How many objects do you think you touch with your hands every day? A lot! Every time you touch something your hands are able to feel how smooth, cold, warm or rough the object is. In fact, your hands and fingers are so good at sensing details of shapes and surface textures that you are able to identify an object just by touch and without seeing it. Here is the challenge though: Do you think your feet are sensitive enough to do the same? Are they able to identify objects just by touching them? Try this activity to find out!
When we touch something, we get a lot of information about the object. This is possible because our skin contains an extensive network of nerve endings and touch receptors, which make it sensitive to many different kinds of stimuli. A stimulus can be anything that triggers the receptors in your skin to a response, such as pressure, temperature, vibrations or pain. Once the receptors are activated by the stimulus, a series of nerve impulses is triggered and transmitted to our brains, which then use this information to identify the object. Just passive contact of an object is not enough to identify it, however. To make out its shape and details, we have to actively explore its surfaces and the object as a whole by moving it in our hands. This is called haptic perception.
To be able to identify an object by just using haptic perception, we use different receptor types that are each responsible for sensing different stimuli. The mechanoreceptors, for example, perceive sensations such as vibrations, pressure or texture whereas the thermoreceptors respond to the temperature of an object. Special pain receptors are responsible for picking up anything that has the potential to damage the skin, and proprioceptors can sense the position of different parts of the body in relation to one another and the surrounding environment. These sensors in combination allow us to pick up an object’s shape and temperature as well as its surface texture just by touching it. The gathered information then makes it possible for our brains to identify it.
But why are we able to identify an object just with our hands? Is it because we had a lifetime of experience seeing objects in front of us as we touched them? Did this combination of visual and haptic perception wire our brains in a way that it is able to combine these two sensory inputs? Are we evolutionary conditioned to “see” with our hands? There is an easy experiment to investigate these questions. What if we use another bodily part to identify a familiar object that has not been trained to do this kind of task: your feet! Do you think your feet can “see”?
- Blindfold (such as a scarf)
- About 20 familiar objects to identify, such as toys, foods, household items, clothes etcetera. (Make sure none of these objects have sharp ends or can break easily. They should be at least the size of your fist or as long as your fingers. Have your helper gather these, and make sure that you do not see them.)
- Sit on a chair. Your feet should still be able to comfortably reach the ground.
- Let your helper blindfold you.
- Have your helper bring over the 20 familiar objects from your environment.
- You will only have 10 seconds to identify each object, so once you are handed an object, your helper has to slowly count to 10 and then take it away again.
- While still blindfolded and sitting on the chair, ask you helper to place one of the objects in your hands. Move the object in both of your hands and explore its shape and texture. How big is the object? Does it feel warm or cold? Is its surface rough or smooth?
- As soon as you think you have identified the object, tell your helper your guess and pass it back. Were you able to identify it within the given 10 seconds? Did you feel it was easy or hard to identify?
- Once your helper gets the object back, without telling you, he or she will place the object in a “Wrong” pile if you could not identify it and in a “Right” pile if you could. This way, you can keep track of your responses.
- After finishing with the first object, repeat the steps with another nine objects, so you have explored a total of 10 objects with both of your hands. Was there any object that you could not guess in time? How easy or difficult did you find the task? Were there any stimuli that helped you more or less in identifying the object?
- For the next 10 objects (they should not be the same as the previous ones), you will use your feet to identify them. Remove your shoes and socks so your feet are bare.
- While still blindfolded and sitting, let your helper place one object close to your feet. Then explore the project with your feet and toes and again try to make a guess of the object’s identity within the first 10 seconds. Do you find it easy to explore the object with your feet? Is it easier or harder than using your hands?
- After 10 seconds make a guess and let your helper take the object away. Your helper should make two separate piles for the feet experiment depending on if you guessed the object right or wrong.
- Follow the same procedure (just using your feet) to identify the remaining nine objects. Can you sense details of the object such as surface texture, shape or temperature with your feet? Were you able to identify all the objects within 10 seconds? Did you have difficulties identifying all of them?
- Once you have completed identifying all 20 objects (10 with your hands and 10 with your feet), remove your blindfold and look at all the objects. First, let your helper explain to you which objects you guessed right and wrong with your hands. Did you guess all the objects right? Which ones were difficult or did you get wrong? Can you think of a reason why?
- Next, let your helper show you which objects you guessed right and wrong with your feet. How many objects did you guess right, wrong or were unable to guess in time? Were you able to identify more objects with your hands or your feet within 10-second limit? Can you explain your results?
- Extra: In addition to using both of your hands and feet, run the same experiment again (using different objects). But this time only use one hand or one foot to explore the objects. Is it easier or more difficult compared with using both hands and feet? Does it make a difference if you use your left or right foot or hand?
- Extra: Instead of allowing only 10 seconds for each object, take your time until you can make a confident guess of the object’s identity. Let your helper time how long you need to identify each object using your hands and feet, respectively. Do you see any trends in your results? Does it take longer using your hands or feet? Does it depend on the type of object?
- Extra: Explore how the object size affects your results. Try the same test with different-size objects. Which are easier to identify—big objects or small?
Observations and results
Did you get all objects right when exploring them with your hands? You were probably able to identify most of the objects when using both of your hands to touch and feel the object. The receptors in your hands are trained and used to recognize various stimuli that come from the object, such as its surface texture, shape and temperature. In combination with the knowledge of how certain objects look and feel, your brain can make a positive identification of the object even though it does not really see it. Ten seconds was probably also long enough to make a good guess for each object—and in case you did not get the object right, it was most likely due to the fact that it was an unfamiliar object that you have not seen or touched that often before.
With your feet, everything gets more complicated. One reason is that your feet have very different anatomy from your hands. Your toes are much shorter than your fingers and much less flexible, which makes it harder to grasp and enclose the object. The other reason is your feet are not used to using their touch receptors to feel and explore objects like your hands do. As a result, you should have noticed that you had more wrong guesses (or could not make a guess in time) when using your feet to identify the object—although you might have been surprised by how many objects you guessed right!
If you measured your response time for each object, you should have found a slower recognition by feet than by hands. Recognition with your feet should have also improved with larger object sizes because small objects are difficult to grasp with your toes. Now that you know that not only your hands but also your feet are capable of identifying objects just by haptics, do you think you can “train” your feet to get as good as your hands?
More to explore
Sense of Touch, from Home Science Tools
Super Powers for the Blind and Deaf, from Scientific American
Recognizing Familiar Objects by Hand and Foot: Haptic Shape Perception Generalizes to Inputs from Unusual Locations and Untrained Body Parts (pdf), from Attention, Perception & Psychophysics
The Touch Response, from Science Buddies
Science Activity for All Ages!, from Science Buddies