Auditory stream segregation is an important paradigm in the study of auditory scene analysis. Performance-based measures of auditory stream segregation have received increasing use as a complement to subjective reports of streaming. For example, the sensitivity in discriminating a temporal shift imposed on one B tone in an ABA sequence consisting of A and B tones that differ in frequency is often used to infer the perceptual organization (one stream vs. two streams). Limitations of these measures are discussed here, and an alternative measure based on the combination of decision weights and sensitivity is suggested. In the experiment, for ABA and ABB sequences varying in tempo (fast/slow) and duration (long/short), the sensitivity (d') in the temporal shift discrimination task did not differ between fast and slow sequences, despite strong differences in perceptual organization. The decision weights assigned to within-stream and between-stream interonset intervals also deviated from the idealized pattern of near-exclusive reliance on between-stream information in the subjectively integrated case, and on within-stream information in the subjectively segregated case. However, an estimate of internal noise computed using a combination of the estimated decision weights and sensitivity differentiated between sequences that were predominantly perceived as integrated or segregated, with significantly higher internal noise estimates for the segregated case. Therefore, the method of using a combination of decision weights and sensitivity provides a measure of auditory stream segregation that overcomes some of the limitations of purely sensitivity-based measures.