The Effects of Proficiency on Sub-Lexical Processing in Bilingual Visual Word Recognition

Systematic psycholinguistic research has considered the nature of the coexistence of two (or more) languages in the cognitive system of a fluent bilingual speaker. There is increasing consensus that when a bilingual is presented with a visual stimulus in one language, both of their languages are initially activated (non-selective access; e.g. Dijkstra & van Heuven 2002a). However, more recent research shows that certain factors may constrain (or eliminate) the activation of a task-irrelevant language (Duyck, van Assche, Drieghe, & Hartsuiker 2007; Elston-Güttler, Gunter, & Kotz 2005). The objective of the research in this thesis was to investigate how cross-linguistic activation is modulated by specific characteristics of a bilingual’s languages. This exploration was mainly limited to an under-investigated area, namely early sub-lexical word processing. The first of two studies focussed on word processing in the presence or absence of critical sub-lexical information. Specifically, I investigated whether onset capitals – a prominent marker indicating nouns in German – acted as a language-specific cue, and the extent to which this cue constrains competitive, lexical interaction between the bilingual’s languages (e.g. Hose-hose, the first being a German word meaning ‘trousers’ in English). This study also considered the extent to which the use of such information is affected by priming for a specific language from a preceding context sentence. The second study arose from a claim that readers employ distinct sub-lexical reading strategies, depending on the extent of spelling-to-sound (in)consistency in their language (e.g. Ziegler, Perry, Jacobs, & Braun 2001). Employing a bilingual population whose two languages were clearly distinguished in terms of such consistency, I explored the reading strategy used by bilingual participants reading in each language. A key issue is competitive activation between sub-lexical orthographic and phonological representations across languages. Each study was conducted with two groups of bilingual speakers, English-German and German-English. Individuals varied in their L2 proficiency, allowing a test of whether sub-lexical processing changed as a consequence of increasing proficiency. The main results from study one demonstrate that bilingual speakers are dependent upon sub-lexical, language-specific information. However, this is influenced by L2 proficiency, with a stronger effect for lower proficiency bilinguals. In addition, lower proficiency bilinguals were more dependent on sub-lexical cues when primed by a sentence in L2. In contrast, bilingual speakers performing in their L1 used these cues largely under very specific circumstances, i.e. when they did not know an item. The central finding of study two is that competition between sub-lexical orthographic and phonological representations across languages largely depends on the amount of spelling-to-sound (in)consistency in the bilinguals’ more dominant language. This is reflected in (1) slower identification of orthographically similar cognates which map onto different phonological representations across two languages, and (2) slower identification of cognates which do not share the same orthographic form across languages but have a common phonological representation. In addition, increasing L2 proficiency is reflected in attenuation of certain effects as processing becomes more automatic, and the development of a common reading strategy accommodating reading in either language. A major contribution of the research conducted is what findings from both studies reveal about how the bilingual lexicon develops as proficiency increases. Furthermore, the findings contribute to our understanding of the organisation of the bilingual mental lexicon and the processes of word identification, and impose constraints on possible cognitive architectures.