Greenwood function

The Greenwood function correlates the position of the hair cells in the inner ear to the frequencies that stimulate their corresponding auditory neurons. Empirically derived in 1961 by Donald D. Greenwood, the relationship has shown to be constant throughout mammalian species when scaled to the appropriate cochlear spiral lengths and audible frequency ranges. Moreover, the Greenwood function provides the mathematical basis for cochlear implant surgical electrode array placement within the cochlea. The Greenwood function correlates the position of the hair cells in the inner ear to the frequencies that stimulate their corresponding auditory neurons. Empirically derived in 1961 by Donald D. Greenwood, the relationship has shown to be constant throughout mammalian species when scaled to the appropriate cochlear spiral lengths and audible frequency ranges. Moreover, the Greenwood function provides the mathematical basis for cochlear implant surgical electrode array placement within the cochlea. In 1961, Professor Donald D. Greenwood utilized experimental methods within the field of psychoacoustics to measure the frequency resolution between critical bands within the human cochlea and develop a function correlating the anatomic location of the inner ear hair cells and the frequencies at which they are stimulated (Greenwood 1961a,b). Georg von Békésy demonstrated physiologically that different frequencies of sound stimulated different regions of the cochlea (Wilson 2004). Based upon the findings of Békésy, Greenwood placed four students under the age of 29 with presumably healthy cochleas in isolation chambers and introduced pure tones within the range of audible frequencies (20-20,000 Hz). Upon application of each tone, he then introduced a second pure tone of the same frequency and then raised and lowered the frequency until it was sufficiently different from the original frequency to become audible (Greenwood 1961a). Subjects responded with a handheld device allowing Greenwood to record exactly at what frequency interval the two pitches were audible and distinct. Experiments were performed over the entire range of audible frequencies (Greenwood 1961a).