Explain the difference between place theory and frequency theory in regard to perception of pitch
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.
Second, we do not know how well the higher levels of the auditory system can extract the temporal information from the auditory nerve. Heinz et al. On the other hand, it is not clear how realistic it is to assume that higher stages of the auditory system can optimally integrate fine timing information in the auditory nerve; certainly the human binaural system, which must rely on temporal fine structure cues to encode interaural time differences, shows a rapid deterioration in sensitivity above 1, Hz, and is not sensitive to temporal fine structure above about 1, Hz.
Similar uncertainty surrounds the coding of place cues in the cochlea. There are no direct measurements of tuning or the sharpness of the place representation in the human cochlea. It has generally been assumed that the human cochlea and auditory nerve are similar to those of commonly studied animals, such as the cat, chinchilla, or guinea pig. However, recent studies suggest that human cochlear tuning may be sharper than that in smaller mammals [ 23 , 24 ]. In terms of general patterns of performance, however, the fact that relative sharpness of tuning quality factor, or Q , remains roughly constant [ 26 ], or even increases with increasing frequency [ 23 ], suggests that a place-based model would not predict the increasing frequency difference limens that have been found with increasing frequency above about 2, Hz [ 11 ].
In light of this mixed evidence, it may be safest to assume that the auditory system uses both place and timing information from the auditory nerve in order to extract the pitch of pure tones. Indeed some theories of pitch explicitly require both accurate place and timing information [ 27 ]. Gaining a better understanding of how the information is extracted remains an important research goal. The question is of particular clinical relevance, as deficits in pitch perception are a common complaint of people with hearing loss and people with cochlear implants.
A clearer understanding of how the brain utilizes information from the cochlea will help researchers to improve the way in which auditory prostheses, such as hearing aids and cochlear implants, present sound to their users. Each harmonic complex tone is comprised of the F0 corresponding to the repetition rate of the entire waveform and upper partials, harmonics, or overtones, with frequencies at integer multiples of the F0.
Several theories have been proposed to account for pitch perception. The temporal theory of pitch perception asserts that frequency is coded by the activity level of a sensory neuron. This would mean that a given hair cell would fire action potentials related to the frequency of the sound wave. While this is a very intuitive explanation, we detect such a broad range of frequencies 20—20, Hz that the frequency of action potentials fired by hair cells cannot account for the entire range.
Because of properties related to sodium channels on the neuronal membrane that are involved in action potentials, there is a point at which a cell cannot fire any faster Shamma, The place theory of pitch perception suggests that different portions of the basilar membrane are sensitive to sounds of different frequencies.
More specifically, the base of the basilar membrane responds best to high frequencies and the tip of the basilar membrane responds best to low frequencies. Therefore, hair cells that are in the base portion would be labeled as high-pitch receptors, while those in the tip of basilar membrane would be labeled as low-pitch receptors Shamma, In reality, both theories explain different aspects of pitch perception. At frequencies up to about Hz, it is clear that both the rate of action potentials and place contribute to our perception of pitch.
However, much higher frequency sounds can only be encoded using place cues Shamma, Sound Localization The ability to locate sound in our environments is an important part of hearing. Localizing sound could be considered similar to the way that we perceive depth in our visual fields. Like the monocular and binocular cues that provided information about depth, the auditory system uses both monaural one-eared and binaural two-eared cues to localize sound.
This interaction provides a monaural cue that is helpful in locating sounds that occur above or below and in front or behind us. Binaural cues, on the other hand, provide information on the location of a sound along a horizontal axis by relying on differences in patterns of vibration of the eardrum between our two ears. If a sound comes from an off-center location, it creates two types of binaural cues: interaural level differences and interaural timing differences.
Interaural level difference refers to the fact that a sound coming from the right side of your body is more intense at your right ear than at your left ear because of the attenuation of the sound wave as it passes through your head. Interaural timing difference refers to the small difference in the time at which a given sound wave arrives at each ear Figure 1.
Certain brain areas monitor these differences to construct where along a horizontal axis a sound originates Grothe et al. Figure 1. Localizing sound involves the use of both monaural and binaural cues. Some people are born without hearing, which is known as congenital deafness.
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What is the difference between place theory and frequency theory quizlet? Place theory states that the perception of pitch depends on what area of the basilar membrane is vibrating. Frequency theory claims that the perception of pitch depends on the rate at which the entire basilar membrane vibrates. The whole basilar membrane vibrates in response to sound. What is place theory and frequency theory?
Place theory is a theory of hearing that states that our perception of sound depends on where each component frequency produces vibrations along the basilar membrane. More generally, schemes that base attributes of auditory perception on the neural firing rate as a function of place are known as rate—place schemes. What is frequency theory?
This theory of how we hear sounds states that there are pulses that travel up the auditory nerve, carrying the information about sound to the brain for processing, and that the rate of this pulse matched the frequency of whatever tone you are hearing exactly.
Is place theory or frequency theory better? The place theory of pitch perception suggests that different portions of the basilar membrane are sensitive to sounds of different frequencies. More specifically, the base of the basilar membrane responds best to high frequencies and the tip of the basilar membrane responds best to low frequencies. What is the problem with frequency theory? The major flaw in frequency theory is that the neurons fire at a maximum of about 1, impulses per second, so frequency theory would not account for sounds above 1, hertz.
Is place theory or frequency theory better? The place theory of pitch perception suggests that different portions of the basilar membrane are sensitive to sounds of different frequencies. More specifically, the base of the basilar membrane responds best to high frequencies and the tip of the basilar membrane responds best to low frequencies. What is the problem with frequency theory? The major flaw in frequency theory is that the neurons fire at a maximum of about 1, impulses per second, so frequency theory would not account for sounds above 1, hertz.
This means that Martin would not be able to hear the high notes of his favorite song! Is the frequency theory correct? Place theory is accurate, except that receptive cells along the inner membrane lack independence in response. They vibrate together as suggested by the frequency theory. Sound waves travel along the membrane, peaking at a given region depending on the frequency.
What is an example of place theory? The place theory of hearing is used to explain how we distinguish high-pitched sounds that possess a frequency that exceeds 5, hertz. For example, a sound that measures 6, hertz would stimulate the spot along the basilar membrane that possesses a characteristic frequency of 6, hertz. What is the problem with place theory?
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