Humans use dominant hand as a constant perceptual 'ruler'

People tend to perceive their dominant hand as staying relatively the same size even when it is magnified, supporting the idea that we use our hand as a constant perceptual "ruler" to measure the world around us, says a study.

This suggests that our bodies are used as perceptual metrics, meaning that we are more likely to attribute changes in the perceived size of the hand to changes in the world.

"Instead of thinking that our hand has become bigger, we are more likely to think that the world around the hand has become smaller instead," explained Sally Linkenauger, psychological scientist from the Lancaster University in Britain.

Linkenauger and colleagues hypothesised that the dominant hand might be the most useful metric for objects of commensurate size because it is one of our primary means of interacting with our environment, through both touch and grasp.

Using magnification, the researchers conducted several experiments to test whether the dominant hand is used as a constant, reliable metric.

Across five experiments, participants viewed their dominant hand, as well as various other items, under 18 percent magnification.

Results showed that participants consistently estimated their dominant hand to be significantly less magnified than non-dominant hand, their foot, an experimenter's hand and foot and a pen.

"In most cases, individuals knew that their dominant hand was under the same degree of magnification as another's hands, feet and objects, yet they persisted to report that what they experience was a smaller degree of magnification for their dominant hand," Linkenauger noted.

Individuals typically like to be consistent and right but this effect seemed to override those affectations, he added.

According to researchers, this may have implications for certain neurological conditions.

The findings were published in the journal Psychological Science.