Background

The interaural time difference is the time interval between when a sound enters one ear and when it enters the other ear. In principle, this is a rather straightforward concept. A sound coming to us from the left will enter our left ear a split second before it enters our right ear. A sound coming to us from the right will enter our right ear a split second before it enters our left ear. Because our auditory system can detect this millisecond difference in timing, we can use the interaural time difference to determine if a sound is coming from the left or right. Thus, the interaural time difference gives us the location of the object along the azimuth.

In this activity, you can explore how sounds arising from different direction lead to this auditory space cue.

Instructions

Full Screen Mode

To see the illustration in full screen, which is recommended, press the Full Screen button, which appears at the top of the page.

Illustration Tab

Settings

Below is a list of the ways that you can alter the illustration. The settings include the following:

Start: Start an animation that traces the sound from the source to the two ears. This travel time will be plotted on the screen as well.
Sound Source X Position: Move the sound source left and right across the screen.
Sound Source Y Position: Moves the disparity object up and down on the screen.
You can also move the sound source by clicking and dragging on the screen with a mouse or by touching the screen.

Reset

Pressing this button restores the settings to their default values.

Try these settings to explore interaural time difference.

In this diagram imagine you are looking down on a person's head who is looking towards the top of the screen. The green dot is a sound source that you can move around the screen with your mouse or finger by clicking, dragging or moving your finger. Move the dot to a desired location outside of the head and then you can press the Start button to animate the time it takes for a sound to arrive at each ear.

During the animation, the path that the sound will take to each ear will be repesented by sine waves being drawn along lines connecting the sound source to each ear. Bars will be drawn representing this time. At the end of the animation the black lines at the top of each bar will indicate the difference in time that the sound took to arrive at each ear. This difference is also represented in text at the bottom of the screen. A positive value means the sound arrived first at the left ear and a negative value means the sound arrive first at the right ear. The values are arbitrary but the relative size of the differences for each direction follow very closely to the real differences.

Move the sound source to different locations and plot the size of the difference in time relative to the different directions. Can you spot a pattern?. Where is the sound source for the smallest differences? where is the sound source for the largest differences?

Proceed to Quiz