Assessment of low-frequency hearing with narrow-band chirp-evoked 40-Hz sinusoidal auditory steady-state response.

Objective To determine the clinical utility of narrow-band chirp-evoked 40-Hz sinusoidal auditory steady state responses (s-ASSR) in the assessment of low-frequency hearing in noisy participants. Design Tone bursts and narrow-band chirps were used to respectively evoke auditory brainstem responses (tb-ABR) and 40-Hz s-ASSR thresholds with the Kalman-weighted filtering technique and were compared to behavioral thresholds at 500, 2000, and 4000 Hz. A repeated measure ANOVA and post-hoc t-tests, and simple regression analyses were performed for each of the three stimulus frequencies. Study sample Thirty young adults aged 18-25 with normal hearing participated in this study. Results When 4000 equivalent response averages were used, the range of mean s-ASSR thresholds from 500, 2000, and 4000 Hz were 17-22 dB lower (better) than when 2000 averages were used. The range of mean tb-ABR thresholds were lower by 11-15 dB for 2000 and 4000 Hz when twice as many equivalent response averages were used, while mean tb-ABR thresholds for 500 Hz were indistinguishable regardless of additional response averaging. Conclusion Narrow-band chirp-evoked 40-Hz s-ASSR requires a ∼15 dB smaller correction factor than tb-ABR for estimating low-frequency auditory threshold in noisy participants when adequate response averaging is used.

Distortion-product otoacoustic emissions and contralateral suppression findings in children with Asperger's Syndrome.

OBJECTIVES: Children with Asperger's Syndrome (AS) often demonstrate auditory behaviors such as hypersensitivity to sounds and poor performance in noisy environments. These auditory behaviors may be related to cochlear dysfunction and abnormal medial olivocochlear bundle (MOCB) activity. The objective of this study was to examine the distortion-product otoacoustic emissions (DPOAEs) with and without contralateral white noise to evaluate outer hair cell activity and MOCB activity in children with AS. METHODS: A case control study where 18 boys with AS and 18 age-matched control subjects participated in the study. For both groups, DPOAEs were recorded at 4031, 2627, 1969, and 1359 Hz f2 frequencies with and without contralateral white noise at 30 dB SL. DPOAE SNRs and difference scores were analyzed for possible differences between both groups and age subgroups (young and old children). RESULTS: In the quiet condition, there were no significant group or ear differences in DPOAEs SNR. However, DPOAEs SNR were larger at 4031 Hz than at lower frequencies in both groups, mostly due to negative effect of background noise on low frequency response. Contralateral noise resulted in both suppression and enhancement of the DPOAE SNRs in 93% of the control group and 90% of the AS group. However, there were no significant differences in suppression and enhancement between the two groups or age subgroups. The young controls had right ear advantage and significantly larger suppression at all frequencies except 4031 Hz than old controls. The young children with AS had slight left ear advantage and significantly larger suppression only at 2672 Hz compared to the old children with AS. CONCLUSIONS: The results, indicating minor differences in DPOAEs and contralateral suppression and enhancement of DPOAEs between both control and AS groups and age subgroups, suggest subtle differences in the function of the outer hair cells and the MOCB activity. Therefore, other central auditory processing in the temporal lobe, limbic system and autonomic nervous system may be involved in the generation of hypersensitivity to sounds and difficulty understanding in noisy environments in children with AS.

DPOAEs and contralateral acoustic stimulation and their link to sound hypersensitivity in children with autism.

OBJECTIVE: The hypersensitivity of children with autism to sound is a relatively unexplained behavior. The goal of the current study was to investigate the DPOAE characteristics of children with autism compared to a control group. DESIGN: DPOAEs with and without contralateral stimuli were measured in two groups in three different conditions. STUDY SAMPLE: The study employed 14 children with autism and a control group with 28 age-matched participants. RESULTS: In the without-contralateral stimulus condition, the overall S/N of DPOAEs was greater for the control group compared to the autism group (p < 0.0005). For both groups, the DPOAE S/N increased as a function of frequency in both ears. In the with contralateral stimulus condition, group and ear effects were noticed, however, no age, frequency, or contralateral stimulus type (BBN vs. 1000 Hz) effect could be detected. CONCLUSIONS: Presence of reduced DPOAEs in the autism group does not support the hypothesis that sound hypersensitivity in children with autism may be related to overactive outer hair cells function; rather it may be due to early cochlear dysfunction. Also, sound hypersensitivity in the autism group may be due to abnormality of the efferent auditory pathway as shown by lack of sufficient contralateral suppression.

Air-conduction auditory steady-state response: comparison of interchannel recording using two modulation frequencies.

BACKGROUND: Two-channel auditory steady-state response (ASSR) recording at high and low MF (modulation frequency) most likely provides an insight about the response amplitude and latency from different directions at the brainstem level and at the thalamus or cortical level. Little is known about the combined relationship between MF (39 and 79 Hz) and electrode montages (ipsilateral and contralateral) to single AM (amplitude modulation) tones on the ASSR amplitude and latency. PURPOSE: To determine if ipsilateral versus contralateral response asymmetries are present at the brainstem level (79 Hz ASSR) and at the thalamus or cortical levels (39 Hz ASSR). RESEARCH DESIGN: Descriptive and inferential statistics for interchannel ipsilateral and contralateral ASSR amplitude and latency to 79 and 39 Hz. STUDY SAMPLE: Twenty-five normal-hearing, right-handed young female adults participated in the study. All participants were right-handed, and their age ranged between 18 to 28 years (mean 24.5 +/- 1.6 years). DATA COLLECTION AND ANALYSIS: Ipsilateral and contralateral ASSR to 39 and 79 Hz MF and 100% AM stimuli were recorded at 500, 2000, and 4000 Hz carrier frequencies at 65 dB SPL. The ASSR amplitudes and phases were determined for each MF across Fc (carrier frequency) for the two channels to the test (right) ear. ASSR amplitude and latency between recording montages for each MF and across carrier frequency were compared by computing two-way repeated measures ANOVA. RESULTS: The mean ipsilateral ASSR amplitudes to 39 Hz across frequency were slightly larger (228.6 +/- 61.6 microV) than the contralateral response amplitude (223.2 +/- 78 microV) while the mean ipsilateral 79 Hz amplitudes were smaller (127.3 +/- 114.8) compared to contralateral 79 Hz amplitude (154.6 +/- 112.7 microV). For latency response, the mean ipsilateral/contralateral latency difference, on average, was 1 msec or less for both MFs. Results, in normal female adults, indicated no significant interchannel ASSR asymmetries for amplitude and latency (p > 0.05) at the brainstem (79 Hz ASSR) and at the thalamus or cortical levels (39 Hz ASSR). CONCLUSIONS: Interchannel ipsilateral and contralateral ASSR amplitude and latency to 79 and 39 Hz are not significantly different in normal, young female adults. Two-channel recording of ASSR to different MFs may be of clinical value in otoneurologic assessment.

Oscillation and its inhibition in a neural oscillator model for tinnitus.

Tinnitus is a symptom of perceiving phantom sounds. As one of its treatment techniques, tinnitus retraining therapy (TRT) has been proposed. It consists of psychotherapy by counseling and physical therapy based on masking theory by external stimuli. Our interest is to explain medical effects of the physical therapy from the viewpoint of engineering. In this paper we proposed a neural oscillator model with plasticity as a model for the tinnitus generation in the auditory central nervous system and its treatment. We investigated not only oscillatory phenomena observed in the model but also inhibition of the oscillation by external stimulus.