Speech production and working memory: The influence of cognitive load on sentence planning

For the last four decades, psycholinguistic research has dealt with the question to what extent elements of simple sentences like “The monk read the book” are planned ahead both on the abstract-lexical and phonological processing level. While a number of studies have shown that all up to the final element can be activated on these two levels, empirical evidence on the flexibility of the respective planning scopes is inconsistent, and a systematic delineation of the influence of different forms of cognitive load has not yet been provided. This thesis presents a series of 9 picture-word interference experiments in which participants produced subject-verb-object sentences while ignoring auditory distractor words. Advance planning was assessed at an abstract-lexical (lemma) level and at a phonological (word form) level under varying working memory load conditions (no load, or visuospatial load, or verbal load). In the absence of a concurrent working memory load and with a concurrent visuospatial working memory load, subject and object nouns were found to be activated at the abstract-lexical and the phonological level prior to speech onset. By contrast, with a concurrent verbal working load, the scope of advance planning at the phonological level was reduced, while the scope of advance planning at the abstract-lexical level remained unaffected. Moreover, sentence planning had a more disruptive effect on verbal working memory performance than on visuospatial working memory performance. Overall, these results suggest that advance planning at the phonological level is more adaptive to external factors than advance planning at the abstract-lexical level. Also, they indicate an overlap of resources allocated to phonological processing in speech production and verbal working memory