The effects of processing requirements on neurophysiological responses to spoken sentences

Ten English speaking subjects listened to sentences that varied in sentential constraint (i.e., the degree to which the context of a sentence predicts the final word of that sentence) and event-related potentials (ERPs) were recorded during the presentation of the final word of each sentence. In the Control condition subjects merely listened to the sentences. In the Orthographic processing condition subjects merely listened to the sentences. In the Orthographic processing condition subjects decided, following each sentence, whether a given letter had been present in the final word of the preceding sentence. In the Phonological processing condition the subjects judged whether a given speech sound was contained in the terminal word. In the Semantic processing condition subjects determined whether the final word was a member of a given semantic category. A previous finding in the visual modality that the N400 component was larger in amplitude for low constraint sentence terminations than for high was extended to the auditory modality. It was also found that the amplitude of a N200-like response was similarly responsive to contextual constraint. The hypothesis that N400 amplitude would vary significantly with the depth of processing of the terminal word was not supported by the data. The "N200" recorded in this language processing context showed the classic frontocentral distribution of the N200. The N400 to spoken sentences had a central/centroparietal distribution similar to the N400 in visual modality experiments. It is suggested that the N400 obtained in these sentence contexts reflects an automatic semantic processing of words that occurs even when semantic analysis is not required to complete a given task. The cooccurrence and topographical dissimilarity of the "N200" and N400 suggest that the N400 may not be a delayed or a generic N200.     

Contextual influences on phonetic identification in aphasia: the effects of speaking rate and semantic bias

Two experiments examined the influence of context on stop-consonant voicing identification in fluent and nonfluent aphasic patients and normal controls. Listeners were required to label the initial stop in a target word varying along a voice onset time (VOT) continuum as either voiced or voiceless ([b]/[p] or [d]/[t]). Target stimuli were presented in sentence contexts in which the rate of speech of the sentence context (Experiment 1) or the semantic bias of the context (Experiment 2) was manipulated. The results revealed that all subject groups were sensitive to the contextual influences, although the extent of the context effects varied somewhat across groups and across experiments. In addition, a number of patients in both the fluent and nonfluent aphasic groups could not consistently identify even endpoint stimuli, confirming phonetic categorization impairments previously shown in such individuals. Results are discussed with respect to the potential reliance by aphasic patients on higher level context to compensate for phonetic perception deficits.     

Syntactic and semantic contributions to sentence comprehension in agrammatism

Five aphasic subjects, who demonstrated agrammatic speech, and eight control subjects were presented with a sentence-picture matching task in which the factors of syntactic complexity, semantic reversibility, and sentence plausibility were independently varied. A subset of the sentences was patterned after that presented by A. Caramazza and E. Zurif (1976, Brain and Language, 5, 572-583) who concluded that Broca's aphasics rely on semantic constraints instead of syntactic information for sentence comprehension. Our aphasic subjects showed the same pattern of performance on this subset of sentences. However, the results from the full set of sentence materials we tested show that the aphasic subjects could perform some sentence level syntactic analyses, even when syntactic information conflicted with semantic constraints. The aphasic subjects correctly interpreted most active and passive sentences. They failed, however, to assign thematic roles and adjectives in center-embedded relative sentences, and instead relied on nonsyntactic information. These results show that both semantic and syntactic information contributed to sentence comprehension in the aphasic subjects we tested, in contrast to previous claims that syntactic and semantic processes are completely dissociated in this population.     

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.     

Dissociation of algorithmic and heuristic processes in language comprehension: Evidence from aphasia

Three groups of aphasic patients, Broca's, Conduction, and Wernicke's, and a nonaphasic patients control group were tested for comprehension of object-relative center-embedded sentences. The sentences were of three types: sentences in which semantic constraints between words allowed the subjects to assign a correct semantic reading of the sentence without decoding the syntax, sentences in which semantic constraints were relaxed and for which a correct reading was only possible with knowledge of syntactic relationships among words, and sentences which described highly improbable events. The subjects' task was to choose which of two pictures captured the meaning expressed in the sentence. Broca's and Conduction aphasics performed near perfectly on sentences where they could use semantic information. Their performance dropped to chance when they had to use syntactic information. These results support a neuropsychological dissociation of heuristic and algorithmic processes based primarily, though not exclusively, on semantic and syntactic information, respectively.     

Semantic cueing effects on word retrieval in aphasic patients with lexical retrieval deficit

We examined lexical access in word production, focusing on lexical retrieval deficit in aphasic patients. These patients were asked to name one picture at a time and we investigated how semantic cueing affected their ability to retrieve the word. When the subjects experienced a retrieval failure, they were presented with one type of cue, and then they tried to name the target picture again. Four types of cues were used: phonological, semantic related, semantic category member, and baseline cue. Both phonological and semantically related cues improved performance. In contrast, category member cues had no effects on releasing the retrieval block. These results can be explained by an interactive activation model in word production (Dell & O'Seaghdha, 1991).     

Differential cognitive processing of Kanji and Kana words: do orthographic and semantic codes function in parallel in word matching task.

Relative engagements of the orthographic and semantic codes in Kanji and Hiragana word recognition were investigated. In Exp. 1, subjects judged whether the pairs of Kanji words (prime and target) presented sequentially were physically identical to each other in the word condition. In the sentence condition, subjects decided whether the target word was valid for the prime sentence presented in advance. The results showed that the response times to the target swords orthographically similar (to the prime) were significantly slower than to semantically related target words in the word condition and that this was also the case in the sentence condition. In Exp. 2, subjects judged whether the target word written in Hiragana was physically identical to the prime word in the word condition. In the sentence condition, subjects decided if the target word was valid for the previously presented prime sentence. Analysis indicated that response times to orthographically similar words were slower than to semantically related words in the word condition but not in the sentence condition wherein the response times to the semantically and orthographically similar words were largely the same. Based on these results, differential contributions of orthographic and semantic codes in cognitive processing of Japanese Kanji and Hiragana words was discussed.     

Sentence context effects and the timecourse of lexical ambiguity resolution in nonfluent aphasia

In the current neurolinguistic literature, two proposals have been put forth to account for the deficit in ambiguous word processing observed in nonfluent aphasic patients. One proposal maintains that these individuals are impaired in the selective access of ambiguous word meanings, while the other argues that they are impaired in the process of contextual selection. In the present study, nonfluent aphasic patients and elderly control subjects participated in a semantic priming experiment, in which ambiguous words were presented in different biasing contexts at both a 0- and 750-ms ISI. At both ISIs, control subjects showed context-selective access, in that only contextually appropriate meanings were activated. In contrast, at the 0-ms ISI, the nonfluent aphasic patients showed activation of both meanings of the ambiguous word regardless of context. Only at the 750-ms ISI did they exhibit context-selective access. These results are consistent with the proposal that left hemisphere damage causing nonfluent aphasia results in an impairment in rapidly integrating lexical-semantic information into context.     

Comparison of the performances of a fluent and a nonfluent aphasic on a pantomimic referential task

The pantomimic performances of a typical Broca's (nonfluent) and Wernicke's (fluent) aphasic were compared with each other and with four normal control subjects on a simple task of nonverbal referential communication. Both aphasic subjects demonstrated only about 50% accuracy in their pantomimic communication. Also, measures were obtained of the motoric fluency of the pantomimes of all subjects and comparisons were made between the fluent and nonfluent aphasics. These measures demonstrated distinct differences in the fluency patterns of the pantomimes of the two aphasic subjects similar to the differences in speech fluency which distinguish and characterize these two types of aphasia; that is, the fluent aphasic pantomimed fluently and like the control subjects and the nonfluent aphasic pantomimed nonfluently. The quantitative and qualitative similarities in the fluency patterns of the speech and the pantomimic behaviors of the aphasic subjects are discussed in terms of their implications for a definition of aphasia.     

Lexical creativity during instances of word-finding difficulty: Broca's vs. Wernicke's aphasia

Lexical innovation--the creation of a word by combining existing morphemes in a novel way (e.g. "map ball" for "globe")--was evaluated as a method for circumventing word-finding difficulty in Broca's and Wernicke's aphasia. Aphasic groups were matched for naming performance and compared to a control group of normal adults matched for age and education. Lexical innovations were collected during the administration of a confrontation naming test, and were then analyzed in terms of the correctness of morpheme combination, semantic accuracy, novelty, and communicative effectiveness. An innovation was considered to be communicatively effective when its intended referent was understood by a naive judge. The lexical innovations of the two aphasic groups were diametrically opposed: as compared to both Broca's aphasics and normal adults, Wernicke's aphasics innovated significantly less often, and their innovations were significantly inferior in terms of: semantic precision, the proper construction of morpheme combination, and communicative effectiveness. This pattern suggests that lack of verbal fluency may be compatible with lexical creativity, while empty logorrheic speech may be an impediment to lexical creativity. Similarly, we conclude that the agrammatism of Broca's asphasia does not interfere with lexical innovation, while the paragrammatism of Wernicke's aphasia does interfere with lexical innovation, thus suggesting that paragrammatism affects morpheme combination at the word level as well as the sentence level.     

句子语境中语义联系效应和句法效应的研究

通过对比研究句子语境中句法成分和语义联系对目标词加工的不同影响,来探讨句子语境的作用机制和作用点问题。实验一采用词汇命名任务研究发现,句法违反对词汇命名会产生抑制作用,而语义违反对词汇命名却没有发现抑制作用。实验二利用词汇决定任务发现,句法和语义成分影响词汇决定任务,句法违反和语义违反对词汇决定任务均会产生抑制作用。结果表明,句子语境加工中,对内容词语义整合过程中存在一个句法成分的独立加工水平。     

The locus of semantic satiation in category membership decision and acceptability judgment

The locus of semantic satiation was investigated in three experiments. In Experiments 1 and 2 subjects performed a category membership decision task following the repetition (3 or 30 times) of the category name. In order to distinguish the effect of semantic satiation from the possible effect of repetition on the identification of the member word, two measures were recorded, namely (a) the member word reading time and (b) response time. A semantic satiation effect was observed on response times in Experiment 1. No satiation effect was observed, however, when, instead of repeating a single word, the subject had to repeat several words corresponding to a category definition. A facilitation effect due to repetition was observed instead (Experiment 2). An inhibition effect was observed again in Experiment 3 with an acceptability judgment task performed on a short sentence. This pattern of results is consistent with the general hypothesis that semantic satiation is linked to the processes involved in accessing the meaning of the repeated word after the repetition is completed.     

Use of semantic context by patients with Alzheimer's disease

In this study we used semantic-priming procedures to examine limitations in the use of semantic context by patients with Alzheimer's disease. We also tried to determine whether any such contextual effects were mediated solely through automatic processes or whether attentional processes were also involved. Three tasks were applied to examine the effect of semantic context on the performance of 18 normal elderly and 18 normal young subjects, and on 18 patients with Alzheimer's disease. When normal and demented subjects were asked to decide whether a given item was a member of a certain category, results showed that their response times were equally affected by the item's dominance in the category. The time that demented patients took to recognize a word was actually affected more by the semantic context provided by a priming sentence than was that of normal subjects. When asked to generate the final word of an incomplete sentence, demented subjects performed very poorly unless potential responses were highly constrained by sentence context.     

汉语语句重音的分类和分布

通过两个独立进行的重音标注实验对汉语语句重音的分类和分布进行了初步探讨。实验l是由60位普通被试参加的音节重音突显度的知觉实验。实验2是由本文三位作者参加的重音类别标注实验,在此实验中语句重音被划分为节奏重音和语义重音。实验2中对于语句重音的分类性标注结果得到了实验l中普通被试对音节重音突显度知觉结果的支持,这说明人们确实能够感知到两种不同类型的重音。实验结果还表明,节奏重音倾向于出现在较大韵律单元内的最末韵律词的末音节上,并且与适当的停延相伴生,语义重音的分布则与语句的韵律结构的关系不大。     

Grammatical class effects in relation to normal and aphasic sentence processing

Agrammatic, Broca's aphasic patients, Wernicke's aphasic patients, and neurologically intact control subjects were asked to detect target letters in prose passages and in a scrambled word passage. The targets were embedded, in some instances, in content words (open-class vocabulary items), and in other instances, in function words (closed-class vocabulary items). With respect to the prose passages, both the control subjects and Wernicke's aphasic patients were more apt to notice target letters when they appeared in the open-class items than when in closed-class items; by contrast, the agrammatic Broca's patients showed no vocabulary class detection difference. The Wernicke's patients were not entirely normal, however: Whereas the normal subjects showed a much smaller vocabulary class effect for letter detection in the scrambled condition, the Wernicke's maintained the pattern they had shown in the prose condition. These and other findings obtained on the letter cancellation task are discussed in relation to lexical access mechanisms geared to sentence parsing.     

Localization of Syntactic Comprehension by Positron Emission Tomography

Positron Emission Tomography (PET) was used to determine regional cerebral blood flow (rCBF) when eight normal right-handed males read and made acceptability judgments about sentences. rCBF was greater in Broca's area (particularly in the pars opercularis) when subjects judged the semantic plausibility of syntactically more complex sentences as compared to syntactically less complex sentences. rCBF was greater in left perisylvian language areas when subjects had to decide whether sentences were semantically plausible than when subjects had to decide whether syntactically identical sentences contained a nonsense word. The results of this experiment suggest that overall sentence processing occurs in regions of the left perisylvian association cortex. The results also provide evidence that one particular aspect of sentence processing (the process that corresponds to the greater difficulty of comprehending center-embedded than right-branching relative clause sentences) is centered in the pars opercularis of Broca's area. This process is likely to be related to the greater memory load associated with processing center-embedded sentences.     

The effects of varying attentional demands on the word retrieval skills of adults with aphasia, right hemisphere brain damage, or no brain damage

Adults with mild aphasia, right hemisphere brain damage (RBD), or no brain damage (NBD) provided one-word phrase completions under isolation, focused attention, and divided attention conditions and in response to relatively constrained or unconstrained phrase stems. Despite comparable word retrieval accuracy among groups during the isolation condition, aphasic and RBD groups performed less accurately than the NBD group during focused and divided attention conditions. Across conditions, there were no significant differences between aphasic and RBD groups. Only aphasic subjects demonstrated a significant effect of phrase type, responding more accurately when completing constrained versus unconstrained stimuli. For aphasic and RBD groups, error type analysis indicated that semantic and phonological aspects of word retrieval were influenced by increased attentional demands. These findings suggest that for adults with aphasia or RBD, there is a negative relation between attention impairments and word retrieval abilities.     

The effect of pictorial context on sentence memory in Broca's and Wernicke's aphasia

Eighteen aphasic patients (8 Broca's and 10 Wernicke's aphasics), 11 right hemisphere damaged patients and 12 normal subjects were tested to assess the effect of pictorial context on verbal memory with a sentence recognition task. The subjects were read aloud a stimulus sentence describing a simple event and simultaneously shown a picture congruent or incongruent with the sentence. Immediately following or after an interval of 30 sec, the subjects were read aloud a second sentence and asked to judge whether this sentence was the same or different from the stimulus sentence. The results indicated that verbal memory was better retained in supportive situations than in distracting situations, and that this contextual effect was greater in aphasic patients than in any of the other groups. Verbal memory declined rapidly after an interval in aphasic patients, but not in normal subjects. The Broca's and the Wernicke's aphasics demonstrated different performance patterns when semantic analysis of sentences was critical.     

The generalizability of context effects on word recognition: A reconsideration of the roles of parafoveal priming and sentence context

In three experiments, subjects named target words preceded by congruous, incongruous, or neutral sentence contexts. There was no evidence that the recognition of the target word was affected by the semantic characteristics of a word presented immediately to the right of it. The nature of the preceding sentence context did affect target-naming speed. However, the magnitude of the context effect was considerably smaller in these experiments, in which nonterminal target words were used, than in previous experiments in which the target word was always the final word of the sentence, was highly predictable from the context, and was often semantically related to words in the sentence. The implications of these two findings for theories of reading and context effects are discussed.