Individual differences in the processing of complex sentences

Individual Differences in the Processing of Complex Sentences Wibke Hachmann (wibke@cognition.uni-freiburg.de) Lars Konieczny (lars@cognition.uni-freiburg.de) Daniel Muller (daniel@cognition.uni-freiburg.de) Center for Cognitive Science, Friedrichstr. 50 79098 Freiburg, Germany Abstract To investigate the relationship of functions that underlie the processing of complex sentences, we conducted a self-paced- reading experiment on single and multiple center embedded subject- and object-extracted relative clauses, accompanied by three tests to measure individual differences. Our data suggest that inhibition and executive functions are better predictors for individual differences in sentence processing than working memory capacity. Keywords: individual difference; sentence processing; executive functions; working memory; inhibition. Introduction According to a prominent view, individual differences in linguistic performance can be attributed to differences in working memory capacity (Gibson, 1998; Just & Carpenter, 1992). A widely accepted way of assessing the individual verbal working memory capacity is the reading span test of Daneman and Carpenter (1980) or a variant thereof. It is designed to tap processing capacity and memory span likewise, but has been subject to debates, first of all concerning the construct validity and second because of weak retest-reliability (Mendelsohn, 2002). The lack of relatedness to well established measures of working memory like digit or word span lead to very diverse interpretations of the results. „Given that the reading span task is the standard task in sentence processing for measuring working memory, these failures to find correlations with other working memory tasks pose serious questions about what specifically the reading span task is measuring” (ibid., p. 28). A further objection is proposed by Baddeley (1996), who notes that the reading span test is unable to distinguish memory capacity from the use of different processing strategies and the ability to dissolve interferences. In contrast to capacity-based approaches, the correlation of reading span and processing performance can alternatively be explained by individual differences in experience with language (MacDonald & Christiansen, 2002), or by variation in executive functions such as inhibition (Gernsbacher & Faust, 1991; Mendelsohn, 2002). Good candidates to disentangle these issues and to gain further insight into the underlying processing mechanisms are center-embedded relative clauses: (1) The reporter that the senator attacked admitted the error. (2) The reporter that attacked the senator admitted the error. Object-extracted relative clauses (ORC, 2) are more difficult to read than subject-extracted relative clauses (SRC, 1), and relative-clause type has been shown to interact with reading span (Just & Carpenter, 1992). These effects have been replicated several times in different languages, and thus provide a good field for evaluating the predictability of different measures of individual differences and their interaction with sentence complexity. Another advantage is that there exist several elaborated attempts to explain these effects, varying in their claims as to which mechanisms are mainly responsible for the differences in processing complexity. Capacity and experience Based on Just and Carpenter’s (1992) single resource assumption, Gibson proposed the dependency locality theory (DLT) as a detailed metric for estimating incremental processing difficulty. There are two crucial factors in this metric: (i) storage of pending predictions, and (ii) integration: the costs of integrating dependent elements across intermediate discourse referents, rising with the number of new discourse referents between the depending elements. According to this model, storage and integration draw on the same resource, and individuals differ with respect to its capacity. According to DLT, center embedding should increase both memory and integration cost during and shortly after the embedded clause. Since in English, there are more referents to be crossed in ORCs than in SRCs when the verb has to be integrated with its arguments, DLT correctly predicts the empirically observable differences in processing speed. MacDonald and Christiansen (2002) on the other hand assume language processing as shaped by the individual’s experience with language and base their theory on connectionist modeling. Thus, processing is highly sensitive to the distributional properties of the linguistic input. They reinterpreted the difference in performance on SRCs and ORCs as a function of frequency and regularity of linguistic forms: subject-extracted relative clauses are easier than object relative clauses because they display the regular S-V- O word order, in contrast to the unusual O-V-S word order