Same-different reaction times (RTs) were obtained to pairs of synthetic speech sounds ranging perceptually from /ba/ through /pa/. Listeners responded "same" if both stimuli in a pair were the same phonetic segments (i.e., /ba/-/ba/ or /pa/-/pa/) or "different" if both stimuli were different phonetic segments (i.e., /ba/-/pa/ or /pa/-/ba/). RT for "same" responses was faster to pairs of acoustically identical stimuli (A-A) than to pairs of acoustically different stimuli (A-a) belonging to the same phonetic category. RT for "different" responses was faster for large acoustic differences across a phonetic boundary than for smaller acoustic differences across a phonetic boundary. The results suggest that acoustic information for stop consonants is available to listeners, although the retrieval of this information in discrimination will depend on the level of processing accessed by the particular information processing task.