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Bilingual lexical access is a new area in the psycholinguistics research, which studies the activation or retrieval process of mental lexicon for people who can speak two languages. Bilingual lexical access can be understood as the complete word processing, which covered all the mental activity from the perception of the word from one language until all its lexical knowledge from the target language is available. For example, when a Dutch-English bilingual is asked to name a picture of a dog in English, he or she will come up with the English word dog. Bilingual lexical access is the mental processes underlie this seemly simple task: the process that makes the connection between the “idea” dog and the word dog in target language.

= History = Early research of bilingual lexical access was generated from the theories of unilingual lexical access, which were more like verbal description without precise specification of how these systems of lexical accesses would work, for example, the theory of serial search models and parallel access models. Serial Search Models demonstrates that when monolinguals encounter a word, they will look through all the lexical entries to distinguish whether the input item is a word not, and then they will only retrieve the necessary information about that word (i.e., its semantics or orthography). Serial search models propose that the lexical access would process sequentially by activating only one lexical entry at a time. In contrast, the Parallel Access Models believe that multiple entries can be activated at once, which means that the perceptual input from a word would activate all lexical items directly, even though some of them might not be necessary. In this way, numbers of potential candidates would be activated simultaneously and then the lexical candidates which are most consistent with the input stimulus would be chosen. Later, the researchers addressed that both the serial and parallel process are accounted for the lexical organization and lexical access, especially, the later one is getting more acceptance at present.

Early models of bilingual lexical access shared similar characters of these unilingual lexical access models. For example, the bilingual models began with focusing on whether the bilingual system might have a single lexicon combining words from both languages or separate lexicons for words in each language. In this case, the models would study whether the lexical access for bilinguals would be different from monolinguals, namely, whether the lexical activation would be processed parallel for both languages or selectively processed for the target language.

With the occurrence of widespread computational modeling, researchers extended the theoretical approaches for the studies of bilingual lexical access. The computational models are now essential component for mainstream theories, for example, the models of Bilingual Interactive Activation [BIA] model (Van Heuven & Dijkstra), the Semantic, Orthographic and Phonological Interactive Activation [SOPIA] model (Grainger), and the Bilingual interactive Model of Lexical Access [BLMOLA] (Grosjean and Lewy ). Since most computational models need to specify sufficiently for all the vague descriptive notions, they force researchers to be more clarified with their theories. Those revised models can also serve as to test the viability of the original theories by comparing the empirical results with data generated from the model. In addition, the computational models can also help to generate new testable hypothesis and allow manipulating conditions which might not be possible in normal experimentation. For example, researchers can investigate and simulate the lexical access systems under various states of damage without using aphasia people. However, there are also some limitations which need to be considered for using computational models. First, the researchers should understand why a model behaves in the way it does and whether the data can really explain what they hypothesized. Second, different type of models would bring different results which might support for different assumptions.

=Two main hypotheses in bilingual lexical access= The aim of bilingual lexical access research is to find out the role of a word in one language played in language production and comprehension. In other word, whether lexical candidates from different languages which share some lexical features would  be activated when a letter of string is presented. For instance, when the Dutch word VORK is activated, is the English word PORK also activated? If the answer is “no”, it might suggest that language selection happens before the recognition of a word, which lexical access is language selective. If the answer is “yes”, it might suggest the other possibility that the recognition of a word is processed in parallel of both languages, in which lexical access is language non-selective.

Language-selective access
Language-selective access is the exclusive activation of information in the contextually appropriate system. It implies that when a bilingual encounter a spoken or written word, the activation is restricted to the target language subsystem, which contains the input word.

One possibility is that bilinguals initially make a decision about the language of the word and then activate the appropriate language-selected lexicon. In this mechanism, there would be an executive system which is capable to direct the language switch for the input word. In the earlier studies, researchers found that bilinguals can comprehend passages composed of words entirely from only one language more quickly than passages composed of words from both languages. They explain this result as that an involuntary switch happens when bilinguals comprehend passages with two languages. When comprehension procedures in one language fails due to the language contextually change, then the switch mechanism will be automatically direct input to another language system. Therefore, bilinguals are slower at reading mixed language passages because they need to spend more time on switching languages. However, those kind of studies failed to noticed that the two languages might activated simultaneously and there might be a later lexical competition for making decision for using one language-specific lexicon. The later lexical completion can also be used to explain why bilinguals spend more time understand passages in mixed languages.

In the studies that investigated whether lexical candidates from different languages are activated selectively or non-selectively during bilingual lexical access, there are two basic types of stimulus are used have two basic types of stimulus: interlingual homographs and cognate. Interlingal homographs are words from two languages that are identical in their orthography, but different in their meaning, or phonology. For example, the English word room means “cream” in Dutch. Cognates are words from two languages which are identical (or very similar) in orthography and also have large overlap in their meaning. For example, the word film is cognate for English and Dutch. Researchers used those types of stimulus to investigate whether bilinguals processes them in the same way as the matched control words which occur only in one language. If the reaction time (RT) of interlexical homographs is same to the controlled monolingual word, then it should be the evidence for language-selective access, otherwise the differences between them would support language-nonselective access.

In most early studies, researchers did not find clear RT difference between test items (interlexical homographs or cognates) and control items. For example, in Gerard and Scarborough’s word recognition research with English monolinguals and Spanish-English bilinguals, they used cognates, homograph non-cognate and nonhomographic control word. The cognates and control word were either with high frequency or with low frequency in both English and Spanish. The homographic noncognates were high frequency in English and low frequency in Spanish or vice versa. The results generally supported the language-selective hypothesis. Even though there is a significant main effect of word type for bilingual group, it mainly caused by the slow response to homographic noncognates which were of low frequency in the target language but of high frequency in the non-target language. Finally, there is no significant difference of the reaction time between bilinguals and monolinguals, which suggested that the lexical access for bilinguals in this research was restricted to only one language.

Language-nonselective access
Language-nonselective Access is the co-activation of information in both linguistic systems. It implies that when a bilingual encounter a spoken or written word, the activation happens in both contextually appropriate and inappropriate linguistic subsystems.

In spite of the observed null results which support for the language-selective access, a sizable number of studies suggested that language-nonselective access indeed took place, which the representation of a word to a bilingual often gives rise to parallel activation in both languages. For example, Dijkstra, van Jaarsveld & Ten Brinke used an English lexical decision task for Dutch-English bilinguals on a list of cognate, homographs and English controlled words. Even though they did not find significant difference in reaction time between interlingual homographs and controlled English words, they found that there was a significant facilitation effect of the cognates, which could be supportive evidence for the assumption of language-nonselective access. Later, De Moor repeated the English lexical decision study by Dijkstra et al. and found that the Dutch meaning of the interlingual homographs was also activated by English-Dutch bilinguals. Followed each homographic trial, she used English trials which were the translation of the Dutch meaning of the previous homographs. For example, after the trial homographic word brand, the English word fire would be presented, which was the English translation of Dutch word brand. De Moor found there was a small but significant translation priming effect for the following English translation trials.It suggested that the lexical information of the Dutch word form was also activated, even though it did not affect the reaction time of the previous homographic trial.

Additionally, the cross-linguistic effects of orthographic and semantic overlap between different languages of cognates and interlingual homographs were also reported in many priming studies. For example, in an early study by, they had French-English bilinguals make English lexical decisions on target strings primed by French words, which was told to the participants. The homographic primes were French word either semantically related to the English words (e.g., coin-money, where coin means corner in French) or not related. The results showed that the bilinguals responded faster in related conditions than unrelated conditions. Even though the participants knew that the prime words were always belonged to their French meaning, they were still affected by the English meaning of the homographic prime words. In the later studies, researchers designed to mask the briefly presented prime words to avoid participants using conscious strategies. For example, Sáchez-Casas et al. used Spanish-English bilinguals for a semantic categorization task on Spanish target words. They used three types of priming conditions: entirely identical cognates or non-cognates (rico-rico; pato-pato), translations of cognates or non-cognates (rich-rico; duck-pato) and non-word primes combined with cognate or non-cognate targets as control condition (rict-rico vs. wuck-pato). They found that the bilinguals responded to the cognate translation conditions as fast as the identical conditions, but the non-cognate translation was as slow as the control conditions.

=Bilingual lexical access in language comprehension= Once bilinguals acquire the lexical information from both languages, the bilingual lexical access will be activated in language comprehension. The lexical access in comprehension is the process how people make contact with lexical representation in their mental lexicon that contains the information, which enables them to understand the words or sentences. Word recognition would be no doubt the most essential process of bilingual lexical access in language comprehension, which researchers investigate the selective or non-selective recognition of isolated words. At the same time, sentence processing also plays an importation role in language comprehension, which researchers can investigate whether the presentation of words in a sentence context would restrict lexical access to the target language only.

Bilingual lexical access in word recognition
Word recognition is a term usually used in both narrow and broad ways. When it is used in a narrow way, it means the moment when a match occurs between a printed word and its orthographic word-form stored in the lexicon, or a match between a spoken word and its phonological word-form. Then only after this match has taken place, all the information stored with this form, which includes the syntactical and morphological information of the word, and the most importantly, the meaning of the word will become accessible for further processing. In a broader way, it refers to lexical access which covers from the match processing until all the lexical information is achieved. In the researches of bilingual lexical access, word recognition refers to the way which uses isolated single/ out-of-context words from both languages to investigate the process of bilingual lexical access.

The main methodological tasks in word recognition
In word recognition studies, the cognate or interlingual homograph effects are most often used with following task:


 * 1) Word naming task: The participants just simply read printed words aloud, and their response latencies and/or reading accuracy are recorded. Even though it is a very simple and useful task, word naming task has its own shortcoming. First, in alphabetic languages, response can be just assembled by applying the phonotactic rules instead of actual recognition. Second, the performance of the naming task involves not only word recognition but also pronunciation. Sometimes, the focus of this task might be uncertain.


 * 1) Lexical decision task:The participants are presented with written letter sequences and asked to decide for each of them whether it is a word or not. Again, response times and/or accuracy are registered. Usually, the nonword stimuli (ones with “no” response) are pseudowords, which are letter strings that obey the orthography and/or phonology of the test language but are lack of meaning. There are two versions of decision task which are developed specially to study bilingual lexical access in word recognition: generalized lexical decision and language-specific lexical decision. In generalized lexical decision task, the lexical decision is made for both languages. The “yes” response is required if the presented letter sequence is a word in either language. In language-specific lexical decision task, the “yes” response must be only given to the words from the target language.


 * 1) Word priming task: The participants are presented with a prime word before they respond to each target word. The prime words are either lexically related or unrelated with the target words, and the effect of the prime on target processing will be measured. A target that follows a related prime is usually responded faster than a target preceded by an unrelated prime.

Bilingual lexical access in sentence process
Most current studies of bilingual lexical access are based on the comprehension of isolated words without considering whether contextual information affects lexical access in bilinguals. However, in everyday communication, words are most often encountered in a meaningful context and not in isolation (e.g. in a newspaper article). Researchers also began to investigate the cognitive nature of bilingual lexical access in context by examining word recognition in sentences. .

The main methodological tasks in sentence processing
In sentence processing, a number of on-line measuring techniques are exploited to detect the cognitive activity at the very moment it takes place or only slightly after. The cognate or interlingual homograph words are often used as a marker inserted in test sentences with following tasks:


 * 1) Self-paced reading: The participants are faced with a screen, on which a text appears in successive segment. They are asked to process each sequent segment by pressing a key. A trial starts with the presentation of groups of dashes separated by spaces. Each group serving as a placeholder for a word in the text, which is to be presented on that trial and each dash representing on letter. When the participant subsequently presses the key, the first segment appears, say the first two words, replacing the corresponding placeholders while the placeholders for the left words remain on the screen. Once pressing the key again, the two words for the first segment are replaced by their placeholders again and the next segment appears, taking the position of the corresponding placeholders. This continues until the whole text has been read. A follow-up comprehension question is presented to ensure that participants indeed pay attention to the meaning of the sentences. The interval between the two successive key presses is measured and registered as the response time.


 * 1) Rapid serial visual presentation:The participants are presented with the successive segments/words one by one at a fixed rate in the same location on the screen. In this task, the participants cannot control the speed of reading, while the experimenter determines the presentation speed. The participants are required to read the words aloud and their reaction time of each segment is registered. Again, a follow-up comprehension question is presented to ensure that participants indeed pay attention to the meaning of the sentences.


 * 1) Eye tracking (or eye-movement recording): A more natural and more sensitive on-line technique, which records the participants’ eye movements and eye fixations while they read a text presented on a computer screen. It documents what the participants are looking at and also how long it takes for them.



Studies of bilingual lexical access in sentence processing
The question whether the presentation of words in a sentence context restricts lexical access to words of the target language only are most studied in bilinguals’ second language (L2) processing. This sentence context effect might be an efficient strategy to speed up lexical search, because it reduces the number of lexical candidates. For example, Elston-Guttler et al. showed that cross-lingual activation is very sensitive to the influence of a sentence context and previous activation state of the two languages in a semantic priming study. In their study, German-English bilinguals were presented with relatively low-constraint sentences in which a homograph (e.g., The woman gave her friend a pretty GIFT; gift means poison in German) or a control word was presented at the end (e.g., The woman gave her friend a pretty SHELL). “Constraint” means the degree to which the sentence frame preceding the target word biased that word. The sentence was then replaced by a target word (poison) for lexical decision task. They found that only for participants who saw a German film prior to experiment and only in the first block of the experiment, participants could recognize the target faster after primed with the related homograph sentence than primed with the controlled sentence. This suggests that bilinguals can quickly “zoom into” the L2 processing situation even the L1 activation was boosted.

Later, Schwartz and Kroll used cognate and homograph as target words presented in low- and high-constraint sentences to Spanish-English bilinguals. They investigated how word presentation and the semantic constraint modulated language lexical access in bilinguals. Schwartz and Kroll used rapid serial visual presentation and the target word had to be named. No homograph effects were found, but less proficient bilinguals made more naming errors, especially in low-constraint sentences. They observed cognate facilitation (nonselective bilingual lexical access) in low-constraint sentences, but not in high-constraint ones. The results suggest that the semantic constraint of a sentence may restrict cross-lingual activation effects. Similar results on cognate effects were obtained by van Hell and de Groot in their study of Dutch-English bilinguals in an L2 lexcial decision task and a translation task in forward (from L1 to L2) and in backward direction (from L2 to L1). Libben and Titone used eye tracking methodology and found that the cognate facilitation in semantically constraint sentences only happened at early stages of comprehension and rapidly resolved at later stages of comprehension.

Although the majority of studies on bilingual sentence processing are focused on L2 processing, there are still a few studies that have investigated cross-language activation during their native language (L1) reading. For example, van Assche et al. replicated the cognate effect in L1 with Dutch-English bilinguals, and found that a non-dominant language may affect native-language sentence reading, both at earliest and at later reading stages. Titone et al. observed this cross-language activation in English-French bilinguals at early reading stages only when the L2 was acquired early in life. They also concluded that the semantic constraint provided by a sentence can attenuate cross-language activation at later reading stages.

=See also=
 * Lexicon
 * Bilingual Lexicon
 * Bilingual memory