Temporal Summation and Backward Masking

Abstract

Appropriate transformations based on the theory of temporal summation were used to determine backward masking as a function of the time interval between the onset of a 1000-cps tone and the onset of 40-, 60-, and 80-dB narrow-band noise bursts that partially masked the tone. It was shown that under these experimental conditions backward masking consists of at least three phases: (1) a short phase immediately preceding the onset of the masking sound in which threshold is determined by the level of the masker; (2) a long phase in which threshold is independent of the level of the masker; and (3) a transition phase that lies between the short and long phases. The short phase and the transition phase each last about 25 msec, while the long phase extends from 50 to about 200 msec ahead of the masking sound. It was also shown that the theory of temporal summation is sufficient to predict threshold differences during the long phase of backward masking, and probably during the short phase also. During the transition phase, however, the threshold for tones does not vary as a function of their duration.