place theory
Summary
Place theory says pitch is coded by where along the basilar membrane in the cochlea the vibration peaks and bends hair cells: high frequencies near the base, low frequencies near the apex. It explains high pitches well; frequency theory (neural firing rate matches frequency) covers low pitches, and both contribute.
Detail
Meaning: Sound makes the oval window push on cochlear fluid, which sets up a traveling wave along the basilar membrane. The membrane is narrow and stiff near the base (next to the oval window) and wide and flexible near the apex. High-frequency waves peak near the base, and low-frequency waves peak near the apex. Hair cells in the organ of Corti at the peak bend most, and the brain reads pitch from which region of the auditory nerve is active. This tonotopic map is tied to Georg von Békésy's work on the traveling wave.
On the MCAT: A passage may describe damage to one region of the cochlea and ask which pitches are lost. Damage near the base impairs high-pitch hearing. Another common item contrasts place theory with frequency (temporal) theory, in which auditory neurons fire at a rate matching the sound's frequency. Neurons cannot fire fast enough for high frequencies, though the volley principle (groups of neurons firing in turn) extends the range. Place theory fits high pitches better, frequency theory fits low pitches better, and both are generally taken to contribute across the middle range.
Common confusion: Students swap base and apex. The base is next to the oval window, is stiff, and responds to high pitch. Place theory is also about pitch, not loudness. Loudness is coded mainly by how many hair cells respond and how fast the neurons fire.
Sources
- Psychology (Myers)
- Sensation and Perception (Wolfe et al.)
Written for the MCAT and checked before it was published. For study reference only. Spotted an error? Let us know.