Long-term audiometric follow-up of click-evoked auditory brainstem response in hearing-impaired infants.

Conventional pure-tone thresholds were collected as determined at ages between 4 and 8 years from a group of 163 infants, tested by auditory brainstem response (ABR) in the age range between 1 and 3 years old for objective hearing assessment. The subjects suffered from a variety of degrees and types of sensorineural hearing impairment. The prognostic value of the ABR peak V thresholds in response to 0.1 ms clicks with respect to the behavioural thresholds at octave frequencies from 125 to 8,000 Hz obtained later is evaluated. Correlation between ABR and behavioural thresholds is largest in the 1,000- to 8,000-Hz frequency range. Predicted pure-tone audiograms (mean and SD) were determined for each 10-dB class of ABR thresholds. SDs are in the order of 15 to 18 dB in the 500- to 4,000-Hz range and slightly higher at adjacent frequencies (i.e., somewhat larger than in comparable adult studies). Mean pure-tone thresholds in the 1,000- to 8,000-Hz frequency range are up to 20 dB worse than ABR thresholds, which is opposite to findings in normally-hearing subjects. Thus, with an increasing degree of sensorineural hearing impairment, pure-tone thresholds increase at a significantly higher rate than ABR thresholds. The observation is explained in terms of reduced temporal integration in cochlear hearing loss. ABR thresholds worse than 80 dB nHL are demonstrated to have very limited predictive value with respect to the amount of residual hearing, not only in the low- but also in the high-frequency range. The presence of otitis media during ABR testing is shown to make estimation errors increase to more than 25 dB (SD).

The prognostic value of electrocochleography in severely hearing-impaired infants.

This paper presents a longitudinal evaluation of electrocochleographic assessment in severely hearing-impaired infants. Electrophysiological data were obtained by transtympanic electrocochleography to tone-burst stimuli at octave frequencies of 500 to 8000 Hz at the age of 0-6 years in a group of 126 subjects. The results are compared with auditory thresholds determined at school age in the same children by means of pure-tone audiometry. Cochlear microphonics could be recorded in virtually all ears, although the majority of subjects had hearing losses of 90 dB and more. Compound action potentials (CAPs) showed waveforms varying from normal to a wide range of abnormalities. Audiometric thresholds correlated generally well with the compound action potential (CAP) thresholds obtained in infancy. The error in the predicted audiometric thresholds is between 15 and 20 dB, as compared with 11 dB reported for more moderate hearing losses. It is shown that, in spite of the high stimulus levels used, substantial frequency-specific threshold information is retained. Occasional large discrepancies in thresholds were often associated with markedly abnormal response waveforms. Among the many cases in which no ABR could be elicited, 68 per cent produced detectable electrocochleographic responses in the 1000-4000 Hz range. It is concluded that electrocochleography is a valuable method for the assessment of residual hearing in infants suspected of having a severe hearing impairment.

Auditory, visual and audiovisual perception of segmental speech features by severely hearing-impaired children.

Auditory alone, visual alone and audiovisual recognition of consonant-vowel consonant syllables were measured in 32 severely hearing-impaired children with hearing loss (PTA) in a narrow range around 90 dB HL when using their hearing aids. Multidimensional scaling analysis (INDSCAL) and information transmission analysis (ITA), applied to the confusion matrices obtained from the responses in each presentation mode and for each phoneme category, revealed perceptual dimensions and percentages of transmitted feature information (PTI). These were studied in relation to PTA, the auditory alone score and in relation to the efficiency of the audiovisual interaction (enhancement) over the probalistic summation of the auditory alone and visual alone score. INDSCAL analysis shows that auditory alone recognition of vowels is based on the perceptual dimensions F2 and F1 and that of consonants on the dimensions 'frication' and 'voicing'. In the auditory mode the interpretation of the INDSCAL dimensions in the stimulus spaces is in reasonable agreement with the ITA results. PTI decreases gradually with decreasing auditory alone phoneme score. Audiovisual recognition of vowels is based on a combination of the auditory dimension 'open/closed' (F1), and the visual dimensions 'lip rounding' and 'vertical lip opening'. Audiovisual recognition of initial consonants is based on a combination of the visual dimension 'front/back' and the auditory dimension 'continuance'. Recognition of final consonants is based on a combination of the visual dimension 'front/back' and an uninterpretable dimension. The perceptual dimensions are independent of both the level of the auditory alone phoneme score and audiovisual enhancement. Audiovisual enhancement is mainly a property of an individual and independent of both auditory alone and visual alone scores. ITA analysis, based on a phonological classification of the features, supports the results of the INDSCAL analysis in the auditory alone mode. It is not useful in the description of the audiovisual interaction, probably due to the phonological basis of the feature classification.

The effect of oestrogen treatment on body proportions in constitutionally tall girls.

Body proportions were studied in 31 girls with constitutional tall stature during treatment with 200 micrograms ethinyl oestradiol per day continuously, combined with 5-10 mg medroxyprogesterone on the first 10 days of each month. Their mean (+/- SD) predicted adult height was 186.0 (+/- 4.0) cm. At the start of therapy, leg length (LL) standard deviation score (SDS) (3.8 +/- 0.7) was significantly greater than the sitting height (SH) SDS (2.3 +/- 1.1). During therapy, the mean sitting height increased by 2.9 cm, in contrast to an increment of only 0.8 cm for LL. The SDS of the ratio between SH and LL remained below zero. The expected gain without therapy, assuming a stable SDS position over time, was 5.4 cm for SH and 4.4 cm for LL, significantly more than the observed gains. In conclusion, tall girls have relatively long legs. Oestrogen therapy leads to an almost complete stop of leg growth, while the growth of the trunk is reduced to a lesser extent. This selective inhibition results in a trunk/leg ratio which is closer to, though still significantly different from that of normal girls.

The perception of complex harmonic patterns by profoundly hearing-impaired listeners.

In providing profoundly hearing-impaired persons with processed speech through a signal-processing hearing aid, it is important that the new speech code matches their auditory capacities. This processing capacity for auditory information was investigated in this study. In part 1, the subjects' ability to judge similarities among 8 different but related harmonic complexes was studied. The patterns contained different numbers of harmonics to a 125-Hz fundamental frequency; the harmonics had been spread over the spectrum in various ways. The perceptual judgments appeared to be based on a temporal cue, beat strength, and a spectral cue, related to the balance of high and low frequency components. In part 2, three sets of synthetic vowels were presented to the subjects. Each vowel was realized by summing harmonically related in-phase sinusoids at two formant frequencies. The sets differed in the number of sinusoids per formant: 1, 2 or 3. It was found that the subjects used spectral cues and vowel length for differentiating among the vowels. The overall results show the limited but perhaps usable ability of the profoundly impaired ear to handle spectral information. Implications of these results for the development of signal-processing hearing aids for the profoundly hearing impaired are discussed.

Auditory pattern perception in the profoundly hearing impaired and lipreading of Dutch phonemes.

Successful rehabilitation of the profoundly hearing impaired by means of a speech-processing hearing aid requires integration of auditory and visual speech information. In two studies we investigated (1) which perceptual dimensions play a role in processing various auditory patterns by profoundly hearing-impaired subjects, and (2) which Dutch consonants and vowels can be identified by the average lipreader. One of the important cues in auditory pattern discrimination seems to be the presence of temporal fluctuations (beats) in the signal, resulting from two closely placed frequency components. However, this feature is confounded with the perception of loudness. A second cue used by some subjects is the presence of high-frequency peaks. In lipreading, at least three groups of consonants and three vowel groups may be distinguished; phonemes within a group cannot be discriminated from each other. Important features for both consonants and vowels are degree of lip opening and lip activity (movement or rounding). These results suggest how the auditory speech signal might be coded so as to provide supplementary information to speechreading.

Residual hearing capacity of severely hearing-impaired subjects.

Speech reception functions (speech reception threshold and maximum discrimination score for phonemes) and auditory functions (hearing threshold, difference limens for intensity and frequency, temporal modulation threshold function, critical ratio and temporal integration) have been investigated in a group of severely hearing-impaired subjects (64 ears, median Fletcher Index of 80 dB). The results were separated into low-, middle- and high-frequency regions. The investigations were intended to describe and quantify the residual hearing capacities and the correlations between the different functions. It was found that the speech functions, the difference limen for frequency, the critical ratio and the time constant of temporal integration deteriorate gradually with increasing hearing loss. These functions show a relatively high mutual correlation in the low-frequency region and considerable scatter in the high-frequency part. The sensitivity for modulations and the difference limen for intensity were least affected. The results revealed that the residual capacity can be described by means of two independent factors: frequency discrimination at the higher frequencies and a decrease in processing efficiency of the system. The latter is dominated by the middle- and low-frequency hearing elements.

Conditions and possibilities for the detection of speech-signal elements by means of vibrotaction.

Investigations have been carried out in order to determine (1) the sensitivity of the two types of skin for sinusoidal mechanical vibrations under different stimulation conditions, and (2) the sensitivity of the skin for amplitude modulations. Maximum sensitivity was found around 200 Hz, with a threshold of 0.03 microns RMS for the glabrous skin of the inner side of the hand under a static force of at least 0.5 N. The sensitivity of the hairy skin of the arm was 12 dB less (static force at least 3 N). The sensitivity increased with increasing contractor area. Maximum modulation sensitivity was found for sinusoidal carriers between 200 and 400 Hz and extended from modulation frequencies of 1 Hz up to 200 Hz (depending on carrier frequency) at a frequency-independent modulation depth of about 0.1. It was concluded that it is certainly possible for the skin to detect the slow amplitude fluctuations of speech signals as a support for lipreading. Attention was paid to the best way of extracting the envelopes from the speech signal and their presentation, as an amplitude modulation, to the skin.

Residual Hearing Capacity of Severely Hearing-impaired Subjects.

Speech reception functions (speech reception threshold and maximum discrimination score for phonemes) and auditory functions (hearing threshold, difference limens for intensity and frequency, temporal modulation threshold function, critical ratio and temporal integration) have been investigated in a group of severely hearing-impaired subjects (64 ears, median Fletcher Index of 80 dB). The results were separated into low-, middle-and high-frequency regions. The investigations were intended to describe and quantify the residual hearing capacities and the correlations between the different functions. It was found that the speech functions, the difference limen for frequency, the critical ratio and the time constant of temporal integration deteriorate gradually with increasing hearing loss. These functions show a relatively high mutual correlation in the low-frequency region and considerable scatter in the high-frequency part. The sensitivity for modulations and the difference limen for intensity were least affected. The results revealed that the residual capacity can be described by means of two independent factors: frequency discrimination at the higher frequencies and a decrease in processing efficiency of the system. The latter is dominated by the middle-and low-frequency hearing elements.

Conditions and Possibilities for the Detection of Speech-signal Elements by Means of Vibrotaction.

Investigations have been carried out in order to determine (1) the sensitivity of the two types of skin for sinusoidal mechanical vibrations under different stimulation conditions, and (2) the sensitivity of the skin for amplitude modulations. Maximum sensitivity was found around 200 Hz, with a threshold of 0.03 µm RMS for the glabrous skin of the inner side of the hand under a static force of at least 0.5 N. The sensitivity of the hairy skin of the arm was 12 dB less (static force at least 3 N). The sensitivity increased with increasing contactor area. Maximum modulation sensitivity was found for sinusoidal carriers between 200 and 400 Hz and extended from modulation frequencies of 1 Hz up to 200 Hz (depending on carrier frequency) at a frequency-independent modulation depth of about 0.1. It was concluded that it is certainly possible for the skin to detect the slow amplitude fluctuations of speech signals as a support for lipreading. Attention was paid to the best way of extracting the envelopes from the speech signal and their presentation, as an amplitude modulation, to the skin.

Evidence for different types of mechanoreceptors from measurements of the psychophysical threshold for vibrations under different stimulation conditions.

The shape of the psychophysical frequency threshold curve for vibrations presented to the skin in the frequency region 5-1000 Hz is strongly dependent on the static force that the vibrator exerts on the skin and on whether there is a rigid surround around the vibrating contactor (presence of contrast). Where there is no rigid surround, an increase in static force reduces the threshold in the high-frequency region and increases it at low frequencies. When the static forces are sufficiently large, the thresholds reach a minimum value above 30 Hz and a maximum one below 30 Hz, this being the crossover frequency. Under these conditions in the frequency region around 200 Hz, where the threshold is determined by the Pacini receptor system, the vibration sensitivities of finger pad and thenar eminence (glabrous skin) are equal, while the value for the inner side of the forearm (hairy skin) is 12 dB higher. However, when a rigid surround is used, the threshold increases above 30 Hz and decreases below 30 Hz. The latter increase in sensitivity, which is introduced by the presence of contrast cues, amounts to about 20 dB and is sharply tuned at 18 Hz for the glabrous skin of the finger. It is argued that in this case the threshold is determined by the Meissner receptor system. This increase in sensitivity is less pronounced (about 10 dB) and less sharply tuned for the other sites. Finally, when the contact of the vibrating surface to the skin is at a minimum, the vibration threshold has the same displacement value (about 3 microns) over the whole frequency region independent of the site of stimulation and whether or not a rigid surround is present.

Inaccuracies in the measurement of auditory brainstem response data in normal hearing and cochlear hearing loss.

In a test-retest experiment inaccuracies in the measurement of the peak latencies and threshold of the auditory brainstem response were determined for a group with normal hearing and for a group with cochlear hearing loss. The inaccuracy of the auditory brainstem response threshold is less than 4 dB in both groups. The inaccuracy in latency was measured as a function of stimulation level. In both groups the latency inaccuracy of peak V varies from 0.1 ms at levels well above threshold to 0.2 ms near the response threshold. Analysis of variance showed that in subjects with normal hearing the intra- and interindividual variabilities of the peak V latencies contribute about equally to the total variance at all stimulation levels. The implications that these findings have for the determination of the horizontal shift of the latency-intensity curve are discussed.

Envelope detection of amplitude-modulated high-frequency sinusoidal signals by skin mechanoreceptors.

High-frequency (1000-2000 Hz) sinusoidal vibrations of the skin, which are normally imperceptible, induce distinct sensations when amplitude modulation is applied in the frequency region around 200 Hz. This phenomenon appears to be initiated in the mechanoreceptor, as a result of rectification in the mechanoelectrical transduction process. The curve for sensitivity to modulation frequency resembles the frequency-sensitivity curve of the Pacini receptor system. The low-frequency slope is flatter than that of comparable psychophysical frequency-threshold curves for sinusoidal stimuli. This finding suggests that mechanical filtering (in the capsule of the Pacinian corpuscle and the surrounding skin tissue) contributes to the detection threshold. The characteristics of such a mechanical filter are estimated.

Investigations of the residual hearing capacity of severely hearing-impaired and profoundly deaf subjects.

Speech reception functions (maximum discrimination score for phonemes, speech reception threshold) and auditory functions (pure-tone audiogram, difference limens for frequency and intensity, temporal modulation transfer function, critical ratio and temporal integration) have been investigated in a group of severely hearing-impaired and deaf subjects (median Fletcher index: 80 dB), for different frequency regions (250, 1 000 and 2 000/4 000 Hz). The correlations between the different functions were calculated on the basis of characteristic numbers, derived from the originally measured functions, in the indicated frequency regions. The residual hearing capacities could be described best with two factors, one reflecting the distortion term in the speech reception threshold and the other representing the frequency discrimination for high-frequency tones. It was found that residual hearing capacities are present, at least up to a Fletcher index of 105 dB.

Reliability of auditory function tests in severely hearing-impaired and deaf subjects.

The test-retest variability of a series of auditory functions has been investigated in a group of severely hearing-impaired and deaf subjects (64 ears, median Fletcher index: 80 dB) and in a group of 10 controls with normal hearing. An adaptive forced-choice procedure was used for both groups. The functions were: tone audiogram, difference limen for intensity, difference limen for frequency, modulation transfer function and critical ratio. In spite of sometimes strongly deviating function values within the hearing-impaired group, the test-retest variability of the two groups was found to be of the same order of magnitude, except for the tone audiogram where the variability in the hearing-impaired group was twice that for the control group.

Vibrotactile threshold for hairy skin and its transformation into equivalent bone-conduction loss for the mastoid.

Vibrotactile thresholds for the glabrous skin of the hand and for the hairy skin of the arm are investigated as a function of frequency in the range from 40 to 2 000 Hz, using a heavy vibrator. These thresholds are expressed as equivalent bone-conduction loss and compared with vibrotactile thresholds determined with bone vibrators on the arm and mastoid for normally hearing and severely hearing-impaired subjects. The results are used to predict the vibrotactile threshold of the hairy skin of the mastoid under conditions of severe hearing impairment and deafness. The frequency characteristics of a number of vibrators are discussed with respect to their suitability for skin stimulation.