Difference between place and frequency theory of pitch
SIMILARITIES BETWEEN PITCH PERCEPTION AND SOUND LOCALIZATION Two main theories of how the inner ear may extract frequency information. Place theory states that the location on the basilar membrane activated during sound sensation corresponds to the pitch of the sound perceived. Frequency theory states that the speed at which the neural impulse travels through the auditory nerve corresponds to the pitch. We'll briefly discuss three of them here: temporal theory, volley theory and place theory. The temporal theory of pitch perception asserts that frequency is. INVESTING BIOTECH FUNDS LEADERS IN 2022
Correspondingly, William Rutherford provided evidence that this hypothesis was true, allowing greater accuracy of the cochlea. In , Rutherford also proposed that the brain interpreted the vibrations of the hair cells and that the cochlea did no frequency or pitch analysis of the sound.
Soon after, Max Friedrich Meyer , among other ideas, theorized that nerves would be excited at the same frequency of the stimulus. In general, it claimed that all sounds were encoded to the brain by neurons firing at a rate that mimics the frequency of the sound. However, because humans can hear frequencies up to 20, Hz but neurons cannot fire at these rates, the frequency theory had a major flaw.
In an effort to combat this fault, Ernest Wever and Charles Bray, in , proposed the volley theory, claiming that multiple neurons could fire in a volley to later combine and equal the frequency of the original sound stimulus.
Through more research, it was determined that because phase synchrony is only accurate up to about Hz, volley theory cannot account for all frequencies at which we hear. Today, it is widely believed that hearing follows the rules of the frequency theory, including volley theory, at frequencies below Hz and place theory at frequencies above Hz.
For sounds with frequencies between and Hz, both theories come into play so the brain can utilize the basilar membrane location and the rate of the impulse. Due to the invasiveness of most hearing related experiments, it is difficult to use human models in the study of the auditory system. However, many findings have been revealed in cats and guinea pigs. Additionally, there are few ways to study the basilar membrane in vivo. Sound Stimuli[ edit ] Many revolutionary concepts regarding hearing and encoding sound in the brain were founded in the late nineteenth and early twentieth centuries.
Various tool were used induce a response in auditory nerves that were to be recorded. Electrophysiology[ edit ] Attempts to electrically record from the auditory nerve began as early as Electrodes were placed into the auditory nerve of various animal models to give insight on the rate at which the neurons are firing. In a experiment involving the auditory nerve of a cat, Wever and Bray found that — Hz sounds played to the cat produced similar frequency firing in the nerve.
This supported the frequency theory and the volley theory. This allowed strobe imaging to capture the movement of the membrane as sounds stimulated the hair cells. This led to the solidification of the idea that high frequencies excite the basal end of the cochlea and provided new information that low frequencies excite a large area of the cochlea. This new finding suggested that specialized properties are occurring for high frequency hearing and that low frequencies involve mechanisms explained in the frequency theory.
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. By applying pure or complex tones, information on pitch perception can be obtained. In , it was shown that subjects with low frequency sensorineural hearing loss demonstrated abnormal psychophysical tuning curves.
Changes in the spatial responses in these subjects showed similar pitch judgment abilities when compared to subjects with normal spatial responses. This was especially true regarding low frequency stimuli. In general, periodicities between about 30 and 5, Hz elicit a sensation of musical pitch [ 3 , 4 ]. Below and above those limits, changes in frequency are perceived but they do not elicit a sufficiently clear sensation of pitch to allow listeners to recognize melodies or make judgments of musical intervals.
Interestingly, these psychophysically determined limits correspond quite well with the lowest and highest notes found on modem musical instruments. For instance, the modem grand piano has lowest and highest notes with fundamental frequencies F0s of The mathematically simplest sound is the pure tone, which is generated through sinusoidal motion.
The most common form of pitch-evoking sound is a harmonic complex tone, which comprises sinusoids with frequencies at the F0, or waveform repetition rate, as well as integer multiples of the F0, which are known as harmonics. The questions of how these components are represented in the auditory system, and how pitch is extracted from them, have been debated for over years [ 5 , 6 ].
Nevertheless, there are many aspects that remain unknown or controversial, and the study of pitch and its neural underpinnings remains an active topic of research today [ 7 — 10 ]. We are very sensitive to changes in the frequency of pure tones. Just-noticeable differences JNDs in the frequency of a pure tone can be as low as 0.
Musicians tend to have lower better frequency JNDs than non-musicians, although the difference tends to vanish once non-musicians have had practice of between 4 and 8 hours at the task [ 12 ]. This result suggests that most people are able to discriminate very fine differences in frequency with relatively little in the way of specialized training.
The first potential code, known as the place code, reflects the mechanical filtering that takes place in the cochlea of the inner ear. The basilar membrane, which runs the length of the fluid-filled cochlea from the base to the apex, vibrates in response to sound. The responses of the basilar membrane are sharply tuned and highly specific: at low to medium sound levels, a certain frequency will cause only a local region of the basilar membrane to vibrate.
Because of its structural properties, the apical end of the basilar membrane responds best to low frequencies, whereas the basal end responds best to high frequencies. This frequency-to-place mapping is known as tonotopic organization, and it is maintained throughout the auditory pathways up to primary auditory cortex, thereby providing a potential neural code for the pitch of pure tones.
This property, known as phase locking, means that the brain could potentially represent the frequency of a pure tone by way of the time intervals between successive spikes, when pooled across the auditory nerve. No data are available from the human auditory nerve, due to the invasive nature of the measurements, but phase locking has been found to extend from very low frequencies up to about 2—4 kHz in other mammals, depending somewhat on the species [ 13 ]. Unlike tonotopic organization, phase locking up to high frequencies is not preserved in higher stations of the auditory pathways.
At the level of the auditory cortex, the limit of phase locking reduces to at best — Hz [ 14 ]. Therefore, most researchers believe that if timing information is extracted from the auditory nerve then it must be transformed to some form of place or rate-based population code at a relatively early stage of auditory processing. There is some psychoacoustical evidence for both place and temporal codes. This frequency is similar to the one above which phase locking in the auditory nerve is strongly degraded [e.
It might even be taken as evidence that the upper pitch limits of musical instruments were determined by the basic physiological limits of the auditory nerve. Nevertheless, some form of pitch perception remains possible even with very high-frequency pure tones [ 11 , 17 ], where it is unlikely that phase locking information is useful [e.
A recent study of pure-tone frequency discrimination found that frequency discrimination thresholds in terms of percentage change in frequency worsened up to frequencies of 8 kHz and then remained roughly constant up to the highest frequency tested of 14 kHz [ 18 ]. This pattern of results may be explained by assuming that frequency discrimination is based on timing information at low frequencies; the timing information degrades at progressively higher frequencies so that beyond 8 kHz the timing information is poorer than the available place information.
These transposed tones are produced by multiplying a half-wave rectified low-frequency tone the modulator with a high-frequency tone the carrier. This procedure results in a high-frequency tone that produces a temporal response in the auditory nerve that is similar although not identical to the auditory-nerve response to a low-frequency tone [ 21 ]. The results suggested that timing information alone may not be sufficient to produce good pitch perception, and that place information may be necessary.
A difficulty in assessing the importance of timing and place information is the uncertainty surrounding the representations in the auditory nerve. First, as mentioned above, we do not have direct recordings from the human auditory nerve, and so we are uncertain about the limits of phase locking.
Rate pitch vs place pitch: an experimental study using cochlear implants.
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|Difference between place and frequency theory of pitch||The resulting vibrations are relayed by the three ossicles, causing the oval window covering the cochlea to vibrate. The results suggested that timing information alone may not be sufficient to produce good pitch perception, and that place information may be necessary. The nerve fiber with characteristic frequency of 10, Hz must be connected to the section of the basilar membrane near the oval window because it is tuned to very high frequencies. This has been shown in guinea pig and cat world sporting. The ear is divided into outer pinna and tympanic membranemiddle the three ossicles: malleus, incus, and stapesand inner cochlea and basilar membrane divisions.|
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