Your inner bat: How many senses do humans have?

Image by Lee Carson via Flickr

We’re taught in school that we have five senses, but that number’s more a consensus than hard fact. Taste is mostly a superposition of smell and touch on your tongue, which could knock the number of senses down to four. Then again, many scientists count your vestibular system — the fluid and sensors in your inner ear that helps you keep your balance — as an additional sense, so maybe we do have five, just not the five we think we do.

Among animals, it’s almost impossible to keep track of different senses. The magnetic sense of migrating birds counts, as does the ability of some fish to detect electric fields. Lowly insects and even bacteria have novel senses, such as “quorum sensing,” the ability to count the number of other bacteria around them. It seems quorum sensing is the key to how bacteria communicate and coordinate behavior, both destructive and beneficial.

Now scientists in Spain have announced the discovery that human beings, despite millions of years of evolutionary divergence, can use echo-location to find their way around, very similar to bats. Of course, unlike bats, humans can’t use ultrasonic squeals, since our hearing isn’t good enough. Instead the scientists recommend a sort of tsk-tsk tongue click, similar to the noise dolphins make.

By making these clicks, the scientists taught themselves to navigate around obstacles while wearing blindfolds, based on how sound waves echoed off the objects. Unlike our “true” senses, this one isn’t inborn — it takes a few weeks of steady practice to acquire “biosonar capacity” — but once you’re really good, the scientists speculate that echo-location can even let you “see” around or through barriers, since sound penetrates and bends in ways that light won’t!

All this reminds me of neuroscientist Paul Bach-y-Rita’s famous dictum that “You see with your brain, not with your eyes.” Sounds like you can see with your ears, too.