The psychophysical research on loudness discrimination of tonal signals (method 2AFC) has been carried out, N=106. The influence of self-regulation (questionnaires: HAKEMP-90, Style of self-regulation of behavior, Self-organization of behavior) on RT and sensory sensitivity index A' was found out. The qualitative analysis of individual ways of discrimination of signals was carried out. The relationships between loudness discrimination effectiveness and self-regulation processes characteristics mediating the sensory task decision were revealed. The applying the principle of subject`s activity to traditional psychophysical research was accomplished in the frameworks of differential-psychological approach in psychophysics (A.N. Gusev). It is developed the idea that the variation of stimuli uncertainty leads to appropriate transformation of the functional organ (A.N. Leontiev, A.A. Ukhtomskiy) relevant to sensory discrimination task.