Processing of lexical ambiguities in aphasia

Wernicke's and Broca's aphasics performed a lexical decision task wherein they had to decide whether the third word of an auditorily presented triplet series of words was "real" or not. The first and third words of each triplet were related to one, both, or neither meaning of the second word which was semantically ambiguous. The performance pattern of the Wernicke's aphasics was similar to that of normals. They showed selective access to different meanings of the ambiguous words, as demonstrated by the fact that the context provided by the first word affected semantic facilitation on the third word. In contrast, Broca's aphasics showed no semantic facilitation in any priming condition. These results are consistent with previous findings, suggesting that semantic representations may be largely spared in Wernicke's aphasics. The failure of the Broca's aphasics to demonstrate facilitation is consistent with the view that they have a processing deficit in automatically accessing the lexical representation of words.     

The Development of Strategic Processing of Ambiguous Words: Riddles Versus Neutral Context

Children in Grades 4 and 6 read isolated target words following the auditory presentation of an ambiguous word (e.g., deck). The ambiguous word occurred as the last word in either a neutral sentence (e.g., “There is the deck”) or as the last word in a riddle (“Why couldn't anybody play poker on the ark? Because Noah sat on the deck). Related target words were consistent with either the dominant meaning (e.g., porch) or the subordinate meaning (cards) of the ambiguous word. In the neutral context, Grade 4 children showed equivalent facilitation for dominant and subordinate targets relative to unrelated target words; Grade 6 children showed facilitation only for the dominant targets. In the riddle context, both groups of children showed equivalent facilitation for the two types of related targets. The neutral context results supported the hypothesis that the two bases of context effects—automatic lexical access and selective access—develop at different rates (Simpson &; Foster, 1986). The results obtained from the riddles suggest that the selective process is strategic (Ceci, 1989).     

Automatic access of the meanings of ambiguous words in context: Some limitations of knowledge-based processing

Five experiments are described on the processing of ambiguous words in sentences. Two classes of ambiguous words (noun-noun and noun-verb) and two types of context (priming and nonpriming) were investigated using a variable stimulus onset asynchrony (SOA) priming paradigm. Noun-noun ambiguities have two semantically unrelated readings that are nouns (e.g., PEN, ORGAN); noun-verb ambiguities have both noun and verb readings that are unrelated (e.g., TIRE, WATCH). Priming contexts contain a word highly semantically or associatively related to one meaning of the ambiguous word; nonpriming contexts favor one meaning of the word through other types of information (e.g., syntactic or pragmatic). In nonpriming contexts, subjects consistently access multiple meanings of words and select one reading within 200 msec. Lexical priming differentially affects the processing of subsequent noun-noun and noun-verb ambiguities, yielding selective access of meaning only in the former case. The results suggest that meaning access is an automatic process which is unaffected by knowledge-based (“top-down”) processing. Whether selective or multiple access of meaning is observed largely depends on the structure of the ambiguous word, not the nature of the context.     

词汇识别中歧义词素语义加工:ERP研究

结合掩蔽启动范式和ERP技术,利用歧义词素的加工,本研究探讨了歧义词素语义的激活。实验采用3×2两因素被试内设计,歧义词素两含义互为启动刺激和目标刺激,两变量分别为启动词类型(歧义词素含义1 vs.含义2 vs.无关词)和目标词类型(歧义词素含义1 vs.含义2)。行为结果发现启动词类型和目标词类型存在交互作用,即只有当共享词素同形同义的情况下,目标词的加工才可能被启动,共享词素同形不同义时并没有产生启动效应。ERP结果进一步肯定了行为结果,在N250和N400两个脑电成分上都发现了启动类型和目标类型交互作用有关的效应,当启动词和目标词共享词素同形同义时,同时引发了N250和N400的变化;当共享词素同形不同义时,时程分析时虽然也发现了N250的变化,但是N250的效应较小,小于同形同义所引发的N250效应,持续时间也较短。实验结果说明,在词汇识别中歧义词素语义可以激活,并对目标词汇加工的早期加工阶段发挥作用。     

无语境条件下汉语词类歧义词的意义激活

以单字词为实验材料,采用启动命名任务,在孤立词条件下考察了汉语词类歧义词不同意义激活的时间进程特点。实验发现,歧义词的两种意义都能被激活,但主要意义激活得较早,次要意义激活速度较慢;当两种意义都激活之后,次要意义的激活水平降低,而主要意义仍维持在一定激活水平。结果表明,汉语词类歧义词的多重激活过程会受到意义相对频率的影响。     

Sensitivity to local sentence context information in lexical ambiguity resolution: evidence from left- and right-hemisphere-damaged individuals

Using a cross-modal semantic priming paradigm, the present study investigated the ability of left-hemisphere-damaged (LHD) nonfluent aphasic, right-hemisphere-damaged (RHD) and non-brain-damaged (NBD) control subjects to use local sentence context information to resolve lexically ambiguous words. Critical sentences were manipulated such that they were either unbiased, or biased toward one of two meanings of sentence-final equibiased ambiguous words. Sentence primes were presented auditorily, followed after a short (0 ms) or long (750 ms) interstimulus interval (ISI) by the presentation of a first- or second-meaning related visual target, on which subjects made a lexical decision. At the short ISI, neither patient group appeared to be influenced by context, in sharp contrast to the performance of the NBD control subjects. LHD nonfluent aphasic subjects activated both meanings of ambiguous words regardless of context, whereas RHD subjects activated only the first meaning in unbiased and second-meaning biased contexts. At the long ISI, LHD nonfluent aphasic subjects failed to show evidence of activation of either meaning, while RHD individuals activated first meanings in unbiased contexts and contextually appropriate meanings in second-meaning biased contexts. These findings suggest that both left (LH) and right hemisphere (RH) damage lead to deficits in using local contextual information to complete the process of ambiguity resolution. LH damage seems to spare initial access to word meanings, but initially impairs the ability to use context and results in a faster than normal decay of lexical activation. RH damage appears to initially disrupt access to context, resulting in an over-reliance on frequency in the activation of ambiguous word meanings.     

Visual word recognition by bilinguals in a sentence context: evidence for nonselective lexical access

Recent research on bilingualism has shown that lexical access in visual word recognition by bilinguals is not selective with respect to language. In the present study, the authors investigated language-independent lexical access in bilinguals reading sentences, which constitutes a strong unilingual linguistic context. In the first experiment, Dutch-English bilinguals performing a 2nd language (L2) lexical decision task were faster to recognize identical and nonidentical cognate words (e.g., banaan-banana) presented in isolation than control words. A second experiment replicated this effect when the same set of cognates was presented as the final words of low-constraint sentences. In a third experiment that used eyetracking, the authors showed that early target reading time measures also yield cognate facilitation but only for identical cognates. These results suggest that a sentence context may influence, but does not nullify, cross-lingual lexical interactions during early visual word recognition by bilinguals.     

Accessing lexical ambiguities during sentence comprehension: Effects of frequency of meaning and contextual bias

Two hypotheses concerning the nature of lexical access, the exhaustive access and the terminating ordered search hypotheses, were examined in two separate studies using a crossmodal lexical priming task. In this task, subjects listened to sentences that were biased toward either the primary interpretation (a meaning occurring 75% or more of the time) or a secondary interpretation (a meaning occurring less than 25% of the time) of a lexical ambiguity that occurred in each sentence. Simultaneously, subjects made lexical decisions about visually presented words. Decisions to words related to both the primary and secondary meanings of the ambiguity were facilitated when presented immediately following occurrence of the ambiguity in the sentence. This effect held under each of the two biasing context conditions. However, when they were presented 1.5 sec following occurrence of the ambiguity, only visual words related to the contextually relevant meaning of the ambiguity were facilitated. These results support the exhaustive access hypothesis. It is argued that lexical access is an autonomous subsystem of the sentence comprehension routine in which all meanings of a word are momentarily accessed, regardless of the factors of contextual bias or bias associated with frequency of use.     

Lexical complexity and fixation times in reading: Effects of word frequency,verb complexity,and lexical ambiguity

Two experiments investigated whether lexical complexity increases a word’s processing time. Subjects read sentences, each containing a target word, while their eye movements were monitored. In experiment 1, mean fixation time on infrequent words was longer than on their more frequent controls, as was the first fixation after the Infrequent Target. Fixation Times on Causative, factive, and negative verbs and ambiguous nouns were no longer than on their controls. Further analyses on the ambiguous nouns, however, suggested that the likelihood of their various meanings affected fixation time. This factor was investigated in experiment 2. subjects spent a longer time fixating ambiguous words with two equally likely meanings than fixating ambiguous words with one highly likely meaning. The results suggest that verb complexity does not affect lexical access time, and that word frequency And the presence of two highly likely meanings may affect lexical access and/or postaccess integration.     

Automatic activation of phonological information in reading: Evidence from the semantic relatedness decision task

A semantic relatedness decision task was used to investigate whether phonological recoding occurs automatically and whether it mediates lexical access in visual word recognition and reading. In this task, subjects read a pair of words and decided whether they were related or unrelated in meaning. In Experiment 1, unrelated word-homophone pairs (e.g., LION-BARE) and their visual controls (e.g., LION-BEAN) as well as related word pairs (e.g., FISH-NET) were presented. Homophone pairs were more likely to be judged as related or more slowly rejected as unrelated than their control pairs, suggesting phonological access of word meanings. In Experiment 2, word-pseudohomophone pairs (e.g., TABLE-CHARE) and their visual controls (e.g., TABLE-CHARK) as well as related and unrelated word pairs were presented. Pseudohomophone pairs were more likely to be judged as related or more slowly rejected as unrelated than their control pairs, again suggesting automatic phonological recoding in reading.     

Hemispheric contributions to lexical ambiguity resolution in a discourse context: evidence from individuals with unilateral left and right hemisphere lesions

In the present study, a cross-modal semantic priming task was used to investigate the ability of left-hemisphere-damaged (LHD) nonfluent aphasic, right-hemisphere-damaged (RHD) and non-brain-damaged (NBD) control subjects to use a discourse context to resolve lexically ambiguous words. Subjects first heard four-sentence discourse passages ending in ambiguous words and after an inter-stimulus interval (ISI) of either 0 or 750 ms, made lexical decisions on first- or second-meaning related visual targets. NBD control subjects, at the 0 ms ISI, only activated contextually appropriate meanings, though significant effects, as a group, were only seen in second-meaning biased contexts. Surprisingly, at the 750 ms ISI, these subjects activated both appropriate and inappropriate meanings in first-meaning biased contexts. With respect to the LHD nonfluent aphasic patients, the majority activated first meanings regardless of context at the 0 ms ISI, though effects for the group were not significant. At the 750 ms ISI, these patients again activated first meanings regardless of context, with significant effects for the group only seen in first-meaning biased contexts. With regard to the RHD patients, the majority activated second meanings regardless of context at the 0 ms ISI and first meanings regardless of context at the 750 ms ISI, though, as a group, the effects were not significant. In light of our previous findings (Grindrod & Baum, 2003, submitted), the present data are interpreted as supporting the notion that damage to the left hemisphere disrupts either lexical access processes or the time course of lexical activation, whereas damage to the right hemisphere impairs the use of context and leads to activation of ambiguous word meanings based on meaning frequency.     

Turning an advantage into a disadvantage: Ambiguity effects in lexical decision versus reading tasks

When performing a lexical decision task, participants can correctly categorize letter strings as words faster if they have multiple meanings (i.e., ambiguous words) than if they have one meaning (i.e., unambiguous words). In contrast, when reading connected text, participants tend to fixate longer on ambiguous words than on unambiguous words. Why are ambiguous words at an advantage in one word recognition task, and at a disadvantage in another? These disparate results can be reconciled if it is assumed that ambiguous words are relatively fast to reach a semantic-blend state sufficient for supporting lexical decisions, but then slow to escape the blend when the task requires a specific meaning be retrieved. We report several experiments that support this possibility.     

Loci of phonological effects in the lexical access of words written in a shallow orthography

Summary Three experiments are reported that extend previous observations on the slowing of lexical decisions by phonologically ambiguous forms of Serbo-Croatian words relative to the phonologically unambiguous forms of the same words. The phonological ambiguity arises from the presence of letters whose phoneme interpretation differs between the two Serbo-Croatian alphabets, the Roman and the Cyrillic. In the first experiment, target words were preceded by asterisks or by context words that were associatively related and alphabetically matched to the targets. The effect of word contexts (i.e., priming) was greater for phonologically ambiguous than for phonologically unambiguous targets. The second experiment manipulated the alphabetic match of context word and target word. The effect of this manipulation was limited to phonologically ambiguous words. The third experiment reproduced the details of the first with the addition of visual degradation of the target stimuli on half of the trials. The results of the first experiment were replicated but no interaction between context and visual degradation was observed. The discussion focused on phonologically mediated access of Serbo-Croatian words. A model was proposed in which phonological codes are assembled prelexically according to weighted grapheme-phoneme correspondence rules.     

The effect of polysemy on lexical decision time: Now you see it,now you don’t

Gernsbacher (1984) found that number of word meanings (polysemy) did not influence lexical decision time when it was operationalized as number of dictionary definitions. This finding supports her contention that subjects do not store all possible dictionary meanings for words in memory. The present experiments extended Gernsbacher's research by determining whether more psychologically valid measures of polysemy affect lexical decision time. Three metrics were used to represent the meanings that subjects actually access from memory (accessible polysemy): (1) the first meanings subjects think of when asked to define stimulus words, (2) all the meanings subjects generate for words, and (3) the average number of meanings subjects generate. The results showed that the second and third metrics of polysemy influenced lexical decision time, whereas the first metric (representing mostly the access to dominant meanings for words) only approached significance.     

Effects of syntactic category assignment on lexical ambiguity resolution in reading: an eye movement analysis

Readers' eye movements were monitored as they read sentences containing lexically ambiguous words whose meanings share a single syntactic category (e.g., calf), lexically ambiguous words whose meanings belong to different syntactic categories (e.g., duck), or unambiguous control words. Information provided prior to the target always unambiguously specified the context-appropriate syntactic-category assignment for the target. Fixation times were longer on ambiguous words whose meanings share a single syntactic category than on controls, both when prior context was semantically consistent with the subordinate interpretation of a biased ambiguous word (Experiment 1) and when prior context was semantically neutral as to the intended interpretation of a balanced ambiguous word (Experiment 2). These ambiguity effects, which resulted from differences in difficulty with meaning resolution, were not found when the ambiguity crossed syntactic categories. These data indicate that, in the absence of syntactic ambiguity, syntactic-category information mediates the semantic-resolution process.     

Unilateral brain damage effects on processing homonymous and polysemous words

Using an auditory semantic priming paradigm, the present study investigated the abilities of left-hemisphere-damaged (LHD) non-fluent aphasic, right-hemisphere-damaged (RHD) and normal control individuals to access, out of context, the multiple meanings of three types of ambiguous words, namely homonyms (e.g., "punch"), metonymies (e.g., "rabbit"), and metaphors (e.g., "star"). In addition, the study tested certain predictions of the "suppression deficit" and "coarse semantic coding" hypotheses that have been proposed to account for the linguistic deficits typically observed after RH damage. Homonymous, metonymous, and metaphorical words were used as primes followed after a short (100 ms) or a long (1000 ms) inter-stimulus interval (ISI) by dominant-meaning-related, subordinate-meaning-related or unrelated target words. No significant group effects were found, and for both ISIs, dominant- and subordinate-related targets were facilitated relative to unrelated control targets for the homonymy and metonymy conditions. In contrast, for the metaphor condition, only targets related to the dominant meaning were facilitated. These findings provide only partial support for the "suppression deficit" hypothesis and no support for the "coarse semantic coding" hypothesis (as interpreted herein) indicating that patients with focal LH or RH damage can access the multiple meanings of ambiguous words and exhibit processing abilities comparable to those of older normal control subjects, at least at the single-word level.     

Lexical ambiguity and the timecourse of attentional allocation in word recognition

In two experiments the allocation of attention during the recognition of ambiguous and unambiguous words was investigated. In Experiment 1, separate groups performed either lexical decision, auditory probe detection, or their combination. In the combined condition probes occurred 90, 180, or 270 ms following the onset of the lexical-decision target. Lexical decisions and probe responses were fastest for ambiguous words, followed by unambiguous words and pseudowords, respectively, which indicated that processing ambiguous words was less attention demanding than unambiguous words or pseudowords. Attention demands decreased across the timecourse of word recognition for all stimulus types. In Experiment 2, one group performed the lexical-decision task alone, whereas another group performed the lexical-decision task during the retention interval of a short-term memory task. The results were consistent with those from Experiment 1 and showed that word recognition is an attention-demanding process and that the demands are inversely related to the number of meanings of the stimulus. These results are discussed with regard to the structure of the mental lexicon (i.e., single vs. multiple lexical entries) and the effect of such a structure on attentional mechanisms.     

Pictures in sentences: understanding without words

To understand a sentence, the meanings of the words in the sentence must be retrieved and combined. Are these meanings represented within the language system (the lexical hypothesis) or are they represented in a general conceptual system that is not restricted to language (the conceptual hypothesis)? To evaluate these hypotheses, sentences were presented in which a pictured object replaced a word (rebus sentences). Previous research has shown that isolated pictures and words are processed equally rapidly in conceptual tasks, but that pictures are markedly slower than words in tasks requiring lexical access. The lexical hypothesis would therefore lead one to expect that rebus sentences will be relatively difficult, whereas the conceptual hypothesis would predict that rebus sentences would be rather easy. Sentences were shown using rapid serial visual presentation (RSVP) at a rate of 10 or 12 words per second. With one set of materials (Experiments 1 and 2), readers took longer to judge the plausibility of rebus sentences than all-word sentences, although the accuracy of judgment and of recall were similar for the two formats. With two new sets of materials (Experiments 3 and 5), rebus and all-word sentences were virtually equivalent except in one circumstance: when a picture replaced the noun in a familiar phrase such as seedless grapes. In contrast, when the task required overt naming of the rebus picture in a sentence context, latency to name the picture was markedly longer than to name the corresponding word, and the appropriateness of the sentence context affected picture naming but not word naming (Experiment 4). The results fail to support theories that place word meanings in a specialized lexical entry. Instead, the results suggest that the lexical representation of a noun or familiar noun phrase provides a pointer to a nonlinguistic conceptual system, and it is in that system that the meaning of a sentence is constructed.     

Processing of lexical ambiguities: a comment on Milberg, Blumstein, and Dworetzky (1987)

In a study by Milberg, Blumstein, and Dworetzky (1987), normal control subjects and Wernicke's and Broca's aphasics performed a lexical decision task on the third element of auditorily presented triplets of words with either a word or a nonword as target. In three of the four types of word triplets, the first and the third words were related to one or both meanings of the second word, which was semantically ambiguous. The fourth type of word triplet consisted of three unrelated, unambiguous words, functioning as baseline. Milberg et al. (1987) claim that the results for their control subjects are similar to those reported by Schvaneveldt, Meyer, and Becker's original study (1976) with the same prime types, and so interpret these as evidence for a selective lexical access of the different meanings of ambiguous words. It is argued here that Milberg et al. only partially replicate the Schvaneveldt et al. results. Moreover, the results of Milberg et al. are not fully in line with the selective access hypothesis adopted. Replication of the Milberg et al. (1987) study with Dutch materials, using both a design without and a design with repetition of the same target words for the same subjects led to the original pattern as reported by Schvaneveldt et al. (1976). In the design with four separate presentations of the same target word, a strong repetition effect was found. It is therefore argued that the discrepancy between the Milberg et al. results on the one hand, and the Schvaneveldt et al. results on the other, might be due to the absence of a control for repetition effects in the within-subject design used by Milberg et al. It is concluded that this makes the results for both normal and aphasic subjects in the latter study difficult to interpret in terms of a selective access model for normal processing.     

Ambiguity Advantage Revisited: Two Meanings are Better than One When Accessing Chinese Nouns

This paper revisits the effect of lexical ambiguity in word recognition, which has been controversial as previous research reported advantage, disadvantage, and null effects. We discuss factors that were not consistently treated in previous research (e.g., the level of lexical ambiguity investigated, parts of speech of the experimental stimuli, and the choice of non-words) and report on a lexical decision experiment with Chinese nouns in which ambiguous nouns with homonymic and/or metaphorical meanings were contrasted with unambiguous nouns. An ambiguity advantage effect was obtained—Chinese nouns with multiple meanings were recognized faster than those with only one meaning. The results suggested that both homonymic and metaphorical meanings are psychologically salient semantic levels actively represented in the mental lexicon. The results supported a probability-based model of random lexical access with multiple meanings represented by separate semantic nodes. We further discuss these results in terms of lexical semantic representation and how different experimental paradigms result in different ambiguity effects in lexical access.