Coding of information pertaining to paired low-frequency tones in single auditory nerve fibers of the squirrel monkey.

Abstract

Discharges in single nerve fibers were studied. When two effective, low frequency tones were presented simultaneously the phase-locked response was in 1 of 3 modes. The discharges were locked to the cycles of: 1st tone only; 2nd tone only; both tones. The prevailing mode was a function of the intensity of the component frequencies and their position in the neuron''s response area. For a given intensity differential between the component frequencies, the less effective component may have a greater influence on the phase-locked response if the intensity of both increased. When responses were locked to both tones the cadence of discharges was determined by cycles of the component frequencies. However, probability that a stimulus cycle will cause a discharge may vary periodically for one of the components. When phase-locked response pertained to one component only the spike count caused by two tones approached the count produced when this component alone was sounded. When responses were locked to both tones the count usually attained a value which was intermediate between counts for each component alone.