Echolocation Demonstration

Research Questions:

• How do we localize sounds?
• What happens when we plug one ear?

The classic swimming pool game, Marco Polo, demonstrates our ability to localize sound. With eyes closed we hear “Marco” then swim towards its direction. This ability is only possible with two ears. Although we can hear with just one ear we are not able to distinguish the location of its source as well as or at all compared to two ears. A single ear can process the amplitude (loudness) and frequency (pitch) of a sound wave. But, together, both ears are able to detect sound location through minute differences in timing. If a sound is coming from our right then the waves arrive at our right ear before the left ear. These timing differences are very small, in milliseconds, unconscious to the listener. Animals are able to locate not only the sound, but also objects. Bats, although blind, are able to fly without running into trees, caves, other bats, etc. They navigate by listening to the echoes produced by their own calls, known as echolocation. To some extent humans are able to use echolocation. The blind use canes to walk around, alerting the user of any objects in his or her path. Tapping the cane allows the user to listen to its echoes and sense objects around them, just as bats. In this experiment students will demonstrate how two ears help us locate sounds.

Materials:

• Blindfold
• Large, quite room
• Earplugs

Experimental Procedure:

1. Recruit at least three subjects to participate.
2. Each subject will perform these tasks alone, one by one.
3. Have the subject stand in the center of the room, blindfolded.
4. To test their ability to locate sound move about the room clapping your hands twice. Each time you clap the subject should turn and face the direction that they think the sound is coming from. Do this several times around the room and record if they are correct or incorrect for each trial.
5. Have the subject plug one ear. Repeat step 4.
6. Did plugging one ear affect the subject’s ability to locate the sound?

Terms/Concepts: Binaural hearing; Echolocation; Sound waves; Amplitude; Frequency;  Wavelength; Doppler effect

References: Blauert, J. Spatial Hearing: The Psychophysics of Human Sound Localization. Cambridge, Massachusetts: MIT Press; 1997.