Effects of natural versus artificial spatial cues on electrophysiological correlates of auditory motion

The effect of the type of the auditory motion stimulus on neural correlates of motion processing were investigated using high-density electroencephalography. Sound motion was implemented by (a) gradual shifts in interaural time or (b) level difference; (c) motion of virtual 3D sound sources; or (d) successive activation of 45 loudspeakers along the horizontal plane. In a subset of trials, listeners (N = 20) performed a two-alternative forced-choice motion discrimination task. Each trial began with a stationary phase of the acoustic stimulus in a central position, immediately followed by a motion of the stimulus. The motion onset elicited a specific cortical response that was dominated by large negative and positive deflections, the so-called change-N1 and change-P2. The temporal dynamics of these components depended on the auditory motion cues presented: Free-field motion and virtual 3D motion were associated with earlier cortical responses and with shorter reaction times than shifts in interaural time or level. Also, free-field motion elicited much stronger onset responses than simulated motion. These findings suggest that natural-like stimulation using stimuli presented in the free sound field allows more reliable conclusions on neural processing of sound motion, whereas artificial motion stimuli, in particular gradual shifts in interaural time or level, seem to be less suited with respect to this aim.