Visual-auditory distance constancy.

Abstract

Engel and Dougherty's report1 on visual–auditory distance constancy states that judged simultaneity of equidistant flashes and clicks varies less as observer–source distance changes than would be predicted from variation in the arrival of clicks at the ears. That is, apparent simultaneity of visual and auditory stimuli exhibits a degree of perceptual constancy with variation in their temporal spacing concomitant on source distance. While this particular instance of auditory constancy has not been noted previously, early work by Mohrmann2 suggests an explanation of the recent observation. Mohrmann required his subjects to judge the loudness of a variety of sounds including speech, music, metronome clicks, noise and tones located at 0.75, 2.37 and 7.50 m. Although the intensity of the sounds at the ear varied with their distance, loudness changed less than predicted from the stimulus. This auditory loudness constancy occurred either in the dark without prior acquaintance with the laboratory, or with blindfolded subjects who viewed the laboratory between tests, or with subjects who viewed the laboratory throughout. Thus, even without visual information, the loudness of sounds is relatively constant as stimulus intensity varies with source distance. It is conceivable that in the Engel and Dougherty experiment the constancy of apparent flash–click simultaneity was secondary to the loudness constancy of the click. That is, constant loud-ness may have provided a basis for judgments of stimulus timing. Such an interpretation seems more plausible than one attributing both forms of constancy to a common base, as loudness constancy is probably correlated with the streaming velocity of the sound3. It would be of interest to compare the degree of auditory loudness constancy with that of flash–click constancy at different distances to establish whether the functions are similar.