Illusory changes in a sound source and outflow theory.

Two experiments, with a total of 220 Ss, were conducted to investigate the possibility of illusory movement of a sound source. In Experiment 1 intensity level (from 10 to 60 db SPL) and frequency of an auditory sound (from 1000 to 5000 Hz) were varied while the Ss head was stabilized with a head rest; in Experiment 2, intensity and frequency were also varied while the S's head was free to move. When head position was fixed, error signal variables such as intensity had no effect on the frequency of illusory direction changes of a sound source. However, when the head position was not fixed, increasing the intensity of the sound source significantly decreased the number of reported illusory direction changes. In addition, in both experiments, illusory changes of intensity were experienced by Ss, and increasing the intensity of the sound source also decreased this illusion. The results were interpreted in the context of an error signal and noise model of autokinetic effects, and the implications for the perception of auditory localization and movement of a sound source were discussed.