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Biomedical subjects

D H Mershon

Publications and source records attributed to D H Mershon.

14 recordsLinked to original sources
PubMed1992

Spectral content as a cue to perceived auditory distance.

Changes in the spectral content of wide-band auditory stimuli have been repeatedly implicated as a possible cue to the distance of a sound source. Few of the previous studies of this factor, however, have considered whether the cue provided by spectral content serves as an absolute or a relative cue. That is, can differences in spectral content indicate systematic differences in distance even on their first presentation to a listener, or must the listener be able to compare sounds with one another in order to perceive some change in their distances? An attempt to answer this question and simultaneously to evaluate the possibly confounding influence of changes in the sound level and/or the loudness of the stimuli are described in this paper. The results indicate that a decrease in high-frequency content (as might physically be produced by passage through a greater amount of air) can lead to increases in perceived auditory distance, but only when compared with similar sounds having a somewhat different high-frequency content, ie spectral information can serve as a relative cue for auditory distance, independent of changes in overall sound level.

Acoustic Stimulation↗
PubMed1989

Effects of room reflectance and background noise on perceived auditory distance.

Perceptions of egocentric auditory distance were investigated within an environment for which the reverberation time could be systematically varied without changes in the size or shape of the room. Two levels of wide-band background noise, differing by 20 dB, were used as a masking stimulus. Target sounds were presented from distances between 0.75 and 6.0 m and verbal reports of distance were collected from 288 listeners in two separate experiments. Changes in physical distance produced variation in reported distance in each configuration. Reported distance was generally proportional to real distance, but considerably underestimated when room reflectance was low. When room reflectance was high (T60 approximately 1.7 s for the range of frequencies used), initial reports of distance were often overestimates; upon repeated presentation, judgments in the high reflectance room became more nearly veridical. The effect of increasing the background noise level was to decrease the perceived distance. These findings are in accord with expectations based upon the importance of reverberation cue(s) to distance and upon previous analyses from this laboratory.

Acoustics↗
PubMed1988

Time-of-day variations in oculomotor function: I. Tonic accommodation and tonic vergence.

Time-of-day variations were studied both in tonic accommodation and in tonic vergence. Thirty-six male volunteers were measured once in the morning and at one other time on the same day. The mean baseline value of tonic accommodation was 2.02 D. Time-of-day variations were found, with a late evening measure being +0.6 D greater than the morning value. No independent time-of-day fluctuations were found in tonic vergence. Post-hoc analysis, however, showed that tonic vergence tended to shift in the same direction as an individual's tonic accommodation during the afternoon. During the evening, tonic vergences tended to shift oppositely to tonic accommodation.

Accommodation, Ocular↗
PubMed1981

Perceived loudness and visually-determined auditory distance.

Three experiments were conducted to determine whether variations in the perceived distance to a test sound could influence its loudness in the absence of physical changes in sound-level. The phenomenon of visual capture provided the means for manipulating apparent distance. A 'dummy' loudspeaker was used to vary the apparent source location of a short noise stimulus while the true source of this sound remained fixed (and hidden) with respect to the observer. Sound-levels from 40 to 75 dB(A) were presented to independent groups of observers in either anechoic or semi-reverberant acoustical environments. In general, reported loudness increased with perceived distance. This finding has implications for conceptualizing the phenomenon of loudness constancy.

Acoustics↗
PubMed1980

Stability of measures of the dark focus of accomodation.

Without visual stimulation, the eye tends to assume an individually-determined intermediate state of accommodation (the "dark focus"). The present study examined the stability of these individual dark focus values over time. Two sets of measurements were obtained with a laser-Badal optometer for each of 39 college-age subjects. For 19 subjects the second test occurred during the same experimental session as the first; for 20 subjects the retest was conducted in a separate session 1 week later. Eye dominance was determined by a pointing task. High correlations between test-retest values were found for both immediate and delayed retest. The average change between the tests was less than +/- 0.3 diopter, even when the retest was a week later. These results indicate a definite stability in individual dark focus values. Eye dominance and subject's sex were both irrelevant.

Accommodation, Ocular↗
PubMed1979

Absolute and relative cues for the auditory perception of egocentric distance.

Three experiments were performed to examine the reverberation cue to egocentric auditory distance and to determine the extent to which such a cue could provide 'absolute', as contrasted with 'relative', information about distance. In experiment 1 independent groups of blindfolded observers (200 altogether) were presented with broadband noise from a speaker at one of five different distances (0.55 to 8 m) in a normal hard-walled room. Half of each group of observers were presented with the sound at 0 deg azimuth, followed (after a delay) by the identical sound at 90 deg azimuth. The order of presentation was reversed for the remaining observers. Perceived distance varied significantly as a function of the physical distance to the speaker, even for the first presentations. The change in the binaural information between the 0 deg and 90 deg presentations did not significantly modify the results. For both orientations, near distances were overestimated and far distances were underestimated. Experiment 2 and 3 were designed to evaluate how much prior auditory exposure to the laboratory environment was necessary. A 200 Hz square-wave signal was presented from one of three distances (1, 2, or 6 m) to observers who had either minimal room information or an exposure which included talking within the room. Perceived distance varied significantly with physical distance regardless to exposure condition.

Acoustic Stimulation↗
PubMed1977

On the use of "calibration equations" in perception research.

Gogel's procedure of using "calibration equations" to obtain reports of perceived distance which are at least partially independent of individual differences in response bias, was examined. The procedure involves determining the relationship between reported and physical distances in a full-cue viewing situation. By making four assumptions, this equation can be used to "calibrate" responses gathered from other situations in which perceived distances are under investigation. In the present experiment, both verbal and string-pull measures of perceived distance were obtained for several objects under reduced viewing conditions. Calibration equations were determined for each response measure in a full-cue setting. The usefulness of the calibration technique was tested by comparing the differences between the two response measures for each object seen in reduced viewing, both before and after the application of the calibration procedure. The results indicated that, consistent with the usefulness of the calibration technique, group differences between the measures were almost always decreased by the procedure. However, no general improvement in the agreement of the measures was found when the data were examined on an individual basis. From the results, a modification of the method of calculating calibration equations was suggested that might increase its usefulness by simplifying the arithmetic operations required for the procedure.

Adolescent↗
PubMed1977

Scalar perceptions of distance in simple binocular configurations.

Under reduced viewing, a single visual object tends to appear about 2 m away. Gogel (1972) found that the far point in a binocular configuration of two points of light also tended to appear about 2 m away, while the near point was displaced toward the observer. Attempts to replicate this latter result with points of light, as well as with a large rectangle for the nearer object, proved generally successful. Under some conditions, however, the far point was perceived to be closer to the observer when seen with the near point than when seen alone or with the rectangle. This unexpected result suggests caution in assuming that the far object in such a configuration will always remain at a stable perceived distance.

Distance Perception↗