You feel what you see

In a blog post today, Dr. Steven Novella discusses an article recently published in the journal Perception. This article, titled "Visual influence on haptic torque perception" looks at how our brains integrate the inputs from our different senses to create a unified, cohesive picture of the world. In particular, in this study the researchers had subjects hold a stick that was weighted to one side or the other and the subjects were asked to determine on which side the stick was weighted (the weighting of the stick produces torque, hence the title of the paper). Not surprisingly, subject could generally tell by touch which side of the stick was weighted. The really interesting aspect of the study is that the researchers then projected an image of the stick to the research subjects. In some cases the image was veridical (accurately showing which side the weight was one), in other cases the image was flipped so that the weight appeared to be on the opposite side of where it actually was. In these cases, the flipped image cased many of the subjects to perceive the weight as being on the opposite of the side it was actually on. In other words, the subject's perception of the object influenced how the object felt! Proof that in many cases we feel what we see.

As Dr. Novella notes, there was a certain threshold such that the effect disappeared when using really large weights. In addition, the illusion persisted even when subjects were aware that they were being tricked. In other words, even when subjects knew the weight was on the right, if they saw a visual image of the weight on the left, it felt to them as if the weight was on the left!

This all reinforces the idea that our brains do not passively receive an impression of the world from the senses, but instead play an active role in constructing our reality. This is further evidence that we need to be wary about basing conclusion on our own experience or the experience of others because our perceptual faculties can lead us to be systematically deceived, even in situations where we are aware that a deception is occurring.