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Several fixed classification experiments test the hypothesis that F(1), f(0), and closure voicing covary between intervocalic stops contrasting for [voice] because they integrate perceptually. The perceptual property produced by the integration of these acoustic properties was at first predicted to be the presence of low frequency energy in the vicinity of the stop, which is considerable in [+voice] stops but slight in [-voice] stops. Both F(1) and f(0) at the edges of vowels flanking the stop were found to integrate perceptually with the continuation of voicing into the stop, but not to integrate with one another. These results indicate that the perceptually relevant property is instead the continuation of low frequency energy across the vowel-consonant border and not merely the amount of low frequency energy present near the stop. Other experiments establish that neither F(1) nor f(0) at vowel edge integrate perceptually with closure duration, which shows that only auditorily similar properties integrate and not any two properties that reliably covary. Finally, the experiments show that these acoustic properties integrate perceptually (or fail to) in the same way in non-speech analogues as in the original speech. This result indicates that integration arises from the auditory similarity of certain acoustic correlates of the [voice] contrast.