Evaluation of Rehabilitation Strategies with Cochlear Implant Patients: Preliminary Report

This research is sponsored by grant NS-17764 from the National Institutes of Health/National Institute of Neurological and Communicative Disorders and Stroke.

Perception of Speech Pattern Contrasts via Cochlear Implants and Limited Hearing

The ability to perceive four suprasegmental and eight segmental speech pattern contrasts was measured in several subject groups. Mean performance of a group of House 3M cochlear implantees was similar to the mean performance of a group of Nucleus implantees with a trend toward better perception of suprasegmentals in the former and better perception of segmentals in the latter. Intersubject variability was higher in the Nucleus implantees, the best subject achieving an open set phoneme recognition score of 40%. Data from a single subject showed considerably superior performance in an aided ear with a 95-dB hearing loss than in an ear implanted with the House 3M device. Data from normal subjects listening to low pass filtered speech provide a basis for evaluating the results obtained by implantees. The results, though limited, illustrate the potential value of analytical tests such as the speech pattern contrast test used in these studies.

Evaluation of the Computer-assisted Speech Perception Assessment Test (CASPA)

Interlist equivalency and short-term practice effects were evaluated for the recorded stimuli of the Computer-Assisted Speech Perception Assessment (CASPA) Test. Twenty lists, each consisting of 10 consonant-vowel-consonant words, were administered to 20 adults with normal hearing. The lists were presented at 50 dB SPL (Leq) in the presence of spectrally matched steady-state noise (55 dB SPL Leq). Phoneme recognition scores for the first list presented were significantly lower than for the second through the twentieth list presented, indicating a small practice effect. Phoneme scores for 4 of the lists (3, 6, 7, and 16) were significantly higher than scores for the remaining 16 lists by approximately 10 percentage points. Eliminating the effects of interlist differences reduced the 95 percent confidence interval of a test score based on a single list from 18.4 to 16.1 percentage points. Although interlist differences have only a small effect on confidence limits, some clinicians may wish to eliminate them by excluding lists 3, 6, 7, and 16 from the test. The practice effect observed here can be eliminated by administering one 10-word practice list before beginning the test.

Cerebral arteriovenous malformation presenting as visual deterioration in a child

A rare case of visual loss as the presenting feature of a central arteriovenous malformation involving the vein of Galen is reported. A 5-year-old girl with a history of deteriorating vision for the past 6 months was examined. Ocular examination showed a left hemianopia, left optic atrophy, and dilated vessels of the right optic disc. MRI revealed a massive deep-seated central arteriovenous malformation involving the vein of Galen. The mechanism of visual loss is likely to be a combination of ischaemic optic atrophy associated with a steal phenomenon and direct compression of the right optic radiation.

Use of a simultaneous sentence perception test to enhance sensitivity to ease of listening

The purpose of the study was to determine if a divided-attention, sentence-recall task was more sensitive to distortion of the speech signal than a conventional focused-attention task. The divided-attention task required listeners to repeat both of two sentences delivered simultaneously to the same ear. The focused-attention task required listeners to repeat a single sentence presented to one ear in quiet or in amplitude-modulated noise (0 dB signal-to-noise ratio). Distortion was introduced by peak clipping. Eighteen listeners with normal hearing were tested under three levels of peak clipping: 0 dB, 11 dB, and 29 dB (re: waveform peak). The effects of clipping were similar, on average, for simultaneous sentences and single sentences in noise. When data were separated by sentence length, however, the effects of clipping were found to be greater for the simultaneous-sentence task, but only for the short sentences (6 words or fewer). The simultaneous-sentence test, in its present form, is not more sensitive to the effects of clipping than is a single-sentence test in noise. Modification of the simultaneous-sentence test to include only short sentences, however, may provide greater test sensitivity than more conventional tests using single sentences in noise.

Speech recognition with reduced spectral cues as a function of age

Adult listeners are able to recognize speech even under conditions of severe spectral degradation. To assess the developmental time course of this robust pattern recognition, speech recognition was measured in two groups of children (5-7 and 10-12 years of age) as a function of the degree of spectral resolution. Results were compared to recognition performance of adults listening to the same materials and conditions. The spectral detail was systematically manipulated using a noise-band vocoder in which filtered noise bands were modulated by the amplitude envelope from the same spectral bands in speech. Performance scores between adults and older children did not differ statistically, whereas scores by younger children were significantly lower; they required more spectral resolution to perform at the same level as adults and older children. Part of the deficit in younger children was due to their inability to utilize fully the sensory information, and part was due to their incomplete linguistic/cognitive development. The fact that young children cannot recognize spectrally degraded speech as well as adults suggests that a long learning period is required for robust acoustic pattern recognition. These findings have implications for the application of auditory sensory devices for young children with early-onset hearing loss.

Cortical, auditory, evoked potentials in response to changes of spectrum and amplitude

The acoustic change complex (ACC) is a scalp-recorded negative-positive voltage swing elicited by a change during an otherwise steady-state sound. The ACC was obtained from eight adults in response to changes of amplitude and/or spectral envelope at the temporal center of a three-formant synthetic vowel lasting 800 ms. In the absence of spectral change, the group mean waveforms showed a clear ACC to amplitude increments of 2 dB or more and decrements of 3 dB or more. In the presence of a change of second formant frequency (from perceived /u/ to perceived /i/), amplitude increments increased the magnitude of the ACC but amplitude decrements had little or no effect. The fact that the just detectable amplitude change is close to the psychoacoustic limits of the auditory system augurs well for the clinical application of the ACC. The failure to find a condition under which the spectrally elicited ACC is diminished by a small change of amplitude supports the conclusion that the observed ACC to a change of spectral envelope reflects some aspect of cortical frequency coding. Taken together, these findings support the potential value of the ACC as an objective index of auditory discrimination capacity.

Ultrasound appearances in chronic appendicitis

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Cortical, auditory, event-related potentials in response to periodic and aperiodic stimuli with the same spectral envelope

OBJECTIVE

1) To determine whether the N1-P2 acoustic change complex is elicited by a change of periodicity in the middle of an ongoing stimulus, in the absence of changes of spectral envelope or rms intensity. 2) To compare the N1-P2 acoustic change complex with the mismatch negativity elicited by the same stimuli in terms of amplitude and signal to noise ratio.

DESIGN

The signals used in this study were a tonal complex and a band of noise having the same spectral envelope and rms intensity. For elicitation of the acoustic change complex, the signals were concatenated to produce two stimuli that changed in the middle (noise-tone, tone-noise). Two control stimuli were created by concatenating two copies of the noise and two copies of the tone (noise-only, tone-only). The stimuli were presented using an onset-to-onset interstimulus interval of 3 sec. For elicitation of the mismatch negativity, the tonal complex and noise band stimuli were presented using an oddball paradigm (deviant probability = 0.14) with an onset-to-onset interstimulus interval of 600 msec. The stimuli were presented via headphones at 80 dB SPL to 10 adults with normal hearing. Subjects watched a silent video during testing.

RESULTS

The responses to the noise-only and tone-only stimuli showed a clear N1-P2 complex to the onset of stimulation followed by a sustained potential that continued until the offset of stimulation. The noise-tone and tone-noise stimuli elicited an additional N1-P2 acoustic change complex in response to the change in periodicity occurring in the middle. The acoustic change complex was larger for the tone-noise stimulus than for the noise-tone stimulus. A clear mismatch negativity was elicited by both the noise band and tonal complex stimuli. In contrast to the acoustic change complex, there was no significant difference in amplitude across the two stimuli. The acoustic change complex was a more sensitive index of peripheral discrimination capacity than the mismatch negativity, primarily because its average amplitude was 2.5 times as large.

CONCLUSIONS

These findings indicate that both the acoustic change complex and the mismatch negativity are sensitive indexes of the neural processing of changes in periodicity, though the acoustic change complex has an advantage in terms of amplitude. The results support the possible utility of the acoustic change complex as a clinical tool in the assessment of peripheral speech perception capacity.

Cortical evoked response to acoustic change within a syllable

OBJECTIVE

To investigate whether the evoked potential to a complex naturally produced speech syllable could be decomposed to reflect the contributions of the acoustic events contained in the constituent phonemes.

DESIGN

Auditory cortical evoked potentials N1 and P2 were obtained in eight adults with normal hearing. Three naturally produced speech stimuli were used: 1) the syllable [sei]; 2) the sibilant [s], extracted from the syllable; 3) the vowel [ei] extracted from the syllable. The isolated sibilant and vowel preserved the same time relationships to the sampling window as they did in the complete syllable. Evoked potentials were collected at Fz, Cz, Pz, A1, and A2, referenced to the nose.

RESULTS

In the group mean waveforms, clear responses were observed to both the sibilant and the isolated vowel. Although the response to the [s] was weaker than that to [ei], both had N1 and P2 components with latencies, in relation to sound onset, appropriate to cortical onset potentials. The vowel onset response was preserved in the response to the complete syllable, though with reduced amplitude. This pattern was observable in six of the eight waveforms from individual subjects.

CONCLUSIONS

It seems likely that the response to [ei] within the complete syllable reflects changes of cortical activation caused by amplitude or spectral change at the transition from consonant to vowel. The change from aperiodic to periodic stimulation may also produce changes in cortical activation that contribute to the observed response. Whatever the mechanism, the important conclusion is that the auditory cortical evoked potential to complex, time-varying speech waveforms can reflect features of the underlying acoustic patterns. Such potentials may have value in the evaluation of speech perception capacity in young hearing-impaired children.

Experiments with classroom FM amplification

OBJECTIVES

1) To quantify the benefits of FM amplification for persons with severe and profound hearing loss; 2) to compare a body-worn and a behind-the-ear FM system; 3) to measure the effects of reducing FM microphone sensitivity relative to hearing aid sensitivity.

DESIGN

Recognition of phonemes in lists of consonant-vowel-consonant words was measured in 13 teenage students with severe and profound hearing loss. Presentation was by live voice at 10 feet from the listeners and 12 inches from the FM microphone/transmitter. Students listened: a) via a body-worn and a behind-the-ear system; b) with the FM microphone/transmitter on and off; c) in noise and in quiet. Systems were adjusted so that sinusoidal inputs of 65 dB SPL gave equal gains via the FM and hearing aid microphones. In a follow-up study, the gain via the FM microphone was reduced so that a sinusoidal input of 65 dB SPL into the hearing aid microphone produced the same output as a sinusoidal input of 80 dB into the FM microphone (as recommended in American Speech-Language-Hearing Association, 1994).

RESULTS

1) Addition of the FM microphone signal to that available from the hearing aid microphone was equivalent, on average, to doubling the number of independent channels of information available to the listeners. 2) FM benefit was present in both quiet and noise but was somewhat greater in noise. 3) Contrary to prediction, however, noise interfered with phoneme recognition even under the aid+FM condition. 4) Differences between the body-worn and behind-the-ear systems were small, but there was a measurable advantage for the body-worn system under the aid+FM condition. 5) Reducing FM microphone sensitivity by 15 dB virtually eliminated the FM benefit. 6) Forty-four percent of the variance in phoneme recognition (averaged across listening conditions) could be explained by better-ear, three-frequency average pure-tone threshold. 7) Vowels were recognized more easily than consonants, and initial consonants were recognized more easily than final consonants, but the FM benefit was present for all three phonemes.

CONCLUSIONS

The findings confirm the value of FM amplification for persons with severe and profound hearing loss, in both quiet and noise. The negative effects of noise were not completely eliminated, however, under the aid+FM condition. This finding can be attributed to a reduction of gain in the FM channel, when speech input was used, because of compression limiting in the microphone transmitter. The superiority of the body-worn system under the aid+FM condition suggests a need for higher saturation sound pressure level in the behind-the-ear system when used with persons having severe and profound hearing loss. The findings do not support use of an "equal output" criterion for adjusting relative gains via the FM and hearing aid microphones--at least for persons with very severe and profound hearing loss operating under the conditions tested in this study.

Torsion of an ovarian cyst mimicking enteric duplication cyst on transabdominal ultrasound: two cases

We describe two girls with abdominal cysts which demonstrated the "double wall" or "muscular rim" sign. On the basis of this, the diagnosis of duplication cyst was made in each case. At surgery, both were found to have ovarian cysts, and histology revealed prominent haemorrhage within the cyst wall. To our knowledge, there has been no previous report of a false-positive "double wall sign".

Age-related changes on a children's test of sensory-level speech perception capacity

Normative data, as a function of age, were obtained on a test designed to assess sensory-level speech perception capacity, the Three-Interval Forced-Choice Test of Speech Pattern Contrast Perception, otherwise known as THRIFTSPAC (or THRIFT for short). Performance under the input modalities of hearing alone, speech-reading alone, and the two combined was measured in 44 normally developing children between the ages of 5 years 7 months and 10 years 9 months. Results revealed that within each condition there were significant influences of age on performance for children below age 7 years. These changes appeared to be related to cognitive and, possibly, to phonological development. Implications for the clinical implementation of THRIFT are discussed.

Magnetic resonance--its current and future role in paediatric cardiac radiology

Cardiac magnetic resonance (MR) has developed rapidly providing a method of both imaging congenital heart disease and assessing function using a variety of techniques. The aim of this review is to identify indications for MR and its relative strengths and weaknesses in comparison to other methods of cardiac imaging. A potential future role for MR is also discussed.

Auditory development of the hearing child

Auditory perception is defined, here, as the interpretation of sensory evidence, derived from sound, in terms of the objects and events that caused the sound. Like other kinds of perception, it involves the use, not only of sensory evidence, but also of contextual evidence, prior knowledge, memory, attention, and processing skills. Auditory speech perception is special because the events to be perceived are those of language. Similarly, the listener's knowledge base and processing skills must include those related to language in general, and spoken language in particular. The auditory system is complete and functional at birth but myelination continues for several years in the higher auditory pathways. This pattern of anatomical maturation is reflected in electrophysiological responses. Similarly, infants display sophisticated discrimination and recognition ability but psychoacoustic performance does not reach adult levels for several years. Empirical data on the development of auditory processing are sparse, but much work has been done on auditory speech perception. Infants at 6 months demonstrate the beginnings of phonemic classification, and performance improves during childhood in a variety of areas. These include: phonetic contrast perception, phoneme recognition, perception of speech in noise, selective attention, and the use of linguistic context. Experience obviously plays a key role in the development of the knowledge and skills required for auditory perception in general and auditory speech perception in particular. It is tempting to assume that the sensory evidence available to the developing child is determined only by the functional integrity of the peripheral auditory system, independent of auditory experience. There is, however, increasing evidence in animals of the influence of auditory experience on the organization of the auditory pathways. Such organization could increase the sensory evidence made available from patterns of neural excitation produced in the cochlea.

Radiation exposure to children during cardiac catheterization

The purpose of this study was to assess the suitability of different radiation dosimetry methods and record radiation exposures during paediatric catheterization. Three methods of dosimetry were employed: thermoluminescent dosimetry (TLD), dose-area product and calculation of entrance surface dose from calibrated exposure factors. Examinations included bi-plane fluoroscopy, and cineangiography for diagnosis and treatment of congenital heart disease. The most suitable method of radiation dosimetry for cardiac catheterization is the use of calculated entrance dose or a dose-area product meter. Children were exposed to high levels of radiation during cardiac catheterization but there was a wide variation in radiation dosage. Careful consideration should be given to the suitability of radiation dosimetry for cardiac catheterization.

Auditory capacity of hearing-impaired children using hearing aids and cochlear implants: issues of efficacy and assessment

The immediate goal of sensory assistance is to provide as much sensory evidence as possible about the sound patterns of speech. To determine how well this goal has been met calls for tests that are sensitive to sensory capacity and insensitive to linguistic and cognitive status. At the same time, the results should have predictive validity in terms of the potential for developing speech perception skills. This paper describes data obtained from paediatric hearing aid and cochlear implant users by means of an imitative test of phonetic contrast perception (IMSPAC). It is shown that the primary predictor of IMSPAC performance for aided subjects is degree of hearing loss, with little or no influence of age and communication mode. The primary predictors for Nucleus implantees, however, are communication mode and duration of use. The distribution of scores in the implant group is similar to that of hearing aid users with hearing losses in the 90 to 99 dB range. The more successful implantees (mostly, but not only, orally trained) perform like hearing aid users with hearing losses in the 70 to 89 dB range. The hearing aid data suggest that the IMSPAC test is effective in measuring auditory sensory capacity without confounding by linguistic status. If this is true, the implant data must be interpreted as evidence of the development of auditory perceptual skills during the post-implant period. This interpretation carries important implications for issues of cortical plasticity, acclimatization, the management of childhood deafness, and the evaluation of sensory aid efficacy.

Effects of spectral smearing on phoneme and word recognition

The principal goal was to measure the effects, on speech perception, of loss of spectral detail in the acoustic signal. Spectral smearing was produced by multiplying the speech waveform by low-pass filtered noise. Performance was measured in normal adults as the percentage of phonemes correctly repeated in lists of monosyllabic words. A smearing bandwidth of 250 Hz (i.e., each tonal component of the instantaneous spectrum replaced by a 250-Hz band of noise) had a small but significant effect on phoneme recognition. A smearing bandwidth of 8000 Hz was required to reduce phoneme recognition to a value that was indistinguishable from that produced by complete smearing. Vowels were somewhat more susceptible to the effects of spectral smearing than were consonants, and initial consonants were more susceptible than were final consonants. In an analysis of errors, place of consonant articulation was more susceptible than either manner of articulation or voicing. These findings are attributable to differences in the relative importance of spectral and temporal cues. Word recognition was more susceptible to the effects of spectral smearing than was phoneme recognition, but this finding was predictable on the basis of the known nonlinear relationship between the two measures. In a second experiment, smearing bandwidths of 707 and 2000 Hz increased phoneme recognition threshold by 12.9 and 16.4 dB, respectively, compared to that found without smearing. (Phoneme recognition threshold is defined, here, as the signal-to-noise ratio at which phoneme recognition is 50% of the value obtained in quiet.) The data are consistent with the hypothesis that reduced spectral resolution affects phoneme recognition to the extent that it reduces access to the formant patterns in the spectral envelope.

Speechreading enhancement: a comparison of spatial-tactile display of voice fundamental frequency (F0) with auditory F0

In two experiments, subjects repeated video-recorded sentences presented via speechreading with and without enhancement by a sensory input derived from the acoustic speech signal. Enhancement was measured as percentage increase in recognized words. In experiment 1, tactile presentation of fundamental frequency (F0) provided, after training, for three of four postlingually deafened adults a mean enhancement of 11%. In experiment 2, using six hearing adults, the auditory presentation of F0 provided a mean enhancement of 50%. This value fell, but only to 37%, when the F0 signal was derived from the processor of the tactile aid used in experiment 1. From these experiments it can be concluded that the unexpectedly small enhancement found in experiment 1 is probably due both to the fact that this tactile aid was not providing effective access to all of the information available in the F0 contour and to limitations related to the tactile processing ability of the kinaesthetic system.

Using naturally produced speech to elicit the mismatch negativity

The mismatch negativity (MMN) was recorded from 10 young adults with normal hearing using naturally produced speech contrasts. Consonant-place and vowel-height contrasts were examined in consonant-vowel (CV) syllables by pairing either the consonant /t/ or /p/ with the vowel /I/ or /E/. Vowel-height was also examined as a pseudovowel; one cycle of the vowel segment of a CV was extracted and replicated over 200 msec. A total of five contrasts were examined: vowel-height following /p/, vowel-height following /t/, consonant-place preceding /E/, consonant-place preceding /I/, and pseudovowels. Significant MMN responses were elicited from all five contrasts, albeit with different amplitudes, latencies, and waveform morphology. The pseudovowel elicited the most well-defined MMN with the greatest amplitude and was found to be significantly different from the other four contrasts. Naturally produced speech stimuli appear to be viable stimuli for eliciting the MMN.

Speech perception of temporally reversed syllables by normally hearing adults

BACKGROUND

The general purpose of this study was to determine the effects of phonological knowledge on performance on a simple task of speech discrimination. If a test can be devised that is independent of the subject's phonological knowledge then it should be possible to measure auditory speech perception capacity in young deaf children before they have developed spoken language skills. In the present study, temporal reversal was used to limit normal subjects' use of phonological knowledge without removing acoustic information.

METHODS

An auditory, 3-interval, forced-choice (oddity) test of phonetic contrast perception was administered to 5 normally hearing adult speakers of English. Perception of place of articulation was measured in stops and fricatives--both voiced and unvoiced. The test was presented both with natural syllables and with the same syllables reversed in time. In addition, the test was administered with a fixed context and a mixed context (i.e., context changing from trial to trial). The subject's task was always to identify the odd-man-out in each presentation of 3 syllables.

RESULTS

Overall, error rate was significantly higher for temporally-reversed than for natural syllables (6.7% versus 1.7%). The effect was, however, present only in stops (11.7% versus 1.7%) and not in fricatives (0.8% versus 0.8%). Changing from a fixed to a mixed context did not influence the effect of reversal. There were, however, significant differences among subjects in the temporally-reversed condition.

CONCLUSIONS

The main effect of reversal supports the hypothesis that performance falls, even on a simple task, when phonetic processing is impeded. The fact that the effect is present only for stops adds further support, because temporal reversal does not affect the essential acoustic properties of fricatives. The presence of inter-subject differences suggests that the ability to switch to an acoustic strategy when phonetic processing is impeded may be affected by aptitude and experience. The fact that error rate was low, even for reversed stops, suggests that a test of this type could be used for assessing speech perception capacity in deaf children with impaired phonology. The procedure is not, however, completely independent of the effects of phonetic processing.

Speechreading supplemented by single-channel and multichannel tactile displays of voice fundamental frequency

The benefits of two tactile codes of voice fundamental frequency (F0) were evaluated as supplements to the speechreading of sentences in two short-term training studies, each using 12 adults with normal hearing. In Experiment 1, a multichannel spatiotemporal display of F0, known as Portapitch, was used to stimulate the index finger. In an attempt to improve on past performance with this display, the coding scheme was modified to better cover the F0 range of the talker in the training materials. For Experiment 2, to engage kinesthetic/proprioceptive pathways, a novel single-channel positional display was built, in which F0 was coded as the vertical displacement of a small finger-rest. Input to both displays consisted of synthesized replicas of the F0 contours of the sentences, prepared and perfected off-line. Training with the two tactile F0 displays included auditory presentation of the synthesized F0 contours in conjunction with the tactile patterns on alternate trials. Speechreading enhancement by the two tactile F0 displays was compared to the enhancement provided when auditory F0 information was available in conjunction with the tactile patterns, by auditory presentation of a sinusoidal indication of the presence or absence of voicing, and by a single-channel tactile display of the speech waveform presented to the index finger. Despite the modified coding strategy, the multichannel Portapitch provided a mean tactile speechreading enhancement of 7 percentage points, which was no greater than that found in previous studies. The novel positional F0 display provided only a 4 percentage point enhancement. Neither F0 display was better than the simple single-channel tactile transform of the full speech waveform, which gave a 7 percentage point enhancement effect. Auditory speechreading enhancement effects were 17 percentage points with the voicing indicator and approximately 35 percentage points when the auditory F0 contour was provided in conjunction with the tactile displays. The findings are consistent with the hypothesis that subjects were not taking full advantage of the F0 variation information available in the outputs of the two experimental tactile displays.

Comparison of two multichannel tactile devices as supplements to speechreading in a postlingually deafened adult

OBJECTIVE

The purpose of this study was to conduct a single-subject comparison of the effectiveness of two multichannel vibrotactile devices that encode different classes of speech information. One device, the Portapitch, is designed to convey fundamental frequency (F0) and its variation over time. The other, the TACTAID 7, is designed to convey the first two formant frequencies (F1 and F2) and their variation over time.

DESIGN

The subject, a postlingually deafened adult, underwent an intensive 17-wk training and testing protocol with the Portapitch and then completed a similar 17-wk protocol with the TACTAID 7. Performance measures were obtained on phonetic-contrast perception by speechreading alone, tactile device alone, and speechreading plus tactile device, and on open-set word and sentence recognition by speechreading alone and speechreading plus tactile device.

RESULTS

On phonetic-contrast testing, the subject demonstrated some ability to perceive voicing, stress, and intonation contrasts using the Portapitch, but gave little evidence of phonetic-contrast perception with the TACTAID 7. On open-set word recognition testing, no significant improvements were seen with either device. On open-set sentence recognition testing, the subject showed a significant 9 percentage point enhancement effect using the Portapitch; the mean 5 percentage point enhancement effect provided by the TACTAID 7 was not statistically significant.

CONCLUSIONS

A small advantage was seen in favor of the tactile display of F0 relative to the tactile display of formant frequency information on both phonetic-contrast testing and open-set sentence recognition. The difference, however, was of questionable significance and could have been confounded with an order effect. Nevertheless, the subject's preference was for the tactile formant frequency display.

Ultrasound: a helpful guide in the treatment of congenital talipes equinovarus

Ultrasound may be used to distinguish the unossified cartilage and the ossification centres of the tarsal bones. The use of ultrasound to image the normal foot and the foot with congenital talipes equinovarus (CTEV) deformity has been assessed. We describe two standard ultrasound planes that enable the normal foot to be distinguished from the foot with a CTEV deformity even before it becomes clinically apparent. The technique does not take much time, is easily tolerated by the child, and may be repeated frequently to assess the response to treatment. It can be learned easily.

The hearing aid input: a phonemic approach to assessing the spectral distribution of speech

OBJECTIVES

The long-term goal is to investigate the feasibility of using real speech as a stimulus for electroacoustic evaluation of nonlinear hearing aids. The goals of the present study were to determine the spectral envelope of speech from acoustic measures of phoneme tokens in running speech, to compare the results with published data on long-term average speech spectra, to measure inter-talker differences of spectral envelope, and to explore the extent to which the intensity variation within and across talkers might be minimized by frequency-selective amplification and automatic gain control.

DESIGN

Seven phonemes were selected to represent the extremes of frequency and intensity in English. Recordings were made of five men and five women producing syllable strings constructed from these phonemes. One-third octave spectra were prepared from the phoneme tokens. The frequencies and intensities of 13 key points in these spectra were measured and used to estimate individual and group spectral envelopes.

RESULTS

The group spectral envelope was similar to that derived from published data on the long-term average spectrum of speech, but there were marked intertalker differences. Some of the differences were gender-related. The overall dynamic range of intensity in these data was 53 dB. Frequency-dependent level adjustment (an 11 dB high-frequency boost) reduced this range to 42 dB, and a combination of frequency-dependent and subject-dependent level adjustment (analogous to 2-band automatic gain control) reduced it to 37 dB.

CONCLUSION

A phonemic approach to determining the spectral envelope of speech offers insights that are not available from long-term average spectra and could offer advantages in the evaluation of nonlinear hearing aids.

Breast masses in childhood and adolescence. A presentation of 17 cases and a review of the literature

Breast masses are uncommon in the first two decades of life. 17 girls aged between 2 and 15 years who presented over a 5-year period are reviewed retrospectively. The cases comprised inflammation (11), asymmetrical gynaecomastia (1), precocious puberty (1), giant juvenile fibroadenoma (1), primary rhabdomyosarcoma (1), lymphoma (1), and metastatic neuroblastoma (1). Ultrasound was useful in all cases in identifying the abnormality and guiding any further investigation.

Recovery of speech perception performance after prolonged auditory deprivation: case study

The case reported here, a 26-year-old woman, has a bilaterally symmetric, severe-to-profound, sensorineural hearing loss, acquired early in life. Phoneme recognition scores were essentially symmetric at the onset of the investigation. She was basically monaurally aided from age 4 to age 24, at which time a loss of function in the aided ear prompted the change to binaural amplification. When monaurally aided, this subject had consistently given phoneme recognition scores around 80 percent and 40 percent in the aided and unaided ears, respectively, even though the pure-tone thresholds were almost identical. After several months of hearing aid use, phoneme recognition in the previously unaided ear rose to 75 percent. At the time of writing, this subject is able to hold unstructured telephone conversations via this ear. These data suggest that the earlier poor performance of the unaided ear was due, not to an irreversible loss of peripheral function, but to a lack of experience in interpreting the patterns of neural stimulation generated by that ear.

Effects of noise and noise suppression on speech perception by cochlear implant users

The recognition of phonemes in consonant-vowel-consonant words, presented in speech-shaped random noise, was measured as a function of signal to noise ratio (S/N) in 10 normally hearing adults and 10 successful adult users of the Nucleus cochlear implant. Optimal scores (measured at a S/N of +25 dB) were 98% for the average normal subject and 42% for the average implantee. Phoneme recognition threshold was defined as the S/N at which the phoneme recognition score fell to 50% of its optimal value. This threshold was -2 dB for the average normal subject and +9 dB for the average implantee. Application of a digital noise suppression algorithm (INTEL) to the mixed speech plus noise signal had no effect on the optimal phoneme recognition score of either group or on the phoneme recognition threshold of the normal group. It did, however, improve the phoneme recognition threshold of the implant group by an average of 4 to 5 dB. These findings illustrate the noise susceptibility of Nucleus cochlear implant users and suggest that single-channel digital noise reduction techniques may offer some relief from this problem.

Spectral distribution of /s/ and the frequency response of hearing aids

The purpose was to determine a target for the upper frequency limit of a hearing aid that will provide access to the important spectral cues for all the sounds of English. The sibilant /s/ was studied because of its high-frequency content. Repeated tokens of /s/ were recorded from five men and five women before and between the vowels /u/, /a/, and /i/. Using fast Fourier transform analysis, the prominent spectral peak with the lowest frequency was identified and its center frequency determined for each token. This frequency averaged around 4.9 kHz for the /u/ context, 5.6 kHz for the /a/ context, and 6.0 kHz for the /i/ context. There were dramatic differences among talkers, with subject means ranging from 3.2 to 8.4 kHz. The women generated consistently higher frequency /s/ sounds than the men, but there were also large differences within gender groups. These data suggest that the upper frequency limit of a high-fidelity hearing aid should be in the region of 10 kHz. If this cannot be accomplished with direct amplification, an alternative might be the selective use of frequency transposition.

Context effects in phoneme and word recognition by young children and older adults

Perception is influenced both by characteristics of the stimulus, and by the context in which it is presented. The relative contributions of each of these factors depend, to some extent, on perceiver characteristics. The contributions of word and sentence context to the perception of phonemes within words and words within sentences, respectively, have been well studied for normal, young adults. However, far less is known about these context effects for much younger and older listeners. In the present study, measures of these context effects were obtained from young children (ages 4 years 6 months to 6 years 6 months) and from older adults (over 62 years), and compared with those of the young adults in an earlier study [A. Boothroyd and S. Nittrouer, J. Acoust. Soc. Am. 84, 101-114 (1988)]. Both children and older adults demonstrated poorer overall recognition scores than did young adults. However, responses of children and older adults demonstrated similar context effects, with two exceptions: Children used the semantic constraints of sentences to a lesser extent than did young or older adults, and older adults used lexical constraints to a greater extent than either of the other two groups.

Perception of speech pattern contrasts from auditory presentation of voice fundamental frequency

The perception of phonologically significant speech pattern contrasts was measured in normally hearing subjects who were presented with F0 contours alone, speechreading alone, and the two in combination. For the suprasegmentals and final consonant voicing, perception in the combined condition was dominated by F0. For the vowel, consonant place, and final consonant continuance contrasts, perception in the combined condition was dominated by vision. For initial consonant voicing and continuance, however, there was clear evidence of interaction between F0 and speechreading. Here, the combined score was higher than either of the single-modality scores, and also higher than could be predicted on the assumption that the auditory and visual channels act as statistically independent channels of information.

A wearable multichannel tactile display of voice fundamental frequency

This paper describes a wearable sensory aid that provides the deaf with tactually encoded information about intonation. Fundamental frequency is represented as both place and rate of vibration in a linear array of solenoids. Pitch extraction is accomplished through low-pass filtering and peak detection. A microcomputer is used to measure pitch period, which in turn determines which of the solenoids is actuated. By comparing consecutive periods, the system discriminates against random, noise-related inputs. The device is switchable between 1-, 8-, and 16-channel operation. The electronics package is contained in a case that may be worn on a belt. The solenoid array is worn on the forearm. The system is powered by five, rechargeable lithium cells and runs for at least 6 hours between charges. Proposed developments include the incorporation of digital pitch extraction methods and the option to use the spatial output dimension to encode speech parameters other than fundamental frequency.

Tactile presentation of voice fundamental frequency as an aid to the speechreading of sentences

In two experiments, the perception of words in sentences was measured by speechreading with and without tactile presentation of voice fundamental frequency (F0). The first experiment involved normally hearing subjects and two kinds of tactile display of F0: (1) a spatial, multichannel display; and (2) a temporal, single-channel display. Mean performance with the tactile displays was found to be slightly, but significantly, better than speechreading alone, but no significant difference was found between the two displays. The second experiment involved hearing-impaired subjects and only the spatial, multi-channel display of F0. For all three subjects, after extended training, speechreading performance was significantly better with the addition of the tactile display than by speechreading alone. The improvement amounted to reductions of word recognition error of 24, 33, and 50% in the three subjects.

Mathematical treatment of context effects in phoneme and word recognition

Percent recognition of phonemes and whole syllables, measured in both consonant-vowel-consonant (CVC) words and CVC nonsense syllables, is reported for normal young adults listening at four signal-to-noise (S/N) ratios. Similar data are reported for the recognition of words and whole sentences in three types of sentence: high predictability (HP) sentences, with both semantic and syntactic constraints; low predictability (LP) sentences, with primarily syntactic constraints; and zero predictability (ZP) sentences, with neither semantic nor syntactic constraints. The probability of recognition of speech units in context (pc) is shown to be related to the probability of recognition without context (pi) by the equation pc = 1 - (1-pi)k, where k is a constant. The factor k is interpreted as the amount by which the channels of statistically independent information are effectively multiplied when contextual constraints are added. Empirical values of k are approximately 1.3 and 2.7 for word and sentence context, respectively. In a second analysis, the probability of recognition of wholes (pw) is shown to be related to the probability of recognition of the constituent parts (pp) by the equation pw = pjp, where j represents the effective number of statistically independent parts within a whole. The empirically determined mean values of j for nonsense materials are not significantly different from the number of parts in a whole, as predicted by the underlying theory. In CVC words, the value of j is constant at approximately 2.5. In the four-word HP sentences, it falls from approximately 2.5 to approximately 1.6 as the inherent recognition probability for words falls from 100% to 0%, demonstrating an increasing tendency to perceive HP sentences either as wholes, or not at all, as S/N ratio deteriorates.

Lipreading with tactile supplements

Lipreading performance, after brief training, was measured in two normal subjects, as the percentage of words recognized in sets of unrelated sentences. Three receptive conditions were used: lipreading alone, lipreading plus a single-channel tactile display of fundamental frequency (temporal only), and lipreading plus a multichannel, tactile, spatial display of fundamental frequency (temporal-spatial). After training, performance with tactile supplements was better than without, but it was not possible to conclude that either of the tactile displays was better than the other. During training, a significant correlation between performance and session number was found for the temporal-spatial display only.

Auditory perception of speech contrasts by subjects with sensorineural hearing loss

The goal of these studies was to find out how much of the acoustical information in amplified speech is accessible to children with varying degrees of sensorineural hearing loss. Context-varying, forced-choice tests of speech perception were presented, without feedback on performance, to orally trained subjects with better ear, three-frequency average hearing losses in the range 55-123 dB HL. As expected, average performance fell with increasing hearing loss. The values of hearing loss at which scores fell to 50% (after correction for chance) were 75 dB HL for consonant place; 85 dB HL for initial consonant voicing; 90 dB HL for initial consonant continuance; 100 dB HL for vowel place (front-back); 105 dB HL for talker sex; 115 dB HL for syllable pattern; and in excess of 115 dB HL for vowel height. Performance on the speech contrast tests was significantly correlated with the intelligibility of the subjects' own speech and with the open-set recognition of phonemes in monosyllabic words, even when pure-tone threshold was held constant.

Assessment of nasalization in the speech of deaf children

Nasality is widely recognized as a problem in the speech of many deaf people. This paper describes one approach to the assessment of nasalization and to the development of visual aids to assist in training of velopharyngeal control. The approach involves detection of the velopharyngeal opening during voiced sounds by means of a small accelerometer attached to the nose, and presentation of the accelerometer output on a computer-controlled visual display. The display may be used as a training aid, or for the purpose of analyzing either recorded or live speech. Objective data are presented on some of the properties of the accelerometer output for the speech of people with normal hearing and of a number of children whose hearing is severely impaired. These data show inadequate velopharyngeal control, particularly improper nasalization of certain vowels, for a significant number of the deaf children. For a group of the hearing-impaired children, subjective judgments of the adequacy of velopharyngeal control and of other speech attributes were obtained. Correlations among these judgments and relations between judgments of adequacy of velopharyngeal control and the objective measures of nasalization are shown. Some comments are made on the development of procedures for the training of velopharyngeal control using the display as an aid.