[Sensitivity of the hearing system to the velocity of auditory motion: difference thresholds and mismatch negativity]

The parallel psychophysical and MMN study focused at the sensitivity of human hearing system to variations in velocity of sound image movement. The motion of sound stimuli with various velocities in the 450 deg/s to 732 deg/s range in increments of 6 deg/s to the left or to the right from the head midline was simulated by introducing linear changes of interaural delay into dichotic stimuli. The psychophysical experiments were designed according to the 2-alternative forced choice paradigm. The subjects were presented by pairs of moving stimuli and were asked to decide which moved faster. The stimuli created for the present study ensured that the subjects performed the discrimination task without relying on associated cues of sound displacement or duration. The psychophysical measures were compared with electrophysiological indexes of sound processing (auditory evoked responses (ERPs) and mismatch negativity (MMN)). Significant MMN was elicited by the difference of 170 deg/s between the reference and test velocity, which corresponded to the relative velocity increase of 38%. At the same time, the difference thresholds for velocity were much higher and exceeded 50%. The results suggest that MMN magnitude depended on the velocity difference between standard and deviant stimuli and was more sensitive to velocity difference than psychophysical measure.