Perception of approaching and withdrawing sound sources after exposure to broadband noise: The importance of spatial domain

Abstract

The existence of space-specific differences in auditory aftereffects has been tested under short-term (5 s) exposure to broadband noise (20–20000 Hz). Adapting stimuli were emitted as constant-amplitude noise sequences. Test stimuli could be of constant and changing amplitude: increasing amplitude of noise pulses in a sequence mimicked an approaching sound source, whereas a decrease in amplitude was perceived as withdrawal. The experiments were done in an anechoic chamber. Auditory aftereffects were assessed under the following conditions: (a) adapting and test stimuli were emitted through a loudspeaker mounted at a distance of 1.1 m from the listener (i.e., subjectively near); (b) both stimuli were emitted from a distance of 4.5 m (subjectively far); (c) adapting and test stimuli were emitted from different distances. The results showed that the characteristics of perception of the imitated sound source motion were similar in proximity and remoteness, which was observed both in the control (without adaptation) and after adaptation to noise. In the absence of adaptation, the psychophysical curves were asymmetrical: the listeners reported approaching of test stimuli more often for both spatial domains. However, the overestimation of test stimuli as drawing closer was more pronounced when they were emitted from the distance of 1.1 m, i.e., from near the listener. After the adaptation to noise, the aftereffects showed spatial specificity and were observed only when adapting and test stimuli belonged to the same spatial domain. These aftereffects were similar in their pattern and strength both in proximity and remoteness: the listeners reported withdrawal of test stimuli more frequently as compared with the control. As a result of these aftereffects, the symmetry of psychometric curves was restored, and the estimation of the direction of sound source motion in the experiment became equiprobable.