Rapid Word-Learning in Normal-Hearing and Hearing-Impaired Children: Effects of Age, Receptive Vocabulary, and High-Frequency Amplification

OBJECTIVE

This study examined rapid word-learning in 5- to 14-year-old children with normal and impaired hearing. The effects of age and receptive vocabulary were examined as well as those of high-frequency amplification. Novel words were low-pass filtered at 4 kHz (typical of current amplification devices) and at 9 kHz. It was hypothesized that (1) the children with normal hearing would learn more words than the children with hearing loss, (2) word-learning would increase with age and receptive vocabulary for both groups, and (3) both groups would benefit from a broader frequency bandwidth.

DESIGN

Sixty children with normal hearing and 37 children with moderate sensorineural hearing losses participated in this study. Each child viewed a 4-minute animated slideshow containing 8 nonsense words created using the 24 English consonant phonemes (3 consonants per word). Each word was repeated 3 times. Half of the 8 words were low-pass filtered at 4 kHz and half were filtered at 9 kHz. After viewing the story twice, each child was asked to identify the words from among pictures in the slide show. Before testing, a measure of current receptive vocabulary was obtained using the Peabody Picture Vocabulary Test (PPVT-III).

RESULTS

The PPVT-III scores of the hearing-impaired children were consistently poorer than those of the normal-hearing children across the age range tested. A similar pattern of results was observed for word-learning in that the performance of the hearing-impaired children was significantly poorer than that of the normal-hearing children. Further analysis of the PPVT and word-learning scores suggested that although word-learning was reduced in the hearing-impaired children, their performance was consistent with their receptive vocabularies. Additionally, no correlation was found between overall performance and the age of identification, age of amplification, or years of amplification in the children with hearing loss. Results also revealed a small increase in performance for both groups in the extended bandwidth condition but the difference was not significant at the traditional p = 0.05 level.

CONCLUSIONS

The ability to learn words rapidly appears to be poorer in children with hearing loss over a wide range of ages. These results coincide with the consistently poorer receptive vocabularies for these children. Neither the word-learning or receptive-vocabulary measures were related to the amplification histories of these children. Finally, providing an extended high-frequency bandwidth did not significantly improve rapid word-learning for either group with these stimuli.

Hearing loss in children and adults: audiometric configuration, asymmetry, and progression

OBJECTIVE

The purpose of this study was to characterize the sensorineural hearing losses of a group of children and adults along three parameters important to the hearing instrument fitting process: 1) audiometric configuration, 2) asymmetry of loss between ears, and 3) progression of loss over several years.

DESIGN

Audiograms for 248 60- and 61-yr-old adults and 227 6-yr-old children were obtained from the audiological database at Boys Town National Research Hospital. Based on right-ear air-conduction thresholds, the configurations were assigned to one of six categories: sloping, rising, flat, u-shaped, tent-shaped, and other. Left- and right-ear thresholds were compared to determine asymmetry of loss. Progression of loss was evaluated for 132 children for whom additional audiograms over an 8-yr period were available.

RESULTS

In general, the children's hearing losses were more evenly distributed across configuration categories while most of the adult's audiograms were sloping or u-shaped in configuration. The variability of loss at each frequency was greater for the children than the adults for all configuration categories. Asymmetrical losses were more common and the degree of asymmetry at each frequency was more extensive among the children than the adults. A small number of children showed either improved or deteriorated hearing levels over time. In those children for whom progressive hearing loss occurred, no frequency was more vulnerable than another.

CONCLUSIONS

The results of the present study suggest that substantial differences in audiological characteristics exist between children and adults. Implications for amplification include the development of appropriate fitting protocols for unusual audiometric configurations as well as protocols for binaural amplification in cases of asymmetric hearing losses.

Effect of stimulus bandwidth on the perception of /s/ in normal- and hearing-impaired children and adults

Recent studies with adults have suggested that amplification at 4 kHz and above fails to improve speech recognition and may even degrade performance when high-frequency thresholds exceed 50-60 dB HL. This study examined the extent to which high frequencies can provide useful information for fricative perception for normal-hearing and hearing-impaired children and adults. Eighty subjects (20 per group) participated. Nonsense syllables containing the phonemes /s/, /f/, and /O/, produced by a male, female, and child talker, were low-pass filtered at 2, 3, 4, 5, 6, and 9 kHz. Frequency shaping was provided for the hearing-impaired subjects only. Results revealed significant differences in recognition between the four groups of subjects. Specifically, both groups of children performed more poorly than their adult counterparts at similar bandwidths. Likewise, both hearing-impaired groups performed more poorly than their normal-hearing counterparts. In addition, significant talker effects for /s/ were observed. For the male talker, optimum performance was reached at a bandwidth of approximately 4-5 kHz, whereas optimum performance for the female and child talkers did not occur until a bandwidth of 9 kHz.

Perception of voiceless fricatives by normal-hearing and hearing-impaired children and adults

This study examined the perceptual-weighting strategies and performance-audibility functions of 11 moderately hearing-impaired (HI) children, 11 age-matched normal-hearing (NH) children, 11 moderately HI adults, and 11 NH adults. The purpose was to (a) determine the perceptual-weighting strategies of HI children relative to the other groups and (b) determine the audibility required by each group to achieve a criterion level of performance. Stimuli were 4 nonsense syllables (see text). The vowel, transition, and fricative segments of each nonsense syllable were identified along the temporal domain, and each segment was amplified randomly within each syllable during presentation. Point-biserial correlation coefficients were calculated using the amplitude variation of each segment and the correct and incorrect responses for the corresponding syllable. Results showed that for /see text/ and /see text/, all four groups heavily weighted the fricative segments during perception, whereas the vowel and transition segments received little or no weight. For /see text/, relatively low weights were given to each segment by all four groups. For /see text/, the NH children and adults weighted the transition segment more so than the vowel and fricative segments, whereas the HI children and adults weighted all three segments equally low. Performance-audibility functions of the fricative segments of /see text/ and /see text/ were constructed for each group. In general, maximum performance for each group was reached at lower audibility levels for /see text/ than for /see text/ and steeper functions were observed for the HI groups relative to the NH groups. A decision theory approach was used to confirm the audibility required by each group to achieve a > or =90% level of performance. Results showed both hearing sensitivity and age effects. The HI listeners required lower levels of audibility than the NH listeners to achieve similar levels of performance. Likewise, the adult listeners required lower levels of audibility than the children, although this difference was more substantial for the NH listeners than for the HI listeners.

The relation between stimulus context, speech audibility, and perception for normal-hearing and hearing-impaired children

In this study, the influence of stimulus context and audibility on sentence recognition was assessed in 60 normal-hearing children, 23 hearing-impaired children, and 20 normal-hearing adults. Performance-intensity (PI) functions were obtained for 60 semantically correct and 60 semantically anomalous sentences. For each participant, an audibility index (AI) was calculated at each presentation level, and a logistic function was fitted to rau-transformed percent-correct values to estimate the SPL and AI required to achieve 70% performance. For both types of sentences, there was a systematic age-related shift in the PI functions, suggesting that young children require a higher AI to achieve performance equivalent to that of adults. Improvement in performance with the addition of semantic context was statistically significant only for the normal-hearing 5-year-olds and adults. Data from the hearing-impaired children showed age-related trends that were similar to those of the normal-hearing children, with the majority of individual data falling within the 5th and 95th percentile of normal. The implications of these findings in terms of hearing-aid fitting strategies for young children are discussed.

Effect of earmold fit on predicted real ear SPL using a real ear to coupler difference procedure

OBJECTIVES

The goal of Experiment I was to quantify the SPL entering the ear canal via a secondary pathway created by a vent in the earmold and/or a slit leak around the earmold. The goal of Experiment II was to determine the validity of a real ear to coupler difference (RECD) procedure under conditions that are likely to produce errors (e.g., when hearing aid gain in the low frequencies is minimal and large negative RECD values occur as a result of venting or a loosely fitting earmold).

DESIGN

In Experiment I, the SPL entering the ear via the secondary pathway was measured in 61 hearing-impaired children and 13 normal-hearing adults. In Experiment II, traditional probe microphone measures of real ear SPL were compared to the SPL predicted using the RECD procedure in five normal-hearing adults with loosely fitting earmolds.

RESULTS

Results of Experiment I indicated that sound entered the ear canal unattenuated at 250 and 500 Hz, regardless of earmold fit, vent size, or subject age. In Experiment II, the largest differences between traditional probe microphone measures of SPL and predicted measures were noted when hearing aid gain was 0 dB and large negative RECD values were present. When hearing aid gain was minimal and the RECD was in the -10 to -22 dB range, predicted values underestimated the real ear SPL by an average of 14 dB.

CONCLUSIONS

Although the results of this study apply only to a limited range of conditions found in clinical practice, in those cases, the errors may influence clinical decisions about the type of hearing aid fitted and the amount of gain provided. Potential solutions to this problem are discussed.

Bandwidth effects on children's perception of the inflectional morpheme /s/: acoustical measurements, auditory detection, and clarity rating

The goal of this study was to examine developmental effects in auditory perception of word-final /s/ in inflectional morpheme contexts as a function of high-frequency (HF) bandwidth. Such developmental effects may support the use of hearing aids with extended bandwidths in young children with impaired hearing. The first part of the study consisted of acoustical measurements on word-initial /s/ and inflectional morpheme /s/ in sentences recorded from a male speaker. For this speaker, recordings of inflectional morpheme /s/ on average were approximately 50 ms shorter and about 5 dB lower in level than word-initial /s/ sounds. They also had a lower spectral center of gravity, but not a higher coefficient of kurtosis. The second part consisted of measurements of psychometric functions relating detection of the inflectional morpheme /s/ sounds to HF bandwidth in normally hearing 5-, 7-, and 10-year-old children and adults. In speech-shaped noise, significant main effects of age were found for detection as a function of bandwidth for both the 30- and 10-dB signal-to-noise ratio (SNR) condition, although there was no interaction between age and SNR condition. The third part consisted of subjective clarity rating as a function of HF bandwidth for the same speech stimuli used in the second part. No differences were found between age groups in the shape of the clarity rating functions, but differences were found in the rating variance. No systematic effects of the spectral composition of inflectional morpheme /s/ sounds on either detection or clarity rating were found. The higher detection thresholds and larger clarity rating variances for the youngest participants support the use of extended high-frequency bandwidths for young children with impaired hearing. The extent to which the potential benefit of extended bandwidths is affected by hearing impairment in this population, however, deserves further investigation.

Recognition performance for four combinations of FM system and hearing aid microphone signals in adverse listening conditions

OBJECTIVE

Children with moderate to severe hearing loss routinely use personal frequency modulated (FM) systems in the classroom to improve the signal to noise ratio of teacher-directed speech with notable success. Attention is now being given to the ability of these children to hear other students via the hearing aid (HA) microphone while using an FM system. As a result, a variety of FM system and HA microphone combinations have been recommended for classroom use. To date, there are no studies regarding the efficacy of these FM/HA combinations. The purpose of this study was to evaluate recognition performance using four FM/HA combinations and to characterize that performance for stimuli received primarily through FM system and HA microphone transmission.

DESIGN

Recognition performance for FM system and HA microphone signals was evaluated for two symmetrical and two asymmetrical FM/HA combinations using two commercially available FM systems (one conventional and one FM-precedence circuit). Eleven children (ages 9 to 12) with moderate to severe sensorineural hearing loss and eight children (ages 10 to 11) with normal hearing served as subjects. The two symmetrical FM/HA combinations included: 1) binaural FM system and HA microphone input using the conventional FM system, and 2) binaural FM and HA input using the FM-precedence circuit. The conventional FM system was used for the two asymmetrical combinations and included: 1) binaural FM input and monaural HA input, and 2) FM input to one ear and HA input to the other. Stimuli were 33 consonants presented in the form of nonsense syllables. The stimuli were presented through three loudspeakers representing a teacher and two fellow students in a classroom environment. Speech shaped noise was presented through two additional loudspeakers.

RESULTS

In general, no statistically significant differences in recognition performance were found between any of the FM/HA combinations. Mean recognition scores for HA microphone transmission (55%) were significantly poorer than those for FM system transmission (75%). As expected, initial consonants were more easily recognized than final consonants via FM system and HA microphone transmission. However, voiceless consonants were more easily recognized than voiced consonants via HA microphone transmission, which was not predicted on the basis of previous research.

CONCLUSIONS

These results suggest that a certain amount of flexibility is present when choosing an FM/HA combination. However, recognition performance via the HA microphones was consistently poorer than performance via FM transmission. Because relevant material also originates from fellow students (e.g., answering teacher-directed questions), input via the HAs is often as important as information originating from the teacher. The results suggest that attempts to improve performance for signals transmitted through the HA microphones in a classroom setting would benefit children with hearing loss.

Subjective effects of peak clipping and compression limiting in normal and hearing-impaired children and adults

Despite many advances in hearing-aid signal processing, compression limiting and peak clipping are still used. To date, perceptual studies have been conducted only with adults. The current study was designed to investigate the clarity of peak-clipped and compressed speech for both adults and children. Subjects were 30 normal-hearing and 30 hearing-impaired individuals in three age ranges (7-9, 10-12, and 16-50 years). Stimuli were processed at 60, 70, 75, and 80 dB SPL using peak clipping and at 80 dB SPL using compression limiting. Paired-comparison measures were used to assess the clarity of sentences, and a signal-to-distortion ratio (SDR) based on a measure of coherence between input and output was computed for each condition. For the peak-clipping conditions, there was a decrease in perceived clarity as the input increased from 60 to 80 dB SPL. This perceptual continuum was most apparent for the normal-hearing adults. The normal-hearing 10-12 year olds and the hearing-impaired adults showed a similar, but less pronounced, pattern. In contrast, the remaining three subject groups showed minimal differences in perceived clarity across conditions. Surprisingly, only the two oldest normal-hearing groups showed a clear preference for compression limiting over peak clipping at the highest input level, and only their results were consistent with the pattern of coherence across stimuli. Judgments of clarity by the normal-hearing subjects correlated best with the SDR in the 500-2000-Hz range, while clarity judgments of the hearing-impaired subjects correlated best with the SDR below 1000 Hz.

Hearing aid outcome measures for children

The provision of appropriate amplification for a young hearing-impaired child is critical as the aided speech signal will be used for the development of speech and language. The purpose of this paper is to provide an overview of the complex issues surrounding the documentation of hearing aid outcomes in the pediatric population. In the first two sections of the paper, the unique characteristics and needs of the pediatric population and factors complicating the measurement of outcome are described in detail. The third section provides a review of literature on existing outcome measures for children and the fourth section is devoted to a discussion of alternative approaches. The final section is an overview of clinical and research needs in the area of hearing aid outcome measures for children.

A comparison of threshold-based fitting strategies for nonlinear hearing aids

OBJECTIVE

In recent years, wide dynamic range compression (WDRC) has been used with increasing success. To optimize the fit with this type of hearing aid circuitry, subjective measures of loudness growth often are used. Unfortunately, these type of measures cannot be performed with infants, young children, and some elderly individuals. The primary purpose of this study was to compare the fitting recommendations of two recently described threshold-based procedures for fitting nonlinear hearing aids (DSL 4.0 and FIG6) to the use gain settings of satisfied adult hearing aid users for whom the fitting was based on subjective measures of loudness growth. Because it cannot be assumed that the use settings for adults will be appropriate for young children, a secondary goal was to quantify the audibility of speech at the use settings derived from loudness growth measures.

DESIGN

Forty-nine adult hearing aid users with mild to severe sensorineural hearing loss participated in this study. For all subjects, loudness growth measures were used to optimize the fit of a 2-channel WDRC hearing aid. The use gain at 50 and 80 dB SPL was compared with the gain recommended by DSL, FIG6, and the manufacturer's threshold-based fitting algorithm.

RESULTS

In general, both DSL and FIG6 prescribed more gain than actually was used by these hearing aid wearers. These discrepancies increased as a function of frequency, and differences in excess of 20 dB were observed in some cases. The manufacturer's algorithm provided a closer approximation to the use gain than either DSL or FIG6. Utilizing these use gain values, an Aided Audibility Index (AAI) was calculated for soft, average, and loud speech across four degrees of hearing loss, ranging from mild to severe (12 conditions). Transfer functions for continuous discourse and nonsense syllables were applied to yield estimated intelligibility scores. For the higher context speech materials, estimated intelligibility was > or = 85% for nine of the 12 conditions. For low-context speech materials, estimated intelligibility was > or = 85% for only three of the 12 conditions.

CONCLUSIONS

Results suggest that the gain recommendations provided by both DSL and FIG6 exceeded the gain actually used by the adult hearing-impaired subjects in this study. Gain recommendations from the manufacturer's algorithm provided a closer approximation to the use gain values of these subjects. These findings suggest that, for adult hearing aid users who cannot perform loudness judgments reliably, the manufacturer's algorithm would be expected to provide a closer approximation to loudness-based use gain values than either DSL or FIG6. However, AAI calculations revealed that the gain recommendations from this algorithm produce adequate audibility of speech only if one assumes linguistic competence. When AAI values are transformed to predict the intelligibility of low-context speech materials, it appears that the degree of audibility may not be appropriate for prelingually hearing-impaired children with more than a moderate hearing loss.

Measures of hearing aid gain for real speech

OBJECTIVE

Non-speech stimuli typically are used to estimate the electroacoustic characteristics of a hearing aid. At present, there is no consensus as to what type of input stimulus will best represent the gain for real speech. The purpose of this study was to measure hearing aid gain using continuous discourse and to compare these values with gain measured with five different types of simpler stimuli.

DESIGN

Hearing aid gain as a function of frequency was measured in a 2 cm3 coupler for 20 commercially available hearing aids. Circuitry included features such as linear peak clipping, compression limiting, 1-, 2-, and 3-channel full dynamic range compression, and adaptive compression. Input stimuli were a) 15 sec of continuous discourse, b) swept pure tones (SPTs), c) speech weighted composite noise (SWCN), d) simulated speech, e) speech weighted warble tones, and f) speech modulated noise. Input levels ranged from 50 to 80 dB SPL.

RESULTS

In general, both SPTs and SWCN tended to underestimate the high-frequency gain for real speech. These discrepancies increased as a function of input intensity. On average, the SPT produced the greatest departure from the gain for real speech, producing differences for individual hearing aids as large as 10 to 14 dB. An analysis by circuit type revealed that discrepancies most likely occurred when a hearing aid was operating in a nonlinear mode. Of the five non-speech stimuli used, speech modulated noise and simulated speech seemed to provide the closest approximation to the gain measured with continuous discourse.

CONCLUSIONS

When a hearing aid is operating in a nonlinear mode, non-speech stimuli will tend to underestimate the gain for real speech, particularly in the high frequencies. Under some conditions, these discrepancies may impact clinical decisions during the hearing aid fitting process. Additional studies are needed to elucidate the factors that contribute to the gain discrepancies observed in this study and to explore the use of additional stimuli (including short speech samples), which may result in better predictions of the gain for speech.

Longitudinal study of FM system use in nonacademic settings: effects on language development

OBJECTIVE

The overall objective of the present study was to assess the efficacy of FM system use in the home setting for a group of preschool children with mild-to-severe sensorineural hearing loss. Changes in language acquisition were monitored and compared with similar measures from a group of children who used hearing aids. Secondarily, the perceived benefits and practical problems associated with FM system use across a variety of nonacademic situations were documented.

DESIGN

Ten children with mild-to-severe sensorineural hearing loss participated in a 2-yr longitudinal study investigating the efficacy of FM system use in the home setting. The subjects were divided into two groups: one group was instructed to use FM systems at home as often as possible while the other used only their personal hearing aids. Changes in language acquisition were monitored in both groups. Subjective benefit and the practical problems associated with use of FM systems outside of traditional academic environments were monitored via daily use logs, a weekly observation inventory, and a situational listening profile.

RESULTS

The majority of children in both groups improved in all measures of language development over the study interval. Although there were relatively large individual differences in performance for some measures, no statistically significant differences between the FM and hearing aid users were found. However, some children in the FM group made unusually large gains in some aspects of language development over the study interval. In addition, both parents and children reported benefits of FM system use in specific listening situations. Throughout the 2-yr study, a number of practical problems associated with FM system use outside the classroom were identified.

CONCLUSIONS

Formal language measures did not yield significant differences between the FM and HA groups, but some subjects had rates of language acquisition which suggested that FM system use may be beneficial in selected cases. In addition, subjective reports of FM system benefit suggest that appropriate use of the device may facilitate effective communication in a variety of listening situations. Although recent advances in FM system design may minimize some of the factors that reportedly restricted consistent FM use in this study, the complexities associated with the modes of operation and problems with FM interference remain issues that require consistent audiologic monitoring of FM system use in nonacademic environments.

The perception of amplified speech by listeners with hearing loss: acoustic correlates

Audibility-based approaches to hearing-aid selection generally have focused on the long-term average speech spectrum (LTASS). Advances in amplification technology (e.g., multiband signal processing, level-dependent frequency shaping, full dynamic range compression, adaptive compression) make it difficult to predict the audibility of short-term components of speech from the amplified LTASS. This study was designed to quantify the audibility of a specific phonemes as processed by two different hearing-aid circuits (linear and full dynamic range compression), and to investigate the relation between audibility and performance on a nonsense syllable recognition task. Data were obtained from three subjects with moderate sensorineural hearing loss. Nine unvoiced consonants were presented in two vowel contexts (/i/ and /a/) in both the pre- and post-vocalic position at three intensities. While the performance on selected conditions appeared to vary by hearing-aid type, only one subject showed a statistically significant difference between the two hearing-aid systems. Acoustic analyses revealed a variety of spectral and temporal changes to the speech signal following processing. Estimates of audibility were based upon each subject's thresholds and an acoustic analysis of the amplified signal that varied across phonemes and consonant position. A signal detection approach was used to predict performance from a simple measure of audibility.

Case of recurrent, reversible, sudden sensorineural hearing loss in a child

This paper describes audiologic, electrophysiologic, and medical test results for a now 10-year-old girl who has had 45 episodes of reversible, sudden sensorineural hearing loss over the last 8 years. Episodes have lasted from 6 to 72 hours and often have been accompanied by a mild illness. Acoustic immittance measures have been consistent with normal middle-ear function with the exception of absent ipsilateral and contralateral acoustic reflexes. Mechanically evoked perioral reflex activity was markedly asymmetric following lower lip stimulation. The asymmetry of R1 activation between right and left side lower lip inputs raises questions about the integrity of central connections within the brain stem, including internuncial pathways coursing between trigeminal sensory relay nuclei and the facial motor nucleus. An electrocochleographic evaluation revealed cochlear microphonic but absent or markedly abnormal whole nerve action potentials. Auditory brainstem responses (ABR) have been either absent or poorly formed and significantly delayed, regardless of hearing sensitivity. Middle and late auditory evoked potentials were essentially normal. Both transient-evoked and distortion-product otoacoustic emissions were present regardless of peripheral auditory sensitivity. All medical tests have been essentially normal. Although no definitive diagnosis has been reached, beta blockers have been used with some success. Taken together, these data document a very unusual case of fluctuating hearing loss. The electrocochleographic and otoacoustic emission data suggest that the outer hair cells are functioning normally and that the loss is not cochlear in origin.(ABSTRACT TRUNCATED AT 250 WORDS)

Preferred hearing-aid frequency responses in simulated listening environments

This study was designed to determine if an adaptive strategy could be used to select frequency/gain characteristics that would be considered appropriate across a variety of listening environments. In Experiment I, the test-retest reliability of the paired comparison procedure used in Experiment II was assessed in quiet for nine subjects and in speech noise for six subjects. For both conditions, results revealed mean standard deviations of < 3 dB from 200 through 4000 Hz. In Experiment II, four subjects selected frequency/gain characteristics for five different listening environments (quiet, speech noise, quiet conference room, reverberant lecture hall, and reverberant lecture hall in noise). In general, subjects did not tend to select different frequency/gain characteristics across the five simulated environments used in this study. When differences in frequency responses were observed, they tended to be alterations in overall gain rather than changes in relative frequency response. Findings support additional evaluation in more diverse listening environments, possibly with systems that incorporate nonlinear signal processing.

Long-term and short-term characteristics of speech: implications for hearing aid selection for young children

This study examined the effects of distance and postural position of both parents and children on the long-term and short-term spectral characteristics of speech produced by the parents. Thirty children (ages 2 months to 3 1/2 years) and their parents (30 mothers and 15 fathers) participated. Third-octave band and overall levels of the long-term average speech spectrum (LTASS) for each speech sample were analyzed in three postural positions and a 1-meter reference condition for each age category. Short-term spectral characteristics of three phonemes (/s/, /integral of/, /t integral of/) also were analyzed. Results show that typical levels at the input to a child's hearing aid microphone may be as much as 20 dB higher than those found in face-to-face adult conversation. Furthermore, the spectral shape may deviate substantially from an idealized version of the LTASS. Results of the short-term analysis reveal that the peak levels of the three selected phonemes often exceed the LTASS by more than the 12 dB that is often quoted to represent the 1% rms levels of speech in relation to the long-term average. Implications of these results for specific hearing losses are discussed.

Real ear to 6-cm3 coupler differences in young children

Real-ear sound pressure levels under supra-aural earphones were measured for a group of young children (9 months to 7 years) and adults. Pure-tone signals were presented at nine test frequencies from 250 to 6000 Hz, and real ear to 6-cm3 coupler differences were computed for each frequency. Results suggest that, by 2 years of age, average real ear to 6-cm3 coupler differences are similar for adults and children. The intersubject variability for all groups supports the need for real-ear threshold measures on an individual basis in cases where the ability to amplify the speech spectrum to a level that is audible across the frequency range is in question.

Localization ability in infants with simulated unilateral hearing loss

This study investigated the feasibility of using a localization task to rule out unilateral hearing loss in infants. Fourcorner localization ability was assessed in 29 normal-hearing infants (9-20 mo) using four different test stimuli. In these same infants, a mild unilateral hearing loss was simulated by occlusion of the external auditory canal and the test sequence was repeated. Analysis of front-back, right-left, and combined errors for each of the test stimuli revealed that this type of task may allow detection of unilateral hearing loss as slight as 25 dB HL.

Evaluation and assessment of FM systems

In the past, frequency modulated (FM) systems were recommended for use only in educational settings for children with severe or profound hearing losses. Recent studies, however, have suggested that FM systems may be appropriate in nonacademic settings and also may benefit children with minimal hearing loss. In addition to the more widespread application of FM use, advances in amplification technology have provided audiologists with a variety of devices and coupling options, resulting in more variables to evaluate in the fitting process. There are three commonly used methods of evaluating FM systems: functional gain measures, probe tube microphone measures, and coupler measures. This paper is intended to provide the audiologist working with FM systems with an overview of the complexities involved in selecting and setting FM systems and the benefits and limitations of each evaluation method. Each evaluation method is examined in view of how well it answers three basic questions related to frequency response, maximum output, and distortion in FM systems. Finally, other issues which may impact on the selection of an FM system for a given individual are discussed.

Relevant factors in the identification of hearing loss

This study examined factors which may affect early identification of hearing loss. The medical records of 123 children with educationally significant hearing impairment were examined. Information about each child's degree and type of hearing loss, etiology, referral source, birth and medical history, additional handicaps, age of suspicion of loss, mode of identification, age of identification, and age at which aided was entered into a database for further analysis. The age range for identification was 7 weeks to 10 yr, with a median age of 2.1 yr. Children with a greater degree of hearing loss, an additional handicap, additional medical conditions, or an etiology strongly associated with hearing loss were identified earlier than those without these factors. Unexpectedly, children with a history of middle ear dysfunction were identified no later than those without, and children with a positive family history of hearing loss were identified later than those with a negative family history. These results agree with other studies which show that, in general, children are identified and habilitated at a later age than that recommended by both the American Speech-Language-Hearing Association Committee and the Joint Committee on Infant Hearing.

The effect of reference microphone placement on sound pressure levels at an ear level hearing aid microphone

The present study was designed to investigate the effects of reference microphone location on probe tube microphone measures of hearing aid response. The reference microphone of a clinical probe tube microphone system was located either at a position on the cheek (position A) or in close proximity to the microphone of an ear level hearing aid (position B). With sound pressure level (SPL) held constant at the reference microphone, the SPL at the position of the hearing aid microphone was measured at 14 test frequencies using a 1/8-inch condenser microphone. Measures were obtained on ten male and ten female subjects. Results indicated large frequency-dependent deviations in SPL at the hearing aid microphone, compared to that measured at the reference microphone, when the reference microphone was at position A. In the 1200 to 2000 Hz range, the SPL at the hearing aid microphone was as much as 9.5 dB higher than at the reference microphone. There were no large frequency-dependent variations with the reference microphone in position B, but the SPL at the hearing aid microphone location was approximately 3 dB higher than at the reference microphone. Results suggest that estimates of hearing aid output can be affected markedly by the reference microphone location. Clinical implications of the impact of reference microphone location on probe microphone measures of hearing aid gain and saturation sound pressure levels are discussed.

Normative thresholds in the 8- to 20-kHz range as a function of age

Using a prototype high-frequency audiometer, auditory thresholds in the 8- to 20-kHz range were obtained from 240 subjects ranging in age from 10-60 years. These measurements were obtained in interest of developing a normative database for frequencies above 8 kHz, and to evaluate intersubject variability as a function of age. An analysis of variance (ANOVA) revealed significant effects of frequency, age, and sex, and a significant frequency-by-age interaction. The largest changes in sensitivity with age occurred between 40 to 59 years. Below approximately 15 kHz, the intersubject variability of threshold estimates increased as a function of both age and frequency. Further analysis revealed that the age-related changes in variability were related to absolute thresholds rather than to age per se. When data are converted to dB HL (relative to the youngest group tested), the region of maximum hearing loss shifts to lower frequencies with increasing age, and threshold shifts with age are greatest in the 13- to 17-kHz range.

Probe-tube microphone measures of ear-canal sound pressure levels in infants and children

Probe-tube microphone measures of ear-canal sound-pressure levels were obtained for 31 children under 5 years of age. These data were compared to similar measures from a group of 21 adults. The intrasubject variability was smallest for the frequency range from 750 to 3000 Hz and at no frequency did the mean standard deviation exceed 3 dB. Real ear to coupler differences for the children showed the same pattern as a function of frequency as for adults but were significantly larger. A systematic decrease in real ear to coupler differences was observed with increasing age between 1000 and 3000 Hz. An estimate of ear-canal volume did not appear to be a clinically useful predictor of real ear to coupler differences.

High-frequency audiometry: test reliability and procedural considerations

This study compared the reliability of a recently developed high-frequency audiometer (HFA) [Stevens et al., J. Acoust. Soc. Am. 81, 470-484 (1987)] with a less complicated system that uses supraaural earphones (Koss system). The new approach permits calibration on an individual basis, making it possible to express thresholds at high frequencies in dB SPL. Data obtained from 50 normal-hearing subjects, ranging in age from 10-60 years, were used to evaluate the effects on reliability of threshold variance, earpiece/earphone fitting variance, and the variance associated with the HFA calibration process. Without earpiece/earphone replacement, the reliability of thresholds for the two systems is similar. With replacement, the HFA showed poorer reliability than the Koss system above 11 kHz, largely due to errors in estimating the calibration function. HFA reliability is greater for subjects with valid calibration functions over the entire frequency range. When average correction factors are applied to the Koss data in an effort to convert threshold estimates to dB SPL, individual transfer functions are not represented accurately. Thus the benefit of being able to express thresholds at high frequencies in dB SPL must be weighed against the additional source of variability introduced by the HFA calibration process.

Probe-tube microphone measures in hearing-impaired children and adults

This study was designed to investigate the reliability of real-ear measurements of sound pressure level (SPL) and to compare these values with two coupler measures of SPL. A commercially available probe tube microphone system was used to measure real ear SPL in both children and adults. Test-retest reliability decreased as a function of frequency for both groups and, in general, was slightly poorer for the children. For both groups, coupler to real ear differences were larger for the 2 cm3 coupler than for the reduced volume coupler; however, no significant differences were observed between groups. In addition, a measure of ear canal volume was not found to be a good predictor of coupler to real ear discrepancies.

Loudness discomfort levels in children

Loudness discomfort levels (LDLs) traditionally have been used to set the saturation sound pressure level (SSPL) or maximum output of a hearing aid. Many procedures have been used to obtain LDLs for adults; however, no systematic study has been conducted to determine if LDLs could be obtained reliably for children. In the present study, LDLs were measured on 20 hearing-impaired children aged 7 to 14 years using a modification of a procedure described by Hawkins, Walden, Montgomery, and Prosek (Ear Hear 1987; 8: 162-169). Test-retest reliability measures were obtained for 8 of the 20 children, and this modified procedure was found to provide reasonably reliable results. Data from the group of 20 children also were compared with similar data obtained from 20 hearing-impaired adults. These results revealed no systematic differences in LDLs between the two groups, suggesting no a priori reason to limit the maximum output of a hearing aid for a child in this age range below the levels that are appropriate for adults. Poor correlation between LDLs and hearing levels for both age groups indicate a need for determining LDLs on an individual basis whenever possible.

The reliability of auditory thresholds in the 8- to 20-kHz range using a prototype audiometer

This study was designed to evaluate both intra- and intertester reliability of auditory thresholds in the 8- to 20-kHz range using a recently developed high-frequency audiometer [Stevens et al., J. Acoust. Soc. Am. 81, 470-484 (1987)]. With this device, signals from a high-frequency transducer are introduced into the ear canal via a plastic tube. A calibration function is calculated for each ear and used to estimate the sound-pressure level (SPL) at the tympanic membrane. Twenty normal-hearing listeners were tested four times, twice by each of two examiners. In the higher frequencies, accurate calibration functions could not be obtained for many subjects; in these cases, values extrapolated from lower frequencies were used to estimate SPL. Findings reveal that the standard error of measurement for both intra- and intertester measures increases as a function of frequency. Intertester variability was only slightly higher than intratester variability. In most cases, variability of threshold estimates in dB SPL was higher than that observed for the uncorrected attenuator settings. Exclusion of extrapolated values improved reliability substantially.

Growth of masking as a measure of response growth in hearing-impaired listeners

Growth-of-masking functions were obtained from 19 normal and 5 hearing-impaired listeners using a simultaneous-masking paradigm. When masker and probe frequency are identical, the slope of masking approximates 1.0 for both normal-hearing and impaired listeners. For masker frequencies less than or greater than probe frequency, the slopes for impaired listeners are shallower than those of normals. These findings are consistent with previously reported physiological data (single-fiber rate versus level and AP masking functions) for animals with induced cochlear lesions. Results are discussed in terms of a potential masking technique to estimate the growth of response in normal and impaired ears.

Relation between frequency selectivity and speech perception following glycerol-induced cochlear changes

Changes in auditory threshold, psychophysical tuning curves, and speech perception (in both quiet and noise) were monitored over a 3-hr period following the ingestion of glycerol. All listeners had sensorineural hearing loss secondary to Menière's disease. Findings were characterized by large intersubject variability and in general did not show a clear relation between changes in threshold, frequency resolution, and speech perception.

Speech perception ability and psychophysical tuning curves in hearing-impaired listeners

Performance-intensity functions for monosyllabic words were obtained as a function of signal-to-noise ratio for broadband and low-pass filtered noise. Subjects were 11 normal-hearing listeners and 13 hearing-impaired listeners with flat, moderate sensorineural hearing losses and good speech-discrimination ability (at least 86%) in quiet. In the broadband-noise condition, only small differences in speech perception were noted between the two groups. In low-pass noise, however, large differences in performance were observed. These findings were correlated with various aspects of psychophysical tuning curves (PTCs) obtained from the same individuals. Results of a multivariate analysis suggest that performance in broadband noise is correlated with filter bandwidth (Q10), while performance in low-pass noise is correlated with changes on the low-frequency side of the PTC.

An alternate method for determining functional gain of hearing aids

The functional gain of a hearing aid typically is determined by comparing aided and unaided behavioral thresholds. With this method, however, true gain may be underestimated in frequency regions of normal or near-normal hearing sensitivity (i.e., in cases of sloping, rising, or trough-shaped audiograms). Internal hearing-aid noise and/or amplified room noise imposes a lower limit on obtainable aided thresholds. In these cases, comparing aided and unaided acoustic-reflex thresholds may be a valuable clinical alternative to traditional means of determining real-ear gain. This study compared sound-field behavioral threshold and acoustic-reflex threshold estimates of functional gain for individuals with a variety of audiometric configurations. The sound-field behavioral threshold measurements were found to underestimate functional gain if unaided thresholds approached the normal hearing range. In regions of greater hearing loss, behavioral and acoustic-reflex estimates of functional gain were in good agreement.

Psychophysical tuning curves in normal-hearing listeners: test reliability and probe level effects

Psychophysical tuning curves (PTCs) were obtained from 19 normal-hearing listeners using a computer-controlled, modified Bekesy tracking procedure which employed a minimum standard error stopping rule. Using an objective procedure, 2000-Hz PTCs were quantified on five dimensions (Q10, tip-to-tail difference, d1-oct, low-frequency slope, and high-frequency slope), and the test-retest reliability of each measure was assessed. To provide a basis for future comparisons between normal-hearing and hearing-impaired listeners, these measures were obtained as a function of increasing probe level.

Temporal characteristics of the acoustic reflex

Temporal aspects of the acoustic reflex response were estimated for normally hearing subjects, subjects with noise-induced hearing loss and children with sensorineural hearing impairment. Onset latency and rise/fall times of admittance change were measured from the averaged responses (8 presentations) to tone bursts of 250 ms durations and 10 ms rise/fall time. Tone burst frequency was varied from 500 to 4 000 Hz. No differences between groups were observed for onset responses. Compared to the data from normally hearing subjects, the offset responses were slightly longer for subjects with noise-induced hearing loss and were considerably longer for hearing-impaired children. Due to the prolongation seen for noise-exposed subjects, it is difficult to interpret these data in terms of site of lesion. Still, the differences between hearing-impaired children and normal subjects suggest that acoustic reflex offset latency may be a useful screening device.

A calibration procedure for the assessment of thresholds above 8000 Hz

A technique is described to estimate the sound pressure level developed by a broad frequency response transducer at the tympanic membrane. Real-ear probe tube measurements near the tympanic membranes of 10 subjects were used to obtain frequency-dependent correction values for a custom-designed flat-plate coupler. These latter measures can be used for routine calibration of the transducer. Audiometric thresholds from 250 to 16000 Hz were obtained on 14 children (5-18 years). Threshold estimates were found to be comparable to previously reported values. Potential application and limitations of this technique are discussed.

Suppression effects for complex stimuli

A pulsation-threshold paradigm was used to evaluate suppression effects within complex stimuli. Stimuli were chosen to represent a continuum of spectral complexity ranging from sinusoids to complexes with one and two suppressors. Results indicate that suppression effects exist between the response to components of complex stimuli. For frequencies above a single suppressor, the suppression region is broad whereas below a suppressor, the region is relatively narrow. With two suppressors, little additivity of suppression is seen. When they are spaced closely, the response to the higher-frequency suppressor is reduced, presumably due to the low-frequency suppressor; this tends to diminish spectral contrasts despite considerable suppression at frequencies between the two suppressors. Enhancement of contrasts is greatest when suppressors are widely spaced and when both are presented at moderate levels (less than or equal to dB SPL). These data suggest that suppression may not play a simple role of "peak enhancement" in the peripheral coding of steady-state vowels.

Characteristics of hearing-impaired children in the public schools: part II--psychoeducational data

Psychoeducational data were collected from the files of 1,250 hearing-impaired children in Iowa public schools in an effort to identify educational and linguistic profiles related to different degrees of hearing loss. The files of most mildly to moderately hearing-impaired children do not reflect complete assessment of language, academic, or intellectual skills even when support services are being provided. The data reveal deficits that often are inconsistent with the reports and patterns of achievement on which the allocation of support services for hearing-impaired children have been based. The appropriateness of many of the assessment tools in use is questionable.

Characteristics of hearing-impaired children in the public schools: part I--demographic data

Survey questionnaires eliciting incidence information about degree and type of hearing loss, educational placement, use of amplification, and other demographic data were completed by audiologists in 13 of the 15 Area Education Agencies in Iowa in an attempt to describe the characteristics of hearing-impaired children in public-school settings. The information revealed patterns of hearing loss related to age and sex, use of hearing aids, and classroom placement that may be useful in planning support services for this population.

Some observations on simultaneous and nonsimultaneous masking

The interactions between phase, signal level, and interstimulus interval (delta t) were examined in the transition region between simultaneous and nonsimultaneous masking. Phase effects as large as 22 dB were observed in forward masking. These trends can be explained by considering the effects of phase upon the stimulus envelope.

Threshold and suprathreshold temporal integration function in normal and cochlear-impaired subjects

Auditory and acoustic reflex threshold temporal integration slopes were obtained for 20 normally hearing and 20 cochlear-impaired subjects. For both groups, the results at auditory threshold are similar to findings reported by other investigators. For the normally hearing subjects, suprathreshold slopes approximated those obtained at auditory threshold. The sensorineural group, however, demonstrated steeper slopes at suprathreshold levels than at auditory threshold. Therefore, at suprathreshold levels there were no significant differences between the slopes of the two groups. The implications of these findings are discussed.