Velocity discrimination of auditory image moving in vertical plane.

This research investigated the ability of humans to discriminate changes in velocity of apparent movement of a sound source (as defined by the time required for the sound to traverse a 180 deg arc) in the median vertical plane. Apparent auditory movement was created by successive switching of the loudspeakers situated over the arc. The broadband noise with band width of 0.25-4 kHz (low-pass noise - LP) and of 4-12.5 kHz (high-pass noise - HP) was employed as stimuli. Discrimination thresholds were calculated for reference velocities of 58 and 115 deg/s under four stimuli types: movement of stepped movement of noise for low-pass noise and for high-pass noise and continuous motion for low-pass noise and for high-pass noise. The result showed that discrimination of the velocity depended on the signal frequency spectrum. The differential thresholds for the signals with low pass noise were significantly higher than those for signals with high pass noise (F(1;78) >> 3.96, p < 0.05). Magnitude of the absolute thresholds was the highest when the velocity was 115 deg/s for each of four types. It is interesting to note that the thresholds magnitude depended on the type of signal motion, that is on whether it was continuous or stepped.