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A previous study found temperature-independent effects of alcohol upon the auditory brain-stem response (ABR): another found only temperature-dependent effects. To understand these paradoxical results, we measured the ABR and brain temperature in unrestrained rats before and after 3 alcohol doses (0.5, 2.5 and 5.0 g/kg). In a separate experiment, blood ethanol concentration (BEC) curves were determined for the same 3 alcohol doses. Integration of dose- and time-related effects of alcohol upon the ABR, brain temperature, and BEC suggested that alcohol has both temperature-dependent and temperature-independent effects, which vary according to dose and BEC curve phase. Temperature-dependent effects are likely during a BEC curve falling phase with a steep slope, following a high alcohol dose. Temperature-independent effects are likely during a BEC curve falling phase with a flatter slope, when BEC is still high following a moderate alcohol dose, or during a BEC curve rising phase soon after alcohol administration. The two previous studies with contradictory results each used procedural combinations likely to produce their respective results. Although both research groups administered similar alcohol doses, their alcohol solutions, administration routes, and time of ABR recording differed; consequently, they probably recorded ABR during different portions of BEC curve falling phases, which differed in slope. In view of the complex interactions among alcohol effects, BEC curve phase, temperature, and the ABR, we recommend temperature measurement during alcohol-ABR studies.

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This paper is the first in a series of three concerning audiological tests and test batteries designed to differentiate cochlear from retrocochlear site-of-lesion. This paper concentrates on the techniques of clinical decision analysis with particular application to audiology. Those principles of clinical decision analysis which are most relevant for the audiologist are presented. Several techniques for measuring test performance are described and evaluated. In addition, this paper considers the problem of comparing test performance to determine the superior test.

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We describe a procedure to record auditory evoked potentials in unrestrained rats. A key feature of this procedure is the attachment of a miniature speaker to the rat's head during recording, so that the distance between the speaker and the rat's ear is held constant. A speaker base is permanently attached to the acrylic supporting the electrode connector. This system enables the recording of reliable auditory evoked potentials over long periods of time with minimal concern for the rat's position or posture.

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6 squirrel monkeys (Saimiri scuireus ) were exposed to an octave band of noise with a center frequency of 500 Hz under both continuous and interrupted conditions. Continuous exposures lasted for 4, 8, 16, 24, 48, 72 and 96 h, with complete recovery of hearing before the next exposure. The interrupted exposure was 96 h, long with 5-min interruptions so that temporary threshold shift (TTS) could be measured at 2, 4, 8, 12, 16, 24, 36, 48, 60, 72 and 84 h of exposure. There were no differences in TTS from 8 to 96 h of exposure between the two conditions. However, at 4 h of exposure, the interrupted exposure showed significantly less TTS (p less than 0.05) than the continuous exposure. The only difference between the exposures was a 5-min interruption at 2 h of exposure during the interrupted exposure. Thus, the interrupted-exposure method is valid for making generalizations about continuous exposures of 8 h or longer. The results also confirmed our previous finding that there was no asymptotic threshold shift for the squirrel monkey although we extended the exposure time to 96 h in this experiment. The similarity of human and squirrel monkey TTS growth functions is consistent with our earlier results and supports the suitability of the squirrel monkey as an animal model for noise-induced hearing loss in humans.

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This paper reviews selected physiology and anatomy of the lizard peripheral auditory system and presents the implications of these data for understanding cochlear micromechanics. The reasons for studying the micromechanics of the lizard ear are presented along with the difficulties in conducting such studies in the mammal. Data from the Anguid and Iguanid families of lizards demonstrate the influence of the hair cell system on neural tuning. In addition, evidence from the Iguanid suggests that cilium length may help determine neural tonotopic organization. In general, the reptilian research presented shows the importance of the hair cell system for determining the tuning of associated nerve fibers and in understanding the transduction process in general.

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A model is presented which is a simple representation of cochlear micromechanics in the lizard and mammal. The model is a linear, time-invariant mechanical system, consisting of two coupled mechanical filters. It is capable of a sharply tuned first and second filter, consistent with the sharply tuned basilar membrane and auditory nerve fibers in the mammal. When parameters are adjusted for the alligator lizard (Gerrhonotus multicarinatus), the model generates a sharply tuned second filter without a sharply tuned first filter. In the alligator lizard, the auditory nerve fibers are sharply tuned but the basilar membrane is not. The model supports the hypothesis that cochlear transduction is not fundamentally different in the mammal and the alligator lizard.

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Five squirrel monkeys were exposed for 1, 2, 4, 8, 16, 24, and 48 h to a 375--750-Hz band noise at an overall SPL of 95 dB. The TTS4.5 growth pattern for the 750-Hz test frequency was biphasic and did not reach an asymptote after 48 h of exposure. For all exposures, the mean thresholds of the five monkeys returned to within 5 dB of the preexposure mean 20 h after exposure. Recovery curves from all exposures at the 750-Hz test frequency appeared biphasic. Increasing SPL from 95 to 105 dB increased TTS4.5 by 4 dB at 750 Hz for a 1-h exposure. Recovery from the 105-dB exposure followed the same pattern as recovery from the 95-DB exposure. When compared with data collected from human subjects under similar conditions, these experiments indicate that the growth and recovery of TTS in squirrel monkeys are sufficiently similar to growth and recovery in man to justify further comparative investigation.

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When the helicotrema was obstructed in guinea pigs, trapezoidal displacement of the round window membrane produced a trapezoidal microphonic which indicated a unidirectional displacement of the entire length of the basilar membrane. Responses of single auditory nerve fibers to the trapezoidal displacement of the round window membrane were recorded after obstruction of the helicotrema. About 39% of the 424 fibers showed tonic responses which demonstrated directional sensitivity. More than 90% of these fibers increased their discharge rate during displacement of the basilar membrane toward the scala tympani and decreased their discharge rate during oppositely directed displacement. Less than 5% of the tonic fibers responded in the reverse manner. About 23% of the auditory nerve fibers responded to onset and/or cessation of trapezoidal motion of the basilar membrane. About 28% showed a combination of the tonic and phasic responses. However it is probably that all phasic responses we observed do not arise from velocity-sensitive fibers but some may represent artifacts. Both possibilities remain open until further studies are performed. The transduction mechanism of the cochlea is discussed on the basis of our data obtained by unidirectional displacement of the basilar membrane.

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