Abstract
Gravity provides an absolute verticality reference for all spatial perception, allowing us to move within and interact effectively with our world. Bayesian inference models explain verticality perception as a combination of online sensory cues with a prior prediction that the head is usually upright. Until now, these Bayesian models have been formulated for judgements of the perceived orientation of visual stimuli. Here, we investigated whether judgements of the verticality of tactile stimuli follow a similar pattern of Bayesian perceptual inference. We also explored whether verticality perception is affected by the postural and balance expertise of dancers. We tested both the subjective visual vertical (SVV) and the subjective tactile vertical (STV) in ballet dancers and non-dancers. A robotic arm traced downward-moving visual or tactile stimuli in separate blocks while participants held their head either upright or tilted 30° to their right. Participants reported whether these stimuli deviated to the left (clockwise) or right (anti-clockwise) of the gravitational vertical. Tilting the head biased the SVV away from the longitudinal head axis (the classical E-effect), consistent with a failure to compensate for the vestibulo-ocular counter-roll reflex. On the contrary, tilting the head biased the STV toward the longitudinal head axis (the classical A-effect), consistent with a strong upright head prior. Critically, tilting the head reduced the precision of verticality perception, particularly for ballet dancers’ STV judgements. Head tilt is thought to increase vestibular noise, so ballet dancers seem to be surprisingly susceptible to degradation of vestibular inputs, giving them an inappropriately high weighting in verticality judgements.
Highlights
Perceiving the direction of gravity is vital for balance and orientation in space
Our study investigated the roles of dance expertise, head posture, and stimulus modality in perception of the direction of gravity
Female ballet dancers and non-dancer control participants judged the angular deviations of downward-moving visual stimuli or tactile stimuli, relative to the gravitational vertical
Summary
Perceiving the direction of gravity is vital for balance and orientation in space. The vestibular system is a key source of sensory information about the orientation of one’s own body relative to the gravitational vertical. Studies have demonstrated the superior balance and proprioceptive abilities of professional dancers, compared with amateur dancers or non-dancers (Chatfield et al, 2007; Crotts et al, 1996; Golomer et al, 1999; Jola et al, 2011; Ramsay and Riddoch, 2001; Rein et al, 2011) Those skills may be associated with a greater reliance on vestibular and proprioceptive cues, rather than exterocep tive cues such as vision, to determine the position and orientation of the body (Golomer et al, 1999; Golomer and Dupui, 2000; Jola et al, 2011). Ballet dancers may integrate multisensory cues to the gravitational vertical differently than non-dancers do, and that difference could manifest as greater precision and less bias in their verticality judgements
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