Working-Memory Capacity Effects in the Processing of Non-adjacent Subject-Verb Agreement: An Event-Related Brain Potentials Study

One question that has received much attention in the past decade or so is whether grammatical processing in the second/foreign language (L2) relies on the same mechanisms as grammatical processing in the native language (L1). Behavioral studies on agreement morphology, in particular, have shown that L2 learners may or may not show sensitivity to such agreement in sentence comprehension (e.g., Bowden, Gelfand, Sanz, & Ullman, 2010; Coughlin & Tremblay, in press; Foote, 2011; Hopp, 2010; Jiang, 2004, 2007; Keating, 2009; McDonald, 2006; Neubauer & Clahsen, 2009; Sagarra & Herschensohn, 2010; Sato & Felser, 2010). While there is still no consensus on the matter, three different hypotheses (among others) have been proposed to address this issue. Ullman’s Declarative/Procedural Model (2001) stipulates that native speakers rely on two distinct memory systems to process morphosyntactic information such as agreement: the declarative memory system stores irregularly inflected words in their whole form (e.g., ate) whereas the procedural memory system decomposes morphologically complex words with regular inflections into a stem and affix (e.g., talk+ed). Ullman proposes that at initial stages of L2 acquisition, “late” L2 learners (i.e., learners who were first exposed to the target language at or after the onset of puberty) over-rely on declarative memory and thus store morphologically complex words in their whole form, but with increased proficiency they may come to rely more on the procedural memory system and decompose morphologically complex words (see also Paradis, 2004, 2009). Thus, according to Ullman’s model, L2 learners show a qualitative shift in their processing of morphologically complex words, going from non-nativelike to nativelike processing with increasing proficiency. Ullman’s model may be somewhat difficult to falsify, however, in that the absence of a qualitative shift in L2 processing could instead be attributed to insufficient variety in the proficiency of the L2 learners tested. By contrast, according to Clahsen and Felser’s (2006a) Shallow Structure Hypothesis, late L2 learners’ grammatical processing differs qualitatively from that of native speakers, irrespective of L2 proficiency: unlike native speakers, L2 learners are unable to build detailed hierarchical syntactic structures and instead over rely on lexical and semantic information when interpreting sentences. Due to these shallow syntactic structures, L2 learners may have difficulty computing morphosyntactic dependencies between words, with nativelike processing being restricted to local domains such as “morphosyntactic agreement between closely adjacent constituents” (Clahsen & Felser, 2006b, p. 111). More recently, Clahsen, Felser, Neubauer, Sato, and Silva (2010) propose that unlike native speakers, L2 learners may not be able to decompose morphologically complex words (see also Neubauer & Clahsen, 2009; Silva & Clahsen, 2008). Clahsen and colleagues’ view can be falsified by data showing that native speakers and L2 learners process morphologically complex words in a qualitatively similar way.