Cumulation of the tendency to segregate auditory streams: resetting by changes in location and loudness.

In four experiments, the accumulation, over time, of a tendency to hear separate high and low streams in a sequence of high (H) and low (L) tones, presented in a galloping rhythm (HLH-HLH-...), was studied. Each trial was composed of two parts, an induction sequence, then a test sequence, with no break between them. The test sequence was always heard at the far left. When the induction sequence and the test sequence were identical, the presence of the induction sequence increased the tendency for the test sequence to split into two streams. However, when the sequences differed in location (cued by differences in interaural timing or intensity over headphones and by loudspeaker placement in a free field) or when they differed in loudness, the accumulation of the segregative tendency was reset, and the test sequence sounded more integrated. When the induction sequence changed in location or loudness in gradual steps toward the value of the test sequence, resetting was much less. It appears that the accumulation of information about streams in different frequency regions is sensitive to sudden changes in parameters, even when they affect the frequency regions equally. This prevents the system from accumulating data across unrelated events.