How Well Do People Judge the Direction of Sounds?

Talk It Over

Can you close your eyes and tell where a sound is coming from? How good a judge are you? How can you measure how well people judge the direction of sound?

Get

• Large outdoor area to work in
• Balls of string in three colors: white, black, and red
• 2 tent stakes (for soft ground) or tape (for a paved surface)
• Flour
• Plastic bag
• Scissors
• Flexible, metal measuring tape (the kind carpenters use)
• 1 listener plus 2 other helpers
• Blindfold
• Protractor
• Jingle bell

Go

Here are some examples:

guessed angle – actual angle = error

1. Find a large area outdoors where you can work. A grassy area in a park or ball field is good. Or you can use a paved playground.
2. Tie all three colors of string to 1 tent stake and put it into the ground at the center of your workspace. (If working on pavement, tape the string to the surface).
3. Put some flour in the plastic bag. Cut a small hole in a corner of the bag. Hold it shut for now so no flour leaks out.
4. You will now mark a circle with a radius of about 5 meters (5 yards). Here's how:
   1. Use the measuring tape to measure 5 meters (5 yards) of the white string.
   2. Walk away from the tent state (or taped string) until the string is taut.
   3. Release the hole in the bag of flour and walk slowly around the stake, keeping the string taut and allowing the flour to fall to the ground.
5. Tie the white string to another tent stake and push it into the ground at a fixed point on the circle (or tape it down). The white string will not move again.
6. Ask the listener to stand in the center of the circle and wear the blindfold. Position the listener facing the white line. Have the listener hold the protractor.
7. Tie a jingle bell to your finger. Ring the bell so the listener knows what to listen for.
8. Instruct the listener to point toward the sound of the jingle bell whenever he or she hears it.
9. When the experiment begins, you and at least two other people start moving randomly (and silently!) around the circle. (You want to confuse the listener about the source and direction of the sound.) After a few seconds, signal everyone to stop. Then ring the jingle bell. The listener points a finger toward the exact spot where the sound seems to be coming from.
10. Now, you and the listener must not move while one of your helpers pulls the black string from the center of the circle to you. The other helper pulls the red string to the outer circle along the exact line in which the listener is pointing, like this:
11. Now the listener removes the blindfold and measures two angles using the protractor. The first is the angle from which the sound actually came, measured from the white, stationary baseline to the black string. The second is the angle that the listener perceived, from the white baseline to the red string. Measure the angles in a clockwise direction from the white string.
12. Continue with the same listener, trying many more angles and getting many more measurements. For each measurement, subtract to find the error:
13. Ignore the sign of the error. Look only at its absolute value. The smaller the error, the more accurately the listener judged the sound's direction.
14. Switch roles and let someone else be the listener. Gather as much data as you can with as many different angles and listeners as possible.

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