Detection of regular and irregular repeated tones in noise: Rhythm helps only if rhythm is detected

Individual thresholds for 1024-Hz, 200-ms tones in noise (PEST, 80% 2IFC) were established in ten listeners, and then tones at this level were presented in a rhythmic pattern or in an irregular temporal pattern with the same average spacing and density of tones. Blocks comprising 200 tones were alternated randomly between the two conditions. A questionnaire administered at the conclusion of the session showed that half the subjects had become aware of the rhythmic pattern. Subjects were separated into two groups for data analysis; those who were aware and those who were unaware of the rhythmic pattern. In a subsequent session, detection threholds were again determined, and the subjects did a five-category rating detection. The rating data showed approximately the detectability predicted by the PEST procedure. No significant difference in this task was found between individuals from the aware the unaware groups. Relative to the detectability established with PEST (d’=1.19), rhythmic presentation yielded greatly enhanced detectability measures in listeners who were aware of the rhythm. Subjects who were unaware of the rhythm showed depressed detectability, both for rhythmic and arhythmic presentation. a)Also at Rotman Res. Inst. of the Baycrest Ctr., 3560 Bathurst Str., North York, ON M6A 2E1, Canada.