Levels of description in consonant/vowel processing: Reply to Knobel and Caramazza

Is it necessary to posit separate, explicit distinctions between representations in order to account for dissociations between consonant and vowel processing? We argue that a cognitive model of speech production based on cumulative lower-level properties is not only sufficient but more parsimonious in accounting for aphasic and dysgraphic patient data. We re-examine a computational model of consonant and vowel processing based on phonological feature representations of phonemes, and show that models based on similar principles are sufficient to account for quantitative and qualitative aspects of the patient data. We argue that the facts that aphasic patients (i) are more likely to have impairment to consonant than vowel representations, (ii) demonstrate varying degrees of impairment to both consonants and vowels in an inverse relationship, and (iii) never indicate complete impairment to only vowels or consonants, are better accounted for in a model that assumes a continuum of representations of consonants and vowels than a model that explicitly encodes the consonant/vowel distinction.