Field W. Rickards

Clinical findings for a group of infants and young children with auditory neuropathy

OBJECTIVE To examine the prevalence of auditory neuropathy in a group of infants at risk for hearing impairment and to present an overview of the clinical findings for affected children. DESIGN Results for 20 subjects who showed repeatable cochlear microphonic potentials in the absence of click-evoked auditory brain stem responses are included in this study. Behavioral and steady state evoked potential thresholds were established in each case. Where possible, otoacoustic emission and speech perception results (unaided and aided) also were obtained. RESULTS One in 433 (0.23%) of the children in our series had evidence of auditory neuropathy. The audiometric findings for these subjects varied significantly, with behavioral thresholds ranging from normal to profound levels. Discrimination skills were also variable. Approximately half of the subjects showed little understanding, or even awareness, of speech inputs in both the unaided and aided conditions. There were, however, a number of children who could score at significant levels on speech discrimination tasks and who benefited from the provision of amplification. CONCLUSION The results suggest that auditory neuropathy is more common in the infant population than previously suspected. The effects of neuropathy on auditory function appear to be idiosyncratic, producing significant variations in both the detection and discrimination of auditory signals. As such, the management of children with this disorder must allow for individual differences.

A comparison of steady‐state evoked potentials to modulated tones in awake and sleeping humans

Steady-state evoked potential responses were measured to binaural amplitude-modulated (AM) and combined amplitude- and frequency-modulated (AM/FM) tones. For awake subjects, AM/FM tones produced larger amplitude responses than did AM tones. Awake and sleeping responses to 30-dB HL AM/FM tones were compared. Response amplitudes were lower during sleep and the extent to which they differed from awake amplitudes was dependent on both carrier and modulation frequencies. Background EEG noise at the stimulus modulation frequency was also reduced during sleep and varied with modulation frequency. A detection efficiency function was used to indicate the modulation frequencies likely to be most suitable for electrical estimation of behavioral threshold. In awake subjects, for all carrier frequencies tested, detection efficiency was highest at a modulation frequency of 45 Hz. In sleeping subjects, the modulation frequency regions of highest efficiency varied with carrier frequency. For carrier frequencies of 250 Hz, 500 Hz, and 1 kHz, the highest efficiencies were found in two modulation frequency regions centered on 45 and 90 Hz. For 2 and 4 kHz, the highest efficiencies were at modulation frequencies above 70 Hz. Sleep stage affected both response amplitude and background EEG noise in a manner that depended on modulation frequency. The results of this study suggest that, for sleeping subjects, modulation frequencies above 70 Hz may be best when using steady-state potentials for hearing threshold estimation.

The automated prediction of hearing thresholds in sleeping subjects using auditory steady-state evoked potentials

Objective To examine the relationship between auditory steady-state evoked potentials (SSEPs) and behavioral thresholds in sleeping subjects. Design 60 adults and children with hearing thresholds ranging from normal to profound were selected on the basis of appropriate audiograms. Behavioral audiograms were determined at the octave frequencies 250-4000 Hz. These behavioral thresholds were then compared with the SSEP thresholds obtained during natural sleep for adults, or natural or sedated sleep for children. Results A strong relationship between behavioral and SSEP thresholds was observed. The strength of the relationship increased with increasing frequency and increasing degree of the loss. On the basis of these data, the prediction of behavioral thresholds from SSEP levels was determined. It was found that the standard deviation of the error in this prediction decreased with increasing frequency and increasing degree of the loss. There was no significant age effect in the results obtained at any of the frequencies. Conclusion The results suggest that the SSEP technique can be used as a predictor of behavioral thresholds in adults and children at the frequencies 250-4000 Hz.

Outcomes of children with mild-profound congenital hearing loss at 7 to 8 years: a population study.

Objectives Improved long-term outcomes of hearing loss at a population level is the underlying reason for interventions such as newborn hearing screening programs. Therefore, high-quality population surveys are needed for older children across the spectrum of hearing losses that might be detected by such programs, against which to assess future secular improvements. Measured outcomes should cover a broad range of parameters, including health-related quality of life. Design Population-based cohort study (CHIVOS, the Children with Hearing Impairment in Victoria Outcome Study). Setting: State of Victoria, Australia. Participants: Eighty-six 7- to 8-yr-old children born in Victoria, who were (a) fitted with hearing aids for congenital hearing loss by 4.5 yr and (b) had no intellectual or major physical disability. Measures: Standardized measures of language (CELF and PPVT), articulation (Goldman-Fristoe Test of Articulation), cognition (WISC), reading, adaptive functioning, health-related quality of life, parent developmental concerns, parent- and teacher-reported intelligibility and behavior, and teacher-reported school functioning. Results Response rate was 67% (N = 89). Of the 86 able to be included in analyses, 53 were boys; 22% had mild, 31% moderate, 17% severe, and 29% profound hearing loss; the mean nonverbal IQ was 104.6 (SD 16.7). The sample scored far below (1.3 to 1.7 SDs) the normative populations on the PPVT and on the Receptive, Expressive and Total CELF scores. On average, children’s reading age was delayed nearly 10 mo. For every outcome measure except physical health, these children scored significantly worse than the relevant normative population. Language and vocabulary scores worsened with increasing severity of hearing loss, but adaptive functioning, health-related quality of life, academic skills and behavior did not. Conclusions Comprehensive data such as these highlight the continuing plight experienced by hearing-impaired children, and will help evaluate over time whether outcomes for children with hearing loss are improving at a population level.

Steady-state evoked potential and behavioral hearing thresholds in a group of children with absent click-evoked auditory brain stem response

Objective: 1) To examine the distribution of behavioral hearing thresholds in a group of children who had shown no click‐evoked auditory brain stem response (ABR) at maximum presentation levels. 2) To describe the relationship between the 90 Hz steady‐state evoked potential (SSEP) and behavioral thresholds in these subjects. Design: A retrospective study based on clinical findings obtained from 108 infants and young children. Each of these children had shown no recordable ABR to clicks presented at maximum levels (100 dB nHL). SSEP audiograms were obtained using AM/FM tones at the octave frequencies 250 to 4000 Hz. The results of these evoked potential assessments were compared with hearing thresholds established behaviorally. Results: Click‐ABR assessment could not differentiate between the subjects in our sample with total hearing losses and those with useful residual hearing. Although some of the ears were anacusic, more than a quarter showed residual hearing at each of the audiometric frequencies. Furthermore, at least 10% of the behavioral thresholds at each frequency fell within the moderate/severe hearing loss range. A far closer relationship was observed between SSEP and hearing thresholds. On occasions where the SSEP was absent at maximum levels, 99.5% of the ears showed either a total loss or a behavioral threshold within 10 dB of that level. When an SSEP was obtained, the hearing threshold was typically within 5 dB of the SSEP threshold. Conclusion: The results suggested that in our group of selected subjects, the SSEP technique was able to assess ears with only minimal amounts of residual hearing. Where the brevity of the acoustic click limits both its frequency specificity and its presentation level, the modulated tones used for SSEP testing allow accurate, frequency‐specific assessment at high presentation levels.

Auditory steady-state evoked potential in newborns

Steady-state evoked potential responses were recorded from 337 normal full-term sleeping newborns to combined amplitude and frequency modulated tones. Responses were automatically detected by statistical analysis of the response phase. Responses were most easily and consistently recorded at carrier frequencies of 500 Hz, 1500 Hz and 4000 Hz when the modulation frequency was between 60 Hz and 100 Hz. In this modulation frequency range, the response latencies were found to be between 11 ms and 15 ms, depending on carrier frequency, and the mean response thresholds for the three carrier frequencies were found to be 41.36 dB HL, 24.41 dB HL and 34.51 dB HL respectively. The results of this study suggest that steady-state evoked potentials at modulation rates in excess of 60 Hz may be useful for frequency specific, automated hearing screening in newborns.

Hearing impairment : a population study of age at diagnosis, severity, and language outcomes at 7-8 years

Background: Better language outcomes are reported for preschool children with hearing impairment (HI) diagnosed very early, irrespective of severity. However, population studies of older children are required to substantiate longer term benefits of early detection. Aims: To study impact of age of diagnosis and severity of HI in a population cohort of 7–8 year old children. Methods: Eighty eight 7–8 year old children born in Victoria, who were (a) fitted with hearing aids for congenital HI by 4.5 years and (b) did not have intellectual or major physical disability were studied. Main outcome measures were Clinical Evaluation of Language Fundamentals (CELF) and Peabody Picture Vocabulary Test (PPVT). Predictors were pure tone average (0.5, 1, 2 kHz) in better ear at diagnosis and age at diagnosis. Marginal (adjusted) means were estimated with general linear models. Results: Response rate was 67% (n = 89; 53 boys). Mean age at diagnosis was 21.6 months (SD 14.4); 21% had mild, 34% moderate, 21% severe, and 24% profound HI; mean non-verbal IQ was 104.6 (SD 16.7). Mean total CELF score was 76.7 (SD 21.4) and mean PPVT score 78.1 (SD 18.1). Age of diagnosis, adjusted for severity and IQ, did not contribute to language scores. In contrast, adjusted mean CELF and PPVT language scores fell sequentially with increasing severity of HI. Conclusions: More severe HI, but not later diagnosis, was strongly related to poorer language outcomes at 7–8 years. Further systematic study is needed to understand why children with hearing impairment have good or poor outcomes.

Slight/mild sensorineural hearing loss in children.

OBJECTIVE. The goal was to determine the prevalence and effects of slight/mild bilateral sensorineural hearing loss among children in elementary school. METHODS. A cross-sectional, cluster-sample survey of 6581 children (response: 85%; grade 1: n = 3367; grade 5: n = 3214) in 89 schools in Melbourne, Australia, was performed. Slight/mild bilateral sensorineural hearing loss was defined as a low-frequency pure-tone average across 0.5, 1, and 2 kHz and/or a high-frequency pure-tone average across 3, 4, and 6 kHz of 16 to 40 dB hearing level in the better ear, with air/bone-conduction gaps of <10 dB. Parents reported childrens health-related quality of life and behavior. Each child with slight/mild bilateral sensorineural hearing loss, matched to 2 normally hearing children (low-frequency pure-tone average and high-frequency pure-tone average of ≤15 dB hearing level in both ears), completed standardized assessments. Whole-sample comparisons were adjusted for type of school, grade level, and gender, and matched-sample comparisons were adjusted for nonverbal IQ scores. RESULTS. Fifty-five children (0.88%) had slight/mild bilateral sensorineural hearing loss. Children with and without sensorineural hearing loss scored similarly in language (mean: 97.2 vs 99.7), reading (101.1 vs 102.8), behavior (8.4 vs 7.0), and parent- and child-reported child health-related quality of life (77.6 vs 80.0 and 76.1 vs 77.0, respectively), but phonologic short-term memory was poorer (91.0 vs 102.8) in the sensorineural hearing loss group. CONCLUSIONS. The prevalence of slight/mild bilateral sensorineural hearing loss was lower than reported in previous studies. There was no strong evidence that slight/mild bilateral sensorineural hearing loss affects adversely language, reading, behavior, or health-related quality of life in children who are otherwise healthy and of normal intelligence.

Spoken Language Development in Oral Preschool Children With Permanent Childhood Deafness

This article documented spoken language outcomes for preschool children with hearing loss and examined the relationships between language abilities and characteristics of children such as degree of hearing loss, cognitive abilities, age at entry to early intervention, and parent involvement in childrens intervention programs. Participants were evaluated using a combination of the Child Development Inventory, the Peabody Picture Vocabulary Test, and the Preschool Clinical Evaluation of Language Fundamentals depending on their age at the time of assessment. Maternal education, cognitive ability, and family involvement were also measured. Over half of the children who participated in this study had poor language outcomes overall. No significant differences were found in language outcomes on any of the measures for children who were diagnosed early and those diagnosed later. Multiple regression analyses showed that family participation, degree of hearing loss, and cognitive ability significantly predicted language outcomes and together accounted for almost 60% of the variance in scores. This article highlights the importance of family participation in intervention programs to enable children to achieve optimal language outcomes. Further work may clarify the effects of early diagnosis on language outcomes for preschool children.

Evoked response audiometer

An evoked response audiometer is disclosed in which the patient is presented with a continuous auditory signal which is amplitude modulated and the evoked brain potentials of the patient (EEG) are recorded. The potentials are amplified and filtered and are averaged over a number of sampling periods to improve the signal to the noise ratio. The averaged signals are then analyzed to determine the amplitude and phase of the main components of the response to determine whether phase locking has occurred. The phase of the main components is then plotted against variation of the modulating frequency and the gradient of the plot provides the latency of the response from which neurological and other factors of significance to the hearing of the patient may be determined. The sound pressure level of the auditory signal is also varied and the amplitude and phase of the response plotted against these changes to provide an indication of the sensitivity of the hearing of the patient.