Chapter 2 Literature Review
2.2 Issues of lexical ambiguity resolution
2.2.2 Syntactic category
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suggesting that biased homographs were resolved on the basis of the relative frequency of the meanings when there was no disambiguating context. The retrieval of the dominant meaning was faster than that of the subordinate meaning.
2.2.2 Syntactic category
Words from different syntactic categories are linguistically, psychologically and neurologically distinct. Some electrophysiological and imaging studies have reported distinct brain responses (ERPs / activation areas) to nouns and verbs (Federmeier, Segal, Lombrozo, & Kutas, 2000; Liu, Hua, & Weekes, 2007; Rösler, Streb, & Haan, 2001; Yokoyama et al., 2006). For example, Federmeier et al. (2000) found ERPs elicited by unambiguous nouns were more negative than those elicited by unambiguous verbs between 250 and 450 ms. In addition, unambiguous verbs preceded by appropriate syntactic context elicited a left-lateralized frontal positivity which was not found for unambiguous nouns. Rösler et al. (2001) also discovered that N400 elicited by nouns had a larger amplitude than that elicited by verbs, and that reaction times were shorter to noun targets than to verb targets in their primed lexical decision task. These findings seem to suggest that nouns and verbs are processed differently in the brain.
As reviewed by Vigliocco, Vinson, Druks, Barber, and Cappa (2011), it may take
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more efforts to process verbs than to process nouns in sentences. Semantically, typical nouns often refer to objects, while verbs are usually used to express actions where participants need to integrate several events. Syntactically, verbs need to assign thematic roles (e.g., agent, patient, theme, etc.) to other words (often nouns) in sentences. Morphologically, verbs are more complex and have more inflections than nouns, especially in the Indo-European languages (e.g., German, French, etc.).
In terms of behavioral differences, a lot of empirical research has reported a processing advantage of nouns over verbs, i.e., nouns were processed faster than verbs.
This processing advantage of nouns were repeatedly replicated in different experimental tasks, such as lexical decision (Rösler et al., 2001; J. A. Sereno, 1999; J.
A. Sereno & Jongman, 1997), noun/verb categorization (J. A. Sereno, 1999), and semantic categorization (Tyler, Russell, Fadili, & Moss, 2001). For example, J. A.
Sereno and Jongman (1997) controlled overall frequency of occurrence and number of letters for unambiguous pure nouns and unambiguous pure verbs in a lexical decision task and found the latencies to nouns were significantly shorter than those to verbs whenever the stimuli were monosyllabic or disyllabic. Their results indicated that processing verbs was more demanding than processing nouns, which they attributed to differences in inflection structure between nouns and verbs. According to them, in English nouns were used with its bare form more frequently than verbs, so
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the responses to nouns were faster than to verbs when the bare form was presented.
Moreover, J. A. Sereno (1999) also replicated the processing advantage of nouns both in a noun/verb categorization task and a lexical decision task. In their experiments, nouns and verbs with either high- or low-frequency were presented to either the left or right visual fields of subjects. Both tasks revealed very similar results: the responses to nouns were significantly faster than those to verbs; however, in the noun/verb categorization task, the advantage of nouns vanished when the stimuli had low-frequency. In addition, the hemispheric difference was shown only for verbs: the responses to verbs were significantly faster in the case of right visual field compared to the case of left visual field.
Other research investigated reasons for the processing difference between nouns and verbs. For instance, Kauschke and Stenneken (2008) used two types of German nouns (man-made vs. biological objects) and verbs (transitive vs. intransitive verbs) with their bare form in a visual lexical decision task. In addition to the processing advantage of nouns over verbs, their results also showed that the responses to intransitive verbs were significantly faster than those to transitive verbs, indicating the influence of syntactic factor since transitive and intransitive verbs differ in their argument structure. In a second experiment, they used inflected word forms by adding plural-suffixes and personal-suffixes to nouns and verbs respectively, constructing
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three subsets (e.g., NELK-EN—RUPFEN: pinks—(to/we/they) pick;
KLUB-S—SIEG-T: clubs—(he/she) wins; HENGST-E—HÜPF-E: stallions—(I) bounce). Their reaction time data again demonstrated the noun advantage in all subsets, suggesting that the noun-verb discrepancies in processing cannot be attributed to word form and morphological complexity.
In addition, from the perspective of language acquisition, the evidence that verbs are acquired later than nouns may reflect the psychological complexity of verbs (Gentner, 1982, 2006). Evidence from eye movement showed that the main verb in simple active sentences received longer fixation durations than other grammatical elements (e.g., function word, the subject, the object, etc.), indicating readers paid more visual attention to the main verb in sentences (Rayner, 1977). Therefore, it is reasonable to consider more processing loads for verbs than for nouns during sentence comprehension.
Actually, the larger difficulties of processing verbs compared to nouns also influence the resolution of ambiguous words. Pickering and Frisson (2001) conducted eye-tracking experiments to investigate the processing of verbs, including verbs with multiple meanings (homographs), verbs with multiple senses (polysemy), and unambiguous verbs. The two types of ambiguous verbs were biased in terms of the frequencies of alternative interpretations. They manipulated whether preceding
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context or succeeding context containing disambiguating information and whether dominant or subordinate interpretation was supported by the disambiguating information. Thus, in the case of ambiguous verbs, four conditions were formed: (a) supportive-dominant, (b) supportive-subordinate, (c) neutral-dominant, and (d) neutral-subordinate. For unambiguous verbs, the presence of disambiguating information in preceding context was the only variable (supportive vs. neutral). For the homographic verbs, they found no context and meaning frequency effects in the measures of initial processing (i.e., first-pass time and first-pass regressions) in the verb region; instead, in the region immediately following the verbs, the context effects were observed on first-pass time and the meaning frequency effects emerged on both total time and second-pass time. Table 1 shows their findings for homographic verbs.
Table 1
The summarized findings for homographic verbs from Pickering and Frisson (2001)
Measures
(Gaze duration) Context Context &
Frequencyb Context First-pass
regression Context
Second-pass time
(Rereading time) Context Frequencya
Total time Context &
Frequencya
Note. Context: neutral > supportive; Frequencya: subordinate > dominant; Frequencyb: subordinate < dominant
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Pickering and Frisson (2001) suggested that the resolution of homographic verbs was delayed in comparison with that of homographic nouns, since the SBE was not observed in the verb region but in the following region. The delayed resolution allowed alternative meanings of homographic verbs to reach a high level of activation.
As a result, the meaning frequency effects did not occur immediately in the verb region. The context effects observed in Region 3 indicated a selection process between multiple meanings. The late occurrence of the meaning frequency effects suggested that the dominant meanings were easier to be integrated into the sentence context than the subordinate meaning.
In addition to ambiguous verbs, another type of homograph involving a verb meaning is syntactic category ambiguous words (SCA words), whose multiple meanings cross different syntactic categories (e.g., watch). People may encounter syntactic category ambiguities when there are SCA words in the sentences. Previous literature on the resolution of syntactic category ambiguities yielded different findings.
Frazier and Rayner (1987) proposed a delay model: When no disambiguating information is provided prior to a syntactic category ambiguity, the resolution would be delayed until helpful information is encountered, regardless of interpretation preference of the ambiguity itself. The delay model can account for Frazier and Rayner’s results: (a) reading times on the ambiguous word phrase (e.g., desert trains)
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were longer when preceded by a disambiguating determiner (e.g., I know that this desert trains young people to be especially tough.) compared to when preceded by a
non-disambiguating determiner (e.g., I know that the desert trains young people to be especially tough.), and (b) reading times on the remainder of the sentence, containing
disambiguating information, showed an opposite pattern. Assuming analyzing syntactic categories of words takes time, these results indicated that syntactic category assignment occurred immediately when there is disambiguating information but delayed until the presence of disambiguating information when the preceding context is neutral.
According to Frazier (1989), the language processor handles ambiguities at each level in different ways. For syntactic ambiguities, only the simplest structure is considered and constructed. For purely semantic ambiguities, multiple meanings are available and selection is rapid based on preference or contextual bias. For syntactic category ambiguities, selection is delayed until the presence of disambiguation, though multiple meanings and syntactic categories are initially available. In short, a delay mechanism was assumed to handle the resolution of syntactic category ambiguity.
However, the resolution of syntactic category ambiguity is delayed probably because it takes more time to process a verb meaning. Pickering and Frisson (2001)
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have suggested that the resolution of ambiguous verbs is delayed due to the inherent processing difficulty of verb meanings. It is reasonable to suspect that the difficulty of processing verbs may also affect the resolution of syntactic category ambiguity. It seems unnecessary to assume a special delay mechanism for syntactic category ambiguities. The empirical evidence that both ambiguous verbs and syntactic category ambiguities are not resolved rapidly indicates the influence of the inherent processing difficulty of verbs.
On the other hand, some studies supported immediate resolution of syntactic category ambiguity (Gibson, 2006; Jones, Folk, & Brusnighan, 2012; Macdonald, 1993). For example, Jones et al. (2012) conducted eye movement experiments to investigate how biased SCA words are resolved in disambiguating or neutral contexts.
In Experiment 1, preceding context provided syntactic category information consistent with either the dominant or subordinate meaning of SCA words (e.g., I was shocked to see him counter the offer so quickly.). The results showed no ambiguity
effects (ambiguity > unambiguous controls) in gaze duration measures whenever the prior context was biased toward the dominant or subordinate meaning, indicating that the syntactically appropriate meaning was initially selected. However, the ambiguity effects indeed emerged in later eye-movement measures, such as regression-out probability from target words and second-pass time on prior disambiguating context,
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only when the subordinate meaning was biased. These processing costs suggested that readers had difficulty in integrating the subordinate meaning due to the activation of the dominant meaning. In Experiment 2, preceding context was neutral and disambiguating information was provided in post-target region (e.g., We watched her duck eat all of the bread.). The results showed ambiguity effects in different measures
consistently in the subordinate-biased condition, including gaze duration on target words2, regression-out probability from post-target regions, second-pass time on target words, and second-pass time in post-target regions. The ambiguity effects indicated processing costs of the inconsistency between the initially selected (dominant) meaning and the context-intended (subordinate) meaning. In addition, in the subordinate-biased post-target region, first-pass times were shorter for the ambiguity condition compared to the control condition. The authors claimed that this resulted from the increased regression-out probability and may indicate that readers tended to recover the context-intended (subordinate) meaning by making regressions.
Taken together, their findings suggested that readers immediately select one meaning for SCA words and rejected the delay model proposed by Frazier and Rayner (1987).
To sum up, it is questionable whether syntactic category ambiguity is resolved by a unique delay mechanism. The delay model was proposed on the basis of the delayed
2 The increased gaze durations for biased syntactic category ambiguities were not predicted by either the delay model or the immediate processing theories. Jones (2012) suggested that the increased gaze durations may be caused by parafoveal-on-foveal processing or undershot saccades.
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resolution observed on balanced SCA words in neutral contexts. However, the investigation on biased SCA words in disambiguating and in neutral contexts did not support the delay model. This indicates that the resolution of syntactic category ambiguity is not always delayed. Instead, like lexical-semantic ambiguity resolution, the probabilistic constraints matter. Previous research has demonstrated the influence of syntactic category of meanings on lexical ambiguity resolution. Presumably, the inherent processing difficulty of verb meanings would delay the semantic resolution of SCA words. Therefore, it is of importance to distinguish homographic nouns, homographic verbs, and SCA words when examining lexical ambiguity resolution.
2.2.3 Contextual constraints