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PubMed1988

Absolute auditory thresholds in three Old World monkey species (Cercopithecus aethiops, C. neglectus, Macaca fuscata) and humans (Homo sapiens).

We investigated the absolute auditory sensitivities of three monkey species (Cercopithecus aethiops, C. neglectus, and Macaca fuscata) and humans (Homo sapiens). Results indicated that species-typical variation exists in these primates. Vervets, which have the smallest interaural distance of the species that we tested, exhibited the greatest high-frequency sensitivity. This result is consistent with Masterton, Heffner, and Ravizza's (1969) observations that head size and high-frequency acuity are inversely correlated in mammals. Vervets were also the most sensitive in the middle frequency range. Furthermore, we found that de Brazza's monkeys, though they produce a specialized, low-pitched boom call, did not show the enhanced low-frequency sensitivity that Brown and Waser (1984) showed for blue monkeys (C. mitis), a species with a similar sound. This discrepancy may be related to differences in the acoustics of the respective habitats of these animals or in the way their boom calls are used. The acuity of Japanese monkeys was found to closely resemble that of rhesus macaques (M. mulatta) that were tested in previous studies. Finally, humans tested in the same apparatus exhibited normative sensitivities. These subjects responded more readily to low frequencies than did the monkeys but rapidly became less sensitive in the high ranges.

Adult↗
PubMed1982

Auditory thresholds in rats of different age and strain. A behavioral and electrophysiological study.

The auditory sensitivity of albino rats was determined behaviorally by conditioned suppression of licking and electrophysiologically by the auditory brain stem response (ABR). The behavioral thresholds were obtained with 10-Hz frequency-modulated tones, and the ABR with 1/1- or 1/3-octave filtered sine waves. Individual variability, reproducibility of responses and the influence of sex, age and strain were investigated. The behavioral and electrophysiological techniques were compared in animals with noise-induced high-frequency hearing losses. The results showed the highest degree of normal auditory sensitivity to be around 12-24 kHz. The variability in 20 rats was about 15 dB. In young animals, strain and sex had no influence. A deterioration in high-frequency hearing sensitivity was observed in aged hypertensive rats, whereas normotensive ones showed only minimal changes. The thresholds obtained with the electrophysiological (ABR) technique were 10-20 dB higher than those obtained behaviorally. Both techniques (behavioral and 1/3-octave ABR) assess high-frequency hearing loss equally well. It was concluded that the ABR (1/3-octave filtered sine waves) is suitable for the determination of hearing thresholds and the assessment of hearing loss, at least in the high-frequency range. The ABR technique is especially useful in long-term experiments during which thresholds are determined repeatedly.

Age Factors↗
PubMed1979

Psychophysical tuning curves and auditory thresholds after hair cell damage in the chinchilla.

Chinchillas were treated with kanamycin sulfate (150--200 mg/kg/day) to produce high-frequency hearing loss extending to about 4.0 kHz. Thresholds and psychophysical tuning curves (PTCs) were obtained before and after treatment, utilizing a shuttlebox avoidance procedure, and cochlear hair cells were evaluated under phase contrast microscopy. Hair cell loss resulting from kanamycin treatment varied from restricted lesions of the outer hair cells (OHCs) in the cochlear base, with no loss of inner hair cells (IHCs), to more extensive lesions involving both OHCs and IHCs. Threshold shift of at least 40 dB was always associated with OHC loss. PTCs obtained from frequency regions exhibiting 40--50 dB of threshold shift were normal in shape. With threshold shift in excess of 50 dB, PTCs were progressively distorted, with truncation of the tip segment and in some cases increased sensitivity of the tail segment. The results suggest that the threshold of optimally functional IHCs after kanamycin-induced OHC loss is about 40 dB higher than normal. Threshold shift in excess of 40 dB may represent IHC damage. IHCs are capable of transducing the fine-frequency information necessary for generating normally sharp PTCs in the absence of OHCs. However, with threshold shift in excess of approximately 50 dB, this frequency resolution is increasingly compromised.

Animals↗