The effect of head roll on perceived auditory zenith.

We studied the influence of static head roll on the perceived auditory zenith in head-centred and world-centred coordinates. Subjects sat either upright, or with their head left/right rolled sideways by about 35° relative to gravity, whilst judging whether a broadband sound was heard left or right from the head-centred or world-centred zenith. When upright, these reference frames coincide. Results show that subjects judged the zenith accurately within different planes, although response variability increased for the midsagittal plane. With the head rolled, head-centred auditory zenith shifted by the same amount and was located as accurately as for upright, indicating unaltered localisation cues by head-on-body roll. Interestingly, when judging world-centred zenith subjects made large systematic errors (10-15°) in the direction of head roll, and response variability increased, which resembles the visual Aubert effect. These results demonstrate a significant influence of the vestibular-collic system on auditory spatial awareness, which sheds new light on the mechanisms underlying multisensory integration and spatial updating in sound localisation behaviour.