Sound Localization

Students investigate how two ears help the brain locate where a sound comes from by comparing the tiny time and loudness differences that reach each ear. Using a stethoscope headset connected to tubing, one partner taps at different positions while the listener identifies whether the sound is from the left or right.

1. Build the apparatus in advance: attach a straight, hard plastic tube to a narrow wooden block with three eyelet screws (one centered), align a ruler with the center, and connect each stethoscope earpiece to the tube ends using short lengths of flexible tubing.
2. Pair students and review how to wear the stethoscope earpieces comfortably and hygienically.
3. Have Student A face away from the block and place the earpieces in their ears; Student B stands behind and uses a pencil/pen to tap the hard tube at random spots along the ruler.
4. Instruct Student A to call out “left” or “right” after each tap; Student B records position and response on the worksheet.
5. Continue with 15–20 trials, including several taps near the center mark.
6. Switch roles and repeat the test so both students collect data.
7. Ask students to analyze where judgments were correct vs. incorrect and identify any region near the center where direction was hard to tell.
8. Discuss how interaural time differences (arrival-time lags) and interaural level differences (loudness) inform the brain about sound direction, and why ambiguity occurs when the source is centered.

Sound Localisation Experiment (similar concept to demonstration)- Dr Rajesh Verma Psychology:

📄 Sound from Left or Right? - ncwit.org: https://www.teachengineering.org/activities/view/umo_ourbodies_lesson02_activity4

• Repeat trials with eyes closed vs. open (facing away) to confirm vision is not providing cues.
• Tap with different materials (eraser, fingernail, wooden dowel) to compare how frequency content affects localization.
• Move the earpieces slightly forward/backward (keeping them safe and comfortable) to see if fit changes judgments.
• Add background noise at a low level to explore how noise affects localization accuracy.
• Extend the tube length and mark more positions to test whether greater spacing improves left/right discrimination.

• Clean and sanitize earpieces between users; provide disposable covers if available.
• Instruct students to insert earpieces gently and never force them; stop immediately if discomfort occurs.
• Tapping should be light—do not strike near faces or ears and avoid loud impacts that could cause discomfort.
• Teachers should handle hot glue and cutting of tubing during setup to prevent burns or cuts.
• Keep the work area clear so students facing away from the setup do not trip.

• Why do two ears help us tell where a sound comes from? (The brain compares tiny differences in arrival time and loudness between ears—interaural time and level differences—to infer direction.)
• Why is it difficult to decide left vs. right when the tap is at the center? (Both ears receive nearly the same time and level information, creating ambiguity.)
• How would unilateral hearing loss affect this activity? (Localization would be much worse because comparisons between ears are reduced or impossible.)
• Which frequencies are easier to localize and why? (High frequencies are easier via level differences due to head shadowing; low frequencies rely more on time differences.)
• How is this principle used in engineering? (Microphone arrays and signal-processing systems mimic binaural cues to localize sound sources.)