There are few things in life as familiar as your own body, but a study published in the journal Perception shows that our sense of self starts to disappear when we lose our sense of sight. In fact, the scientists report that people have a difficult time identifying their own toes when their eyes are closed.
The study participants were touched on their fingers and toes without their being able to see which digit was being touched, and then asked to identify the digit being singled out.
Fingers were a cinch, with testers identifying the correct one about 99 percent of the time. Accuracy dropped slightly, to 94 percent, for the big and pinky toes. But it plummeted with the three middle toes, to as low as 57 percent. These little piggies gave testers the toughest time.
“The key issue was distinguishing between the second and third toes [the toes next to the big toe],” said Dr. Nela Cicmil of Oxford's Department of Physiology.
While some did better than others, every participant had some degree of difficulty in identifying the correct toes. This sort of misidentification is called “agnosia.” The National Institute of Neurological Disorders and Stroke describes it as “an inability to recognize and identify objects or persons.”
Not only did people share the struggle to correctly identify their digits, they exhibited a similar pattern in which the second toe was believed to be the third, and the third toe was believed to be the fourth. The troubles were even worse when testing the nondominant foot. The most surprising discovery: Nearly half of the testers reported feeling as if one toe were gone.
The results could be a valuable tool for understanding more about how agnosia or other body misperceptions work. Moreover, the fact that the healthy humans in the study still had trouble with what might have been considered an easy task could also hold answers for future brain-damage testing.