Abstract
The role of spatial vision in tactile, somatosensory and auditory tasks is well documented and neural substrates possibly underlying such interactions have been identified. Body position sense, for example, depends on touch, proprioception and spatial vision of the limb. It is however unknown if more fundamental visual information interacts with somatosensation such as in the position sense of body parts that cannot generally be seen. Here we expand on previous work (Wolfe et al., 2003) revealing an illusion that demonstrates that the position sense of the eyelid partly depends on information on the relative light intensities reported by the two eyes. When only one eye is dark-adapted (DA) and both eyes are exposed to a dim environment, the lid of the non-dark-adapted (NDA) eye feels closed or “droopy.” In three experiments each involving 7–14 subjects we show that subjects report significant decreases (p<0.001) in this effect when covering either eye by hand or with a patch, thus introducing tactile information congruent with the unequal visual inputs from the two eyes. Using a transparent disk as a cover, the effect decreases only when the NDA eye is covered, but remains unchanged when the DA eye is covered. Finally a decrease results when the illumination of both eyes is either reduced or increased such that the asymmetry in input the brain receives from the two eyes decreases. Our findings reveal an integration of vision with touch and proprioception that is not restricted to higher-level spatial vision but appears to be a more fundamental aspect of sensory processing than previously shown. Our results suggest that cross-modal percepts might result from a mechanism by which specific sensory inputs become coupled according to Bayes' rule. Wolfe U, Comee JA, Arvidson EM & Sherman BS (2003). A visually induced somatosensory illusion. ARVO Abstracts 4832