What causes the ability to localize a sound source in a listener?

The ability to localize a sound source primarily relies on the differences in phase for sounds arriving simultaneously at both ears. This phenomenon, known as interaural time difference (ITD), occurs because sound travels at a finite speed, which means that a sound reaching one ear slightly earlier than the other can create a perception of direction. The brain processes these timing differences, allowing individuals to discern the location of the sound.

For high-frequency sounds, the head casts a "shadow," causing amplitude differences between the ears, known as interaural level differences (ILD). However, phase differences are crucial for localizing lower-frequency sounds, where the timing of incoming waves is more significant than volume changes.

Understanding the mechanisms of sound localization highlights the sophistication of auditory processing, where the brain uses subtle cues from both timing and volume to create a spatial map of sounds in the environment.