Monkeys (Macaca) were trained by operant conditioning techniques to report the minimum detectable change in location of a sound in space, and were tested with a series of recorded coo or clear call vocalizations. Acuity of localization varied from approximately 4 degrees to 15 degrees and was a function of the magnitude of the change in pitch (frequency modulation) of the different clear calls.
Unlike the macaques and most commonly used species of laboratory animals, the African military monkey (Erythrocebus patas) is sensitive to the ototoxic action of dihydrostreptomycin (DHSM) administered daily in doses ranging from 100 to as low as 20 mg/kg. Progressive hearing loss (from high to low frequencies) develops during treatment and continues for some time thereafter. It is irreversible and is correlated with extensive cochlear histopathology, typical of ototoxic injury, including loss of inner and outer hair cells and supporting cells, and degeneration of auditory nerve fibers. The Asian pigtail monkey (Macaca nemestrina), although sensitive to other aminoglycosidic antibiotics (e.g., neomycin and kanamycin), is unaffected by DHSM 100 mg/kg given daily for as long as eight months. This striking difference in sensitivity to DHSM may be related to differences in physiologic function which reflect adaptation to the dissimilar environments in which the patas and the nemestrina live. [Supported by NIH Program Project Grant 05785 and by Research Grants NS 05065 and NS 05077.]
The effect of chronic kanamycin administration on absolute auditory thresholds measured with the operant conditioning procedure described in the previous paper was examined in four guinea pigs. The absolute threshold for five different frequencies was measured daily, thus permitting construction of an audiogram which ranged from 125 Hz to 34 kHz within a two-day period. Following establishment of a predrug baseline the animals received 200-mg/kg injections of kanamycin daily for 15 to 30 consecutive days. In the course of drug treatment the animals suffered permanent hearing losses which progressed gradually from the higher to the lower frequencies. The maximum threshold shift observed at any of the test frequencies was approximately 50 dB. In fact, shifts in absolute threshold at frequencies most severely affected by the drug were within a range of 35–50 dB. The correspondence between the hearing impairments determined behaviorally and the cytocochleograms constructed from light microscopic examinations of surface preparations of the organ of Corti will be discussed. [Supported by Research Grants NS05077 and NS05065 and by Program Project Grant NS05785 from NINCDS.]
An attempt is being made to psychophysically characterize the Japanese macaque's perception of sounds drawn from its vocal communication system. In the course of constructing a vocal ethogram for this species, Green (Primate Behavier 4, 1–101 (1975)] identified several distinct classes of vocalizations which differ in acoustic structure and form as well as the sociobehavioral context in which they are likely to occur. Six fuscata and three control (non-fuscata) monkeys have been operantly conditioned, via positive reinforcement techniques, to discriminate between two different types of vocal sounds from Green's classification scheme—the smooth early (SE) and smooth Late (SL) highs. While contacting a metal operandum with its hand an animal is presented a series of natural exemplars from the SL class. Occasionally, and randomly, an exemplar from the SL class is inserted into the series. If the animal correctly reports detection of the SE by breaking contact with the operandum it receives a food pellet. Results from several experiments employing this general procedure will be discussed including studies of perceptual constancy, selective attention, and the classification of synthetic versions of these communication signals. One important and consistent finding is that, although the fuscata and control animals have basically the same auditory capabilities, their perception of the communication sounds, at least during acquisition of the discrimination, differs: the fuscata seem to attend to the communication-relevant features of the sounds while the controls appear to attend predominantly to the communication-irrelevant aspects of the stimuli. [Supported by NSF Research Grants BMS 74-20050 and 5-27092, NINCDS Program Project Grant NS 5785, and NIGMS Training Grant GM-01789.]
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