Donald W. Nielsen

Interaural attenuation versus frequency for guinea pig and chinchilla CM response.

Interaural attenuation was estimated for the guinea pig and the chinchilla by determining isopotential curves for the cochlear microphonic (CM) response produced by contralateral and by ipsilateral stimulation at frequencies from 300 Hz to 14.3 kHz. Intracochlear electrodes were used to record the CM from the basal turn. For ipsilateral stimulation, bulla‐sealed to bulla‐open sound pressure ratios showed effects similar to those reported by other investigators: 10–12‐dB loss for chinchilla and 20–22‐dB loss for the guinea pig for the bulla‐sealed condition. The variability of the sound pressure measures, considered across animals, was larger in chinchillas than in guinea pigs, and the variance was greatest at frequencies near those at which the external auditory canals and bulla cavities show resonant peaks. There appears to be additional low‐frequency resonances associated with contralateral stimulation for the closed bulla in the chinchilla, largest at 1.1 kHz for frequencies sampled in this report. The...

Interaural time vs. interaural intensity in a lateralization paradigm

In a two-interval lateralization procedure, observers judged whether a stimulus presented with an interaural intensive difference was right or left in lateral space of the same stimulus presented with only an interaural temporal difference. The stimuli were pure tones of 500 and 1,000 Hz and 1,000-Hz low-pass noise. All stimuli were presented at both 65 and 55 dB SPL. For each of several values of interaural time (ranging from 0 to 1,000 microsec across all stimuli), a function was determined which related proportion of “right” relative position judgments to the value of the interaural intensive difference. The intercepts of these functions indicated that a progressively smaller amount of interaural intensive difference was required for the two stimuli to occupy a similar lateral location as the interaural temporal difference was increased. The slopes of the function suggested that the images associated with larger values of the interaural temporal differences are less distinct and blend together more than the images associated with small values of the temporal difference. Thus, the procedure provided a means for comparing the lateral location of images produced by interaural differences of time and intensity.

Variation in cortical evoked responses as a function of performance criterion

Averaged evoked cortical responses (CER) from the scalp of human Ss were recorded within an experimental paradigm that permitted the performance criterion to be varied. The signals evoking the cortical responses were contingent upon S’s pressing a button to bisect a temporal interval within certain tolerance limits. Under passive conditions averaged response waveforms lacked a second, late component that became prominent under temporal bisection conditions. The late component P2 - N2 increased regularly in magnitude as the performance criterion was made more stringent. The effect of performance criterion on the earlier component, N1 - P2, was neither as large nor as systematic as that shown by P2 - N2.

Tone-on-tone binaural masking with an antiphasic masker

One pure tone (500 Hz) was used to mask another pure tone of the same frequency and duration. The signal and masker were presented in three binaural stimulus configurations, Mo-So, Mo-Sπ, and Mπ -So. The Mo-So condition is a diotic condition; the Mo-Sβ condition is a dichotic condition in which the masker is homophasic and the signal is antiphasic; and the Mπ-So condition is a dichotic condition in which the masker is antiphasic and the signal homophasic. The signal-to-masker ratio required for detection was measured in each condition as a function of the signal-plus-masker phase angle, α. The data showed that the difference in detection between the Mo-Sπ and Mπ-So conditions varied between 0 dB when α=0 deg and 11 dB when α=90 deg. The difference in detection between the Mo-Sπ and Mπ-So conditions is due to the Os’ sensitivities to the interaural phase difference present in the Mo-Sπ and Mπ-So conditions. The results are similar to those obtained in investigations involving lateralization. The difference between detection in either the Mo-Sπ or Mπ-So condition and that in the Mo-So condition (the MLD) was variable due to differences in the Os’ sensitivities in the Mo-So condition.

Squirrel monkey temporary threshold shift from 48‐h exposures to low‐frequency noise

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.

Comparison of the response of the two‐fiber populations in the auditory nerve of the alligator lizard

The basilar papilla of the alligator lizard (Gerrhonotus multicarinatus) contains two anatomically distinct hair cell populations. The apical population has unidirectional orientation and is associated with a tectorial membrane. The dorsal population has bidirectional orientation and free‐standing cilia. On the basis of tuning curve properties, the primary auditory nerve fibers have been categorized into low ( 0.9 kHz) CF populations. These two populations have been associated with the apical and basal regions of the papilla, respectively [Weiss, Mulroy, Turper, and Pike, J. Acoust. Soc. Am. 55, S84(A) (1974)]. The objective of the present study was to determine if other measures of the physiological response of the fibers could distinguish the two fiber populations. Action potentials were recorded from single, primary auditory nerve fibers in response to click, tone burst, and noise burst stimuli. The data indicate significant differences in the response of the two‐fiber populations t...

Discharges of auditory nerve fibers in the alligator lizard in relation to basilar papilla morphology

In the ventral region of the basilar papilla of the alligator lizard (Gerrhonotus multicarinatus) hair cell orientation is unidirectional, in the dorsal region, bidirectional. On the basis of differences in the shape of tuning curves, the auditory nerve fibers have been categorized into a low (CF 1 kHz) frequency group; these groups have been associated with the ventral and dorsal regions, respectively [Weiss et al., J. Acoust. Soc. Am. 55, S84 (1974)]. In the present study, action potentials were recorded from single high‐ and low‐frequency fibers in response to condensation and rare‐faction clicks, filtered clicks, and tone bursts. The discharge patterns of high‐ and low‐frequency fibers depended upon stimulus polarity. High‐frequency fibers were categorized as type 1 and type 2. The response of a type 1 fiber to a stimulus of one polarity was the same as the response of a type 2 fiber to that simulus with opposite polarity. The two response categories for high‐frequency fibers and the lack of equivalent categories for low‐frequency fibers appear related to the bidirectional and unidirectional orientations of the hair cells. [Work supported by NIH grants NS07287, NS06459, and NS05475.]

Interaural time versus interaural intensity in a lateralization paradigm

In a two‐interval lateralization procedure, observers were to judge if a stimulus presented with an interaural intensive difference was right or left in lateral space of the same stimulus presented with only an interaural temporal difference. The stimuli were pure tones of 500 and 1000 Hz, and a 1000‐Hz low‐pass noise. All stimuli were presented at both 65 and 55 dB SPL. For each value of interaural time (ranging from 0 to 1000 μsec across all stimuli), a function was determined which related proportion of “right” judgments to the value of the interaural intensive difference. Changes in interaural time moved the lateral image a decreasing amount of lateral distance as the interaural temporal difference increased from zero. Changes in interaural intensity, however, mapped linearly onto lateral position. Thus, the procedure provided a means for comparing the lateral location of images produced by interaural differences of time and intensity. [These experiments were conducted with support from National Institute of Health (NIH) Program Project Grant, an NIH training Grant, and an NIH Research Grant.]

Frequency discrimination and masking effectiveness.

Previous research has shown a positive relationship, across frequencies, between frequency discrimination limens and critical‐ratio size; these were based upon data obtained from groups of subjects (Ss). The question was therefore raised as to whether or not the critical ratio was related to the frequency‐discrimination ability of individual Ss. The present study shows a complete lack of relationship between critical ratios and frequency discrimination limens of individual Ss at a frequency of 1000 Hz.

Hot topics in physiological acoustics

For those in the Society whose main interest lies in other acoustic fields, the presentation will review current topics in physiology of audition. Much basic physiological research has been focused on the micromechanics of the cochlea, the end organ of hearing. For many years the cochlear tuning process was through to be passive and mechanical; however, recent studies indicate that active motion of one group of cochlear hair cells adds to and sharpens the tuning. The results and implications of studies of outer hair cell motion will be discussed. Also discussed will be the cochlear implant, a device that addresses injury or loss of cochlear hair cells, the cause of most incurable forms of deafness. With this device, the electric fields of electrodes surgically implanted in the cochlea stimulate the nerve supply in the absence of normal hair cells. Also presented will be recent advances in molecular biology that attempt to induce growth or regrowth of hair cells in cochleae that have none.