Most people think they can keep track of their body parts fairly well. But a new study shows that telling the difference between any of the three middle toes is very difficult for most people to do without looking at them, reports Agence France-Presse (via South China Morning Post).
Researchers led by Nela Cicmil at Oxford University prodded the digits on the hands or feet of volunteers who kept their eyes closed. Like in an earlier study, people were whizzes at identifying which finger hand been touched (99 percent got it right), but they weren’t so hot at identifying the toes.
"The key issue was distinguishing between the second and third toes," Cicmil says in a press release. Apparently the piggy that stayed home and the piggy that got roast beef masquerade as each other, or perhaps people’s brains get them mixed up. The volunteers could only identify which of the three middle toes had been touched 57, 60 and 79 percent of the time. (People were good at identifying a touch to their big toe, with a 94 percent success rate, perhaps because that toe is important enough to merit a prosthesis when it’s missing.)
"Perhaps most amazingly, not a single participant was able to identify which of their toes was being prodded 100 percent of the time and some people could only get the right answer 20 percent of time," writes Gizmodo's Jamie Condliffe.
The researchers published the results of their toe-poking in the journal Perception.
The study may seem odd, but the confusion over body parts is part of a real phenomenon broadly called 'agnosia.' People with this condition have trouble processing sensory information. It can come in the form of loss of smell, inability to name specific classes of objects or trouble recognizing faces (also called prosopagnosia). Any of these conditions can come from strokes, trauma or neurological disorders.
Yet the Oxford-based researchers noticed something else peculiar. Slightly less than half of the participants reported that it felt like one of their toes was missing. "We do know of medical conditions that can cause people to lose the sense of one of their digits," Cicmil says. "The people being tested here were healthy, yet some were reporting the feeling of a missing toe."
The researchers suggest the brain may build a sensory map that that involves five 'blocks,' but the edges of those areas don’t necessarily correspond with the gaps between the toes. Furthermore, they point out that it seems to be typical for the brain to have such errors, so this test can’t be relied upon as a diagnostic tool for brain damage. At least, not without further study to compare the rates of toe ID error between healthy people and those brain damage.
“A better understanding of the brain mechanisms that underlie simpler mistakes of body representation, such as mistaken toe identity in our study, will help us to understand disturbance of body image in more complex cases like anorexia,” Cicmil told Agence France-Presse.