Pruning the right branch : working memory and understanding sentences

Abstract

An experiment was conducted to determine whether tests used to assess working memory in different disciplines (neuroimaging, psycholinguistics, neuropsychology) are highly correlated, and thus whether they are equivalent measures of a unitary underlying function. Scores on the different tests (N-back, reading span, backward digit span) did not correlate highly, and were predicted by measures of different hypothesized components of working memory. These results indicate that working memory is best conceived of as a system of multiple, interacting components that contribute to different aspects of task performance, rather than as a single, unified resource, and that currently popular tests of working memory cannot be used interchangeably to measure working memory. A second experiment was conducted to examine the relation between sentence memory and working memory, and to determine whether memory for sentences is a function of the number of clauses in the sentence, or the number of new discourse referents. Subjects heard sentences of different lengths (2 - 5 clauses) and structures (relative clause, sentential complement, double object). Double object sentences contained one additional discourse referent per clause than the other two sentence types.

(cont.) If new discourse referents are the units of sentence memory, performance should be worse on double object sentences. If clauses are the unit of sentence memory, accuracy should be the same for all three sentence types. There were no reliable differences between double object sentences and the other two sentences types, indicating the clauses are the units of sentence memory. Subjects recalled 2-clause sentences highly accurately, and recalled 4-clause and 5-clause sentences poorly. There were large individual differences in the recall of 3-clause sentences. Over half of this variance was accounted for by individual differences in working memory. Measures of two hypothesized working memory components, the central executive and the short-term store, each accounted for independent variance in the sentence memory score.