place identification in other types of sensorineural hearing impairment.

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 F1s and relatively low-frequency F2s. SSs 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.

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.

Original Papers · Travaux originaux: Patterns of Phoneme Identification Error in Cochlear and Eighth-Nerve Disorders

The purpose of this study was to determine whether patterns of phoneme identification error differ among listeners with cochlear and retrocochlear auditory disorder. Speech intelligibility performance was analyzed in 15 patients with confirmed eighth-nerve disorder and in 15 patients with cochlear disorders, matched to the retrocochlear group for age and audiometric configuration, using confusion matrices derived from responses to a monosyllabic word list. Results indicated that: (1) vowel errors were more prevalent in the retrocochlear group and varied directly with increasing stimulus presentation level; and (2) consonant errors did not differ in type or relative frequency between the two groups, nor was there a level-dependent effect for consonant errors. These results are supported by the results of closed-set vowel identification tests and thus do not appear to be an artifact of open-set testing. Vowel errors may account for a major part of the speech ‘rollover’ phenomenon typical of retrocochlear au...

Nonlinear auditory coding of vowel formants at high sound pressure levels

To study vowel intelligibility in the absence of the acoustic reflex, ten synthetic vowels whose duration was shorter than the effective latency of the acoustic reflex were presented to normal hearing listeners at levels ranging from 72 to 106 dB SPL. Signal intelligibility varied as a function of both SPL and vowel identity. Vowels with widely spaced formants, i.e., /i/ and /ɪ/, were unaffected by presentation level. Vowels with more proximal formants began to show a decrement in intelligibility at 96 dB and suffered as much as a 40% decrement at 106 dB. Confusion errors were not symmetrical in F1‐F2 space suggesting a systematic distortion in the auditory coding of formant location. These data indicate another source of distortion for many severely hearing‐impaired listeners who commonly listen to speech amplified to greater than 100 dB and who do not have measureable acoustic reflexes. [Research supported by NIH.]

Procedures which alter the intelligibility of voiced stop consonants for hearing impaired listeners

To assess the hypothesis that spread of masking from F1 is responsible for poor identification of voiced stop consonants by hearing impaired listeners, /bdg/ were synthesized with bursts and formant transitions in configurations with and without the first formant. Synthesis in the /eI/ environment allowed minimal acoustic differences to cue the contrasts. To maximize the probability of finding evidence of masking spread the stimuli were presented at levels both above and below the point of maximum intelligibility. At no point on the function was performance without the first formant better than performance with the first formant. To investigate other ways in which the intelligibility of /bd/ could be enhanced, we altered, in separate manipulations, the amplitude and duration at signal onset of the cues for place of articulation. Increasing the amplitude of the onset cues improved identification accuracy for /d/ but not for /b/ or /g/. In contrast, increasing the duration of the onset cues improved identif...