Estudios epidemiológicos sobre morbimortalidad cardiovascular 1 Estudios no randomizados.

The main question to be addressed in this section on preschool bilingual language development is whether each o f the two languages’ lexicon and syntax is acquired at the same rate and sequence experienced by monolingual children. The history o f bilingual research has been riddled with methodological shortcomings. Some researchers have included in their samples children who can speak or

understand a second language even to a minimal degree, others have not specified the time, context and reason o f second language acquisition or the frequency o f usage o f the two languages (methodological issues that have been highlighted in the reviews o f the literature by for instance Abudarham, 1987; de Houwer, 1995; Meisel, 1989). These methodological problems are particularly apparent when considering the acquisition and size o f the lexicon. This has been mainly a measurement problem. For instance, is it a fair representation o f the child’s vocabulary size to compare the number o f words known in one o f their languages to the size o f the lexicon o f a monolingual child acquiring this language since one o f the languages might also be less dominant than the other? Even when the entire number o f words in both languages are combined the question arises as to how translation equivalents should be counted (see Aburdarham, 1987 for a discussion o f the alternatives). To overcome

some o f these difficulties some researchers attempt to create groups that are comparable in all respects but their bilingualism. However even when careful selection criteria were applied, studies using the Peabody Picture Vocabulary Test (PPVT) have frequently shown differences in the scores between mono- and bilingual children - bilingual children scoring lower (Ben-Zeev, 1977; Bialystok, 1988;

Merriman & Kutlesic, 1993; Rosenblum & Pinker, 1983; Umbel, Pearson, Fernandez, & Oiler, 1992). Using a different measure, i.e. the MacArthur parental report

inventories, Pearson, Fernandez and Oiler (1993) and Pearson and Fernandez (1994) provided a comprehensive source o f data from bilingual Spanish/English infants for toddlers between 8 and 30 months, based on longitudinal research in Miami. Their findings were analysed using four measures: the vocabulary size in each language, the combined vocabulary size in both languages and the conceptual range (which is the number o f unique concepts labelled in either language). When group percentages were used (Pearson et al., 1993) the total productive vocabulary size was not found to be different to that o f monolingual children. However when individual vocabulary size was investigated (Person & Fernandez, 1994) it was reported that even though the majority o f children fell within the normative range over forty percent o f their sample were well below these levels placing them at the 10th percentile or lower for the monolingual norms. As highlighted above this is again consistent with the fact that individual differences are generally large in vocabulary growth which from this description seems to apply to both monolingual and bilingual children.

With respect to syntax studies in the literature have attempted to establish whether there are differences between children who learn two systems at once compared to those just learning one. Reviewing this literature Romaine (1999) reported that the majority o f studies show that the developmental sequence o f the

bilingual child is the same ‘in many respects’ as that o f the monolingual. Acquisition o f syntax has been linked to the question whether the child has one or two linguistic systems (in relation to both the phonology and the lexicon) from the very beginning of speech. A commonly-held view in the early research was that the bilingual child goes through a unitary system stage before he or she succeeds in differentiating the two linguistic systems (the most elaborate model o f such a process was proposed by Volterra & Taeschner, 1978). This hypothesis was predominantly based on the finding that bilingual children’s language mixing - i.e. the usage o f both languages within an utterance - decreased during the first few years o f productive speech. As pointed out by Nicoladis and Genesee (1997) virtually all bilingual children code mix and there are vast individual differences in mixing and rates o f mixing do not

necessarily decrease. They go on to present evidence for early differentiation in respect o f the lexicon and syntax (as well as phonological and pragmatic

differentiation which are not covered here). In the case o f lexical differentiation they cite research which highlights that even early in development, bilingual children possess a vast percentage o f translation equivalents. In respect o f syntax they describe research that shows that bilingual children use the appropriate word order, verb- agreement morphology, gender assignment and placement o f negative markers for both o f their languages from the earliest combinatorial utterances onwards (Meisel,

1989; Meisel & Muller, 1992; Muller, 1990).

On the whole there is now a general consensus that bilingual children differentiate their two languages at an early stage of language (most influentially argued by: de Houwer, 1995; Genesee, 1989; Meisel, 1989). From these two extreme positions (unitary - completely separate) research has recently emerged that further refined the ‘separate language hypothesis’ arguing that even though separate from

early on the two languages are in contact and may have some influence on each other (see for instance Dopke, 1998; Hulk & van der Linden, 1996; Muller, 1998). In this line o f research it has been suggested that some o f the input could be problematic for children to cope with. Problematic input is seen as language combinations where there is generally a large overlap with some exceptions (Dopke, 1998; Hulk, 2000; Hulk & Muller, 2000). Children acquiring English and German would be a good test case for such views since both these languages are closely related, but show differences as indicated in chapter one. And in fact bilingual language research has shown that the English-German combination generates more cross-linguistically influenced structures (Dopke, 1998; 1999; 2000; Gawlitzek-Maiwald, 1997; Tracy, 1995) than French-English (Paradis & Genesee, 1996; 1997) or French-German (Meisel, 1990; 2001) combinations. (Also see the introduction o f the next chapter for more details on this topic.) In sum the review o f the literature, even though hotly debated, indicates that there is some delay in lexical acquisition for bilingual children. On the whole the development o f the two grammatical systems seems to take the same sequence and there is no consistent evidence o f delays. The consensus in the literature indicates that children differentiate the two languages from early on and that there is evidence o f cross-linguistic influences. One o f the measures that was employed with bilingual infants to investigate this process was picture naming. A model that accounts for lexical retrieval in bilinguals is discussed next.

5.1.2.1 Grosjean’s (1988) bilingual model o f lexical access (B IM O L A )

Grosjean’s BIMOLA is a connectionist model inspired by TRACE (McClelland & Elman, 1986). According to TRACE language is processed via activation (either excitatory or inhibitory) of units in a network. Each o f these units is continuously updating its activation levels on the basis o f the input o f other units to

which it is connected. These units are organised into three levels: features, phonemes and words (with bidirectional connections between those levels). If activation o f a unit is above a threshold it sends out excitatory signals to other levels and inhibitory signals to units that are connected to it. These basic principles also apply to BIMOLA. But where TRACE consists only o f one such network BIMOLA assumes that there are two language networks (i.e. two sets o f features, phonemes and words). These two language networks are independent but interconnected. The interconnection aspect accounts for the fact that bilinguals sometimes show interference between the two languages and can code switch when talking to other bilinguals. This interconnection also links in with the cross linguistic influences that were described in the previous section because the links between the two networks can activate each other. A second assumption o f this model is that bilingual speakers have two different language modes. In the monolingual mode one language network is strongly activated whereas the other is at resting level whereas in the bilingual mode both language networks are activated, but one more so than the other. Both word frequency and close neighbours effects in the other language are represented in the size and inter-connections o f the units (size o f the units and shading in the model see Figure 23).

BIMOLA (Bilingual Model of (.exical A c c e s s )

Global la n g u a g e activation Higher linguistic information

L a n g u a g e ac tivation

L g .A Lg. B WORDS

in

Bimola is not specifically a developmental model but in can be presumed that in the acquisition stages the connections and activation levels, both excitatory and inhibitory, are all being developed in the child’s networks. This would take place both through signal inputs from the language environment o f the child and the child’s own language use. PHONEMES L a n g u a g e a n d p h o n o ta c t ic activation ACOUSTIC WAVE

F ig u re 23: G ra p h ic a l r e p r e s e n ta tio n o f th e B IM O L A m odel o f lexical access b ilin g u a ls ( re p ro d u c e d fro m G ro s je a n , 1997).

This means that the effects o f cross-linguistic influences in early development can be accounted for by a BIMOLA model in which neither the excitatory nor the inhibitory connected pathways are fully matured. In this way when both languages are activated at any one time the activation can spread from one language to the other without being blocked in the process. When the child gets older these connections develop more fully and cross language transfer becomes less frequent.