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The main objective of this dissertation is to investigate the effects of acquiring a second language (L2) at later periods of language development and native-like homonym processing in the first language (L1) from the perspective of Event-Related brain Potentials (ERP) using a cross-modal lexical decision task. To date, there is a lack of neurophysiological investigations into the effect that acquiring an L2 can have on processing strategies in the L1, and whether or not there is a precise age at which L2 exposure no longer affects native-like language processing. As such, my goal is to pinpoint this sensitive period specifically for homonym processing. To achieve this, I will present and discuss the results of two studies. The first study employs behavioural response measures using a cross-modal lexical decision task where participants simultaneously heard a sentence and made a decision to a visually-presented pseudoword or real word. The second study employs ERP measures using a novel ERP paradigm which investigates not only the main objective of this dissertation, but the second objective as well. This second objective is for this dissertation to become the first to evaluate the outcome of combining the cross-modal lexical decision task with ERPs. The behavioural and neurophysiological results for the monolingual group support the Reordered Access Model (Duffy, Morris, & Rayner, 1988) while the results for the bilingual groups do not. The results of the current studies indicate that those bilinguals who acquired French as an L2 rather than as a second native L1 show increasing divergence from monolingual native speakers in L1 homonym processing, with later acquirers exhibiting an exponentially marked divergence. This was found even though the task was carried out in English, the L1 (or one of the L1s) of all participants. The diverging performances of the bilinguals from the monolinguals were apparent in behavioural responses as well as in the amplitude, scalp distribution, and latency of ERP components, These differences were unique to each group, which supports the hypothesis that the acquisition of an L2 influences processing in the L1 (Dussias & Sagarra, 2007). Specifically, the early and late bilingual groups exhibited a marked divergence from the monolingual group as they revealed syntactic priming effects (p<.001) as well as lexical frequency effects (p<.001). They also revealed the greatest P600-like effect as they processed target words which were inappropriately- related to the priming homonyms (such as skin in Richard had a shed in the back of the garden). This suggests a heightened sensitivity to surface cues due to the L2 influencing homonym processing in the L1 (Cook, 2003; Dussias & Sagarra, 2007). Comparatively, the monolingual group revealed equal N400-like effects for lexical ambiguities overall compared to the unrelated conditions, and a context-by-frequency-interaction slowing their processing of the target word that is appropriately-related to the subordinate reading of the priming homonym, suggesting that they are not as sensitive to these same surface cues. Importantly, these results confirm that using ERPs along with a cross-modal lexical decision task is a promising paradigm to further study language processing.

The main objective of this dissertation is to investigate the effects of acquiring a second language (L2) at later periods of language development and native-like homonym processing in the first language (L1) from the perspective of Event-Related brain Potentials (ERP) using a cross-modal lexical decision task. To date, there is a lack of neurophysiological investigations into the effect that acquiring an L2 can have on processing strategies in the L1, and whether or not there is a precise age at which L2 exposure no longer affects native-like language processing. As such, my goal is to pinpoint this sensitive period specifically for homonym processing. To achieve this, I will present and discuss the results of two studies. The first study employs behavioural response measures using a cross-modal lexical decision task where participants simultaneously heard a sentence and made a decision to a visually-presented pseudoword or real word. The second study employs ERP measures using a novel ERP paradigm which investigates not only the main objective of this dissertation, but the second objective as well. This second objective is for this dissertation to become the first to evaluate the outcome of combining the cross-modal lexical decision task with ERPs. The behavioural and neurophysiological results for the monolingual group support the Reordered Access Model (Duffy, Morris, & Rayner, 1988) while the results for the bilingual groups do not. The results of the current studies indicate that those bilinguals who acquired French as an L2 rather than as a second native L1 show increasing divergence from monolingual native speakers in L1 homonym processing, with later acquirers exhibiting an exponentially marked divergence. This was found even though the task was carried out in English, the L1 (or one of the L1s) of all participants. The diverging performances of the bilinguals from the monolinguals were apparent in behavioural responses as well as in the amplitude, scalp distribution, and latency of ERP components, These differences were unique to each group, which supports the hypothesis that the acquisition of an L2 influences processing in the L1 (Dussias & Sagarra, 2007). Specifically, the early and late bilingual groups exhibited a marked divergence from the monolingual group as they revealed syntactic priming effects (p<.001) as well as lexical frequency effects (p<.001). They also revealed the greatest P600-like effect as they processed target words which were inappropriately- related to the priming homonyms (such as skin in Richard had a shed in the back of the garden). This suggests a heightened sensitivity to surface cues due to the L2 influencing homonym processing in the L1 (Cook, 2003; Dussias & Sagarra, 2007). Comparatively, the monolingual group revealed equal N400-like effects for lexical ambiguities overall compared to the unrelated conditions, and a context-by-frequency-interaction slowing their processing of the target word that is appropriately-related to the subordinate reading of the priming homonym, suggesting that they are not as sensitive to these same surface cues. Importantly, these results confirm that using ERPs along with a cross-modal lexical decision task is a promising paradigm to further study language processing.

兩種語句處理模型曾被提出以解釋閱讀句子時語法及語意資訊的互動。句法優先模型(syntax-first models)認為詞性判斷必定先於語意分析，而制約滿足模型(constraint-satisfaction models)則認為不同的資訊在語句理解的過程中會同時被處理。本研究檢驗兩種語句處理模型能否解釋語句中的詞彙歧義解困(lexical ambiguity resolution)。 許多眼動研究曾發現詞彙歧義詞的次要語義偏向效應(subordinate bias effect)，顯示語意偏向次要語義的語境能加速激發歧義詞的次要語義並且產生語義競爭。然而，語境的語法在詞彙歧義解困中扮演的角色並不清楚。因而，不同語義分屬不同詞性的詞性歧義詞便提供我們一個媒介以檢驗詞彙歧義解困中詞性及語意限制的互動。 本研究的目的有二：(一) 檢驗詞性限制能否決定中文詞性歧義詞的語義解困；(二) 檢驗中文歧義詞語義的詞性是否會影響次要語義偏向效應。實驗一我們將四種不同類型的中文非均勢同形異義詞置於語法及語意皆為次要語義偏向的句子裡；實驗二則將四種不同類型的中文非均勢同形異義詞置於語法為次要語義偏向但語意中立的句子裡。受試者閱讀句子時的眼動表現會即時被記錄。 實驗一的結果發現：(一) 四類型歧義詞的次要語義偏向效應只反映在目標詞後區域的二次閱讀指標上；(二) 就效果量而言，NV歧義詞的次要語義偏向效應在目標詞及目標詞後兩個區域都比VN歧義詞來得大。實驗二的結果則發現：(一) VN歧義詞的次要語義偏向效應從目標詞區的首次閱讀指標就出現，並且持續至目標詞及目標詞後兩個區域的二次閱讀指標；(二) 另外三類型歧義詞的次要語義偏向效應直到所有分析區域的二次閱讀指標才反映出來；(三) NV歧義詞的次要語義偏向效應比VN歧義詞出現得更晚也更不明顯。整體而言，本研究的結果顯示詞性限制並不是影響中文詞性歧義詞語義解困的唯一因素。此結果支持制約滿足模型，並反對句法優先模型的預測。 / Two primary sentence processing models have been proposed to account for the interaction between syntactic and semantic information in reading sentences: Syntax-first models assume that syntactic-category assignment must precede semantic analysis, while constraint-satisfaction models propose that information from different sources is processed and weighed at the same time during sentence comprehension. The present study examined whether these sentence processing models, which assume different contribution of syntactic category and semantic context, can explain the resolution of lexical ambiguity in sentences. Several eye movement studies have demonstrated the subordinate bias effect (SBE) for lexical-semantic ambiguous words (i.e., NN/VV homographs), indicating that a subordinate-biased semantic context can boost the activation of the subordinate meaning of ambiguous words and causes meaning competition (Duffy, Morris, & Rayner, 1988). However, the role of syntactic context in lexical ambiguity resolution is less clear. Syntactic category ambiguous words (i.e., SCA words; VN/NV homographs), whose alternative meanings differ in syntactic category (e.g., watch in English), serve as a means of examining the interaction between syntactic category and semantic constraints during lexical ambiguity resolution. The purpose of the present study was twofold: (a) to examine whether the syntactic category constraint can determine the semantic resolution of Chinese SCA words, and (b) to investigate whether syntactic category of alternative meanings of Chinese homographs can influence the SBE during lexical ambiguity resolution. Four types of Chinese biased homographs (NN, VV, VN, and NV) were embedded into syntactically and semantically subordinate-biased sentences (Experiment 1) and into syntactically subordinate-biased but semantically neutral sentences (Experiment 2). Participants’ eye movements were recorded as they read each sentence. In Experiment 1, the results showed: (1) The SBE for the four types of homographs was significant only in the second-pass reading on the post-target words. (2) Numerically, the NV homographs revealed a larger effect size of SBE than VN homographs on both target and post-target words. In Experiment 2, the results showed: (1) The SBE for VN appeared from the first-pass reading on the target words and lasted to the second-pass reading on the target and post-target words. (2) The SBE for the other types of homographs did not occur until the second-pass reading in all analyzed regions. (3) The SBE for NV occurred much later and less obviously than that for VN. In general, our findings support the constraint-satisfaction models and reject the prediction of the syntax-first models, suggesting that the syntactic category constraint is not the only factor influencing the semantic resolution of SCA words.

過去二十多年來，心理語言學研究關注詞彙歧義解困 (lexical ambiguity resolution)歷程發生時，語義脈絡與多義詞的語義頻率之間的交互作用。許多研究發現，當語境支持非均勢同形異義詞 (unbalanced homograph) 的次要語義時，同形異義詞的凝視時間長於與其有相同字形頻率的單義詞 (unambiguous control)，此為次要語義偏向效應 (subordinate bias effect)。根據再排序觸接模型 (reordered-access model)，次要語義偏向效應來自於主要語義與次要語義的競爭；相對地，選擇觸接模型 (selective access model)則認為只有與語境相關的語義被激發，因此，次要語義偏向效應是因為提取到一個使用頻率較低的語義。本論文進行兩個眼動實驗。實驗一檢視中文多義詞的次要語義偏向效應以區辨兩種詞彙歧義解困模型分別提出的解釋。本實驗的材料使用了低頻同形異義詞、低頻單義詞、以及高頻單義詞。結果顯示，當使用的單義詞與多義詞字形頻率相同時，在目標詞及後目標詞上(目標詞後一個詞)皆發生了次要語義偏向效應。實驗二利用口語理解─視覺典範中透過受試者理解語音訊息時同步記錄眼動的作業方式來探究次要語義偏向效應是否來自於主要語義的激發。當口語句子中的目標詞被唸出後，會計算出隨著時間增加眼睛落在四個雙字詞的凝視比例。結果發現次要語義因為語境的選擇在聽到目標詞後大約500毫秒時就可被激發，主要語義則在一聽完多義詞後被激發。因此，多義詞的兩個語義在聽到目標詞後大約900至1300毫秒時(相當於在後目標詞時)發生競爭。整體而言，本研究顯示即使語境支持多義詞的次要語義，主要語義依然會被激發。因此，次要語義偏向效應是由兩個語義競爭後所造成的結果，符合再排序觸接模型的解釋。 / Research in psycholinguistics throughout the last two decades has focused on the interaction between linguistic context and meaning dominance during lexical ambiguity resolution. Many studies demonstrated the subordinate bias effect when the preceding context biased for the subordinate meaning (i.e. infrequent meaning) of an unbalanced homograph. According to the reordered access model, the SBE is due to competition between the dominant and subordinate meanings. On the contrary, the selective access model assumes only the context-relevant meaning is activated and the SBE is a result of access to a low frequent meaning. Two eye tracking experiments of sentence reading and sentence listening were conducted. Experiment 1 examined the SBE of Chinese homographs to differentiate the two accounts. We utilized low frequency homographs along with their matched low and high-frequency unambiguous words. The results showed the SBE emerging in fixation durations of the target region and post-target region (i.e. next two words of the target), when unambiguous controls were matched to the word-form frequency of ambiguous words. Experiment 2 used visual world paradigm to explore temporal dynamics of dominant meaning activation responsible for the SBE in an instructional eyetracking-during-listening task. Fixation probabilities on four disyllabic printed words were analyzed during a time period after a target word was uttered in a spoken sentence. The results supported the reordered access model. The subordinate meaning was activated by contextual information at about 500 ms after the onset of acoustic homograph at the time when context penetrated to make its favored meaning available. Soon after the offset of homograph, the dominant meaning became active. Both meanings associated with the homograph were activated during the time windows of 901 ms to 1300 ms, which approximately corresponding to the acoustic onset of post target. In sum, our studies demonstrate that the dominant meaning is activated even when the contextual information biases to the subordinate meaning of a homograph. The subordinate bias effect is the result of competition from two meanings, conforming to the reordered access model.