Perceptual collapse: The fusion of spatially distinct tactile cues into a single percept

This work investigates how haptic percepts are combined across two fingertips. Two single-degree-of-freedom haptic interfaces were used to present virtual bumps to the thumb and index finger of subjects' right hand. As subjects slid the two interfaces from left to right while maintaining a fixed finger separation, they would encounter one bump with the index finger and one with the thumb. The objective bump locations were varied randomly, from spatially coincident to separated by slightly more than the fingertips. Subjects were asked to report the number of bumps in the objective world and the number of times they encountered each bump, and also to point to the locations of the bumps. We found that subjects exhibited a strong bias toward reporting a single objective bump in the virtual world. However, the percept varied from one bump encountered twice, when the two virtual bumps were nearly spatially coincident, to one bump encountered once, which occurred when the two virtual bumps were close to finger separation and therefore encountered nearly simultaneously. The latter result is evidence for a kinesthetic grouping phenomenon: temporally synchronized sensations at multiple fingers can be perceptually collapsed into a single percept in both time and space.