Biomedical subjects

D B Moody

Publications and source records attributed to D B Moody.

At least 55 records · Page 3Linked to original sources

PubMed1986

Sound localization of frequency-modulated sinusoids by Old World monkeys.

Directional hearing acuity, as measured by the minimum audible angle (MAA), was determined in four Old World monkeys, Macaca radiata. The acoustic stimuli were linear changes in frequency (sweeps) for different frequency ranges and sweep rates. The sweeps ranged between 0.5 and 1.3 kHz, at two durations, 100 and 200 ms. In upsweeps which began at 0.5 kHz and were 200 ms in duration, MAA decreased as sweep rate and frequency range increased. These thresholds were compared to MAAs of sweeps which traversed the same range of frequencies but at a different rate, to MAAs of sweeps with identical rates but over different frequency ranges, and to the MAAs of downsweeps. These comparisons indicated that range, and not sweep rate, exerts the greatest effect on the MAA. Interaural phase differences derived from the upper limits of the frequency range are discussed as potential FM localization cues.

Acoustic Stimulation↗

PubMed1986

The role of frequency modulation in the perception of complex stimuli by primates.

Frequency modulation is a common feature of acoustic communication signals, including both human speech and many animal calls. In this study, linear frequency upsweeps were used as simple abstractions of the modulations found in communication signals. Macaque monkeys were trained using positive reinforcement operant conditioning procedures to respond when an ongoing repetitive acoustic signal changed from unmodulated (pure tone) to modulated (sweep). Thresholds for detecting modulation were determined using the psychophysical method of constant stimuli. In the first experiment, it was shown that the monkeys were most sensitive to modulation around a center frequency of 500 Hz. Subsequent experiments were carried out at that frequency, and varied stimulus duration and the frequency relationship between standard and comparison stimuli. The results of these studies indicated that subjects were responding primarily to discrete frequency cues rather than to the presence of modulation. When a premium was placed on attending to modulation by presenting discrete shifts between successive unmodulated stimuli thereby making such shifts an unreliable indicator of the presence of modulation, subjects continued to respond to the presence of the discrete shifts. These results are taken as evidence that the auditory system may deal with frequency modulation near threshold by recoding it as a discrete frequency percept.

Animal Communication↗

PubMed1984

Neural lateralization of vocalizations by Japanese macaques: communicative significance is more important than acoustic structure.

The study was designed to determine whether the neural lateralization of vocal perception in Japanese macaques depends on the acoustic properties of the calls used or their communicative significance. Four monkeys--two Japanese macaques and two comparison macaques--were trained to discriminate among monaurally presented exemplars of two classes of vocalizations from the Japanese macaque's repertoire. Once the subjects mastered the discrimination, they performed at equivalent accuracy levels for 150 sessions. However, during this time the Japanese monkeys showed a right ear performance advantage, whereas the comparison monkeys showed no ear advantage. In order to assess whether the comparison and Japanese monkeys were attending to the same acoustic cue when performing the discrimination, a generalization test was conducted with 27 novel vocalizations. The individual monkeys' generalization gradients were highly similar and revealed that all subjects were in fact listening to the same feature of the calls. These findings, coupled with the fact that the calls were of biological significance to the Japanese monkeys alone, suggest that the laterality effect is related, in some fashion, to the communicative valence of the signals rather than their purely physical characteristics.

Animals↗

PubMed1984

Evidence for a reappraisal of the psychophysical selective adaptation paradigm.

The human psychophysical adaptation literature infers the existence of channels in the auditory system sensitive to frequency modulation (FM) from selective increases in FM detection thresholds following adaptation with FM stimuli. Using this psychophysical paradigm to characterize the attributes of feature-sensitive channels requires knowledge of the phenomenon's stability over repeated testing. In this study FM detection thresholds were measured in human subjects with continued testing over numerous sessions. During adapting intervals within the sessions either FM upsweeps or silence was presented. Exposure to FM upsweeps initially resulted in an increase in FM detection thresholds by a factor of 2 to 3 relative to those measured following silence. These initial threshold elevations decreased markedly with repeated testing (more than five 30-min experimental sessions). Final threshold differences between adapted and nonadapted conditions approached zero. In one subject, such asymptotic threshold values were regained in a single session, after a 4-month hiatus. The findings suggest multiple determinants of the selective adaptation function, as well as a reevaluation of inferred mechanisms.

Adaptation, Physiological↗

PubMed1982

Frequency selectivity of the monkey's auditory system: psychophysical tuning curves.

Frequency selectivity was examined in three monkeys (Macaca nemestrina) by means of psychophysical tuning curves which were obtained under both simultaneous- and forward-masking conditions. The results showed that tuning curves obtained under the two masking conditions were qualitatively similar, sharing many of the same basic properties--sharply tuned tip segments, and greater selectivity at high frequencies than at low frequencies. As measured by Q10dB values, however, the forward-masking tuning curves were more sharply tuned than the simultaneous-masking curves. Additionally, the two procedures resulted in different conclusions regarding how frequency selectivity varies as a function of probe frequency. The simultaneous-masking results suggested that frequency selectivity improves up to at least 16 kHz, the highest frequency tested. The results from forward masking showed frequency selectivity to be greatest in the frequency region of 1-4 kHz. The results are discussed in terms of possible differences between the procedures, and in terms of their relationship to previous studies of psychophysical tuning cures in other species.

Animals↗

PubMed1981

Auditory intensity discrimination after selective loss of cochlear outer hair cells.

The contributions of the inner and outer hair cells of the mammalian cochlea to auditory intensity discrimination were evaluated in a combined behavioral-anatomical study of the guinea pig. Intensity difference thresholds were unchanged from baseline values after selective destruction of outer hair cells, suggesting that those cells are unnecessary for normal intensity discrimination.

Acoustic Stimulation↗

PubMed1980

Effect of ethanol and of noise on reaction time in the monkey: variation with stimulus level.

To determine whether the latency-increasing effects of ethanol were differential with respect to the intensity of the stimulus that initiated the response, three rhesus monkeys were trained on a behavioral task in which the latency of a simple motor response was measured following the onset of a pure tone stimulus. Following training, the animals were tested at a number of different tone intensities and functions relating latency to tone intensity were constructed. When these were stable, the animals were given ethanol in doses of 1.0-2.5 g/kg and the effects on response latencies to different tone intensities were determined. It was found that for all except the lowest stimulus levels, the effect of ethanol was dose-related, while for a given dose the effect was equal across intensity. These results indicate that the effects of ethanol in this situation are on response execution rather than stimulus detection. The effects of ethanol were compared to those of exposure to high intensity noise. This treatment, which affects primarily the inner ear, resulted in substantial increases in latency to low intensity tones, but little, if any, shift at high intensities.

Acoustic Stimulation↗

PubMed1980

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 macaque's 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 monkey's range of audibility.

Animals↗

PubMed1979

Species-specific perceptual processing of vocal sounds by monkeys.

Monkeys of four species were trained to discriminate between sets of natural tonal calls of Japanese macaques (Macaca fuscata) by the position of a frequency-inflection peak or by initial pitch. The Japanese macaques consistently performed best on peak position and the other species on pitch. The results imply special strategies for perceptional processing of vocal sounds and suggest parallels with human speech perception.

Animals↗

PubMed1979

Electrocochleography and experimentally induced loudness recruitment.

The relationship between changes in loudness and the cochlear whole-nerve potential following experimentally produced deafness was studied in an animal model. Reaction time of a subject's response to an auditory stimulus has been shown to be an index of loudness in human experiments and has been adapted to nonhuman primates. In a series of experiments, four macaque monkeys were operantly conditioned to respond to 8-kHz tones over a range of 3--80 dB SPL, and their reaction times to pure tone stimuli were measured. Whole-nerve cochlear action potentials were recorded from chronic inner-ear electrodes. The relationship between behavioral and electrical measures of loudness recruitment were examined in animals with both temporary and permanent noise-induced hearing loss. Loudness recruitment was demonstrated experimentally after a 1-h exposure to a high-intensity 8-kHz octave band of noise. Excellent agreement was observed between the reaction time function and the action potential input-output function at intervals of 0.5, 12, 24, 48, and 84 h after exposure. Permanent hearing loss was produced in some of these animals by a much longer duration of exposure to the 8-kHz octave band of noise. Recruitment was observed in both the behavioral and the electrical measures. Histological studies of these damaged cochleas revealed primarily outer hair cell destruction, with a relative sparing of inner hair cells and nerve supply. The findings of this study are interpreted as strong support for the clinical electrocochleogram as an objective indicator of the presence of loudness recruitment.

Action Potentials↗

PubMed1979

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.

Animals↗

PubMed1979

Perception of conspecific vocalizations by Japanese macaques. Evidence for selective attention and neural lateralization.

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 and do not respond to a second class. A measure of neural lateralization was obtained by presenting the stimuli randomly to the right or the left ear, and comparing performance in the two ears (ear advantage method). Vocalizations were from Steven Green's field tapes. In experiment I, the two classes were Green's 'smooth early high coos' (SE) and 'smooth late high coos' (SL). Experiment II utilized the same vocalizations, but sorted into a high-pitched and a low-pitched class, i.e., orthogonally to the communication-relevant dimension. We found that (a) Japanese macaques learned the SE-SL discrimination faster than the pitch discrimination; (b) the reverse was true for the controls; (c) Japanese macaques showed a right-ear advantage (presumed left hemisphere advantage) for the SE-SL distinction, but not for the pitch discrimination, and (d) controls (with one exception) showed no ear advantage for either discrimination. These demonstrations of selective attention to communication-relevant parameters of conspecific vocalizations, and neural lateralization in the perception of these vocalizations, parallel similar findings in human speech perception.

Animals↗

PubMed1979

Comparative behavioral toxicology.

Behavioral conditioning together with conventional sensory testing methods may be used in the evaluation of toxic effects on sensory systems in experimental animal models. Such procedures yield precise quantitative estimates of impairment in absolute and differential acuity and in sensory perception. Additionally, these behavioral changes can be related to the presence of histopathology in peripheral sensory structures; this orderly relation between structure and function may aid in our understanding of the basis for sensory coding in the normal end organ.

Aminoglycosides↗

PubMed1978

Neural lateralization of species-specific vocalizations by Japanese macaques (Macaca fuscata).

Five Japanese macaques and five other Old World monkeys were trained to discriminate among field-recorded Japanese macaque vocalizations. One task required discrimination of a communicatively relevant acoustic feature ("peak"), and a second required discrimination of an orthogonal feature of the same vocalizations ("pitch"). The Japanese animals more proficiently discriminated the peak feature when stimuli were presented to the right ear (primarily left cerebral hemisphere), as opposed to the left ear (primarily right hemisphere). In discriminating the pitch feature, the Japanese animals either showed (i) a left-ear processing advantage or (ii) no ear advantage. The comparison animals, with one exception, showed no ear advantage in processing either feature of the vocalizations. The results suggest that Japanese macaques engage left-hemisphere processors for the analysis of communicatively significant sounds that are analogous to the lateralized mechanisms used by humans listening to speech.

Animals↗

PubMed1978

Localization of primate calls by old world monkeys.

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.

Animals↗

PubMed1978

Hearing loss and cochlear pathology in the monkey (Macaca) following exposure to high levels of noise.

Eight Old World monkeys were exposed 8 h daily for 20 days to octave-band noise having center frequencies from 0.5--8 kHz at levels of 117--120 dB SPL. Two additional animals received exposures to wide-band, 120-dB SPL noise on the same schedule, and one animal was exposed to the 2-kHz octave band for 40 h continuously. Behavioral audiograms were measured throughout exposure and during a 1-month recovery period. Following recovery, the animals were sacrificed and their ears examined histologically. Monaural audiograms are presented showing initial and final TTS and PTS measured at the end of the recovery period. These are compared with complete cytocochleograms for each ear. Hair cell loss was generally restricted to the outer rows, and was reasonably well correlated with pattern of hearing loss. Some cell loss, including inner hair cells, was found in the extreme basal turn, usually without associated high-frequency hearing loss. The relationships between exposure frequency, hearing loss, and locus of cochlear pathology are discussed, as are changes in TTS during exposure.

Animals↗

PubMed1978

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.

Animals↗

PubMed1977

Behavioral system and apparatus for tone-detection and choice reaction times in the cat.

An efficacious operant-conditioning procedure for psychophysical experiments with cats is described. The system features (a) restraint of the cat and the use of the liquid reinforcement delivery cup to control orientation with respect to the stimuli, (b) a minimum of apparatus between the cat and a free-field sound source, (c) two response pedals so that separate "Yes" and "No" responses are defined, (d) a discrete trial procedure with reaction time (RT) defined as the time from the onset of a trial until the occurrence of a response, and (e) an effective liquid reinforcer and simple delivery system. Operation of the system was demonstrated with the method of constant stimuli. Detectability was directly related, and median RT for correct "Yes" responses inversely related, to tone sound pressure.

Animals↗