Relationships of intensity discrimination to sensation and loudness levels: dependence on sound frequency.

The main purpose of the experiments described in this article was to establish the frequency dependence of auditory intensity jnd's (just noticeable differences) for pure tones as functions of loudness level (LL). For this purpose, two sets of experiments were performed. In the first, the jnd's were measured as functions of sensation level (SL) at sound frequencies of 0.125, 0.5, 1, 2, 4, 6, and 8 kHz. The SLs were set at 10, 20, 40, 60, and 80 dB in a random order. In the second, LLs corresponding to the set of the SL at 1 kHz were obtained, and the relationship of the jnd's to LL was determined. We investigated to what extent the constant loudness-constant jnd relationship found previously intrafrequency can be applied interfrequency. The detection experiments were performed with a continuous-pedestal paradigm and an adaptive two-alternative, forced-choice (2AFC) procedure that converges on 75% of correct responses. We found that the jnd's in dB plotted versus SL decreased roughly according to power functions, the rate of decrease depending on sound frequency. The jnd's increased with sound frequency at low SLs but became practically constant at high SLs. According to the second experiment, the jnd's followed approximately the same function of LL at all sound frequencies, except for a multiplicative constant, irrespective of the slope of the loudness level function. Thus, the constant loudness-constant jnd relationship appears to apply interfrequency except for a multiplicative constant that, with the continuous-pedestal paradigm, grew monotonically with the frequency.