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Biomedical subjects

R A Butler

Publications and source records attributed to R A Butler.

At least 37 records · Page 2Linked to original sources
PubMed1986

The bandwidth effect on monaural and binaural localization.

Listeners located, monaurally and binaurally, an 8.0 kHz centered noise burst whose bandwidth was set at 2.0, 4.0, 6.0 and 8.0 kHz. Loudspeakers, placed 7.5 degrees apart, covered an arc extending from 15 degrees to 165 degrees to the left of midline. Listeners reported the number of that loudspeaker from which the noise bursts appeared. A significant reduction in localization errors was associated with increments in bandwidth and for binaural localization, this was attained largely through fewer instances of confusing sounds from the front with those from the rear. While overall, binaural accuracy exceeded monaural accuracy when sounds came from the front or rear, no appreciable differences between the two listening conditions were noted when the sounds came from the middle section of the arc. Only when broadband noise was employed, as it was in a supplementary set of observations, did binaural localization uniformly surpass monaural localization in accuracy - a finding attributed to the introduction of low frequencies which resulted in the addition of interaural ongoing phase differences to the constellation of localization cues.

Acoustics↗
PubMed1985

Influence of monaural spectral cues on binaural localization.

Seven subjects located, monaurally and binaurally, narrow bands of noise originating in the horizontal plane. The stimuli were 1.0 kHz wide and centered at 4.0-14.0 kHz in steps of 0.5 kHz. The loudspeakers, 15 deg apart, were arranged in a semicircle (0-270-180 deg, azimuth). In the first part of the experiment all sounds emanated from the loudspeaker at 270 deg, but their apparent locations varied widely as a function of their center frequency. For each subject, the pattern of location judgments under the binaural listening condition corresponded to that recorded for the monaural condition. In the second part of the experiment the loudspeaker from which each of the same narrow bands of noise emanated was varied in irregular order. Again, monaural location judgments were governed by the frequency content of the noise bands. Binaural location judgments were strongly influenced by the sounds' frequency composition when the stimuli originated from 315-225 deg, notwithstanding the presence of interaural differences in time and intensity. For narrow bands of noise emanating off midline, monaural spectral cues significantly override binaural difference cues, and they also determine the resolution of front-back ambiguities.

Auditory Perception↗
PubMed1984

The psychophysical basis of monaural localization.

Listeners were required to locate, monaurally, noise bursts emanating from the horizontal plane ipsilateral to the functioning ear. Loudspeakers were positioned from 0 through 180 degrees azimuth, separated by 15 degrees. Stimulus bandwidth was 1.0 kHz, and centered at 4.0-14.0 kHz in steps of 0.5 kHz. The location judgments were governed by the frequency composition of the stimuli, not by their place of origin. With a miniature microphone positioned at the entrance of the external ear canal, the relative amplification provided by the pinna was obtained for the stimuli employed in the localization tests. For each differently centered noise burst, that loudspeaker position re other positions which was associated with the greatest amplification of the stimulus was the one most likely to have been chosen as the source of that stimulus during the localization tests.

Auditory Perception↗
PubMed1984

The influence of pinnae-based spectral cues on sound localization.

The role of pinnae-based spectral cues was investigated by requiring listeners to locate sound, binaurally, in the horizontal plane with and without partial occlusion of their external ears. The main finding was that the high frequencies were necessary for optimal performance. When the stimulus contained the higher audio frequencies, e.g., broadband and 4.0-kHz high-pass noise, localization accuracy was significantly superior to that recorded for stimuli consisting only of the lower frequencies (4.0- and 1.0-kHz low-pass noise). This finding was attributed to the influence of the spectral cues furnished by the pinnae, for when the stimulus composition included high frequencies, pinnae occlusion resulted in a marked decline in localization accuracy. Numerous front-rear reversals occurred. Moreover, the ability to distinguish among sounds originating within the same quadrant also suffered. Performance proficiency for the low-pass stimuli was not further degraded under conditions of pinnae occlusion. In locating the 4.0-kHz high-pass noise when both, neither, or only one ear was occluded, the data demonstrated unequivocally that the pinna-based cues of the "near" ear contributed powerfully toward localization accuracy.

Auditory Perception↗
PubMed1982

Sound as a reinforcer for infants' manipulations of toys.

We investigated the effectiveness of sound as a reinforcer of manipulative responses by infants. Fifty subjects, 4-12 months of age, were presented five different toys: (a) a barbell rattle; (b) a rattle shaped in the form of a whale; (c) a bracelet with bells; (d) a rubber pig that squeaked when squeezed; and (e) a drum that resonated when struck. The noise-making component of another set of identical toys was either removed or modified so that shaking the toy or striking it resulted in either no sound or a sharply attenuated one. Toys were presented singly for two minutes. Two observers, each equipped with a microswitch, recorded manipulations of each toy. The data were registered on magnetic tape and later displayed graphically. Noisy toys were manipulated significantly more frequent than quiet ones with infants from 6 to 10 months old. They were relatively more responsive to noisy toys than were our younger and older subjects. Since infants show a strong proclivity to make sounds, a reasonable assumption is that this propensity could be incorporated into a behavioral test for hearing. Simply stated, infants with profound hearing losses would not prefer noisy toys over quiet ones. Further research would be required for adapting the test situation to infants with more moderate hearing losses.

Age Factors↗
PubMed1980

Apparent distance of sounds recorded in echoic and anechoic chambers.

With miniature microphones inserted into the external ear canals of a model and the sound source 90 degrees to left of midline, low-pass, and broadband noise bursts were picked up and recorded on magnetic tape. The bursts were generated in two highly contrasting acoustic environments: an anechoic and an echoic chamber. The taped sounds were played back monaurally and binaurally via headphones to 16 listeners seated in an acoustically neutral setting. They were instructed to estimate the distance of the stimuli. Apparent distances of bursts recorded in the echoic or reverberant chamber far exceeded those recorded in the anechoic chamber. It mattered not whether the sounds were presented monaurally or binaurally. What did influence distance estimates dramatically was the frequency composition of the stimuli. Low-pass sounds recorded in either acoustic environment were consistently judged to be further removed than high-pass sounds recorded in the same setting. They were also more likely to appear from behind the listener. In our moment-to-moment transaction with the acoustic environment, distant sounds generally have less acoustic energy in the higher audio frequency. We suggest that this lifetime of auditory experience influenced our listeners' scale of relative distance.

Auditory Perception↗
PubMed1979

Estimation of distances of recorded sounds presented through headphones.

Intermittent sounds generated at 270 degrees azimuth and from distances ranging from 2 to 10 feet were recorded on magnetic tape and played back to listeners via headphones. Loudness cues for relative distance were eliminated at the time of recording. Listeners were required to estimate the apparent distance of the recorded sounds when heard monoaurally and binaurally. Most subjects estimated the order of distances correctly. Distance estimations were as proficient when listening monaurally as when listening binaurally. Performance was more accurate for high-pass (greater than 4.0 kHz) noise bursts than for low-pass (less than 1.0 kHz) noise bursts. In a second study, broad-band noise bursts were recorded from azimuthal positions of 360 degrees, 330 degrees, 300 degrees and 270 degrees again at distances ranging from 2 to 10 feet. Estimations of the distances of the sounds, presented via headphones, were most proficient when azimuthal position of the original stimuli was 330 degrees.

Acoustic Stimulation↗
PubMed1978

Directional hearing under progressive impoverishment of binaural cues.

Auditory stimuli--bursts of broadband, 4.0-kHz high-pass and 1.0-kHz low-pass noise--generated by loudspeakers arrayed in the horizontal plane were picked up by miniature microphones placed in the external ear canals and recorded on tape. When these recorded sounds were presented through headphones, listeners were able to identify the various loudspeakers that originally generated the sounds about as accurately as they could when the sounds were presented free-field. When the recorded sounds were processed so that either one or more of the interaural difference cues were removed directly or their removal was approximated, performance proficiency depended upon the frequency composition of the stimulus. It appeared that accuracy in identifying the loudspeaker that originally generated the broadband and 1.0-kHz low-pass noises could be maintained by the presence of interaural temporal differences. Accuracy on the task for the 4.0-kHz high-pass noise depended in large part on the presence of interaural intensity differences. No one performed proficiently when only interaural spectral differences were available.

Acoustic Stimulation↗
PubMed1978

Stimulus factors which influence the perceived externalization of sound presented through headphones.

Several experimental conditions were arranged to study the influence of binaural difference cues on the externalization of sound. Broadband, high- and low-pass noise bursts were generated in a sound-treated but not echo-free room and tape recorded from electret microphones placed at the entrance to the ear canals in a live model. The tapes were processed in special ways in an attempt to dissociate the binaural differences in time, intensity, and spectrum which normally appear together and congruently when listening to a sound 90 degrees off midline. These variously processed tapes of trains of noise bursts were played back via headphones to 12 normal-hearing Ss; they were asked to estimate the apparent distance of the acoustic image. No significant differences in distance judgments were found among listening conditions which consisted of: (1) interaural differences in time, intensity, and spectrum (i.e., simulating free-field listening); (2) interaural differences in time and spectrum only; and (3) interaural differences in time only. With respect to interaural time differences, it was found in a second experiment with 16 normal-hearing Ss that differences in time of stimulus arrival promoted externalization of sound, since when these were eliminated (leaving only interaural differences in the ongoing aspects of the fine structure of the stimuli) all sounds appeared significantly nearer the head. A consistent finding was that high-pass noise bursts appeared nearer the head than low-pass noise bursts irrespective of the conditions of stimulus presentation.

Acoustic Stimulation↗