The ear resolves low-frequency direction by measuring phase shift

Evidence

This is a very small delay but a variation from this to zero determines the direction of sounds at low frequencies. Figure 2.25 shows how this delay varies as a function of angle, where positive delay corresponds to a source at the right of the median plane and negative delay corresponds to a source on the left. Note that there is no difference in the delay between front and back positions at the same angle. This means that we must use different mechanisms and strategies to differentiate between front and back sounds. There is also a frequency limit to the way in which sound direc­ tion can be resolved by the ear in this way. This is due to the fact that the ear appears to use the phase shift in the wave caused by the interaural time difference to resolve the direction; that is, the ear measures the phase shift given by: where the phase difference between the ears in radia ITD Φ  ( ns and the frequency in Hz When this phase shift is greater than  radians (180°) there will be an unre­ solvable ambiguity in the direction because there are two possible angles- one to the left and one to the right-that could cause such a phase shift. — David Howard, Jamie Angus, coustics and Psychoacoustics, 712

There is also a frequency limit to the way in which sound direction can be resolved by the ear in this way. This is due to the fact that the ear appears to use the phase shift in the wave caused by the interaural time difference to resolve the direction; that is, the ear measures the phase shift given by: FIGURE 2. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 717

Categorization

• DEFINE: Explains the mechanism of interaural time difference and how phase measurement resolves direction.
• XREF: Relates to both ears forming a coincidence-detection system, paralleling neural delay-line models in auditory neuroscience. — connects to: The human ear is largely insensitive to signal phase — David Howard, Jamie Angus, coustics and Psychoacoustics, 451; The superior olivary complex sharpens phase locking to enable left-right sound localization; The ear lacks the eye’s directional receptors, relying on canal analysis (+8 more)
• corroborated: 3 independent passages support this claim — David Howard, Jamie Angus, coustics and Psychoacoustics, 712; David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 717

Broader Connections

• Binaural phase disparities improve tone detection by up to 25 dB. #expands (0.78)
• Diotic phase-shift controls rule out monaural sources of interaural-phase responses #corroborates (0.74)
• An interaural phase transition in noise evokes a pitch sensation #expands (0.70) — Dijk, Pim van, Physiology, Psychoacoustics and…, 1043