Working memory components in written sentence generation

College students wrote either simple or complex sentences using 2 prompt nouns while components of working memory were distracted with a concurrent task. Loads on the visual and spatial components of working memory (retain a shape) and verbal component (retain 3 or 6 digits) were compared with a no-load control. Only the 6-digit load reliably reduced sentence length relative to the control, suggesting that unimpeded sentence generation requires verbal working memory. The sentence length effect may arise from a failure to retrieve and maintain lexical representations during grammatical encoding. Memory load had no effect on grammatical and spelling errors, implying that syntactic and orthographic processing were undisturbed. Other possibilities locate the difficulty in planning conceptual content or in phonological encoding, but some evidence speaks against them.