Neural correlates of pitch and roughness : toward the neural code for melody and harmony

The universality of many aspects of music, such as octave-based tuning systems and the use of dissonance and consonance to create harmonic tension and resolution, suggests that their perception may have fundamental neurophysiological bases. Thus, music provides a natural set of stimuli and associated percepts with which the auditory system can be studied. Here, we seek correlates of pitch, the essential element of melody, and roughness, a primary component of dissonance, in responses of single auditory neurons in anesthetized cats. Pitch, the perceived highness or lowness of sound, is generally thought to be based on a neurophysiological representation of frequency. Because neural responses (spikes) phaselock to low stimulus frequencies, interspike intervals (ISIs) reflect the stimulus period and can be used to estimate frequency. To rigorously test this potential code for pitch, we look for correlates of pitch under conditions where the percept deviates from a simple function of frequency. One such condition is the octave enlargement effect, listeners' preference for pure-tone octave ratios slightly greater than 2:1. Another is the pitch of a complex tone missing the fundamental frequency: the pitch matches that of the missing fundamental even when different harmonics are presented to opposite ears. We show that a correlate of the octave enlargement effect exists in ISIs of auditory nerve (AN) fibers and a correlate of the missing-fundamental pitch exists in ISIs of neurons in the inferior colliculus, the principal auditory nucleus of the midbrain. Results also reveal greater degradation of pitch representation at the midbrain compared to the periphery.

Department dc:contributor.department

Harvard University--MIT Division of Health Sciences and Technology.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2001

Author dc:creator

• McKinney, Martin Franciscus, 1964-

Advisor dc:contributor.advisor

• Bertrand Delgutte.

• Harvard University--MIT Division of Health Sciences and Technology.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/8347

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/8347