nature of the curve and is determined by the lower frequency audible limit in the species. Applications of the Greenwood function The Greenwood function is species-dependent and has shown to be preserved in mammals when normalized to the species-dependent range of auditory frequencies and cochlear spiral length (Greenwood 1990). For humans, the recommended values for the constants are (Greenwood 1990). According to Greenwood's paper, a = 2.1, if x is relative to the cochlea length, and a = 0.06 if x is calculated in mm. For individuals with sensorineural hearing loss surgical implantation of a cochlear implant is indicated. The success of a cochlear implant relies in part upon electrode array placement within the cochlea in which the positioning is based on the frequency-spatial relationship empirically described by the Greenwood function. By aligning the electrodes with the positions of the auditory ganglia contacting the basilar membrane as described by the Greenwood function, the cochlear implant electrode array stimulates auditory ganglia associated with the reception of frequencies associated with speech recognition. Electrode array insertion depth is guided by the frequency map created by the Greenwood function, and allows electrical stimulation of neurons involved in stimulating the area of the brain responsible for speech recognition while minimizing ganglia stimulation in noise-generating regions. Well-placed electrode arrays in patients receiving cochlear implants can allow otherwise deafened auditory systems to achieve hearing and recognize speech. (Chivukula et al. 2006, Wilson 2004) Greenwood function applied A typical cochlear implant electrode array may be inserted at a depth of 22–25 mm into the cochlea . At an insertion depth of 25mm into the base of the cochlear spiral, the distance from the apex of the cochlea to the deepest electrode is 10 mm using the mean value of 35 mm for the length of a standard human cochlea translating to x=10/35 in the Greenwood function (Greenwood 1990). Therefore, the lowest frequency heard by someone wearing this cochlear implant is calculated by the Greenwood function to be: 513 Hz equates roughly to the frequency of a C5 key of a piano. Lower frequency stimulation has been theorized to lead to a greater degree of background noise that impedes rather than aids speech recognition (Wilson 2004). See also Bark scale Critical band Equivalent rectangular bandwidth Mel scale References Hearing