'Action Space' Is Determined by Our Hands

Researchers at the Hebrew University of Jerusalem and Hadassah Hospital-Mount Scopus have recently published the results of a new study they conducted, which shows that our hands play a crucial part in our perception of the space immediately around us. In addition to denoting something close to us, the expression “within the reach of our hands” also symbolizes something called “action space.” This is the area around us that we can reach with our hands, to perform tasks such as grabbing and touching.

The team determined that, within this space, the position of objects was ordered inside our brains based on hand-centered coordinates. This means that the brain processes these objects in regards to the positions of our own hands. But the group was curious in learning whether the amputation of the hands in any way affected this ability. Their results seem to show that it does. It was found that, in people who had lost one or both hands, the visuospatial perception in the action space was severely distorted.

The investigation was conducted on participants with either left- or right-hand amputations. They had to participate in a rather simple test to prove the team's hypothesis. They were asked to look at a cross, displayed at the center of a computer screen. While they were focusing their attention on it, white squares briefly flashed on the right- or left-hand side, and they had to indicate which of the two was further away from the central cross. It was additionally found that both types of amputees tended to underestimate the distance at which the squares appeared from the cross, AlphaGalileo reports.

“This shows that the possibility for action in near space shapes our perception – the space near our hands is really special, and our ability to move in that space affects how we perceive it,” the team explains. “Current rehabilitation approaches that emphasize action on the affected side may reverse this process,” it adds. Details of the work appear in the latest issue of the respected scientific journal Psychological Science. Authors include neuroscientists Dr. Tamar R. Makin, Meytal Wilf and Dr. Ehud Zohary of the Alexander Silberman Institute of Life Sciences at the Hebrew University of Jerusalem, who collaborated closely with colleague Dr. Isabella Schwartz, from the Hadassah Mount Scopus Hospital.