Individual differences in the improvement in spectral shape discrimination due to increasing number of nonsignal tones.

The effect of the number of nonsignal tones on the just-discriminable difference in spectral shape was evaluated for 12 naive subjects. The signal was an intensity increment to the center tone of a multitone complex. The tones were spaced at equal frequency ratios and, except for the signal increment, were equal in level. The number of nonsignal tones ranged from 2 to 20. Consistent with previous studies using equally spaced components, group mean thresholds improved monotonically with increasing number of tones. Group mean thresholds improved about 8 dB over the range of reference spectra employed. Large differences were found across subjects in overall performance, and in the magnitude of the improvement with increasing number of nonsignal tones. The greatest intersubject variability was observed for the stimuli composed of the fewest components. It was concluded that the differences reported in the literature concerning the presence and magnitude of the improvement are due both to differences in the procedures used and to the large individual differences that occur among subjects.