Differences In Auditory Sensitivity Research Articles

Age-related differences in cochlear microcirculation and auditory brain stem response.

To examine possible age-related differences in auditory sensitivity and cochlear vascular properties. This study is designed to provide information regarding cochlear function using physiological and audiological measures. Each animal underwent intravital microscopic evaluation of red blood cell velocity, vessel diameter, and vascular permeability in the second turn of the cochlear lateral wall. Auditory brain stem responses were used to determine hearing sensitivity. Four age ranges of male Fischer rats were studied: young, 2 to 4 months (n = 9); mid-young, 9 to 11 months (n = 8); mid-old, 18 to 20 months (n = 6); and old, 30 to 34 months (n = 10). Auditory brain stem response testing showed an age-related decrease in auditory sensitivity. Intravital microscopic analysis showed age-related statistically significant decreases in red blood cell velocity and increased vascular permeability with a trend for reduced capillary diameters. The process of aging is associated with many biochemical and physiological changes that include decrease in cellular water concentration, ionic changes, and decreased elasticity of cellular membranes. One contributing factor to this process may be altered vascular characteristics, such as reduced flow and vascular plasticity, as well as increased vascular permeability. These age-related changes may result in reductions in oxygen and nutrient delivery, and also waste elimination. Our results suggest that progressive age-associated vascular compromise may be a contributing factor in presbycusis.

Vocal-auditory functions in the chimpanzee: Vowel perception

The perception of vowels was studied in chimpanzees and humans, using a reaction time task in which reaction times for discrimination of vowels were taken as an index of similarity between vowels. Vowels used were five synthetic and natural Japanese vowels and eight natural French vowels. The chimpanzees required long reaction times for discrimination of synthetic [i] from [u] and [e] from [o], that is, they need long latencies for discrimination between vowels based on differences in frequency of the second formant. A similar tendency was observed for discrimination of natural [i] from [u]. The human subject required long reaction times for discrimination between vowels along the first formant axis. These differences can be explained by differences in auditory sensitivity between the two species and the motor theory of speech perception. A vowel, which is pronounced by different speakers, has different acoustic properties. However, humans can perceive these speech sounds as the same vowel. The phenomenon of perceptual constancy in speech perception was studied in chimpanzees using natural vowels and a synthetic [o]- [a] continuum. The chimpanzees ignored the difference in the sex of the speakers and showed a capacity for vocal tract normalization.

Temporal Auditory Acuity in Blind and Sighted Subjects: A Signal Detection Analysis

Temporal auditory sensitivity was compared in five adventitiously blind and five normally sighted subjects in a signal-detection paradigm. Following determination of individual auditory flutter fusion (AFF) thresholds the subjects were required to make forced-choice responses between a fluttering and fused white noise under stimulus probabilities of 0.25, 0.50, and 0.75. From these data indices of sensory sensitivity (d') and response bias (Beta) were computed and compared. Analysis indicated no significant differences in auditory sensitivity between the two groups. These findings further weaken the traditional hypothesis of sensory compensation.

Differential effects of lesions in medial and dorsal raphe of the rat: latent inhibition and septohippocampal serotonin levels.

Rats received either 0 or 30 preexposures to a tone which was later used as a conditioned stimulus (CS) in a two-way avoidance task. Tone preexposure resulted in retarded conditioning in normal animals and animals with dorsal raphe lesions. This latent inhibition effect, however, was not present in animals with medial raphe lesions. The failure of CS preexposure to retard conditioning in animals with medial raphe lesions was not due to differences in auditory sensitivity or shock reactivity. Biochemical analysis indicated that whereas medial raphe lesions significantly reduced serotonin in the septohippocampal complex, dorsal raphe lesions had no such effect. The results are discussed in terms of the differing roles of the mesolimbic and mesostriatal serotonergic systems in learning to ignore irrelevant stimuli.

Differences in Auditory Sensitivity Between Guinea Pig and Chinchilla

Species differences in (a) acoustic impedance at the tympanic membrane and (b) the ratio of sound pressure at the tympanic membrane to sound pressure in the field (Pd/Pf) contribute significantly to species differences in (1) behavioral auditory thresholds and (2) sensitivity to noise-induced cochlear fatigue. Chinchillas exposed continuously for two or more days to an octave band of noise centered at 0.5 kHz at 105 dB SPL or centered at 4.0 kHz at 80 dB SPL show shifts in behavioral auditory thresholds of more than 50 dB at appropriate frequencies and corresponding loss of sensitivity for cochlear microphonic responses. Guinea pigs show only trivial loss of CM under the same exposure conditions. CM measurements indicate that in the chinchilla the transmission ratio, bulla closed/bulla open, is approximately 0 dB, but at low frequencies in the guinea pig transmission ratios of about −18 dB corresponding to impedance changes described by Zwislocki [J. Acoust. Soc. Amer. 35, 1034 (1963)] are confirmed. Also, in the guinea pig resonances for Pd/Pf occur at 7.5 to 10 kHz in contrast to the resonances at 2.5 to 5 kHz in the chinchilla [G. von Bismarck, M. S. Thesis, MIT, Cambridge, Mass. (1967)].

Auditory capacities in fishes: Threshold variability in the blue-striped grunt, Haemulon sciurus

Auditory thresholds in the blue-striped grunt, Haemulon sciurus (Pisces, Family Pomadasyidae) were determined by the use of avoidance conditioning. A total of 421 threshold determinations on 23 subjects showed both intra-and inter-individual variability. The thresholds from 50 c.p.s. to 200 c.p.s. averaged about 20 db below one microbar, and from 300 c.p.s. the threshold curve rose along an exponential curve to a maximum of 39 db above one microbar at 1,000 c.p.s. The accuracy of the obtained thresholds was about ±2·5 db taking both equipment and testing errors into account. Repeated tests of the same animals at the same frequencies resulted in progressively lower thresholds, and three successive tests were generally required to determine the lowest threshold. This variation was greatest at frequencies below 300 c.p.s. Individual differences in auditory sensitivity among the several animals were distinct, with variations over 10 db at some frequencies. These individual differences were most apparent at frequencies below 300 c.p.s. The latency of response to the signal rose as the threshold was approached, but the frequency of intertrial crossings decreased significantly. The testing method was based on the “staircase” technique, and both 2 db and 5 db steps were used. No significant difference in threshold was observed for the two step sizes.

RACE DIFFERENCE IN AUDITORY SENSITIVITY.

Two separate studies investigated race and sex differences in normal auditory sensitivity. Study I measured thresholds at 500, 1000, and 2000 cps of 23 white men, 26 white women, 21 negro men, and 24 negro women using the method of limits. In Study II thresholds of 10 white men, 10 white women, 10 negro men, and 10 negro women were measured at 1000 cps using four different stimulus conditions and the method of adjustment by means of Bekesy audiometry. Results indicated that the white men and women in Study I heard significantly better than their negro counterparts at 1000 and 2000 cps. There were no significant differences between the average thresholds measured at 1000 cps of the white and negro men in Study II. White women produced better auditory thresholds with three stimulus conditions and significantly more sensitive thresholds with the slow pulsed stimulus than did the negro women in Study II.

Susceptibility and Sex

Hearing surveys invariably indicate that women have more sensitive hearing than men, the difference increasing with age. This is generally attributed to the fact that women are, on the average, exposed to less noise and gunfire than are men. A possible alternative, however, is that women are less susceptible than men: that in the same noise environment, men will suffer more permanent loss than women. If this were so, one might expect the same to be true of temporary threshold shift (TTS). Therefore the effects of one hour of exposure to 100‐db 1200‐24OO‐cps noise were determined for two groups of normal‐hearing college students: 15 men and 15 women. There were no significant differences, either in growth or recovery of TTS at 3 and 4 kc, between the groups. These results strengthen the hypothesis that differential exposure, rather than differential susceptibility, is responsible for the observed differences in auditory sensitivity between men and women. (Research supported by research grant B‐1122 from the National Institutes of Neurological Diseases and Blindness, Public Health Service.)

Susceptibility and Sex

Hearing surveys invariably indicate that women have more sensitive hearing than men, the difference increasing with age. This is generally attributed to the fact that women are, on the average, exposed to less noise and gunfire than are men. A possible alternative, however, is that women are less susceptible than men: that in the same noise environment, men will suffer more permanent loss than women. If this were so, one might expect the same to be true of temporary threshold shift (TTS). Therefore the effects of one hour of exposure to 100-db 1200-24OO-cps noise were determined for two groups of normal-hearing college students: 15 men and 15 women. There were no significant differences, either in growth or recovery of TTS at 3 and 4 kc, between the groups. These results strengthen the hypothesis that differential exposure, rather than differential susceptibility, is responsible for the observed differences in auditory sensitivity between men and women. (Research supported by research grant B-1122 from the National Institutes of Neurological Diseases and Blindness, Public Health Service.)