Ear offset from the head’s center makes arrival time shift with source azimuth

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 (#expands, via linked claim)

Categorization

• XREF: connects to: Head size alone predicts interaural time differences well across azimuth angles; Head separation between ears produces arrival-time and intensity cues for direction; The ear resolves low-frequency direction by measuring phase shift — David Howard, Jamie Angus, coustics and Psychoacoustics, 712 (+1 more)

Related

• The ear resolves low-frequency direction by measuring phase shift (similarity 0.90)
• The ear is far less sensitive to phase than to amplitude of frequency components (similarity 0.90)
• The ear lacks the eye’s directional receptors, relying on canal analysis (similarity 0.89)
• Sound reaching the far ear must travel around the head (similarity 0.89)
• The ear sits 8 cm off-center, so source-ear distance changes with azimuth (similarity 0.88)
• Head separation between ears produces arrival-time and intensity cues for direction (similarity 0.88)
• Head size alone predicts interaural time differences well across azimuth angles (similarity 0.88)
• The human ear is largely insensitive to signal phase (similarity 0.87)
• Phase-based directional hearing works only below about 743 hertz (similarity 0.87)
• Phase delays beyond 180 degrees make direction judgments ambiguous (similarity 0.87)
• Ears detect direction changes as small as 5 degrees via 50-microsecond delays (similarity 0.86)
• Directional hearing rests on interaural time and intensity differences. (similarity 0.85)
• Head shading creates interaural level differences used for sound localization (similarity 0.85)
• Interaural time delay calculations must account for sound traveling around the head (similarity 0.84)
• Interaural time and intensity cues can cancel each other in direction perception. (similarity 0.83)

Broader Connections

• The ear resolves low-frequency direction by measuring phase shift #expands (0.80) — David Howard, Jamie Angus, coustics and Psychoacoustics, 712