Head separation between ears produces arrival-time and intensity cues for direction

Evidence

Acoustically, the entire head (and shoulders) makes part of the external ear. The distance between the two ears, located at opposite sides of the head, causes an arrival time difference of the sound wavefront that depends on the angle of incidence. A difference in sound level appears at high frequencies due to shadowing by the head to the side that is opposite to the sound source. — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 726 (#exemplifies, via linked claim)

Lord Rayleigh (James William Strutt, 1843–1919) was strongly influenced by the work of Helmholtz. His book The Theory of Sound also discussed acoustic problems using mathematics. This work laid the groundwork for future study linking acoustics with perception. Rayleigh was also keenly interested in the ability to localize sounds in space. He proposed that two acoustic cues are used for sound localization: intensity differences and time differences across the ears. The intensity differences were produced by the presence of the head in the sound field, which can effectively block sound transmission. The time differences were produced by the differential travel times of sound across the ears. This theory, called the Duplex Theory of Sound Localization, has been validated numerous times (see Chapter 7). — Jennifer Lentz, Psychoacoustics- Perception of Normal…, 70 (#expands, via linked claim)

Categorization

• XREF: connects to: Binaural microphones capture exact tympanum signals but depend on one’s own head shape; Head size alone predicts interaural time differences well across azimuth angles; Hearing evolved as an omnidirectional alarm system complementing directional vision — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 1519 (+12 more)

Related

• Binaural sound localization depends on ear-level temporal and intensity encoding efficiency (similarity 0.93)
• Head shading creates interaural level differences used for sound localization (similarity 0.91)
• Cortical intensity encoding becomes ear-independent through strong interhemispheric connections (similarity 0.90)
• Directional hearing rests on interaural time and intensity differences. (similarity 0.88)
• Ear offset from the head’s center makes arrival time shift with source azimuth (similarity 0.88)
• Sound reaching the far ear must travel around the head (similarity 0.88)
• Head, torso, and shoulder acoustics shape the localization cues reaching each ear. (similarity 0.87)
• Head orientation is necessary because interaural level differences plateau off-midline (similarity 0.87)
• HRTFs encode direction through head, ear, and torso shape filtering (similarity 0.86)
• The head shadows and reflects sound to create level differences between the ears. (similarity 0.85)
• Head shadowing gives roughly 6 dB interaural amplitude difference near 1.85 kHz (similarity 0.85)
• Head shadow attenuates sound arriving at the far ear unless the source is centered (similarity 0.85)
• Head intensity-shading fails below the frequency where head size reaches one-third wavelength (similarity 0.85)
• Binaural localization accuracy depends on monaural coding efficiency before interaural comparison (similarity 0.85)
• Interaural level differences and time shifts trade off to control lateralization (similarity 0.84)

Broader Connections

• Ear offset from the head’s center makes arrival time shift with source azimuth #expands (0.92)
• Head shading creates interaural level differences used for sound localization #exemplifies (0.85) — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 726
• Binaural sound localization depends on ear-level temporal and intensity encoding efficiency #expands (0.75) — Jennifer Lentz, Psychoacoustics- Perception of Normal…, 70
• Localization improves as we learn our own ears’ direction cues through experience #expands (0.72)