Chapter 6 General Discussion
6.1 Dynamic processing of context influence and meaning dominance
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6.1 Dynamic processing of context influence and meaning dominance
The results from the present two eye-tracking experiments demonstrate the interaction of contextual influence and lexical activation during lexical ambiguity resolution. In Experiment 1, the fixation times of homographs were compared to those of low frequency unambiguous words. Subordinate bias effect emerged consistently as the control used form-matched unambiguous word (Sereno et al., 1992). Sereno et al. (2006) found SBE was not attenuated even in a strongly biasing context. They suggested the reason may be due to the special situation that the word form of ambiguous word was a HF word but its functional link to context was subordinate in terms of meaning. However, the results from Experiment 1 indicated that SBE occurred as the homograph was an LF word both in terms of its word form and meaning.
Experiment 2 provides a comprehensive time course of lexical ambiguity resolution on spoken word recognition which reveals the temporal information of the contextual influence on lexical activations. When listeners are given sufficient contextual information, they produce a greater fixation proportions towards the contextually-selected semantic associative words. The consistent results were found in
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both homograph and monograph conditions that context influences occur from about 500 ms, shortly after the acoustic onset of the target word. This may indicate that at an earlier stage, the context is acting on the access of the subordinate meaning of the homograph. We found the dominant meaning was activated from 901 ms to 1300 ms, approximately after the acoustic offset of the spoken target and before the completion of next word. The converging evidence from both visual and auditory presenting experiments shows the robust SBE and the activation of the dominant meaning.
We then compare our results with those in cross-modal priming studies to gauge the theoretical implications of temporal dynamics of lexical activation and contextual influence. Generally, two levels of semantic access are distinguished based on the results of lexical decision studies. Pre-lexical stage involves word recognition and meaning activation, while post-lexical stage deals with semantic selection and integration. Onifer and Swinney (1981) presented sentences that biased for the dominant or for the subordinate meaning of an ambiguous word. The results demonstrated the activation of multiple meanings irrespective of the context when presenting visual target word at the auditory offset of ambiguous words. According to the exhaustive or multiple access model, context can only penetrate lexical activation at post-lexical stage, but not at the earlier stage. It is likely that the frequency effect emerged after the multiple meanings associated with a word were accessed.
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Seidenberg et al. (1982) delayed the presentation of visual target until 200 ms or more after the spoken homophone, by that time, demonstrating that a single meaning had been selected after initially activating multiple candidates. It is assumed to reflect post-lexical stage of using context to select an appropriate meaning.
From the results of our Experiment 2, sentential information aids the processing of Chinese homographs from early on within the acoustic boundary of the homograph in natural speech. The influence of sentential context is thus pushed to a much earlier stage than what has been proposed by the multiple access model. At a subsequent time, after the homograph is being heard, the dominant meaning is activated, thus semantic competition occurs. However, it was hard to separate the stage of this activation possibly occurred at the level of lexical or post-lexical processing. So it may be more likely to view the lexical ambiguity resolution as the continuous graded constraint of context and frequency effects rather than an order-based of two-stage processing for different meanings (Mirman, 2008). In terms of continuous graded constraints, it seems that both contextual bias and meaning dominance are used in parallel by the comprehenders. Two implications thus can be drawn from these findings, first, contextual information affects the ambiguity resolution occurring early before the acoustic offset of homograph. Second, the context reorders the processing of different meanings, the unselected but frequent meaning becomes activated later.
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6.2 The competition account of subordinate bias effect
Both reordered-access and selective-access models predicted the rapid and early use of context. Consistent with both models, experiment one have shown context affected the fixation proportions on the subordinate meaning (SR associate), starting from 500 ms after the homograph onset. However, the discrepancy of the two models lies in whether the dominant meaning was activated. Our results are more consistent with the reordered access model according to the two findings reported here. First, in Experiment one, longer processing time is demonstrated in both target and post-target region when readers process ambiguous words. Under the selective view, no initial processing time cost should be observed when the context is sufficiently constraining.
Second, in Experiment two, the dominant meaning (DR associate) attracted more looks of fixations than those to the unrelated distractors and above chance level even in the subordinate-biased context. Two meanings were activated at the same time, therefore, competition or processing difficulty occurred which were evident in longer fixation durations in experiment one, supporting the reordered access model. In sum, the dominant meaning was still available though it was delayed. Therefore, the selective access view was ruled out and the homographs were not merely treated as low frequency words.
Another issue was how the context affected the status of contextually-
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inappropriate meaning. According to reordered access model, two meanings are activated independently. Contexts speed access to the appropriate meaning, while no effect was on the activation of the inappropriate meaning. On the other hand, based on selective access model, given sufficiently constraining contextual information, only the contextually-appropriate meaning should be activated; therefore, the inappropriate meaning is not supposed to be activated after selection. In Experiment two, the dominant meaning occurred shortly after the offset of the homographs. The theoretical implication lies in the automatic processing in terms of their relative meaning dominance associated with the ambiguous words.
6.3 Time course of activation of ‘unselected’ semantic representation
Multiple access of both selected and unselected meanings is inconsistent with the prediction of selective access model, which posits the elimination of the SBE in strongly biasing contexts. As we have discussed, both our norming data and the immediate effects of context suggest that our subordinate-biased contexts were truly strongly biasing. Generally, both reordered access and selective access model are capable of accounting for the early penetrate of the context. However, although the activation of dominant meaning is consistent with reordered access model, the relative time of activation is not accounted by reordered access model.
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The meanings of individual homonymy are also represented separately in the mental lexicon which may lead to the ambiguity effects. Therefore, there would be more differentiated semantic representations for the dominant and subordinate meanings of biased homographs. The advantage for high-frequency meaning of lexical ambiguity resolution is that higher frequency words have stronger bottom-up connections since they have been used more. The results of Dahan et al. (2001) and Magnuson, Dixon, Tanenhaus, and Aslin (2007) showed that word frequency or meaning frequency effects on spoken word recognition occurred early and increased gradually. The dominant meaning activation from the present results can become active only after the activation of the subordinate meaning.. It indicates that the biasing contextual information may change the order of activation, which demonstrated the situation of contextual re-ordering. However, in the present study, the activation of subordinate meaning may be due to both contextual facilitation and lexical meaning itself. Therefore, the context effect should be build up first in an attempt to separate two sources of meaning activation. Alternative possible explanation for the delay of the dominant meaning is taken from the perspective of speech perception. Frauenfelder et al., (1990) suggested that lexical effects tend to be strongest after the uniqueness point when the context become explicit to a particular word. Therefore, the stronger form-meaning mapping in lexicon represented the
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dominance after uniqueness point. Moreover, the dominant meaning somewhat maintained active until 2800 ms. It may result from the task demand in experiments of visual world paradigm. Listen-only task features its unconstrained nature of free viewing and listening; however, no explicit selection of visual targets may be the reason that the fixations proportions of the dominant meaning did not gradually decrease even though it was the contextually-inappropriate meaning.
The relative timing of accessing form and semantic information of ambiguous word can be demonstrated by the time course of activating contextually-selected and -unselected meanings. When listeners hear an ambiguous word embedded in context, contextual information and meaning dominance are combined to resolve the ambiguity. The initial activation of semantic representation was due to the function of context biasing. At subsequent, the unselected semantic representation was also activated because of its meaning dominance. After revising the inappropriate meaning, a single plausible meaning was selected and integrated into text representation. In short, we can conclude the successful ambiguity resolution depends on the continuous on-line interaction among contextual, lexical, and syntactic information carried in the sentences. This is similar to the real world communication, the discourse, pragmatic, and syntactic factors are combined to determine sentential interpretations.
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6.4 Future Research
First of all, in order to further investigate how the context affects the activation of both dominant and subordinate meanings, additional neutral contexts would be needed, so as to further provide strong evidence to support the context reordering.
Then, in terms of the experimental stimuli, we did not use meaning-frequency matched unambiguous words because Chinese homographs are basically low-frequency words. If the homographs with relatively higher frequency can be utilized, it may provide more direct evidence to examine the frequency account. More specifically, if the access is selective, processing of a biased homograph in a context that supports the subordinate interpretation should be similar to processing of an unambiguous word matched the subordinate meaning frequency.
On the other hand, another issue is the relationship between syntactic-category information and semantic ambiguity resolution. Most research of lexical ambiguity resolution have used ambiguous nouns or verbs as the target words, but the homograph with syntactic category ambiguity, such as 過節 which bears two meanings with different word class: “celebrate the day” or “enmities” is another interesting issue for further research. Whether the syntactic category information can facilitate ambiguity resolution and the subordinate bias effect is eliminated by the syntactically legal continuation of the sentential context can provide theoretical
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explanations for the interplay of syntactic and semantic processing.
Moreover, one of the advantages of using visual world paradigm lies in its simple and natural task. The unconstrained nature of free viewing of picture displays and listening are particularly suited for studies with young children or some special populations, such as, individuals with specific language impairment, with mild Alzheimer’s disease or with autism. The issue of ambiguous words’ processing can also be applied to examine the developmental differences on how context influences homonym processing as children acquire more knowledge of lexical meaning at different ages. Booth, Harasaki, and Burman (2006) investigated both lexical and sentence level context effects by asking children (9-, 10- and 12-year-olds) to read aloud written sentences that biased either the dominant or subordinate meaning of a sentence-final homonym or that were ambiguous. The results showed a lexical level facilitation for dominant and subordinate meanings regardless of biasing context for younger children or lower skill readers. In contrast, no lexical level, but a reliable sentence level facilitation was found for targets consistent with the sentence context for older children or high skill readers. It seems that the older or higher skill readers are better to use sentential context to facilitate the contextually-appropriate meaning of homonymy than younger or lower skill readers. Numerous studies with adults have shown processing differences between unbalanced and balanced homonyms. The
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factor of meaning dominance could be examined in age differences in future developmental studies.
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