Abstract/Results:
| ABSTRACT:
Humans possess an internal model of gravity, which allows the accurate perception of what is up and what is down, or, in other words, what is vertical. The integration of vestibular-gravitational information with other somatic signals is essential for sensing
verticality. Vestibular cues are known to influence verticality representation in visual domain. However, it remains unclear how we perceive verticality for stimuli applied to the skin surface. Theoretically, as bipedal animals, the neuraxis, as well as vestibular signals, might represent a proxy for verticality. To address this question, a psychophysical subjective tactile vertical task has been combined with galvanic vestibular stimulation (GVS) in healthy participants. Brief left anodal and right cathodal GVS, or right anodal and left cathodal GVS, or sham stimulation were delivered at random while participants judged the orientation of lines drawn on their forehead. Online vestibular signals induced by GVS did not produce misperceptions of tactile verticality. Conversely, asking participant to tilt the head induced a clear bias in verticality judgements toward the neuraxis. This bias was present also for stimuli not aligned with the body midline. Taking together, these results support the idea of two distinct representations of verticality: a vestibular representation, based on the direction of gravity, which is adopted as reference for visual verticality judgements, and a somatosensory representation which is not based on any online vestibular-gravitational signal, nor on the midline. The neuraxis is a critical reference for this representation.
|
Reference:
| Ferrè, E. R, Gallagher, M., & Haggard, P. (2016, June). Two signals for verticality. Paper presented at the Barany Society, Seoul, Korea.
|