What is the definition of sound localization?

• A. The brain's ability to locate the source of a sound using pitch cues.
• B. The brain's ability to infer the direction of a sound source using ITD and ILD cues.
• C. The brain's ability to recognize the meaning of sounds.
• D. The brain's ability to measure sound intensity.

Answer: (B)

Sound localization is the brain’s ability to determine where a sound is coming from in space by comparing what each ear hears. The best description uses interaural time differences (ITD) and interaural level differences (ILD) as the cues the brain uses to infer direction. ITD arises because a sound reaches the two ears at slightly different times, which the brain can detect to judge left–right position, especially for low-frequency sounds. ILD comes from the head shadowing the sound, so the ear closer to the source receives a higher intensity, helping refine the direction, particularly for high-frequency sounds. These binaural cues are processed to compute the source’s azimuth.

This isn’t about recognizing what a sound means, nor about simply measuring how loud it is or about pitch cues, which are not the primary basis for determining direction. To localize vertically, the brain also uses spectral cues from the outer ear, but the horizontal localization hinges on ITD and ILD.