Hearing perceives sound-source locations {source location} {sound location}, in space. Most space locations are silent. One space location can have several sound sources. Hearing determines sound location separately and independently of perceiving tones.
azimuth
Hearing can calculate angle to right or left, from straight-ahead to straight-behind, in horizontal plane.
elevation
Hearing can calculate height and angle above horizontal plane. People perceive lower frequencies as slightly lower than actual elevation. People perceive higher frequencies as slightly higher than actual elevation.
frequency and distance
Sound sources farther than 1000 meters have fewer high frequencies, because of air damping.
sound reflection and distance
Sound energy comes directly from sources and reflects from other surfaces. Close sounds have more direct energy than reflected energy. Far sounds have more reflected energy than direct energy. Reflected sounds have fewer high frequencies than direct sounds, because longer distances cause more air damping.
Hearing can separate complex sounds from one source into independent continuous sound streams {auditory stream segregation}.
Sound grouping has same Gestalt laws as visual grouping.
If one ear hears melody with large ascending and descending tone jumps, and other ear hears another melody with large ascending and descending tone jumps, people do not hear left-ear melody and right-ear melody but hear two melodies, different than either original melodies, that depend on alternating-tone proximities.
People separate sounds from multiple sources into independent continuous sound streams {auditory scene analysis} {source segregation}. Hearing separates sounds from different locations into independent continuous sound streams {spatial separation, hearing}.
Having two ears {binauralism} allows calculating time and amplitude differences between left-ear and right-ear sound streams from same space location.
Hearing can reject unwanted messages {focusing, hearing}, using binauralism to localize sounds.
The same sound reaches right and left ear at different intensity levels {interaural level difference} (ILD). Level difference can be as small as 1 dB. Intensity difference reflects stimulus distance, approaching or receding sounds, and body sound damping. Slight head movements are enough to eliminate direction ambiguity. Intensity differences due only to sound distance, or to approaching or receding sounds, are useful up to one or two meters. Beyond two meters, differences are too small to detect.
damping
Pinnae and head bones absorb sounds with frequencies higher than 1500 Hz, according to their frequency-related dampening function. Pinnae and head-bone damping differs on right and left, depending on source location, and hearing uses the intensity differences to determine space directions and distances beyond one or two meters.
brain
Lateral superior olive detects intensity-level differences between left-right ears and right-left ears, to make opponent systems. To find distance, two receptor outputs go to two different neurons, which both send to difference-finding neuron. Opposite-ear output goes to trapezoid-body medial nucleus, which lies beside pons lateral superior olive and inhibits same-ear lateral-superior-olive output. Interaural time difference and interaural level difference work together.
The same sound reaches right and left ear at different times {interaural time difference, hearing} (ITD), because distances from source location to ear differ, and ears have distance between them. Hearing can detect several microseconds of time difference. Slight head movements are enough to eliminate direction ambiguity. Interaural time difference uses frequencies lower than 1500 Hz, because they have no body damping.
Medial superior olive detects time differences between left-right ears and right-left ears, to make opponent systems. To find distances, two receptor outputs go to two different neurons, which both send to difference-finding neuron. Interaural time difference and interaural level difference work together.
In a cone {cone of confusion} {confusion cone} from head center into space, sounds have same intensity and timing, because ear timing differences (interaural time difference) and intensity differences (interaural level difference) are zero.
1-Consciousness-Sense-Hearing-Physiology
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Date Modified: 2022.0225