The detectability of a tone added to narrow bands of equal-energy noise.

The ability to detect a 2000-Hz tone added to bands of noise centered at 2000 Hz was measured using a two-interval, forced-choice, pulsed-masker paradigm. The stimuli ranged in duration from 50-200 ms, and the maskers ranged in bandwidth from 5-320 Hz. In one condition, the bands of noise had equal energy across the two intervals of each trial and in a second condition the levels of the stimuli were independently and randomly chosen from a 30-dB range on a presentation-by-presentation basis. The energy model failed to predict the data obtained either in the presence or in the absence of level variation. Control experiments showed that exposure to level variation yielded an overall reduction in sensitivity, suggesting that the presence of level variation leads to changes in the listeners' detection strategies. Computer simulations indicated that changes in either the fine structure or envelopes of the waveforms were sufficient to account for detection when changes in stimulus energy were not reliable.