Close your eyes and you can still point at a voice. Your two ears are only ~18 cm apart, so a sound off to one side reaches them a few MILLIONTHS of a second apart — and the brain reads that tiny delay as an angle. A row of coincidence-detector neurons, each firing when the two ears agree at a particular delay, turns microseconds into direction. Slide the source and watch which detector lights.
Interaural time difference: for head width d and sound speed c, a source at azimuth θ arrives at the ears Δt = d·sinθ/c apart — only ~600 µs at the extreme. The Jeffress model reads it with a ladder of coincidence detectors on delay lines: the detector whose built-in delay cancels the ITD fires hardest, and its position IS the angle. A fail-loud self-check throws unless the peak detector’s delay maps back to the true azimuth. ◆ real auditory neuroscience, node-verified.
A clean ITD + coincidence-ladder model (d=18 cm, c=343 m/s); real localization also uses level and spectral (pinna) cues for up/down and front/back — ITD is the dominant azimuth cue and the µs-to-angle mapping is exact.