Detecting changes in distance in an anechoic and echoic environment

Abstract

Increasing the distance to an acoustic source produces: (a) low-pass filtering of the spectrum through absorption by the medium, (b) reduction in the overall sound-pressure level of the stimulus, and (c) changes in the temporal and directional relations between sounds along the primary acoustic pathway and those on secondary pathways (echoes). A simulated open-field environment [Hafter etal., J. Acoust. Soc. Am. 92, 2334 (1992)] consisting of an anechoic chamber and multiple computer-controlled speakers was used to study the discriminability of changes in distance. Simulated acoustic reflections were from a single, fully reflective wall. Assuming spectral cues would be ineffective with small changes of distance, the primary concern was with the roles of level and echoes. Other considerations included the changing temporal overlap of primary and secondary stimuli for lengthening trains of wideband, midfrequency (4-kHz center) impulses, and distance perception for single words and short phrases. Subjects reported that with echoes they always heard a change in distance, but without echoes, they heard either a change in distance orloudness. Thresholds were smallest when the changes were interpreted as distance, thus performance was generally better with echoes.