Grasp Aperture

Grasp aperture is the distance between the thumb and opposing finger(s) as the hand opens to receive an object during a reach. It scales with perceived object size, peaks before contact at a value typically larger than the object itself, and then closes to grip - a well-studied kinematic signature of motor planning. In accessibility research, grasp aperture is used as a behavioural measure of pre-grasp planning: excessive aperture or a failure to scale with size signals that the user lacks anticipatory information about the object, a pattern commonly seen when visually impaired users reach without assistive cues.