Verbal Working Memory in Sentence Comprehension

Verbal Working Memory in Sentence Comprehension Evelina Fedorenko (evelina9@mit.edu) Department of Brain and Cognitive Sciences, 77 Mass Ave, NE20-437d Cambridge, MA 02139 USA Edward Gibson (egibson@mit.edu) Department of Brain and Cognitive Sciences, 77 Mass Ave, NE20-459 Cambridge, MA 02139 USA Douglas Rohde (dr@tedlab.mit.edu) Department of Brain and Cognitive Sciences, 77 Mass Ave, NE20-437 Cambridge, MA 02139 USA One way to address this question is via dual-task paradigms in which participants perform two tasks simultaneously: (1) on-line sentence processing, and (2) a non-linguistic verbally-mediated task. The underlying assumption is that we should observe a super-additive interaction when the complexity of both tasks is high only if the two tasks rely on overlapping pools of resources. Previous dual-task experiments found either no interaction or only a suggestion of one (e.g. King & Just, 1991; Just & Carpenter, 1992; Caplan & Waters, 1999; Gordon et al., 2002). In all of the previous experiments, however, the secondary task involved storage of words or digits across the sentence-processing task. Although storage – in a very general sense of keeping track of previously encountered information – plays an important role in on-line sentence comprehension (e.g., Chomsky & Miller, 1963; Kimball, 1973; Gibson, 1991; 1998; Lewis, 1996), it may be qualitatively different from the kind of storage involved in the secondary tasks in the earlier experiments. According to one recent resource-based theory of on-line syntactic processing, the dependency locality theory (DLT; Gibson, 1998, 2000), there are two working memory components to sentence comprehension: storage and integration. The storage component involves keeping track of partially processed syntactic dependencies that are still awaiting their second element in order for the sentence to be grammatical, whereas the integration component involves connecting a newly input word into the structure that has been built so far. Critically, the storage component of on- line sentence comprehension is unlike the storage involved in keeping track of a list of unconnected items. Consequently, it is possible that the lack of on-line interactions between syntactic complexity and memory load in earlier studies could be a result of the distinct nature of the storage processes involved. Moreover, there have been no previous attempts to explore the potential interaction between integration processes in sentence comprehension and secondary verbally-mediated tasks, which involve similar but non-linguistic on-line integration processes. In the current paper, we propose a novel paradigm to address this issue. Abstract This paper investigates the nature of verbal working memory (WM) in sentence comprehension and provides evidence for overlapping pools of verbal WM resources between on-line sentence comprehension and other verbally-mediated tasks. We report the results of two dual-task experiments. In Experiment 1, participants simultaneously performed a self- paced reading task and a self-paced arithmetic addition task in a 2x2 design crossing syntactic complexity (low, high) and arithmetic complexity (low, high). In addition to two main effects, the most interesting result was a significant interaction between syntactic and arithmetic complexity during the critical region of the linguistic materials: participants processed the complex/complex condition more slowly than would be expected if the two tasks relied on independent resource pools. To address a potential confound of shared attentional resources, Experiment 2 was conducted, where participants simultaneously performed a self-paced reading task and a self-paced spatial-rotation task in a similar 2x2 design crossing syntactic complexity with the complexity of the spatial task. As in Experiment 1, there were two main effects of complexity in the critical region. However, in contrast to Experiment 1, these effects were strictly additive, with no trace of interaction. The results of the two experiments therefore support a WM framework where on- line linguistic processing and on-line arithmetic processing rely on overlapping pools of verbal WM resources. Introduction A major question in psycholinguistic research concerns the nature of the working memory (WM) resources used in language processing. Empirical research has suggested that different pools of WM resources are used for processing visuo-spatial information and verbal information (e.g., Baddeley & Hitch, 1974; Baddeley, 1986; Vallar & Shallice, 1990; Hanley et al., 1991; Jonides et al., 1993; Shah & Miyake, 1996). Some researchers (Caplan & Waters, 1999; cf. Just & Carpenter, 1992) have hypothesized that the verbal WM pool can be further divided into two sub-pools: (1) verbal WM for natural language comprehension and production; and (2) verbal WM for non-linguistic verbally-mediated cognitive tasks. This paper attempts to empirically evaluate this hypothesis.