Suprathreshold Hearing Research Articles

Representation of intensity and frequency information in auditory cortex of monkeys performing a simple auditory task

Intensity functions were measured for single neurons at the cell's best frequency and at surrounding frequencies within the receptive field. Subjects for these experiments were adult male rhesus monkeys. Single neurons were isolated using a vertical approach to the superior temporal plane. Subsequent electrophysiological and anatomical data indicated that cells were located in cortical areas A1, CM, L, and RL [Merzenich and Brugge Brain Res. 50, 275–296 (1973)]. Data were collected while monkeys were performing a simple auditory reaction‐time task. As shown in this and many previous studies, in the absence of such a uniform behavioral control much variation in responses of auditory cortex neurons is encountered. The reaction time task was also used to provide an ongoing measure of the subject's threshold and suprathreshold hearing during recording of neural responses. Data are reported for encoding of stimulus intensity and frequency and discussed relation to behaviorally measured hearing. [Supported by NIH Grants NS‐08181, PR‐00166, and GM‐00260.]

Choline salicylate. Effects on cochlear function.

The influence of choline salicylate ototoxicity on tone-evoked cochlear microphonics and click-evoked N1potentials as recorded from the round window of anesthetized guinea pigs was studied. An increased threshold for the 1-μv sensitivity curve was found, and more dramatically, a marked reduction in dynamic range of cochlear microphonics was observed. Whereas, no effect was found on the latency of nerve evoked potential response, amplitude was reduced following choline salicylate ingestion. These effects were dose dependent and followed a specific time course. The findings of this study are interpreted to indicate that the functional target site of salicylates in the cochlea is the hair cell. Moreover, the results suggest that clinical tests of suprathreshold hearing function may be a more sensitive indicator of salicylate toxicity than threshold evaluation.

Reaction Time as a Measure of Threshold and Suprathreshold Hearing. I. Normal Man and Monkey

Reaction time to auditory stimuli has been suggested as a measure of loudness in nonverbal animals [Stebbins, J. Exp. Anal. Behav. 9, 135 (1966)]. The reaction time task can also be used to measure threshold. We have compared the relationship of this measure to other psychophysical measures of loudness and threhsold hearing in man, and have compared hearing in man and monkey under similar experimental conditions. Absolute sensitivity functions derived from human reaction time data closely matched clinical threshold measures and were an average of 5 dB above thresholds measured by a forced-choice method. Human equal-reaction time contours matched closely equal-loudness contours derived in the same subject by loudness matching. The human and monkey equal-reaction time contours are similar throughout the overlapping hearing range of the two species. The results of this study support the suggestion that response latency can be used as a measure of threshold hearing and loudness and have application to the study of mechanisms underlying hearing in the animal model. [Work supported by PHS Grants NS 08181, RR 00166, NS 50637, and NS 05082.]

Reaction Time as a Measure of Threshold and Suprathreshold Hearing. II. Subjects with Impaired Hearing

Reaction time has been used as a measure to evaluate hearing and hearing changes associated with drugs, lesions, and noise exposure. In this paper, experimentally produced hearing changes in monkeys are compared to hearing changes in man. Reaction time and other psychoacoustic measures are compared in human subjects. Temporary hearing loss was produced in monkey and man by exposure to pure tones one-half octave below a selected test frequency. Exposures produced threshold shifts and changes in the intensity function which were similar for both man and monkeys. These changes are similar to those reported by Moody [Adv. in Otorhinolaryngol. 20, (1973)] for the monkey and are comparable to hearing changes in human subjects with clinically diagnosed sensorineural hearing loss and recruitment. They can be contrasted to the hearing loss seen in man and monkey with a conductive loss. In the humans, the changes in hearing reflected in reaction time performance are similar to those observed in loudness matching studies in the laboratory and in the clinic. The results confirm that the reaction time task is indeed applicable to the experimental study of conductive and cochlear hearing losses and to physiological studies of threshold and loudness coding. [Work supported by PHS Grants NS 08181, RR 00166, NS S0637, and NS 05082.]

Reaction Time as a Measure of Threshold and Supra-threshold Hearing. III. The Effect of Stimulus Duration

White noise thresholds were investigated as a function of stimulus duration in a monkey performing an auditory reaction time task. Latency-intensity functions were obtained for six durations, ranging from S to over 200 msec. Threshold was defined for each duration from ogive functions relating percentage of correct responses to stimulus intensity. Increasing stimulus duration resulted in lower thresholds. The slope of the threshold-duration function was asymptotic to a minimum value as duration was increased. Suprathreshold hearing functions in the form of equal latency contours will be described. In addition, the effect of aspirin upon threshold was studied at three stimulus durations. The subject showed a temporary threshold hearing change similar to that observed using "brief-tone" audiometry in humans with a cochlear hearing loss. A general elevation of threshold was observed. The greatest change occurred with the longest duration stimulus. [Work supported by PHS Grants NS 08181, RR 00166, NS 50637, and GM 00260.]