Manfred Pienemann offers an interesting, fair-minded, and systematic account of the role of processability constraints in explaining language development. Thus he opens up a wide field of research in the area of the interaction of grammatical knowledge and processing constraints, and Pienemann should be applauded for this kick-off. In my view, this field should be explored in a non-partisan manner. Rather than pushing either grammar or processing at the expense of the other, we should be looking at the division of labour between different mental capacities, and at potential sites of overlap, conflict, and convergence. L2 development is crucial in this research, because it may show how much can be accomplished with non-grammatical processing. I will limit myself here to a number of disjointed remarks on some directions for research.

Pienemann's Processability Theory is an interesting and well thought out attempt to account for the developmental problem in L1 and L2. If correct, it would relieve the genetically specified knowledge base of what he views as its burdensome task of having to specify a great deal of genetically encoded linguistic knowledge and transfer at least part of that task to the processing mechanisms available for the acquisition of procedural skills needed for language processing. He posits a set of processing resources forming an implicational hierarchy such that the resource of a certain level is a prerequisite for the functioning of the next higher level. He posits further that the processing devices will be acquired in their predetermined sequence of activation in the production process. A consequence of this is that acquirers of both the first and the second language will follow the same sequence of acquisition of the processing hierarchy. The differences in the courses of development can be attributed, he says, to the knowledge base with which the learner comes to the acquisition task. In the case of L1, he says, many would see UG as the knowledge base; in the case of L2, only the surface syntactic features of the target language are available (and, presumably, knowledge of the L1).

Natascha Müller presents a very interesting analysis of the structure of the German subordinate clause in bilingual first language acquisition. The main issue in this paper is to explain the fact that some bilingual children – but not all of them – display non-target language structures in German subordinate clauses. That is, the finite verb does not appear in the final position of the subordinate clause. These non-target structures can in part be explained by transfer, but this cannot be the whole story, because some monolingual children produce these structures as well. Bilingual children, though, appear to have problems with the German subordinate clause more frequently than monolingual children. Interestingly, acquiring the target structures is a slow process for children who produce non-target structures. Ivar, the French-German child Müller discusses in most detail, for example, needs two years to acquire the correct position of the finite verb in German subordinate clauses. Müller argues that the problems arise because the input children receive is ambiguous: the finite verb does not always appear in the finite position in German subordinate clauses in adult speech. The ambiguity of this situation opens the way to transfer. In their uncertainty, the children turn to their other language as a relief strategy.

A surprisingly large part of the population of the world is at least bilingual. The question as to how people are able to control their language system is an important one and has been a topic for highly active research in recent years. Until now, models have been quite simplistic, but Green places his model in a wider framework of attention and control, drawing our attention to the fact that the mechanisms involved in language control share basic properties with the systems in other cognitive domains. Green introduces the (not language-specific) supervisory attentional system in combination with language task schemas which make it possible to adapt to the situation in which the bilingual system is functioning. Models of bilingual processing should be able to explain how lexical processing is affected by, among others, task demands (see also Dijkstra, van Jaarsveld, and ten Brinke, 1998). By adding a general mechanism of attentional control that is independently motivated by general cognitive mechanisms, Green has enriched his previous model considerably. In what follows we will first make some general remarks about the model Green proposes. In the second part we will discuss some recent results from our group that nicely tie in with some of the basic properties of the model outlined by Green.

In his contribution Green proposes a very interesting model of bilingual speech processing, the inhibitory control (IC) model. The model's aim is to account for the way in which bilinguals control their two language systems. Although the model was not developed to account for code-switching, the author explicitly goes into implications of his model for code-switching and this makes it very relevant for linguists working in that field. Until now, psycholinguistic aspects of code-switching have received far less attention in the literature than the syntactic aspects of code-switching. The model therefore offers an excellent starting point for incorporating insights from psycholinguistics into code-switching research and vice versa.

The main thesis Pienemann puts forward is that while L1 acquisition and L2 acquisition of a particular language (e.g. German) exhibit non-parallel paths of development, such a difference does not entail that the processing resources claimed to be responsible for transitioning from one stage to the next are any different in the two situations. The cause of the difference in routes, he suggests, is the difference in departure points. In the German case at hand, L1 acquirers begin with an SOV grammar, while L2 acquisition, according to Pienemann, starts off SVO (“canonical order”). “Generative entrenchment” of SVO is what makes the ensuing development distinct from that of L1 German: “once a decision has been made and a new structure has been added, it is very costly, if not impossible, for the developmental process to move to a different developmental path.” I think there's something very right about this general picture – but also that part of it is “wrong-headed.”

From the beginning of this century fascinating work has been carried out on the simultaneous acquisition of two languages from birth in the form of diary studies for example, that by Ronjat (1913). Many aspects of monolingual language acquisition have been studied in the same way, whereby researchers generally observed their own children, for example, Stern and Stern (1928). The modern research strategy is to audiotape or videotape the speech of young children at fixed intervals. Of course, a quantitative analysis can be carried out for both diary studies and more recent types of longitudinal study. However, researchers such as Ronjat (1913) do not provide us with exact quantitative results. Notwithstanding, these studies deserve to be taken seriously and I think it is possible to interpret some of the observations they contain as good and “reliable” evidence and compare these with results from modern longitudinal studies, where exact quantification is an important issue. I therefore think that the quantitative results of my review of existing studies on the acquisition of German subordinate clauses in bilingual children can be taken seriously, although I agree with François Grosjean and Elizabeth Lanza, who object that the quantitative differences between monolingual and bilingual children's errors are perhaps artefacts of the setting in which the children have been recorded. That I considered diary studies as well disappointed one commentator, Annick De Houwer, who would have preferred a comparison of modern studies only.

A word association experiment examined conceptual representation in bilingual memory. Dutch-English bilinguals associated twice to nouns and verbs that varied on concreteness and cognate status, once in the language of the stimuli (within-language), and once in the other language (between-language). Within- and between-language associations for concrete words and for cognates were more often translations of one another than those for abstract words and noncognates, and nouns evoked more translations than verbs. In both within- and between-language association, retrieving an associate was easier to concrete than to abstract words, to cognates than to noncognates, and to nouns than to verbs. These findings suggest that conceptual representation in bilingual memory depends on word-type and grammatical class: concrete translations, cognates, and noun translations more often share, or share larger parts of, a conceptual representation than abstract translations, noncognates, and verb translations. The results are discussed within the framework of distributed memory representation.

Given that my paper touched upon many aspects of L1 an L2 acquisition, it is not surprising that the commentaries have raised a diverse range of issues. Nevertheless, one should not lose sight of the fact that the paper has a tightly defined focus, namely to delineate the influence of language processing factors and developmental dynamics on developmental trajectories in L1 and L2 acquisition, and this is done in a very explicit manner. As Carroll rightly puts it in her commentary, this “[e]xplicitness allows us to formulate questions which could otherwise not be asked.”

The commentators raise many important issues and suggest fruitful lines of development. I thank all of them for their efforts. My paper focused on how bilingual speakers control the lexico-semantic system rather than on the nature of that system. It glossed over the processes of word recognition (Carr, Dijkstra) and considered only cursorily issues such as the mapping of thought into language (Schreuder & Hermans), the role of conceptual activation in lemma selection (Kroll & Michael) and the range and nature of the semantic relationships between words (Schreuder & Hermans, Treffers-Daller, Li). I will comment on these matters as I address three concerns about the proposed control processes: (1) the nature of schemas and their role in control (Carr, de Groot, Dijkstra); (2) the notion of a tag: its psychological reality (Li, Treffers-Daller), its relationship to a language node (Dijkstra) and its role in selection (Carr); and (3) the question of inhibition as the general means of lemma selection (Carr, de Groot, Roelofs).

While it is now commonly accepted that simultaneous bilingual children can differentiate their two languages from very early in development, it is still not very well understood how they come to understand that there are two languages in their input. The purpose of this study was to examine how a bilingual child might come to an understanding of the existence of two languages in terms of pragmatic differentiation (use of the appropriate language for the context) and lexical differentiation (use of translation equivalents). Using data from a Portuguese-English bilingual child from 1;0 to 1;6, this study showed that the child showed evidence of pragmatic differentiation before lexical differentiation. If these results are replicated, they suggest that bilingual children's understanding of the appropriate social use of their two languages may lead to an understanding that the translation equivalents in their vocabulary belong to two distinct input languages.

We construct a production model of code-switched discourse, in order to explain empirical observations about switch point distribution, well-formedness of monolingual fragments, conservation of constituent structure and lack of constraint between successive switch points. The two monolingual grammars are modeled by congruent context-free phrase structure grammars. Each code-switched sentence makes alternate reference to two virtual monolingual sentences, one in each language, and, in the immediate vicinity of switch points, to their constituent structures. Imposing conservative conditions on when a constituent should be labeled as to language, and invoking a constraint against real-time “look-ahead” from one code-switch to the next, we prove that the existence of a consistent tree labeling, easily monitored by the speaker, implies a constraint on local equivalence of constituent order in the two languages around a switch point. This constitutes an explanation, without invoking a “code-switching grammar”, of the observed tendency for equivalence-point code-switching.

Two picture-word interference experiments were conducted to investigate whether or not words from a first and more dominant language are activated during lexical access in a foreign and less dominant language. Native speakers of Dutch were instructed to name pictures in their foreign language English. Our experiments show that the Dutch name of a picture is activated during initial stages of the process of lexical in English as a foreign language. We conclude that bilingual speakers cannot suppress activation from their first language while naming pictures in a foreign language. The implications for bilingual speech production theories are discussed.

A series of three lexical decision experiments showed that interlingual homographs may be recognized faster than, slower than, or as fast as monolingual control words depending on task requirements and language intermixing. In Experiment 1, Dutch bilingual participants performed an English lexical decision task including English/Dutch homographs, cognates, and purely English control words. Reaction times to interlingual homographs were unaffected by the frequency of the Dutch reading and did not differ from monolingual controls. In contrast, cognates were recognized faster than controls. In Experiment 2, Dutch participants again performed an English lexical decision task on homographs, but, apart from nonwords, Dutch words were included which required a “no” reaction. Strong inhibition effects were obtained which depended on the relative frequency difference of the two readings of the homograph. These turned into frequency-dependent facilitation effects in Experiment 3, where participants performed a general lexical decision task, responding “yes” if a word of either language was presented. It is argued that bilingual word recognition models can only account for the series of experiments if they explain how lexical processing is affected by task demands and stimulus list composition.

This paper identifies two versions of the question as to whether there is a single initial system in the syntax of developing bilinguals. Version 1 asks whether there are early mixed utterances, and if so, attributes this to a single initial system. Version 2 asks whether the utterances containing words from one of the child's languages exhibit the same syntax as the utterances containing words from the child's other language. We argue with reference to our own data (from an English-Spanish bilingual from ages 1;7 to 1;9) that Version 1 is not tenable because of the paucity of lexical resources when the child begins to produce two-word utterances. However, we argue that the early two-word utterances in our data do seem to exhibit a single rudimentary syntax, based on a predicate-argument structure found in all utterance types, mixed and non-mixed. We then argue in relation to Version 2 of the question, that it can only be answered once the child's utterances can be identified as language-specific in the two languages, and that this is not possible before the emergence of morphological marking. This is illustrated by an analysis of our data from ages 1;8 to 2;3. We argue that language-specific morphology allows us to identify the language of the utterances in our data and to see evidence for the appearance of two differentiated morphosyntactic systems.

Two experiments examine the view that the variation in bilingual short-term memory capacity is determined by differential rates of subvocal rehearsal between the languages. Auditory memory span and articulation time were measured for three bilingual groups who spoke Finnish at home and Swedish at school (FS), and either Finnish (FF) or Swedish (SS) in both the home and the school. The results of Experiment 1 indicate that memory span for words varied in a lawful manner as a function of both articulation time and language dominance for SS and FF. For FS, however, an equivalent memory span between the languages was noted despite a shorter articulation time in Finnish than Swedish. Experiment 2 found that for items with no pre-existing lexical representations (nonwords), articulation time was a more reliable predictor of memory span than language dominance for all three groups. The finding that within-language memory span was greater for short items than long items shows that, ceteris paribus, bilingual short-term memory capacity is sensitive to the effects of word length in both the dominant and non-dominant language. Taken together, these findings moderate the view that bilingual short-term memory capacity is mediated exclusively by subvocal rehearsal and indicate an influential contribution from factors related to language fluency and the strength of lexico-semantic representations.

Because the field of bilingualism is still relatively new, studies in the linguistics, psycholinguistics, language development and neurolinguistics of bilingualism have often produced conflicting results. It will be argued in this paper that some of the difficulties encountered by researchers could have been lessened, if not avoided, had close attention been paid to methodological and conceptual issues. Among the issues covered are bilingual participants, language mode, stimuli, tasks as well as models of bilingual representation and processing. Each issue is dealt with in the following way: first it is explained, then the problems it causes are discussed, and, finally, tentative solutions are proposed. Examples are taken from descriptive and experimental studies of normal bilingual adults and children as well as bilinguals suffering from aphasia and dementia.