On the basis of a number of vowel and stop-consonant discrimination experiments (AX and 2IFC fixed and roving) with natural stimuli, it is concluded that stop-consonant perception is highly categorical: there were few significant differences between the discrimination results and the phoneme identification results. Moreover, the discrimination and identification response maxima differed significantly from the other data points. Vowel perception was much less categorical: the maxima in the functions were much less significant, and there were significant differences between the various paradigms. Consonant discrimination was much less (if at all) subject to range effects than vowel discrimination. All these results point to different memory types for stop consonants and vowels, and, consequently, to a combination of two different theories of speech sound discrimination: dual-process theory (DPT) for consonants, and trace-context theory (TCT) for vowels.