Twelve adult aphasics and 12 nonaphasic controls were tested for ability to discriminate (AX method) place differences between synthetic stop‐consonants as a function of formant transition duration. Two 11‐item arrays were generated, one with 40‐ms transitions and the second with 25‐ms transitions, and each array ranging in equal acoustic steps from [ba] through [da]to [ga]. Syllables were paired within these arrays at a two‐step difference level. The Iwo sets of stimulus pairs were intermixed for discrimination testing. Discrimination functions were computed by pooling response data across subjects within each subject group and stimulus set. Rank correlation coefficients (tau) were computed to compare discrimination functions within subject groups and to compare stimulus matched discrimination functions between subject groups. The within‐group comparisons revealed a greater association between the two functions within the control group than within the aphasic group. The between‐group comparisons revealed a greater association between the two functions obtained with 40‐ms transition stimuli. Formant transition duration significantly affected phonetic category boundries only in the aphasic group.