Dichotic Summation of Loudness over Time

The loudness of two 5-msec tone bursts, presented dichotically, was measured as a function of the temporal separation, ΔT, between the onset of the burst in one ear and the onset in the other ear. Measurements were made at 40, 70, and 90 dB SPL. Over-all loudness did not change as ΔT was increased from 0 msec (when the signal was binaural) to about 10 msec. Beyond 10 msec, the loudness decreased steadily until, at a ΔT greater than 200 msec, the two bursts were no louder than either alone. Similar results were obtained with 5-msec bursts of white noise. These results also resemble those obtained with monaurally presented tone bursts. However, the absence of peripheral adaptation in the dichotic presentation may account for some differences between the dichotic and monaural results. For example, whereas summation between two monaural bursts decreases at high levels, summation between two dichotic bursts is independent of level. [Research supported by a grant from the National Institute of Neurological Diseases and Stroke.]