Horizontal localization uses binaural cues while vertical localization does not

Evidence

Because human ears are in the horizontal plane we can localize with great precision in that plane. Differences in the timing (interaural time difference, ITD) and amplitude (interaural amplitude difference, IAD) of sounds at the two ears provide us with the basic binaural cues. This is well-explored territory, and I won’t go into it. However, localization in the vertical plane, in elevation, is different. Here the ITD and IAD cues still contribute information, but only when the head is in motion and the sound source is stationary. The amount of movement to demonstrate the effect can be substantial—e.g. ±30° swings in the Perrett and Noble (1997) experiments, a ridiculous amount not employed in recreational listening. For home and cinema entertainment head movements are unlikely to contribute much information, and the sound sources of interest are not always stationary, especially in blockbuster movies with aircraft and superheroes whizzing overhead. Obviously, there must be more information. — Toole, Floyd E, Sound reproduction- the acoustics and…, 741

Categorization

• XREF: Connects to ITD/IAD binaural cue theory from psychoacoustics fundamentals; the contrast with elevation cues is foundational for understanding HRTF.