Sound frequency affects the auditory motion-onset response in humans

The current study examines the modulation of the motion-onset response based on the frequency-range of sound stimuli. Delayed motion-onset and stationary stimuli were presented in a free-field by sequentially activating loudspeakers on an azimuthal plane keeping the natural percept of externalized sound presentation. The sounds were presented in low- or high-frequency ranges and had different motion direction within each hemifield. Difference waves were calculated by contrasting the moving and stationary sounds to isolate the motion-onset responses. Analyses carried out at the peak amplitudes and latencies on the difference waves showed that the early part of the motion response (cN1) was modulated by the frequency range of the sounds with stronger amplitudes elicited by stimuli with high frequency range. Subsequent post hoc analysis of the normalized amplitude of the motion response confirmed the previous finding by excluding the possibility that the frequency range had an overall effect on the waveform, and showing that this effect was instead limited to the motion response. These results support the idea of a modular organization of the motion-onset response with the processing of primary sound motion characteristics being reflected in the early part of the response. Also, the article highlights the importance of specificity in auditory stimulus design.