Perhaps, cochlea has band-pass filters {critical band theory}.
Perhaps, brain detects sounds by adding harmonic frequencies below 20 Hz, weighted by ratios {harmonic weighting}. 360 Hz uses 180/2, 120/3, 90/4, 72/5, 60/6, 51.4/7, 45/8, 40/9, 36/10, 32.7/11, 30/12, and so on. 720 Hz uses 360/2, 240/3, 180/4, 144/5, 120/6, 102.8/7, 90/8, 80/9, 72/10, 65.4/11, 60/12, 51.4/14, 45/16, 40/18, 36/20, 32.7/22, 30/24, and so on.
At frequencies above 900 Hz, brain detects stimulus frequency by cochlea-hair maximum-amplitude location {place coding} {place theory}, so pitch depends on activity distribution across nerve fibers.
At frequencies below 900 Hz, brain detects stimulus frequency by impulse timing {temporal theory} {temporal code}, because timing tracks frequency. Adjacent auditory neurons fire at same phase {phase locking, code} and frequency, because adjacent hair cells link and so push and pull at same time.
Perhaps, sound intensity depends on number of activated basilar-membrane sense cells and special high-threshold cells {threshold, hearing} [Wilson, 1971] [Wilson, 1975] [Wilson, 1998].
For frequencies less than 2400 Hz, frequency detection depends on cooperation between neuron groups firing in phase {volley theory} {volley code}. For frequencies less than 800 Hz, auditory-neuron subsets fire every cycle. For frequencies above 800 Hz and less than 1600 Hz, auditory-neuron subsets fire every other cycle. For frequencies above 1600 Hz and less than 2400 Hz, auditory-neuron subsets fire every third cycle {volley principle}. For example, three neurons firing at 600 Hz every third cycle can represent frequency of 1800 Hz.
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Date Modified: 2022.0225