Abstract:
This experiment was designed to determine whether or not polyrhythmic structure and attentional set influence auditory stream segregation. In sequences where streaming does not occur listeners are often quite accurate in detecting small time changes, but this is not true when sequences stream. Here a two-alternative forced-choice task was used to examine time discrimination within polyrhythmic patterns involving two different tone frequencies (high, low). Polyrhythms with narrow, medium, and wide frequency separations between high and low tones were presented to each subject; single frequency control patterns were also used. Listeners determined whether a small time change in the rhythm occurred early or late in a recurrent presentation of each pattern. In addition to manipulation of frequency separation, rhythmic structure (simple, complex) and attentional set (selective, divided) were varied. Results indicated that both frequency separation (narrow, medium, wide) and rhythm (simple, complex) affected time-change detection. These findings have implications for theories of attention and stream segregation. [Work supported by NSF.]