Otoacoustic emissions in normal-cycling females.

The purpose of this study was to determine if the menstrual cycle influences the amplitude of transient (TEOAEs) and distortion-product (DPOAEs) otoacoustic emissions. Thirteen normal-hearing, normal-cycling females were monitored weekly for 12 weeks. TEOAE and DPOAE amplitudes were analyzed to determine if amplitude changes could be detected and correlated to phases of the menstrual cycle. No systematic amplitude changes were observed, demonstrating that evoked OAEs are unaffected by physiologic changes associated with the menstrual cycle.

Adaptation of the auditory brainstem response: effects of click intensity, polarity, and position.

The aim of this research was to study the effects of several stimulus parameters on adaptation characteristics of the auditory brainstem response (ABR). Recordings were obtained from normal hearing adults to separate trains of 5 rarefaction and 5 condensation clicks with interclick intervals of 10 msec and intertrain intervals of 500 msec at three intensities. Absolute latencies for waves I, III, and V were essentially unchanged by polarity; latency shifts, however, were induced by parametric manipulations of click intensity, polarity, and position in the train. Furthermore, variations in ABR wave morphology appeared with changes in intensity and polarity. Adaptation, as measured by amplitude, was considerable; the measures of adaptation, however, were not related in a simple manner to the latency shifts. The findings indicate that adaptation of the ABR is a consequence of an interplay of central and peripheral processes to click polarity, sequence, and intensity. Finally, the results provide evidence that when fast stimulus presentation rates are used to estimate thresholds rapidly, one must be aware that certain stimulus parameters can alter the ABR waveforms.

Evaluation of frequency-following potentials in man: masking and clinical studies.

The frequency-following potential (FFP) can have applicability in the assessment of hearing-impaired subjects only if it can be shown that its generation is initiated by neurons which have low best frequencies (2.0 kHz or lower). This study presents results from five subjects with high frequency hearing losses and three subjects with normal hearing. Using 500 Hz tone bursts in the presence of continuous noise of various configurations, it has attempted to determine how in normal hearing subjects, the amplitude and latency of the FFP may be affected. Recordings of the FFP in the presence of noise and wave forms from hearing imparied subjects provide evidence that the FFP is initiated in the cochlea largely by neurons whose best frequencies are 2.0 kHz or lower. Hearing impaired subjects may exhibit 'deviant' responses to tone bursts. These FFP responses may be related to peculiarities of the hearing loss and provide, therefore, a potential means for assessing the temporal viability of the low frequency channels of the auditory neuraxis.

Components of the frequency-following potential in man.

The scalp recorded frequency-following potentials (FFP) are a composite of several FFP's which may be distinguished by comparing simultaneously recorded waveforms from vertical and horizontal derivations in response to tones of very low frequently (below 350 Hz). The two most prominent FFP's were designated FFP1 and FFP2. FFP1 was recorded equally well in vertical and horizontal derivations and at a high stimulus intensities tended to be the predominant FFP. FFP2 followed FFP1 usually by about 1.7 msec and was optimally recorded in the vertical derivation. FFP2 threshold was about 10 dB lower than threshold for FFP1 and in several subjects, FFP2 was observed at 25 dB SL. Two other FFP's, a far-field recorded cochlear microphonic potential and a low-amplitude FFP, the latter presumably of neural origin, were also studied.

Early tone-evoked responses in normal and hearing-impaired subjects.

Early evoked responses to 500-Hz tone bursts were recorded from normal and hearing-impaired children and adults. The threshold values of the early evoked responses provide useful estimates of auditory functioning, even among difficult-to-test populations, such as deaf-blind children. Latency measures indicate that the early response is generated at the brain stem. Latency measures from hearing-impaired subjects show that the response can identify recruitment. Several subjects having a history of nonspecific communication disorders, e.g., dyslexia, exhibited aberrant early evoked response waveforms. The early-evoked response measures, therefore, amy be useful in detecting and assessing communication disorders which are believed to be of cortical origin, but now should be considered to have a basis in brain stem dysfunction.

Human frequency-following responses to monaural and binaural stimuli.

Frequency-following responses, with latencies circa 6 msec, were recorded from five normal-hearing human subjects to brief 500 c/sec tone bursts presented monaurally. The frequency-following responses appear as peaks occurring at 2 msec intervals superimposed on a slow wave (pedestal-like) component. Comparisons were made between the frequency-following responses evoked by binaural and monaural stimuli. The results show that the binaural responses may be interpreted as the sum of two monaural responses. It is concluded, therefore, that there are two independent populations of neurons, each capable of generating a frequency-following response is not a microphonic-like response but rather that the individual waves in the frequency-following response are evoked by the collective activity of phase-locked single units. Finally, on the basis of the distinctness of the individual waves in the frequency-following response, it is concluded that the neural generators of the response must be spatially compact.