The selective impairment of the phonological output buffer.

A single case study is presented of a patient, LT, with a reproduction conduction aphasic pattern of performance on word reproduction tasks; thus he made substitutions, insertions, deletions, and transpositions in reading, writing, and repetition of words and nonwords, as well as in sentence production, and in spoken and written picture and action naming. Further analyses revealed that there was no effect of semantic or syntactic structure on performance, and that reading was slightly better than repetition and writing. Finally, the observed effects of lexicality, length, and word frequency were similar to those found in other phonological output buffer patients. Overall, the pattern observed fits the characteristics typical of phonological output buffer patients, as characterised by Caramazza, Miceli, and Villa (1986). We discuss the implications of these results for understanding the role of the output phonological buffer in neuropsychological and computational models of writing, reading, and repetition. From the perspective of LT's performance, the hypothesis suggested by Caramazza et al. (1986), and that of Hartley and Houghton (1996), that word production in reading and repetition uses an additional route to access articulatory or phoneme-level representations from the phonological output lexicon, is unnecessary; instead, word-nonword differences in other patients can be attributed to resource demand differences between the two types of stimuli. LT's preserved span fit with the assumption that two phonological buffers exist, one for input and the other for output. Results from a word repetition experiment, in which word syllable structure was manipulated, are in conflict with one further noncentral aspect of the Hartley and Houghton's model, which otherwise fits the results well.