Introduction to Psychology 1/IPSY103/Hearing/Pitch perception

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Different frequencies of sound waves are associated with differences in our perception of the pitch of those sounds. Low-frequency sounds are lower pitched, and high-frequency sounds are higher pitched. How does the auditory system differentiate among various pitches? Several theories have been proposed to account for pitch perception. We’ll discuss two of them here: temporal theory and place theory. 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 (20–20,000 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, 2001). 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, 2001). In reality, both theories explain different aspects of pitch perception. At frequencies up to about 4000 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, 2001).


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Video Learning

This video is based on an online experiment whose aim is to discover the minimum change in frequency that the human ear is able to detect. You will hear the following sequence of eight frequency intervals: 440 Hz - 441 Hz; 440 Hz - 442 Hz; 440 Hz, 443 Hz - 440 Hz - 444 Hz, ... , 440 Hz - 448 Hz; for five seconds each pair of frequencies with no pause in between the change in frequency, and with 1 second of silence among each interval.

  1. Note the frequency interval at which you can just hear a difference between the two frequencies.
  2. Also notice how the pitch (a psychological property) of each sound increases as its frequency (a physical property) increases.