Efficient comprehension of sentences requires rapidly and continuously accessing and integrating different sources of information in real time. Psycholinguists have developed detailed models and theories to account for the processes involved in on-line sentence comprehension as well as a number of sophisticated experimental designs for studying these processes. But how about real-time sentence processing in bilinguals? The study of bilingual sentence processing has received considerable attention and has led to a remarkable growth of experimental studies over the last 10 years. The focus of these studies has been on late bilinguals, i.e., on second-language (L2) learners who learned a non-native language after early childhood, as adolescents or adults. These studies have revealed both similarities and differences between native (L1) and non-native (L2) sentence processing. Several proposals have been made to account for the experimental findings, but the significance and nature of native vs. non-native differences in sentence processing has remained controversial. Some researchers have claimed that L1 and L2 sentence processing are essentially the same and that observed performance differences between native and non-native sentence comprehension are due to peripheral factors, e.g., decoding problems, working memory limitations, slower processing speed, difficulties with lexical access and retrieval, or a reduced ability to predict during L2 processing (e.g., McDonald, Reference McDonald2006; Hopp, Reference Hopp2016; Kaan, Reference Kaan2014). Others have posited more substantial differences between L1 and L2 processing. One prominent proposal is Clahsen and Felser's (Reference Clahsen and Felser2006a, Reference Clahsen and Felserb) Shallow-Structure Hypothesis (SSH). Assuming multi-stream models of language processing (e.g., Ferreira & Patson, Reference Ferreira and Patson2007) with two routes from form to meaning, a heuristic one that employs surface-form information, lexical and semantic cues, and an algorithmic route that relies on a full grammatical parse, the SSH holds that L2 processing relies less on grammatical and more on non-grammatical information sources, in comparison to L1 processing of syntactic (and morphological) phenomena.

Against this background, our keynote article (Cunnings, Reference Cunnings2017a) offers a critical review of recent research on the topic and puts forward a novel proposal of how sentence comprehension in late bilinguals differs from native L1 processing. Adopting psycholinguistic models of sentence comprehension, specifically models which assume that comprehension essentially involves skilled memory retrieval (e.g., Lewis, Vasishth & Van Dyke, Reference Lewis, Vasishth and Van Dyke2006), Cunnings attributes non-nativelike L2 processing patterns to an increased susceptibility to retrieval interference during memory access in non-native relative to native processing. Considering previous research findings from the point of view of memory retrieval models of processing provides a fresh and, to our minds, a very interesting perspective on the topic.

Cunnings’ keynote article elicited 16 commentaries, an exceptionally large number of responses, from well-known experts in experimental psycholinguists and/or bilingualism research. Many commentators applaud Cunnings’ attempt to derive the specifics of non-native sentence comprehension from difficulties in cue-based memory retrieval. At the same time, however, commentators are concerned that Cunnings’ account may not be explicit enough (Malko, Ehrenhofer & Phillips, Reference Malko, Ehrenhofer and Phillips2017; Tremblay & Coughlin, Reference Tremblay and Coughlin2017; Kaan, Reference Kaan2017) and in some cases may go beyond what is currently supported by empirical evidence (Dillon, Reference Dillon2017), that core notions may be too vague and in need of clarification (Juffs, Reference Juffs2017; Gabriele, Fiorentino & Covey, Reference Gabriele, Fiorentino and Covey2017), and that attested L1/L2 differences remain that are hard to explain in terms of interference and retrieval difficulties (Jacob, Lago & Patterson, Reference Jacob, Lago and Patterson2017). Experts in bilingualism raise methodological concerns and draw attention to factors neglected by Cunnings, such as the potential influence of an L2 on an individual's skills in the L1 (Dussias, Beatty-Martínez & Perrotti, Reference Dussias, Beatty-Martínez and Perrotti2017) and the role of individual differences (Montrul & Tanner, Reference Montrul and Tanner2017; Hopp, Reference Hopp2017; Keating, Reference Keating2017). In addition, some commentators point out that Cunnings’ proposal may indeed be compatible with alternative accounts of L2 grammatical processing such as the Shallow Structure Hypothesis, Sorace's Interface Hypothesis or Ullman's Declarative/Procedural Model (Hamrick & Ullman, Reference Hamrick and Ullman2017; Kaiser, Reference Kaiser2017) and with alternative memory-based models of sentence processing (Futrell & Gibson, Reference Futrell and Gibson2017; Wagers, Reference Wagers2017). Omaki (Reference Omaki2017) notes that in some respects Cunnings’ account even “lost some of the empirical strength and theoretical virtues of the SSH”. Cunnings (Reference Cunnings2017b) uses the opportunity of his response for a detailed rebuttal of the points raised by the commentators. In particular, Cunnings’ response includes a discussion of recent findings from L2 sentence processing studies that cannot be easily accounted for in terms of increased memory interference during L2 processing (e.g., Boxell & Felser, Reference Boxell and Felser2017) and lays out specific predictions for future studies that would allow us to decide to what extent L1/L2 processing differences are due to memory interference and to what extent to shallow parsing. Together with the commentaries and the author's response, this keynote article contributes to linking different fields of research (viz., psycholinguistics, memory research, and the study of bilingualism) in what we think is a very promising attempt at a deeper understanding of the differences between native and non-native language processing.

We hope our readers will enjoy the keynote article together with the commentaries and the author's response as well as the interesting regular research articles presented in the current issue.