What a Rat Feels

We have been told what it’s like to be a bat or a bird; now Prof. Ehud Ahissar and Dr. Avi Saig are getting people to experience what it’s like to be a rat. Specifically, they want the participants in their studies to learn what it’s like to locate things in the dark by twitching their whiskers.

The point, of course, is not to get humans to pretend they are actually rats, but to see how they learn to sense the world with a new sense. Whisking is a fairly complex sense, involving spatial coordinates – horizontal, vertical and distance from the base of the whisker – and timing. It only works when the rat swishes its whiskers back and forth repetitively. Tiny rat brains then translate timing and other cues into location in space.

The “whiskers” Ahissar and Saig used in their experiments were thin plastic hairs with force and position sensors at their bases, scotch-taped to the subjects’ index fingers. Blindfolded and seated, they were asked to feel the locations of two poles placed to their sides and slightly forward – one more so than the other. They then had to tell the experimenter which pole was farther back.

Here’s what they discovered: People can learn, with just a bit of practice, to sense like a rat. Not only that, but after a night’s sleep (a known learning aid) they instinctively understand how to improve the sensitivity of their whisking. That is, they figure out the best way to move their hands to sense the location of those poles. In some cases, they improved overnight from being able to distinguish a displacement of 8 cm to feeling out the difference when the hind pole was just 1 cm farther back.

What do we learn from this? Whisking is an extreme form of “active sensing,” but all of our senses are active to some extent. Fingers move to touch; eyes move to see; we actively take in smells and tastes; we even turn our heads to locate sounds. By analyzing the data from the whisking experiments, the researchers could actually construct a model of active sensing that can be used to understand the senses we normally use – especially sight and touch.

There might be practical applications, as well. Blind people already use their sense of touch to “see,” but insights into how physical muscle movements affect our perception and how our brains can learn to translate timing into location could greatly improve aids for them. For instance, the team envisions that tiny finger mounted cameras that translate visual information into mechanical stimulation might be particularly effective if they worked on the “whisker principle.”