Synchrony-dependent autocorrelation in eighth-nerve-fiber response to rippled noise

Autocorrelograms and interval and delay histograms of the eighth-nerve-fiber response in cats to cosine noise were recorded. A good detectability level for the delay oscillations in the autocorrelograms was always found, when the fiber had a high value of the synchronization index at characteristic frequency (CF). In order to study their relationship, autocorrelograms for cosine noise stimulation were computed by the substitution of synchronization indices in the Poisson distribution formulas for higher-order intervals. The approach was made possible through a further exploration of Johnson's synchronization theory [D. H. Johnson, "The response of single auditory-nerve fibers in the cat to single tones: synchrony and average discharge rate," Ph. D. thesis, MIT, Cambridge, MA (1974)]. It was shown that computed autocorrelograms somewhat resembled experimental ones. The differences between them concerned the envelopes of the "onset" and "delay" oscillations, viz., in their constrictions and amplitudes. These constrictions were shown to be significant only in recordings at delays greater than or equal to 4/CF, corresponding to the dominant region for human repetition pitch.