The Relationship Between Phoneme Discrimination, Speech Production, and Language Comprehension in Cerebral-Palsied Individuals

Twenty-four individuals with impaired speech (anarthria or dysarthria) were compared on tests of receptive language to a control group with normal speech. All subjects were cerebral-palsied and groups were matched on age and nonverbal ability. The speech-impaired subjects performed less well than controls on a phoneme discrimination task in which they were required to judge whether pairs of nonwords were the same or different. They were also impaired relative to controls on a receptive vocabulary test, but not in understanding of grammatical structure. One year later, phoneme discrimination skills were reassessed in this sample, using another same-different task, plus a new task in which subjects were required to judge if the name of a picture was spoken correctly or altered by one sound. Speech-impaired subjects performed as well as controls on the word judgment task, indicating that they can discriminate phoneme contrasts adequately. However, the same-different task again resulted in highly significant differences between speech-impaired and control groups. It is concluded that poor performance on the same-different task reflects weak memory for novel phonological strings, rather than impaired phoneme perception. It is proposed that retention of unfamiliar words is facilitated by overt or covert repetition, so individuals who cannot speak fluently have difficulty remembering nonwords. This explanation can account both for the poor performance of speech-impaired subjects on the same-different task, and for their selective deficit in vocabulary acquisition.