Auditory brainstem responses were recorded from 20 normally hearing subjects using tone-burst stimuli that were gated with cosine-squared functions. Clear responses were observed over a wide range of frequencies and levels. These responses were highly reproducible within individual subjects and were reliably measured by two independent examiners. ABR thresholds were higher than behavioral thresholds for all frequencies, especially for lower frequencies. Intersubject variability also was greater for lower frequencies. Wave-V latencies decreased with increases in both frequency and level for frequencies from 250 to 8000 HZ and for levels from 20 to 100 dB SPL. The standard deviations seldom exceeded 10% of the mean wave-V latency for any combination of level and frequency. These lateneies can be viewed as the sum of both a peripheral and a central component. Assuming that the central component is relatively independent of both frequency and level, changes of wave V latency must be related to peripheral factors, such as travel time along the cochlear partition, and to stimulus characteristics, such as rise time.
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.
One hundred sixty-six youngsters (3 to 19 years of age) with severe-to-profound hearing impairments underwent vestibular evaluations with electronystagmography as part of a comprehensive medical and psychoeducational test battery. Twenty-two percent of the children had unilateral or bilateral labyrinthine weakness in response to caloric stimulation, and 21% demonstrated spontaneous or positional nystagmus. The tandem Romberg test was most predictive of those patients with caloric labyrinthine weakness. The performance of mental alerting tasks (using sign language when appropriate) by the patients during testing proved essential in overcoming a marked tendency toward central suppression of nystagmus.
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