Unimpaired Short-term Memory and Rhyme Judgement in Congenitally Speechless Individuals: Implications for the Notion of “Articulatory Coding”

In normal adults, concurrent articulation impairs short-term memory, abolishing both the phonological similarity effect and the word length effect when visual presentation is used. It also interferes with ability to judge whether visually presented words rhyme. It is generally assumed that concurrent articulation impairs performance because it prevents people from recoding material into an articulatory form. If this is the explanation, then individuals who are congenitally speechless (anarthric) or speech-impaired (dysarthric) should show the same impairments as normal individuals who are concurrently articulating—i.e. they should have reduced memory spans, fail to show word length and phonological similarity effects in short-term memory, and find rhyme judgement difficult. These predictions were tested in a study of 48 cerebral palsied individuals: 12 anarthric, 12 dysarthric, and 24 controls individually matched to the speech-impaired subjects. There was no impairment of memory span in speech-impaired subjects, who showed normal phonological similarity and word-length effects in short-term memory. Speech-impaired subjects did not differ from their controls in ability to tell whether names of pairs of pictures rhymed. These results challenge the notion that “articulatory coding” is implicated in short-term memory and rhyme judgement and suggests that processes such as rehearsal and phonemic segmentation involve generation of a more abstract central phonological code.