Dani Tomlin

Maturation of Auditory Steady-state Responses in Normal Babies

Objective: To track the development of the auditory steady-state response (ASSR) through the neonatal and early infant periods in a group of normal-hearing babies. Design: This longitudinal study involved assessment at four data collection points. ASSR thresholds to modulated 500 Hz and 4 kHz tones were established in 20 full-term subjects at 0, 2, 4, and 6 wks of age. Results: Significant developmental changes were observed for both test frequencies. Mean ASSR threshold levels decreased by approximately 10 dB between the week 0 and week 6 data collection points. Conclusions: The results of this study indicate that ASSR threshold levels in normal-hearing neonates and young infants are different from those observed in older subjects. Clinical application of the ASSR procedure in this population will need to take into account developmental changes occurring in the first weeks of life. Furthermore, the findings indicate that ASSR thresholds in normal-hearing babies at 6 wks of age are not yet mature.

An opinion on the assessment of people who may have an auditory processing disorder.

We need to rethink how we assess auditory processing disorder (APD). The current use of test batteries, while necessary and well accepted, is at risk of failing as the size of these batteries increases. To counter the statistical, fatigue, and clinical efficiency problems of large test batteries, we propose a hierarchical approach to APD assessment. This begins with an overall test of listening difficulty in which performance is measurably affected for anyone with an impaired ability to understand speech in difficult listening conditions. It proceeds with a master test battery containing a small number of single tests, each of which assesses a different group of skills necessary for understanding speech in difficult listening conditions. It ends with a detailed test battery, where the individual tests administered from this battery are only those that differentiate the skills assessed by the failed test(s) from the master test battery, so that the specific form of APD can be diagnosed. An example of how hierarchical interpretation of test results could be performed is illustrated using the Listening in Spatialized Noise-Sentences test (LiSN-S). Although consideration of what abilities fall within the realm of auditory processing should remain an important issue for research, we argue that patients will be best served by focusing on whether they have difficulty understanding speech, identifying the specific characteristics of this difficulty, and specifically remediating and/or managing those characteristics.

Comparison of auditory steady-state responses and tone-burst auditory brainstem responses in normal babies

Objective: To follow the development of tone-burst auditory brainstem response (TB-ABR) and auditory steady-state response (ASSR) thresholds in a group of normal babies through the first 6 wk of life. Design: This longitudinal study involved assessment at four data-collection points. TB-ABR and ASSR thresholds to 500-Hz and 4-kHz stimuli were established in 17 full-term subjects at 0, 2, 4, and 6 wk of age. Stimulus-modulation rates for ASSR assessment were 74 Hz (for 500-Hz tones) and 95 Hz (for 4-kHz tones). TB-ABR responses were recorded to stimuli presented at 39.1 Hz. Results: Mean ASSR thresholds (calibrated in dBHL) at 500 Hz ranged from 44.4 to 39.7 dB HL across the recording period, and at 4 kHz they ranged from 37.9 to 32.1 dB HL. TB-ABR thresholds (calibrated in dBnHL) were significantly lower, ranging from 36.8 to 36.2 dB nHL at 500 Hz and from 16.5 to 15.9 dB nHL at 4 kHz. However, when the stimuli used for each test were calibrated in the same units (peak equivalent dB SPL), the results were similar. That is, the differences between the two techniques were only an artifact of the calibration. ASSR thresholds were more variable than TB-ABR, particularly at the neonatal measurement point. Within-subject changes across the test period were observed for ASSR thresholds but not for TB-ABR. Conclusions: The longitudinal findings presented in this study suggest that for normal neonates, the TB-ABR technique may offer a more reliable basis for prediction of hearing levels than ASSR assessment. This is not because TB-ABR thresholds (calibrated in dBnHL) are lower, but because the response is less affected by maturational development in the first weeks of life and is less variable across subjects.

The impact of auditory processing and cognitive abilities in children

Objectives: To examine the links between auditory processing (AP) test results, functional deficits, and cognitive abilities. Design: One hundred and fifty-five children, ages 7–12 years, comprising 50 control children and 105 children referred for AP assessment, all with normal peripheral hearing, completed an AP and cognitive (sustained attention, auditory working memory, and nonverbal intelligence) test battery. Functional outcome measures of listening ability (developed using questionnaires from parent, teacher, and child respondents) and reading fluency were also collected. Results: AP scores for dichotic digits, frequency pattern, and listening in spatialized noise-sentences test baseline scores showed significant intertask correlations, and significant correlations with functional outcomes. The gaps in noise task showed correlation with reading fluency only. The AP tasks of masking level differences and spatial advantage showed no correlation with listening ability or reading fluency. Results showed significantly poorer cognitive abilities overall in the children referred for AP assessment compared with the control group. Within the referred group, children diagnosed with an auditory processing disorder had significantly poorer cognitive abilities than those passing the test battery. Correlation and regression studies showed significant associations between AP and cognitive scores. The results of multilinear regression analyses showed that the associations of AP scores with listening and academic results were no longer significant when cognitive scores were also included as predictors. Conclusions: A complex interaction of cognitive abilities and AP scores is evident. For many children with listening difficulties, who perform poorly on AP tasks, cognitive deficits are also in place. Although the direction of causality is unclear, it is likely that these cognitive deficits are causing the perceived difficulty and/or are having a significant effect on the test results. Interpretation of AP tests requires consideration of how cognitive abilities may have impacted on not only task results but also the functional difficulties experienced by the child.

A comparison of 40 Hz auditory steady-state response (ASSR) and cortical auditory evoked potential (CAEP) thresholds in awake adult subjects

Evoked potential thresholds using the 40 Hz auditory steady-state response (ASSR) and cortical auditory evoked potential (CAEP) were recorded at 500 Hz and 4000 Hz test frequencies in 36 subjects with normal acuity, and 30 subjects with sensorineural hearing loss. ASSR threshold sensation levels (SLs) were lower in ears with greater degrees of hearing loss, and for the 500 Hz stimulus. Mean SLs (maximum duration of a single recording: 89 seconds) were as follows at 500 Hz and 4000 Hz respectively: normal hearing group, 16.9±10.3 dB and 42.4±14.4 dB; mild-moderate group, 10.6±8.8 dB and 23.8±8.1 dB; severe-profound group, 10.0±13.2 dB and 21.5±18.9 dB. CAEP SLs showed no change with hearing level and CAEP/behavioural differences were similar at each test frequency. Mean SLs for CAEP threshold (single recording duration: 84 seconds) at 500 Hz and 4000 Hz respectively were: normal hearing group, 10.3±6.4 dB and 11.5±3.8 dB; mild-moderate group, 8.4±7.4 dB and 13.2±12.4 dB; severe-profound group, 11.0±6.6 dB and 15.9±16.4 dB. The results of this study suggest that while both 40 Hz ASSR and CAEP can reflect the behavioural audiogram, CAEPs may provide a more reliable estimate of hearing in awake adults.

Long-term hearing deficits after childhood middle ear disease.

Objectives: To investigate the long-term impact of childhood otitis media on listening ability in school-aged children. Design: Speech perception in background noise was measured in two groups of 35 children, aged 6 to 12 years, with normal middle ear function and sound detection at assessment. The first consisted of children who had previously suffered middle ear disease; the second those with no history of middle ear disease. Results: Binaural speech perception ability was significantly poorer in the children with prior middle ear disease. Furthermore, spatial listening (the ability to selectively attend to a sound signal from one location) was also significantly impaired. Significant correlations were demonstrated between both the age of onset and the duration of childhood otitis media and speech perception ability (onset: r = −0.58, p < 0.001; duration: r = −0.63, p < 0.001). Conclusions: These results demonstrate the risk of long-term functional hearing deficit for children with middle ear disease history in childhood. They also indicate that this risk is increased with earlier onset and longer duration. The findings highlight the need for early intervention and an awareness of the potential for reduced functional listening ability even after sound detection has returned to normal.

Auditory processing deficits in individuals with primary open-angle glaucoma

Abstract Objective: The high energy demand of the auditory and visual pathways render these sensory systems prone to diseases that impair mitochondrial function. Primary open-angle glaucoma, a neurodegenerative disease of the optic nerve, has recently been associated with a spectrum of mitochondrial abnormalities. This study sought to investigate auditory processing in individuals with open-angle glaucoma. Design/Study sample: Twenty-seven subjects with open-angle glaucoma underwent electrophysiologic (auditory brainstem response), auditory temporal processing (amplitude modulation detection), and speech perception (monosyllabic words in quiet and background noise) assessment in each ear. A cohort of age, gender and hearing level matched control subjects was also tested. Results: While the majority of glaucoma subjects in this study demonstrated normal auditory function, there were a significant number (6/27 subjects, 22%) who showed abnormal auditory brainstem responses and impaired auditory perception in one or both ears. Conclusions: The finding that a significant proportion of subjects with open-angle glaucoma presented with auditory dysfunction provides evidence of systemic neuronal susceptibility. Affected individuals may suffer significant communication difficulties in everyday listening situations.

Maturation of the Central Auditory Nervous System in Children with Auditory Processing Disorder.

Neurodevelopmental delay has been proposed as the underlying cause of the majority of cases of auditory processing disorder (APD). The current study employs the cortical auditory evoked potential (CAEP) to assess if maturational differences of the central auditory nervous system (CANS) can be identified between children who do and do not meet the diagnostic criterion for APD. The P1-N1 complex of the CAEP has previously been used for tracking development of the CANS in children with hearing impairment. Twenty-seven children (7 to 12 years old) who failed an APD behavioral test battery were age-matched (within 3 months) to children who had passed the same battery. CAEP responses to 500-Hz tone burst stimuli were recorded and analyzed for latency and amplitude measures. The P1-N1 complex of the CAEP, which has previously been used for tracking development of the CANS in children with hearing impairment, showed significant group differences. The children diagnosed with APD showed significantly increased latency (∼10 milliseconds) and significantly reduced amplitude (∼10 μV) of the early components of the CAEP compared with children with normal auditory processing. No significant differences were seen in the later P2 wave. The normal developmental course is for a decrease in latency and increase in amplitude as a function of age. The results of this study are, therefore, consistent with an immaturity of the CANS as an underlying cause of APD in children.

Allowing for asymmetric distributions when comparing auditory processing test percentage scores with normative data.

BACKGROUND Raw percentage scores can be transformed to age-specific Z scores, despite the asymmetric distribution of normative data using a process that is applicable to any percentage (or proportion)-based result. PURPOSE Normative values are generated for the commonly used dichotic digit and frequency pattern behavioral tests of auditory processing. STUDY SAMPLE A total of 180 normal-hearing children aged 7 yr 0 mo to 12 yr 2 mo took part in this study. RESEARCH DESIGN A transformation and regression method is incorporated that allows for the asymmetric distribution of normative results and the development of the response across the 7-12-yr-age range. DATA COLLECTION AND ANALYSIS Percentage correct scores were determined for each ear in the dichotic digit and frequency pattern tests, delivered at 50 dB HL. The scores were arcsine transformed, then regressed against using an exponential equation, providing an age specific estimated mean score. The residual error of the regression was then used to estimate age specific variance. RESULTS AND CONCLUSIONS The ability to express results along an age continuum (while accounting for the asymmetric distribution and significant developmental influences) as a standard unit across all ages enables a simplified expression of performance ability on a task.

Auditory steady-state responses in babies with normal hearing and with temporary conductive hearing loss

Abstract Objectives: To investigate whether test age and middle ear dysfunction had a significant effect on the variability of Auditory Steady-State Response (ASSR) thresholds when this test was undertaken on referrals from the newborn hearing screen. Methods: ASSR thresholds were measured at octave intervals from 500 Hz to 4000 Hz. They were recorded in 389 ears with normal hearing and middle ear function, and in a further 189 ears with temporary middle ear dysfunction. The modal corrected age at which the tests were undertaken was four weeks, with a minimum of one week and maximum corrected age of 26 weeks. Results: The mean ASSR thresholds of those with normal hearing were 47dB HL at 500 Hz, 36dB HL at 1000 Hz, and 34dB HL at both 2000 Hz and 4000 Hz. Standard deviations (SDs) from the mean ranged from 7.7 to 9.9dB. For those with middle ear dysfunction the mean ASSR thresholds were significantly greater at each frequency, with thresholds of 65dB HL at 500 Hz, 55dB HL at 1000 Hz, 53dB HL at 2000 Hz and 52dB HL at 4000 Hz. SDs from the mean ranged from 12.9 to 17.9dB. Mean thresholds decreased at all frequencies during the first half of infancy. In those with normal middle ear function the decrease was only 2dB at 500 Hz, but was over 5dB at both 1000 and 2000 Hz and was 4dB at 4000 Hz. A similar decrease was seen over the same period in those with middle ear dysfunction. Conclusions: ASSR thresholds measured in early infancy are affected by both test age and the presence of middle ear dysfunction and are more variable than ABR thresholds measured in babies with normal hearing or a mild conductive loss. A flexible test battery for gaining frequency specific information is therefore required at this age.