David B. Moody

Perception of Conspecific Vocalizations by Japanese Macaques

Japanese macaques (Macaca fuscata) and control species (vervet, pigtailed macaque, bonnet macaque) were trained for food to respond to one class of recorded fuscata vocalizations an

Regulation of voice amplitude by the monkey

Old World monkeys (Macaca) were trained to vocalize at a steady rate in the laboratory by the use of operant conditioning techniques with food as a reinforcer. While the animals were vocalizing, they were subjected to one of two noise bands (200–500 Hz or 8–16 kHz) at different sound pressure levels (70, 80, and 90 dB SPL). Vocal amplitude was measured as a function of the SPL of the noise bands. The monkeys increased voice amplitude to the band of low‐frequency noise but not to the high‐frequency band. These results suggest that in monkey, as in man, a relation exists between speaking and hearing: both man and monkey will increase voice amplitude in the presence of masking noise of the appropriate spectral composition. Subject Classification: 65.22; 70.20.

Auditory thresholds and kanamycin‐induced hearing loss in the guinea pig assessed by a positive reinforcement procedure

Absolute thresholds from 125 Hz to 52 kHz are determined for six guinea pigs trained by a positive reinforcement method. Four to five hundred trials were conducted during daily testing sessions and little between- or within-subject variability was found. Two of the six animals were subsequently treated with kanamycin and the development of a hearing loss for the high frequencies was followed. Loss of outer and to a lesser extent inner hair cells was well correlated with the threshold shift observed. Contrary to the experience of previous investigators, this operant training procedure has proved as efficient as that for other species of experimental animals, such as the monkey and the chinchilla. It holds excellent promise for future auditory behavioral work with the guinea pig.

Return of auditory function following structural regeneration after acoustic trauma: Behavioral measures from quail

After measuring baseline behavioral audiograms, three of four behaviorally trained quail and fifteen untrained cohorts were exposed to a 1.5-kHz octave-band noise at 116-dB SPL for 4 h. The trained birds were tested daily following the exposure and showed a steady recovery of absolute sensitivity with a return to normal absolute thresholds by post-exposure days 8-10. Thirteen untrained cohorts were sacrificed after various survival times to evaluate the structural condition of the ear. The cohorts all showed regeneration of sensory cells similar to that seen in chicks. The effects of repeated acoustic trauma on recovery of sensitivity were evaluated by re-exposing the three trained birds and two untrained cohorts 106 days after the first exposure. One of the trained birds was exposed a third time, 113 days following the second exposure. The findings demonstrate that, following acoustic trauma, normal sensitivity returns prior to complete structural regeneration of the sensory epithelium and that repeated acoustic trauma may increase the time course of recovery of normal hearing sensitivity.

Formant frequency discrimination by Japanese macaques (Macaca fuscata)

These studies investigated formant frequency discrimination by Japanese macaques (Macaca fuscata) using an AX discrimination procedure and techniques of operant conditioning. Nonhuman subjects were significantly more sensitive to increments in the center frequency of either the first (F1) or second (F2) formant of single-formant complexes than to corresponding pure-tone frequency shifts. Furthermore, difference limens (DLs) for multiformant signals were not significantly different than those for single-formant stimuli. These results suggest that Japanese monkeys process formant and pure-tone frequency increments differentially and that the same mechanisms mediate formant frequency discrimination in single-formant and vowel-like complexes. The importance of two of the cues available to mediate formant frequency discrimination, changes in the phase and the amplitude spectra of the signals, was investigated by independently manipulating these two parameters. Results of the studies indicated that phase cues were not a significant feature of formant frequency discrimination by Japanese macaques. Rather, subjects attended to relative level changes in harmonics within a narrow frequency range near F1 and F2 to detect formant frequency increments. These findings are compared to human formant discrimination data and suggest that both species rely on detecting alterations in spectral shape to discriminate formant frequency shifts. Implications of the results for animal models of speech perception are discussed.

Speech sound discrimination by monkeys and humans

Old World monkeys were trained with an operant conditioning technique to discriminate the natural speech sounds /ba/–/da/ and transferred to synthetic speech. Human and monkey difference thresholds for formant transitions were then compared along a seven‐step /ba/–/da/ continuum. Monkeys were not as sensitive as humans to differences in formant transition: the just noticeable difference for monkeys was about 320 Hz, and for humans, about 160 Hz. Although humans were more adept at intraphonemic discriminations than monkeys, their latencies to stimulus changes revealed evidence of ’’categorical perception’’ of the continuum: While latencies for the monkeys increased linearly as stimulus difference was decreased, human latencies were essentially constant for all interphonemic comparisons, but increased sharply for intraphonemic comparisons. We view these data as evidence for (a) similar sensory capacities in monkeys and humans, but (b) unique speech processing capacities in humans.Subject Classification: [43...

Reaction Time as an Index of Sensory Function

It is probably quite apparent from the contents of this book that there are many techniques which can be used to determine either the minimum levels of stimulation or the minimum difference in levels of stimulation necessary to produce behavioral consequences. These techniques all produce a measure of sensitivity conventionally called the threshold; they all determine something about the fineness with which an organism can discriminate certain elements of his environment from other similar elements.

Hearing Loss and Cochlear Pathology in Monkeys After Noise Exposure

Old World monkeys were exposed to octaveband noise from 0.5 to 8 kHz at 120 dB SPL, 8 hours daily for 20 days. Restricted permanent threshold shifts and localized loss of outer hair cells were produced, which were reasonably well correlated with the exposure frequencies. There was also a loss of both inner and outer hair cells at the extreme basal end of Cortis organ, regardless of the exposure frequency. Implications for human inner ear pathology are discussed.

Hearing thresholds with outer and inner hair cell loss

Hearing impairment and related cochlear histopathologic changes were evaluated in experimental animals after treatment with aminoglycoside antibiotics or exposure to intense sound. In the course of treatment with kanamycin, neomycin, or dihydrostreptomycin, permanent hearing loss in monkeys and guinea pigs occurred first at the high frequencies and progressed toward the lows. Exposure to different octave bands of noise at 120 dB SPL in monkeys and chinchillas produced permanent hearing loss at frequencies related to the spectral characteristics of the octave band. In most instances loss of outer hair cells was substantially greater than that of inner hair cells. In fact, the pattern and location of missing outer hair cells on the basilar membrane were most often correlated with threshold shifts of 50 dB or less. Generally inner hair cell loss was observed when the threshold shift was greater than 50 dB. Our data support the place principle and the inference that the outer hair cells are essential for hearing from threshold to about 50 dB SL. The inner hair cells, if functioning normally, apparently take over above that level. Although there is little doubt that such a generalization will, in the long term, be found to have been greatly oversimplified, there is every reason to believe that a combination of behavioral and morphologic procedures, as used in this study, will play an important part in elucidating the differences in functional significance of the two types of hair cells.

Localization of noise bands by Old World monkeys

The acuity of auditory localization in Old World monkeys (Macaca) was determined psychophysically for 44 noise bands graded in bandwidth and center frequency. The acuity of localization was assessed through the method of constant stimuli under free-field conditions in an anechoic chamber. Monkeys were trained through positive-reinforcement operant-conditioning procedures to report a change in azimuth of the signal by releasing a response disk. The results show that localization thresholds are dependent upon the bandwidth of the signal over much of the macaques range of audibility. Thresholds for the detection of a change in location varied from 18 degrees (for a signal 250 Hz in bandwidth centered at 11 200 Hz) to 4 degrees (for a signal 8000 Hz in bandwidth centered at 8000 Hz). The results suggest that the localization of spectrally complex signals is determined by a mechanism sensitive to periodicity (time-domain) information across the monkeys range of audibility.