The present study examines whether listeners flexibly adapt to unfamiliar speech patterns such as those encountered in foreign-accented English vowels, where the relative informativeness of primary (spectral quality) and secondary (duration) cues tends to be reversed (ambiguous spectral quality vs. exaggerated duration). This study further tests whether listeners’ adaptive strategies are related to individual differences in phoneme categorization gradiency and cognitive abilities. Native English listeners (N=36) listened to continuum of vowels /ɛ/ and /æ/ (as in head and had) varying spectral and duration values to complete a perceptual adaptation task and a visual analogue scaling (VAS) task. Participants also completed cognitive tasks examining executive function capacities. Results showed that listeners mostly used spectral quality to signal vowel category at baseline, but rapidly adapted by up-weighting reliance on duration when spectral quality became no longer diagnostic. The VAS task showed substantial individual differences in categorization gradiency but these differences were not linked to their adaptive patterns. Results of cognitive tasks revealed that individual differences in inhibitory control correlated with the amount of adaptation. Together, these findings suggest that listeners flexibly adapt to unfamiliar speech categories using distributional information in the input and individual differences in cognitive abilities influence their adaptability.