A spreading-activation theory of lemma retrieval in speaking.

This paper presents a spreading-activation theory of conceptually driven lemma retrieval--the first stage of lexical access in speaking, where lexical items specified with respect to meaning and syntactic properties are activated and selected. The mental lexicon is conceived of as a network consisting of concept, lemma, and word-form nodes and labelled links, with each lexical concept represented as an independent node. A lemma is retrieved by enhancing the activation level of the node representing the to-be-verbalized concept. This activation then spreads towards the lemma level, and the highest activated lemma node is selected. The theory resolves questions such as the hypernym problem (Levelt, 1989). Furthermore, a computer model that implements the theory is shown to be able to account for many basic findings on the time course of object naming, object categorization, and word categorization in the picture-word interference paradigm. In addition, non-trivial predictions regarding the time course of semantic facilitation for hypernyms, hyponyms, and cohyponyms are experimentally tested, and shown to be valid.     

An fMRI study on conceptual, grammatical, and morpho-phonological processing

The aim of the present study was to determine whether processing of syntactic word information (lemma) is subserved by the same neural substrate as processing of conceptual or word form information (lexeme). We measured BOLD responses in 14 native speakers of German in three different decision tasks, each focussing specifically on one level of lexical processing (conceptual, syntactic, and morpho-phonological). The test parameters were natural gender, grammatical gender, and word form derivation, respectively. Discrimination between words played backwards and complex sounds served as control task. Complex contrasts revealed a functional fractionation of the left inferior frontal gyrus for each level of lexical processing.     

句法歧义消解影响因素、认知机制及其神经基础

句法歧义消解主要是指人们在面临多种句法分析可能性的情况下,句法分析器抑制不正确的句法分析而选择正确句法分析的认知过程。研究表明,该过程受到工作记忆、认知控制能力、语言分布频率、语境、韵律等因素的影响。为有效说明人们是如何完成句法歧义消解的,研究者们建构了诸如花园路径模型、约束满意理论、弱交互作用句法分析理论等相关模型。另外,基于脑成像技术研究表明,左侧额下回、左侧颞叶后部、中部和前部在句法消歧任务中都有显著激活。未来研究当围绕着句法消歧中的语义效应、句法和词汇歧义消解机制的异同、句法消歧中抑制能力的效应等方面展开。     

Lexical access in the production of pronouns

Speakers can use pronouns when their conceptual referents are accessible from the preceding discourse, as in 'The flower is red. It turns blue'. Theories of language production agree that in order to produce a noun semantic, syntactic, and phonological information must be accessed. However, little is known about lexical access to pronouns. In this paper, we propose a model of pronoun access in German. Since the forms of German pronouns depend on the grammatical gender of the nouns they replace, the model claims that speakers must access the syntactic representation of the replaced noun (its lemma) to select a pronoun. In two experiments using the lexical decision during naming paradigm [Levelt, W.J.M., Schriefers, H., Vorberg, D., Meyer, A.S., Pechmann, T., Havinga, J., 1991a. The time course of lexical access in speech production: a study of picture naming. Psychological Review 98, 122-142], we investigated whether lemma access automatically entails the activation of the corresponding word form or whether a word form is only activated when the noun itself is produced, but not when it is replaced by a pronoun. Experiment 1 showed that during pronoun production the phonological form of the replaced noun is activated. Experiment 2 demonstrated that this phonological activation was not a residual of the use of the noun in the preceding sentence. Thus, when a pronoun is produced, the lemma and the phonological form of the replaced noun become reactivated.     

Studying the grammatical aspects of word recognition: lexical priming,parsing, and syntactic ambiguity resolution

Two experiments are reported examining the relationship between lexical and syntactic processing during language comprehension, combining techniques common to the on-line study of syntactic ambiguity resolution with priming techniques common to the study of lexical processing. By manipulating grammatical properties of lexical primes, we explore how lexically based knowledge is activated and guides combinatory sentence processing. Particularly, we find that nouns (like verbs, see Trueswell & Kim, 1998) can activate detailed lexically specific syntactic information and that these representations guide the resolution of relevant syntactic ambiguities pertaining to verb argument structure. These findings suggest that certain principles of knowledge representation common to theories of lexical knowledge—such as overlapping and distributed representations—also characterize grammatical knowledge. Additionally, observations from an auditory comprehension study suggest similar conclusions about the lexical nature of parsing in spoken language comprehension. They also suggest that thematic role and syntactic preferences are activated during word recognition and that both influence combinatory processing.     

Disorders of lexical selection.

Errors in lexical processing are commonplace in language pathologies resulting from brain injury or disease. This discussion considers some of the major recent developments in the interpretation of such errors. The focus is on behavioral systems, rather than neuroanatomical or neurophysiological issues. The objective is to comment on some plausible mutual implications of generally attested pathologies and normal models of lexical retrieval for production, particularly with respect to the roles of semantic and syntactic categories.     

Does word frequency affect lexical selection in speech production?

We evaluated whether lexical selection in speech production is affected by word frequency by means of two experiments. In Experiment 1 participants named pictures using utterances with the structure “pronoun + verb + adjective”. In Experiment 2 participants had to perform a gender decision task on the same pictures. Access to the noun's grammatical gender is needed in both tasks, and therefore lexical selection (lemma retrieval) is required. However, retrieval of the phonological properties (lexeme retrieval) of the referent noun is not needed to perform the tasks. In both experiments we observed faster latencies for high-frequency pictures than for low-frequency pictures. This frequency effect was stable over four repetitions of the stimuli. Our results suggest that lexical selection (lemma retrieval) is sensitive to word frequency. This interpretation runs against the hypothesis that a word's frequency exerts its effects only at the level at which the phonological properties of words are retrieved.     

Does word frequency affect lexical selection in speech production?

We evaluated whether lexical selection in speech production is affected by word frequency by means of two experiments. In Experiment 1 participants named pictures using utterances with the structure “pronoun + verb + adjective”. In Experiment 2 participants had to perform a gender decision task on the same pictures. Access to the noun's grammatical gender is needed in both tasks, and therefore lexical selection (lemma retrieval) is required. However, retrieval of the phonological properties (lexeme retrieval) of the referent noun is not needed to perform the tasks. In both experiments we observed faster latencies for high-frequency pictures than for low-frequency pictures. This frequency effect was stable over four repetitions of the stimuli. Our results suggest that lexical selection (lemma retrieval) is sensitive to word frequency. This interpretation runs against the hypothesis that a word's frequency exerts its effects only at the level at which the phonological properties of words are retrieved.     

Syntactic mediation is not obligatory during lexical access: evidence from a single-case study of Welsh Aphasia

Current models of word production assume the existence of functionally distinct lexical-syntactic and word-form representations. However, there are competing hypotheses about whether prior access to syntactic properties of words is obligatory during lexical retrieval. In this paper we report preliminary evidence from the single case study of a Welsh-speaking patient with a lexical access deficit. We examined the patient's ability to access word forms and to retrieve information about the grammatical gender of Welsh nouns. The data show no correlation between the retrieval of word-form and grammatical gender information. This pattern of performance is inconsistent with hypotheses postulating obligatory syntactic mediation in lexical production.     

Robust effects of syntactic structure on visual word processing

A series of experiments explored the effect of the syntactic structure of a sentence fragment on the processing of a subsequent target word. In both a naming and a lexical decision task, modal verb contexts followed by main verb targets and preposition contexts followed by noun targets produced faster response times than did the opposite pairings (i.e., modal/noun and preposition/ verb). This syntactic context effect occurred across several different variations in the method of context presentation. Also, unlike some previous findings on syntactic priming, the present effects did not disappear when a naming task was employed. The magnitude of the syntactic priming effect was similar in the naming and lexical decision tasks when the response times were slow, but was larger in the lexical decision task when the response times were faster. The implications of these results for recent discussions of the relationship between task structure and the locus of observed contextual effects are discussed.     

How left inferior frontal cortex participates in syntactic processing: Evidence from aphasia

We report on three experiments that provide a real-time processing perspective on the poor comprehension of Broca’s aphasic patients for non-canonically structured sentences. In the first experiment we presented sentences (via a Cross Modal Lexical Priming (CMLP) paradigm) to Broca’s patients at a normal rate of speech. Unlike the pattern found with unimpaired control participants, we observed a general slowing of lexical activation and a concomitant delay in the formation of syntactic dependencies involving “moved” constituents and empty elements. Our second experiment presented these same sentences at a slower rate of speech. In this circumstance, Broca’s patients formed syntactic dependencies as soon as they were structurally licensed (again, a different pattern from that demonstrated by the unimpaired control group). The third experiment used a sentence-picture matching paradigm to chart Broca’s comprehension for non-canonically structured sentences (presented at both normal and slow rates). Here we observed significantly better scores in the slow rate condition. We discuss these findings in terms of the functional commitment of the left anterior cortical region implicated in Broca’s aphasia and conclude that this region is crucially involved in the formation of syntactically-governed dependency relations, not because it supports knowledge of syntactic dependencies, but rather because it supports the real-time implementation of these specific representations by sustaining, at the least, a lexical activation rise-time parameter.     

Learning to divide the labor: an account of deficits in light and heavy verb production

Theories of sentence production that involve a convergence of activation from conceptual‐semantic and syntactic‐sequential units inspired a connectionist model that was trained to produce simple sentences. The model used a learning algorithm that resulted in a sharing of responsibility (or “division of labor”) between syntactic and semantic inputs for lexical activation according to their predictive power. Semantically rich, or “heavy”, verbs in the model came to rely on semantic cues more than on syntactic cues, whereas semantically impoverished, or “light”, verbs relied more on syntactic cues. When the syntactic and semantic inputs were lesioned, the model exhibited patterns of production characteristic of agrammatic and anomic aphasic patients, respectively. Anomic models tended to lose the ability to retrieve heavy verbs, whereas agrammatic models were more impaired in retrieving light verbs. These results obtained in both sentence production and single‐word naming simulations. Moreover, simulated agrammatic lexical retrieval was more impaired overall in sentences than in single‐word tasks, in agreement with the literature. The results provide a demonstration of the division‐of‐labor principle, as well as general support for the claim that connectionist learning principles can contribute to the understanding of non‐transparent neuropsychological dissociations.     

Adult age differences in visual word identification: functional neuroanatomy by positron emission tomography

Adult age differences in the neural systems mediating semantic (context-independent) memory were investigated using positron emission tomography (PET). Younger (20-29 years) and older (62-70 years) participants performed lexical decision (word/nonword discrimination) and nonsemantic (simple visual search) baseline tasks during PET scanning. Within the lexical decision task, display duration and presentation rate were varied across scans. The behavioral data suggested that although an age-related slowing was evident in visual feature and response processing, the retrieval of semantic/lexical information was similar for younger and older adults. For both age groups, lexical-related activation occurred in inferior prefrontal and occipitotemporal regions of the left hemisphere. Differential activation, as a function of age group, was observed in the left occipitotemporal pathway as a result of older adults' maintaining higher levels of neural activity in striate cortex (during visual search) and in inferior temporal cortex (during lexical decision). The prefrontal activation was similar for the two age groups. Thus, although this form of semantic memory retrieval does not undergo significant age-related decline, an age-related change in the associated pattern of neural activation is evident. These findings differ from previous neuroimaging studies of episodic (context-dependent) memory retrieval, which have suggested that age-related compensatory mechanisms are expressed primarily by greater activation of prefrontal regions for older adults than for younger adults.     

Lexical retrieval constrained by sound structure: the role of the left inferior frontal gyrus

Positron emission tomography was used to investigate two competing hypotheses about the role of the left inferior frontal gyrus (IFG) in word generation. One proposes a domain-specific organization, with neural activation dependent on the type of information being processed, i.e., surface sound structure or semantic. The other proposes a process-specific organization, with activation dependent on processing demands, such as the amount of selection needed to decide between competing lexical alternatives. In a novel word retrieval task, word reconstruction (WR), subjects generated real words from heard non-words by the substitution of either a vowel or consonant. Both types of lexical retrieval, informed by sound structure alone, produced activation within anterior and posterior left IFG regions. Within these regions there was greater activity for consonant WR, which is more difficult and imposes greater processing demands. These results support a process-specific organization of the anterior left IFG.     

汉语单音节词汇产生中的激活反馈

采取图画-词汇干扰实验范式,探索汉语词汇产生中词条选择和音韵编码两个阶段之间是否存在激活的反馈。实验一探索的是字形激活能否反馈至语义层产生语义激活,结果发现,与无关条件相比,目标图画(如“锯”)的字形中介(“镇”)的语义相关字(“村”)条件显著地延长了图画命名的时间。这表明在汉语词汇产生过程中,字形层的激活能反馈至语义层。实验二探索的是语音激活能否反馈至语义层产生语义激活,结果发现,与无关条件相比,目标图画(“梨”)的语音中介(“厘”)的语义相关字(“毫”)条件并未显著地影响图画命名的时间。这表明语音层的激活不能反馈至语义层,或者反馈回的激活太微弱不能影响图画命名过程。实验一和二的结果更倾向于支持词汇产生中词条选择和音韵编码两个阶段独立的观点。     

句法结构和动词重复对汉语句子口语产生中句法启动效应的影响

研究中采用启动范式和图片描述任务, 利用句法选择比率和句子产生潜伏期的两个指标, 考察了启动句句法结构、动词是否相同和延时对汉语口语句子产生中句法启动效应的影响。结果发现在选择比率上, 句法结构产生的启动效应随延时变化保持稳定, 由启动句和目标句动词相同导致的启动效应的提高量(词汇增强效应)快速衰退, 首次为句子产生过程的句法选择阶段和计划阶段提供了证据。在句子产生潜伏期上, 仅发现启动句和目标句句法结构相同时缩短了句子产生潜伏期, 这可能是由于启动句句法结构激活水平的提高, 使得说话者在目标句产生的句法计划和选择阶段都更快引起的。选择阶段的加工影响句法选择比率, 而选择阶段和计划阶段共同影响了句子产生的潜伏期, 实验结果支持了两阶段竞争理论的观点。     

中心词和非中心词在句法启动的词汇增强效应中存在不同的机制

句法启动中, 非中心词和中心词重复是否诱发出相似强度的词汇增强效应, 目前存在着较大的理论争议。本研究在汉语双宾结构和介宾结构上分别操纵中心词和非中心词重复, 并在确保具有合适统计检验力基础上, 完成了3个句法启动实验。实验结果清楚地显示中心词重复诱发了稳定的词汇增强效应, 非中心词中的直接宾语重复也诱发了稳定但相对较弱的词汇增强效应。在此基础上, 我们尝试提出一个解释框架以调和现有的理论争议。     

汉语词汇产生中词汇选择和音韵编码之间的交互作用

采取图画－词汇干扰实验范式,探索汉语单音节词汇产生中词汇选择和音韵编码之间的交互作用。实验一探测目标图画语义相关项的语音激活,观察到了非目标项的语音激活。实验二探测目标图画语义相关项的字形激活,未发现非目标项的字形激活。在改进实验条件的基础上,实验三验证实验一和二,并探测目标图画字形相关项的语音激活以及语音相关项的字形激活,结果未探测到语义相关项的字形或语音激活、语音相关项的字形激活,只发现了字形相关项的语音激活。实验一至三的结果表明汉语词汇产生中存在目标字字形相关项的语音激活,但不存在从音韵编码阶段至词汇选择阶段的激活反馈。综合上述结果,从是否存在多重的字形或语音激活,以及是否存在从音韵编码至词汇选择的反馈两个方面进行了讨论。研究结果倾向于支持词汇产生中层叠式理论的观点     

汉语阅读中先行词词频对代词加工影响的眼动研究

采用眼动分析法考察先行词词频对代词加工的影响。结果表明,先行词的词频对其代词加工的难易没有影响,即当先行词为高频词时对代词后区域的阅读时间与低频条件没有差异。研究结果支持了代词加工的词条重新通达假说,该理论认为读者在加工代词时只需通达先行词的部分词汇信息。     

Syntactic priming effects in aphasia: an investigation of local syntactic dependencies

This study explored on-line processing of local syntactic dependencies in normal subjects and in Broca's and Wernicke's aphasics using a lexical decision paradigm. In addition, subjects performed a grammatically judgement task on the real word pairs used in the lexical decision tasks. Results of two experiments for normal subjects indicated different syntactic priming effects as a function of the type of local syntactic dependency. Word pairs that formed a single constituent phrase, i.e., a verb phrase, showed both facilitory and inhibitory effects, whereas word pairs that reflected local syntactic dependencies across a phrase boundary, i.e., pronoun verb, showed only inhibitory effects. Broca's aphasics failed to show facilitory effects when presented with word pairs forming a single constituent phrase but, similar to normals, did show inhibition when presented with word pairs that reflected local syntactic dependencies across a phrase boundary. In contrast, Wernicke's aphasics failed to show inhibitory effects in both experiments. The implications of these results for theories of language processing deficits in aphasia are considered.