Effect of duration on pitch discrimination of complex signals

Abstract

Discrimination of modulation frequency was measured using trains of n clicks (n = 4 to 52) presented at a rate of 250/s. Each click was the product of a 3500‐Hz sinusoid and a Gaussian envelope. Three spectral envelopes were tested, having standard deviations of 350, 560, and 933 Hz. The rate of improvement in performance over duration is reflected in a plot of log‐threshold vs log‐n. These functions are well defined by two straight lines: for small values of n, the slopes are near −1.0, and for larger n's, the slopes approach −0.5. This suggests a model in which two factors influence the discrimination process. For small n's, the spectral width of individual components in the amplitude spectrum are reduced in proportion to the length of the click train; thus the slope of −1.0. With further increases in n, statistical averaging reduces the effect of neural noise by a factor of the square‐root of n; hence the slope of −0.5. The model fit well to all of the data, except those obtained with the widest spectral envelope. This may be due to greater sensitivity to temporal information available in the low‐frequency regions of these wideband clicks. [Supported by NIH.]