A psychological illusion is making people think they are thinner than they are

Australian researchers have discovered that a psychological trick could make people think they are thinner than they are | VIDEO

Our brains trick us when we gain weight, and researchers have learned the fascinating reason.

Researchers at The University of Western Australia have discovered that a psychological illusion could be making people think they are thinner than they actually are.

Jason Bell’s team from UWA’s School of Psychological Science worked with the Pisa Vision group in Italy and found evidence that how we perceive our body is actually a distortion created by our blended past observations of ourselves and others. In short, our brains average out how we used to look with how we look now. It works in reverse too, helping to explain why someone who is anorexic can not see how underweight they are. The inherent bias works the same way when we look at other people we know.

This is known as serial dependence and is an effect of our brain blending information over time.

“The data show body size judgments are biased towards prior experience,” Dr Bell said.

“As a person’s weight increases above the average, so too does the likelihood that their prior experience involves smaller bodies. Because the brain combines our past and present experiences, it creates an illusion whereby we appear thinner than we actually are.”

The study involved 103 female participants who were shown a set of images of female bodies ranging from underweight, normal-weight to overweight and obese.

The participants were required to judge the perceived size of the body type by positioning a marker along a visual analogue scale, known as the body-line.

The results revealed evidence of a serial bias in perceived body size, with size judgments tending to correspond towards the previously viewed body.

“The research demonstrates human observers are often poor at estimating their own body size, and the size of others. Crucially, body size judgments are not always accurate and can be biased by various factors. Sometimes it’s influenced just by the people we stand next to,” Dr Bell said.

“These findings have important implications for weight loss approaches, including our chances of dieting successfully. What makes this particularly interesting from a health perspective is that misperceiving body size is a common symptom of eating disorders or obesity.”

“Ideally we’d like to correct these illusions, so people are able to make an accurate assessment of their weight and whether it has changed for better or worse.

Dr Bell told The Australian he believed the research could be useful in fighting obesity. According to the Australian Bureau of Statistics, more than 60 percent of adult Australians and 25 percent of children are overweight or obese.

Dr Bell and his colleagues hope to develop an online tool – possibly an app – that would allow the public to test the extent of their bias, which he said varied between individuals.