Persistent perceptual delay for active head movement onset relative to sound onset with and without vision.

Knowing when the head moves is crucial information for the central nervous system to maintain a veridical representation of the self in the world for perception and action. Previous studies have shown that active head movement onset has to precede a sound by approximately 80 ms to be perceived as simultaneous, suggesting that the perceived timing of head movement is slow. However, this research was conducted with closed eyes. Given that visual information is available for most natural head movements, could perceptual delays in head movement onset be related to removing vision? Here, we examined whether visual information affects the perceived timing of active head movement onset. Participants performed a series of temporal order judgment tasks between their active head movement and an auditory tone presented at various stimulus onset asynchronies. Visual information was either absent (eyes closed) or present while either maintaining fixation on an earth or head-fixed target in the dark or in the light. Results show that head movement onset has to precede a sound by 76 ms with eyes closed confirming previous work. The results also suggest that head movement onset must still precede a sound when fixating targets in the dark with a trend for the head having to move with less lead time with visual information and with the vestibulo-ocular reflex active or suppressed (70 to 48 ms). Together, these results suggest that the perception of head movement onset is persistently delayed and is not fully resolved even with full field visual input.