User:Rachel Candace Law/sandbox/Volley theory
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Volley theory states that to overcome the fact that primary auditory neurons cannot fire at the maximum frequency at which we hear, many neurons must combine their action potentials prior to the sound arriving at the cochlear nerve which sends the stimuli to the brain. This theory was proposed by Wever and Bray in 1937[1] and it is thought of as a supplement to the frequency theory or temporal theory of hearing.
Description
The volley theory was well explained in Dr. Ernest Wever's 1949 book, Theory of Hearing[2] Groups of neurons in the cochlea individually fire at subharmonic frequencies of the sound being heard and collectively phase-lock to match the total sound heard.
Harmonic Spectrums
Sounds are often sums of multiple frequency tones. When these frequencies are whole number multiples of a fundamental frequency they make a harmonic. When groups of auditory neurons are presented with harmonics, each neuron fires at one frequency and when combined, the entire harmonic is encoded into the brain. This is the basis of volley theory.
Phase Locking
Phase locking is known as matching amplitude times to a certain phase of another waveform. In the case of auditory neurons, this means firing an action potential at a certain phase of a stimulus sound being delivered. It has been seen that when being played a pure tone, auditory nerve fibers will fire at the same frequency as the tone.[3] Volley theory suggests that groups of auditory neurons use phase locking to represent subharmonic frequencies of one harmonic sound. This has been shown in guinea pig and cat models.
Pitch Perception
Pitch is an assigned, perceptual property in which the brain orders frequencies from low to high. Pitch is hypothesized to be determined by receiving phase locked input from neuronal axons and combining that information into harmonics.
Discovery
Dr. Ernest Wever proposed the volley theory in 1937 with his paper "The Perception of Low Tones and the Resonance-Volley Theory"[1] . In this paper he discusses previous theories of hearing and introduces volley theory using results of his own experiments.
Relation to Frequency Theory
Frequency theory is the idea that at low frequencies, the entire basilar membrane vibrates, instead of specific areas which correlate to certain frequencies.
Experimental Evidence
Experiments by Helmohltz, Schafer, Wever, and Bray have involved the use of organ pipes, stretched springs, loaded reeds, lamellas, vibrating forks, beats, and interruption tones. Little can be done in human subjects due to the invasiveness of most experiments, however some things have been shown in cats and guinea pigs. Additionally, there are not many ways to study the basilar membrane in vivo.
Missing Fundamental
A fundamental frequency is the lowest frequency of a harmonic. In some cases, sound can have all the frequencies of a harmonic but be missing the fundamental frequency, this is known as missing fundamental. When listening to a sound with a missing fundamental, the human brain still receives information for all frequencies, including the fundamental frequency which does not exist in the sound. This implies that sound is encoded by neurons firing at all frequencies of a harmonic, therefore, the neurons must be locked in some way to result in the hearing of one sound. [4]
External Links
If needed later.
References
- ^ a b Wever, Ernest (1937). "The Perception of Low Tones and the Resonance-Volley Theory". The Journal of Psychology: Interdisciplinary and Applied. 3 (1): 101–114.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Wever, Ernest (1949). Theory of Hearing. New York: John Wiley and Sons.
- ^ Liu, Palmer, Wallace, Liang-Fa, Alan, Mark (2006). "Phase-Locked Responses to Pure Tones in the Inferior Colliculus". Journal of Neurophysiology (95): 1926. doi:10.1152/jn.00497.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ^ Goldstein, J (1973). "An optimum processor theory for the central formation of the pitch of complex tones". The Journal of the Acoustical Society of America (54): 1496.