Sensitivity of the hearing system to the velocity of auditory motion: Discrimination thresholds and mismatch negativity

Abstract

The capacity to discriminate velocity of moving sounds is an important characteristic of the hearing system in terms of sound localization. Experiments have shown that the human hearing system distin guishes fast sound movements worse than slow ones. The sensitivity to spatial displacement of the stimulus gradually decreases with increasing stimulus velocity. This is quantitatively expressed in a linear increase in the minimum audible angle of stimulus displacement with an increase in the stimulus velocity (reviewed in [1]). The decrease in the spatial resolution of the hear ing system is accompanied by a decline of its sensitivity to the change in the stimulus motion velocity. The absolute value of the velocity discrimination threshold monotonically increases with increasing stimulus motion velocity [2-6].The neuronal mechanisms of human perception of the sound motion velocity are not entirely clear to date. Studies on the electrical brain activity show that the characteristics of auditory event related potentials (ERPs), such as the N1P2 component, may vary depending on the motion velocity. An increase in the velocity leads to an increase in the N1P2 amplitude and decrease in its latency. These characteristics of the response are distinct at high motion velocities (more than 90°/s) and disappear as the velocity decreases [7]. The insensitivity of ERPs to slow movements of sound stimuli has been confirmed by experiments where the stimulus began moving after a delay relative to its onset [8][9][10][11]. Under these conditions, the ERP correspon ding to the moving fragment of the signal was absent at low velocities, appeared at velocities of 90-100°/s, and then monotonically increased with increasing velocity.In studying ERPs, the response to the stimulus motion velocity is estimated by the change in the response strength when the velocity is changed. A similar index can be obtained for experiments where the mismatch negativity (MMN) potential is recorded. MMN is the negative component of the auditory ERP generated in response to various changes in the sound stimulus. To date, the phenome non of MMN during sound motion has been studied under the conditions of dichotic auditory stimulation simulating azimuthal sound movement [12][13][14]. The classical oddball paradigm was used, with stationary and moving stimuli serving as the standard and deviant signals, respectively. The stimulus motion velocity was varied by using different combinations of the angular trajectory length and stimulus movement time. Under these conditions, the MMN increased with increasing trajectory length and stimulus velocity. This study has shown that the sensitivity of MMN to the change in the stimulus velocity is largely determined by simulta neous changes in the angular trajectory length.The interrelation of motion parameters (time, dis tance, and velocity) is the key problem in subjective discrimination of velocity. The motion velocity is determined by the distance travelled and the time of motion, which may themselves serve as cues for d...