Categorical perception: effects of the extent and rate of spectral change

Two experiments evaluated a potential explanation of categorical perception (CP) for place of articulation - namely, that listeners derive limited information from rapid spectral changes. Experiment 1 examined vowel context effects for /b/-/d/ continua that included consonant-vowel tokens with F2 onset frequencies that varied systematically from the F2 frequencies of their corresponding steady-states. Phoneme categorisation sharply shifted with F2 direction at locations along the continuum where discrimination performance peaked, indicating CP. Experiment 2 compared findings for a replicated condition against conditions with vowels reduced to match consonant duration or consonants extended to match vowels. CP was similarly obtained for replicated and vowel-reduced conditions. However, listeners frequently perceived diphthongs centrally on the consonant-extended continuum. Some listeners demonstrated CP, although aggregate performance appeared more continuous. These experiments indicate a model based upon the perceived direction of frequency transitions.