Dynamic auditory localization: systematic replication of the auditory velocity function

Two experiments explored the capability of normal-hearing adults to judge the apparent velocity of an unseen moving sound source. In exper. I, 9 naive and, 1 experienced S judged the velocity of a moving source emitting a .5-kc/s tone at 50 db SPL. S's head was in the center of a circle of 1.88-m radius swept by a small loudspeaker. In exper. II the sound was a low-pass-filtered (0.1-1 kc/s) noise at 50 db sound spectrum level. In both experiments perceived velocity was directly proportional to the actual velocity of the source. These results support out initial observations (Waugh et al, J. Aud. Res., 1979, 19, 103-1 10) that auditory velocity discrimination can be described as a power function with an exponent of 1.0. In exper. II the Ss also varied the sound source velocity by means of a variable resistor to produce a perceived velocity of 100 degrees/sec. Performance on the adaptive velocity production task was successfully predicted from the data of the absolute velocity judgment task. The Weber fraction was .052 for relatively fast-moving sound sources (100 degrees/sec). The ability to discriminate sound source velocity appears to be a well-defined feature of the dynamic binaural spatial system.