To probe how episodic and abstract processes contribute to flexible perception of phonetically variable speech, we evaluated Australian (Aus) listeners' perception of Aus-accented vowels versus those of an unfamiliar accent: Newcastle UK (Ncl). Aus listeners first heard a round-robin story told by multiple talkers of Aus or Ncl, then categorized multi-talker tokens of 20 vowels in nonce words spoken in the Aus or Ncl accent. Categorization was variable even across Aus nonce vowels (Maccuracy ranged from 21-80%). Perceptual assimilation of Ncl vowels (Aus passage/Ncl nonce) was diverse: Some were categorized very much like the corresponding Aus vowel. Some showed within-category differentiation from Aus; others were heard as a different vowel altogether. Perception of some Ncl vowels changed after Ncl passage exposure, including both positive adaptation (improved categorization: e.g., MOUTH, FLEECE, TRAP) and negative shifts (increased differentiation from the corresponding Aus vowel: e.g., NURSE, FOOT). Assimilation and adaptation patterns were largely consistent with similarities and dissimilarities between the Aus and Ncl vowel spaces. Implications of the results for episodic and abstract contributions to perceptual flexibility are discussed. We also consider the possibility that listeners perceptually adjust to other-accent vowels as a system, rather than treating each vowel as an independent entity.