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The precedence effect refers to the phenomenon which characterizes noise tolerance of the auditory system during sound source localization. The effect provides capability of the auditory system to select spatial information for the direct sound from a source by suppression information for reflections (echo) interfering with the
direct sound. This study examined the precedence effect for stationary and moving sound stimuli in conditions of the horizontal and vertical sound source localization.
Experiments were conducted for normal hearing subjects in an anechoic chamber. Sound stimuli were presented through an array of 49 stationary loudspeakers mounted on a semicircular rotating hoop. A leading stimulus simulating the direct sound was delivered from a stationary loudspeaker. A lagging echo was a moving stimulus produced by presenting sound bursts sequentially from the loudspeakers in the array. A time delays between the leading and lagging stimuli were varied within 1-120 ms. In this conditions the subjective trajectory of the echo movement shifted toward the location of the leading sound source and shortened in length. At shortest delays (several ms) the impression of echo motion could be vanished and combined with perception of the lead-lag stimulus near the location of the leading stimulus. With increasing delays the perceived location of the starting point of the echo movement trajectory shifted monotonically toward the starting point of the moving echo with simultaneous increasing of the subjective trajectory length. Comparison of the precedence effect in the horizontal and vertical planes revealed a substantial weakening of this effect in the horizontal plane.