As you have learned in this segment of SAF, animals use two ears to locate the direction from which a sound emanates. Using two ears (a detection called stereo or binaural hearing) exploits both the difference in sound level and the difference in sound arrival time at each of the two ears. The brain analyzes this disparate information and uses these differences to calculate the most likely direction in which the sound arrived

This activity page will offer:

• Insight into binaural hearing
• A hands-on exploration of how sound is located
• A chance to explore the characteristics of binaural hearing

Ear Extenders
In this activity, you'll explore binaural hearing in humans. You'll see how two ears are utilized in determining the direction of a sound's origin. Then, you'll produce auditory illusions by reversing and extending the detection site for each ear.

Materials

• Four plastic funnels
• Two 3-foot sections of plastic flexible tubing (that fits over the funnels' spout)
• Mild soap and water (to wash and clean the funnels and tubing)
  

Steps (For the set-up)

1. Work with two partners. Obtain two lengths of plastic tubing and four plastic funnels.
2. Wash, rinse, and dry the funnels before using them in this activity.
3. Insert a funnel into each end of the plastic tubing so that two "ear extenders" are formed. Each extender consists of a length of tubing with an attached funnel at each end.
4. The subject sits in the center of the room and closes his/her eyes. The subject holds one funnel from each of the two "ear extenders" over each outer ear.
   CAUTION: Do not speak loudly into the other end of the extender. Also, never place any object into the ear canal. This can cause permanent hearing damage.
5. A second student, called the helper, positions the free end of each extender at each ear. For this first trial, the right ear extender is positioned near the right ear. The left ear extender is positioned near the left ear.
6. The third student is the sound source. The sound source stands about ten feet away and recites a sequence of numbers. The subject must identify the location of the sound source as it moves around the room.
7. For the second trial, the helper reverses the positions of the extenders so that the left extender is near the right ear. The right extender is placed near the left ear.
8. Step 6 is repeated and the subject is asked to identify the position of the moving sound source.
9. For the third trial, the helper returns the extenders so that match correctly to the side of the body on which that ear is positioned. The helper holds these extenders away from the subject's body, creating a greater distance between the funnels. Again, the subject must identify the location of the moving sound source.
   

Questions

1. Which was the least confusing trial for the subject?
   
2. Which was the most confusing trial for the subject?
   
3. Did the quality of the sound differ as detected by the right and left ear?
   

Electronic Connection
In this activity, you explored the binaural nature of hearing using sound that traveled through a plastic tube. Could you duplicate this inquiry strategy using electronic devices? Think about it. How could you assemble a circuit using headphones and microphones to produce this type of exploration? Share your design with your instructor and with his/her permission construct the circuit.

Interpretive Dance
In theater, movement can convey all sorts of concepts. Could it also be used to explain binaural hearing? Work with a group of students and compose a dance that demonstrates how binaural hearing is used to locate objects. Movements should convey concepts such as sound waves, nerve messages, and differences in volume and arrival time of sounds. Perform this piece of kinesthetic communication for you classmates

Sounds Like Stroop
The Stroop effect is most often performed using words that are spelled out in conflicting colors. The subject must then identify the color of the letters, not the meaning of the word. Find out more about Stroop here. (http://faculty.washington.edu/chudler/words.html)
What happens when you apply this type of confused message processing to binaural hearing? Use a group of students to create an arena for this type of inquiry. Have a subject identify the direction from which a word describing a conflicting direction originates. For example, the blindfolded subject hears the word "right", but it is spoken from the left side of the subject. In response, the subject must quickly point to the left.

Web Connection

http://www.biols.susx.ac.uk/home/Michael_Akeroyd/itd1.html
Background on binaural (two ear) hearing and how it is used to locate sound sources

http://ear.berkeley.edu/auditory_lab/binaural2.html
A source of sound files that confuse the arrival times and sound levels to create interesting auditory illusions

http://www.news.wisc.edu/view.html?get=7525
Discusses another advantage of binaural hearing - the ability to discriminate sounds.

Academic Advisors for this Guide:
Suzanne Panico, Science Teacher Mentor, Cambridge Public Schools, Cambridge, MA
Anne E. Jones, Science Department, Wayland Middle School, Wayland, MA
Gary Pinkall, Middle School Science Teacher, Great Bend Public Schools, Great Bend, KS