Comparison of spectral and nonspectral frequency difference limens for human and nonhuman primates.

Difference limens for frequency were measured in normal-hearing human and nonhuman-primate (macaque) subjects. Stimuli were 1-kHz pure tones, containing both spectral and temporal cues, and 100-Hz sinusoidally amplitude modulated broadband noise (SAM noise), containing only temporal (nonspectral) cues. Subjects were tested for a minimum of 20 sessions and until difference limens were stable over time for each stimulus at each of several sensation levels. Difference limens for pure-tone stimuli showed almost no overlap between human and nonhuman-primate subjects. Difference limens for SAM-noise stimuli for human and nonhuman-primate subjects overlapped considerably. The correlations between performance for the pure-tone stimuli and performance for the SAM noise stimuli averaged 0.60. These data suggest that at least two factors influence pure-tone frequency discrimination. One factor is dependent on the presence of place mechanisms while the other factor, or group of factors, seems to influence both spectral and nonspectral frequency discrimination.