itd

Interaural time difference (ITD) refers to the difference in the arrival time of a sound at the two ears. It is a primary cue used by many animals, including humans, to localize sounds in the horizontal plane. When a sound originates from the left, it reaches the left ear slightly earlier than the right ear, producing a positive ITD; the opposite yields a negative ITD. The brain encodes ITD primarily in the brainstem's superior olive, using specialized neurons that act as coincidence detectors. The classic theoretical framework is the Jeffress model, which posits delay lines and coincidence detectors that map ITD to spatial location.

Typically measured in microseconds; the range in humans is about -700 to +700 microseconds, with maximum ITD around 600-700 µs, depending on head size and individual anatomy. ITD is more effective for low-frequency sounds (below about 1500 Hz) where the waveform phase is preserved across the ears; at higher frequencies, phase ambiguity reduces ITD reliability and interaural level differences become more important. Real-world listening adds reverberation and spectral cues from the pinna that influence perceived location.

Applications and relevance: ITD is central to psychoacoustics and audiology; devices like binaural hearing aids aim to preserve ITD cues to enable natural localization; research uses ITD to study neural coding and auditory scene analysis.