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.
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.
A study was performed on the human factors characteristics of a mirror traffic control aid. The mirror aid studied was installed at a "T" intersection as an attempt to improve the detection of vehicles proceeding along a curved through street. The intention of the traffic engineers was that the mirror aid be used in combination with direct viewing of these vehicles.Three experiments were performed at the intersection. Experiment 1 was an unobtrusive observation of the use of the mirror by drivers stopping at the intersection. Experiment 2 was a door-to-door survey of drivers living in the neighborhood adjacent to the intersection. Driver profiles and attitudes toward mirror effectiveness were sought in the survey. Experiment 3 assessed the physical characteristics and perceptual and cognitive demands of the mirror aid upon drivers.by drivers proceeding through the intersection. Drivers found the mirror to be generally ineffective: They claimed that its images were too small to be easily seen, that cues to distance, depth, speed, and direction of motion were deceptive, and that normal climactic variations made the mirror unusable during much of the time. Physical measurements confirmed these subjective observations. for the improvement of driver performance and security at intersections where a mirror aid is considered.
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