The area within arm's length - in other words, the area with which we can directly interact - is called the "action space." Previous research had indicated that the brain judges distance within the action space in terms of the hands.
However, it had not been confirmed whether the hands merely help our brains better understand spatial positions or if they are actually required to figure out where objects in the action space are.
To test this question, a research team at the Hebrew University of Jerusalem and Hadassah Hospital-Mount Scopus tested a group of people who had had their hands amputated to see how their visual perception of nearby objects had been affected. The volunteers were told to focus on a screen where a cross was projected in the center. On either side were squares of variable distance from the cross. The subjects were asked to judge which of the two squares was farther away.
The results reveal that hand amputations affect visuospatial perception. When the right square was slightly farther away from the center, participants with right-hand amputations tended to perceive it as being at the same distance from the center as the left square; this suggests that these volunteers underestimated the distance of the right square relative to the left. Conversely, when the left square was farther away, left-hand amputees perceived both squares as being equally far away from the center — these participants underestimated the left side of near space.
Interestingly, when the volunteers were seated farther away from the screen, they were more accurate in judging the distances, indicating that hand amputations may only affect perception of the space close to the body.