Multiband detection of energy fluctuations.

this study sought to characterize the integration of synchronous energy fluctuations across relatively independent spectral regions. The detection of four classes of signal was examined where each class of signal was associated with a change in energy over time. The four signal types were: (1) multicomponent tonal complexes, with each component centered in a narrow band of noise; (2) intensity increments in multiple narrow bands of noise; (3) intensity decrements in multiple narrow bands of noise; and (4) temporal gaps in multiple narrow bands of noise. Each signal type was examined in a separate experiment, although stimulus characteristics such as presentation level and frequency location were held constant. Experiment 1 confirmed that the detection of multitonal complexes masked by narrow bands of noise is linearly related to the square root of N, where N is the number of signal components. Experiment 2 extended this to show that, when the signal was an increment in the level of a noise band carrier, threshold continued to be a linear function of the square root of N, although threshold was about 2 dB higher than for a comparable tonal signal. Experiment 3 indicated that the detection of a decrement in energy in one or more noise bands was relatively poorer in terms of absolute level changes than was the detection of an energy increment in the same stimulus. Examination of psychometric functions for decrement detection suggested that performance improved by less than the square root of N. Experiment 4 found that gap detection improved with increasing N but by a factor greater than the square root of N expected on statistical grounds. Examination of the underlying psychometric functions confirmed this effect. The results of these experiments suggest that, for energy increments, the auditory system integrates information from across the spectrum in a statistically independent manner, at least over the frequency range examined here. This does not appear to be the case for the detection of energy gaps or decrements.