大脑视觉词形区及其在阅读神经网络中的作用

大脑梭状回中部被认为是视觉词形加工区(Visual Word Form Area, VWFA)。近年来的研究对VWFA的功能提出了质疑, 研究者开始关注VWFA作为复杂阅读网络的一部分与其它脑区的动态联结机制, 主要集中在三个方面：一是梭状回中部对于视觉词形选择性敏感的本质; 二是它在词汇阅读的神经网络中的作用; 最后是语言经验对于VWFA认知神经功能的塑造作用。结合以上研究的最新进展, 文中指明从动态神经网络的角度揭示大脑功能成为今后认知神经科学研究的最新取向。     

Letter processing in the visual system: different activation patterns for single letters and strings

One would expect that a lifetime of experience recognizing letters would have an important influence on the visual system. Surprisingly, there is limited evidence of a specific neural response to letters over visual control stimuli. We measured brain activation during a sequential matching task using isolated characters (Roman letters, digits, and Chinese characters) and strings of characters. We localized the visual word form area (VWFA) by contrasting the response to pseudowords against that for letter strings, but this region did not show any other sign of visual specialization for letters. In addition, a left fusiform area posterior to the VWFA was selective for letter strings, whereas a more anterior left fusiform region showed selectivity for single letters. The results of different analyses using both large regions of interest and inspections of individual patterns of response reveal a dissociation between selectivity for letter strings and selectivity for single letters. The results suggest that reading experience fine-tunes visual representations at different levels of processing. An important conclusion is that the processing of nonpronounceable letter strings cannot be assumed to be equivalent to single-letter perception.     

Functional specificity of the visual word form area: general activation for words and symbols but specific network activation for words

The functional specificity of the brain region known as the Visual Word Form Area (VWFA) was examined using fMRI. We explored whether this area serves a general role in processing symbolic stimuli, rather than being selective for the processing of words. Brain activity was measured during a visual 1-back task to English words, meaningful symbols (e.g., $, %), digits, words in an unfamiliar language (Hebrew), and geometric control stimuli. Mean activity in the functionally defined VWFA, as well as a pattern of whole-brain activity identified using a multivariate technique, did not differ for words and symbols, but was distinguished from that seen with other stimuli. However, functional connectivity analysis of this region identified a network of regions that was specific to words, including the left hippocampus, left lateral temporal, and left prefrontal cortex. Results support the hypothesis that activity in the VWFA plays a general role in processing abstract stimuli; however, the left VWFA is part of a unique network of brain regions active only during the word condition. These findings suggest that it is the neural "context" of the VWFA, i.e., the broader activity distributed in the brain that is correlated with VWFA, that is specific for visual word representation, not activity in this brain region per se.     

The neural basis of obligatory decomposition of suffixed words

Recent neurolinguistic studies present somewhat conflicting evidence concerning the role of the inferior temporal cortex (IT) in visual word recognition within the first 200 ms after presentation. On the one hand, fMRI studies of the Visual Word Form Area (VWFA) suggest that the IT might recover representations of the orthographic form of words. On the other hand, influential MEG studies of responses from the occipito-temporal regions around 150 ms post-stimulus onset indicate recognition of letters as opposed to symbols but not a sensitivity to statistical properties of letter strings associated with word form representations. Recent MEG experiments support the position that the IT does represent the visual word forms of morphemes and performs morphological decomposition modulated by the statistical relations between morphemes by 170 ms post presentation (at the M170 response). Responses to heteronyms show that the M170 does not make contact with the mental lexicon where word forms are connected to meanings. We report here an MEG study of pseudo-affixed words like brother, which masked priming studies have shown are decomposed in recognition. If the M170 response from IT does index obligatory morphological decomposition based on visual word forms but not lexical entries, we should find that the statistical relation between pseudo-stem and pseudo-suffix modulates the M170 for pseudo-affixed words, as for truly affixed words. The results of this experiment confirm this prediction. In addition, surface form frequency for these words also modulates the M170, providing some support for dual route recognition for words for which decomposition is a garden path.     

藏语母语者汉语词汇识别的眼动研究

采用眼动技术,通过两个实验考察了藏语母语者在不同语境中阅读汉语句子时,字形、语音信息在词汇识别中分别发挥的作用以及词频效应。结果发现：（1）在高限制性句子语境中,字形和语音共同作用;（2）在低限制性句子语境中,语音作用显著;（3）词频效应出现在高限制性语境的晚期,以及低限制性语境的中期和晚期。该结果表明,在藏语母语者阅读汉语的过程中,句子语境影响词汇识别过程中字形、语音的作用及作用的时间进程,藏语母语者汉语词汇识别符合双通道理论。     

Effects of depression upon reading: a case for distinguishing effortful from automatic processes

This study was designed to test the view that depression would have selective effects upon effortful but not automatic aspects of reading. Relationships were determined between 59 fifth graders' depression scores (on the Children's Depression Inventory and a teacher's rating of depression) and their performance on measures of automatic aspects of reading (word recognition and word attack skills) and effortful aspects of reading (comprehension). A stepwise multiple regression, using statistical controls for sex and mental ability, showed expected relationships of depression to over-all comprehension for the 7 teachers' ratings, but not for the inventory. As expected, relationships of depression to word recognition and word attack scores were statistically non-significant.     

Early development of letter specialization in left fusiform is associated with better word reading and smaller fusiform face area

A functional region of left fusiform gyrus termed “the visual word form area” (VWFA) develops during reading acquisition to respond more strongly to printed words than to other visual stimuli. Here, we examined responses to letters among 5‐ and 6‐year‐old early kindergarten children (N = 48) with little or no school‐based reading instruction who varied in their reading ability. We used functional magnetic resonance imaging (fMRI) to measure responses to individual letters, false fonts, and faces in left and right fusiform gyri. We then evaluated whether signal change and size (spatial extent) of letter‐sensitive cortex (greater activation for letters versus faces) and letter‐specific cortex (greater activation for letters versus false fonts) in these regions related to (a) standardized measures of word‐reading ability and (b) signal change and size of face‐sensitive cortex (fusiform face area or FFA; greater activation for faces versus letters). Greater letter specificity, but not letter sensitivity, in left fusiform gyrus correlated positively with word reading scores. Across children, in the left fusiform gyrus, greater size of letter‐sensitive cortex correlated with lesser size of FFA. These findings are the first to suggest that in beginning readers, development of letter responsivity in left fusiform cortex is associated with both better reading ability and also a reduction of the size of left FFA that may result in right‐hemisphere dominance for face perception.     

Sentence Context and Word Recognition in Children with Average Reading Ability and with a Specific Reading Disability

The inhibitory and facilitatory effects of context on word recognition were investigated in 24 8-to 10-year-old children with a specific reading disability in comparison with a group of 24 children matched for reading ability and a group of 24 children matched for chronological age. To avoid confounding the effects of reading level with those of word difficulty, target words of equivalent relative familiarity for each participant were presented in congruous, neutral, and incongruous sentence contexts. In agreement with previous studies, there was clear evidence of both general inhibitory and facilitatory effects. In contrast to previous findings, however, reading level did not have a major impact on the inhibition of word recognition in incongruous contexts compared with neutral contexts, although it may have led to greater facilitation in congruous contexts compared with neutral contexts. Although further research is required, these results suggest that if reading-age appropriate materials are selected, less skilled readers and those with a reading disability may not be as influenced by context as has been claimed previously.     

Word recognition and face recognition following posterior cerebral artery stroke: Overlapping networks and selective contributions

It has been suggested that word- and face recognition rely on a common cerebral network for perceptual processing. To further explore this hypothesis, face- and word recognition were assessed in seven patients with focal lesions after stroke of the posterior cerebral artery in either hemisphere. The aim was to investigate if problems in face- and word recognition would co-occur, if testing was sensitive and patients were not pre-selected based on behavioural symptoms. Patients and matched controls were given a reading test and a delayed matching paradigm with faces, objects, and words. Interestingly, all patients with word recognition difficulties had problems in face recognition, independently of the affected hemisphere, supporting the existence of a bilateral perceptual network for faces and words. However, two patients showed selective face recognition problems after unilateral damage to either hemisphere, suggesting that parts of this network may be more critical for face than for word recognition.     

Revisiting Huey: On the importance of the upper part of words during reading

Recent research has shown that that the upper part of words enjoys an advantage over the lower part of words in the recognition of isolated words. The goal of the present article was to examine how removing the upper/lower part of the words influences eye movement control during silent normal reading. The participants?? eye movements were monitored when reading intact sentences and when reading sentences in which the upper or the lower portion of the text was deleted. Results showed a greater reading cost (longer fixations) when the upper part of the text was removed than when the lower part of the text was removed (i.e., it influenced when to move the eyes). However, there was little influence on the initial landing position on a target word (i.e., on the decision as to where to move the eyes). In addition, lexical-processing difficulty (as inferred from the magnitude of the word frequency effect on a target word) was affected by text degradation. The implications of these findings for models of visual-word recognition and reading are discussed.     

词边界信息对读者阅读歧义短语时眼跳策略的影响

采用Eye Link 2000眼动仪,选取60个歧义短语,要求大学生被试阅读包含有歧义短语的句子。句子的呈现设置了四种条件:正常无阴影、词间阴影、歧义阴影和字间阴影,以探讨词边界信息是否影响读者阅读歧义短语时的注视位置效应。结果发现:读者对歧义短语的首次注视位置在四种条件下基本一致;词边界信息影响读者对歧义短语的再注视概率。结果表明,词边界信息对歧义短语的影响主要体现在眼跳行动(即"where")的晚期阶段。     

Visual laterality patterns for pure- versus mixed-list presentation

In Experiment 1, an overall left visual field advantage for nonverbal form recognition was found in a pure list of forms, but an overall right visual field form recognition advantage was found when the form trials were randomly intermixed with word recognition trials. Form complexity also influenced the form recognition laterality pattern, but the complexity effects were independent of (i.e., additive with) those produced by randomly mixing forms with words. Experiment 2 found that the mixed-list laterality pattern was unchanged by a pretrial cue indicating whether a word or form would follow. Experiments 3 and 4 demonstrated that holding two nouns in memory on each trial in a pure list of forms has much the same effect on laterality pattern as mixing forms with words but that the combined effect of these two variables is no larger than the effect of either variable alone. The entire pattern of results suggests that (a) laterality patterns are caused by the interaction of several factors, (b) the effects of random mixing and concurrent verbal memory are both caused by selective left-hemisphere activation, and (c) the form-complexity effects are caused by some other mechanism--perhaps subtle difference in stimulus codability.     

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.     

视觉词汇加工的动态神经网络及其形成

揭示大脑加工的神经网络机制成为认知神经科学研究的最新取向.本研究以视觉词汇加工脑区(VWFA)的神经功能作为切入点,探讨视觉词汇加工神经网络的动态机制及其形成.研究一考察VWFA在刺激驱动和任务调节下的动态激活,及其与语音、语义脑区所组成神经网络的动态机制.研究二通过跨文化对比以及儿童阅读发展研究,阐明语言经验对视觉词汇加工网络的塑造作用.研究三对比功能网络、静息网络以及白质纤维束联结,探讨视觉词汇加工网络的动态联结及其形成.研究结果有助于建构视觉词汇加工的神经生理模型,为基于脑科学的阅读教学和阅读障碍矫治奠定理论基础,为认知神经科学研究提供了新的思路.     

Use of colour for language processing during reading

The study examined whether literal correspondence is necessary for the use of visual features during word recognition and text comprehension. Eye movements were recorded during reading and used to change the colour of dialogue when it was fixated. In symbolically congruent colour conditions, dialogue of female and male characters was shown in orchid and blue, respectively. The reversed assignment was used in incongruent conditions, and no colouring was applied in a control condition. Analyses of oculomotor activity revealed Stroop-type congruency effects during dialogue reading, with shorter viewing durations in congruent than incongruent conditions. Colour influenced oculomotor measures that index the recognition and integration of words, indicating that it influenced multiple stages of language processing.     

Letter position dyslexia in Arabic: from form to position

This study reports the reading of 11 Arabic-speaking individuals with letter position dyslexia (LPD), and the effect of letter form on their reading errors. LPD is a peripheral dyslexia caused by a selective deficit to letter position encoding in the orthographic-visual analyzer, which results in migration of letters within words, primarily of middle letters. The Arabic orthography is especially interesting for the study of LPD because Arabic letters have different forms in different positions in the word. As a result, some letter position errors require letter form change. We compared the rate of letter migrations that change letter form with migrations that do not change letter form in 10 Arabic-speaking individuals with developmental LPD, and one bilingual Arabic and Hebrew-speaking individual with acquired LPD. The results indicated that the participants made 40% letter position errors in migratable words when the resulting word included the letters in the same form, whereas migrations that changed letter form almost never occurred. The error rate of the Arabic-Hebrew bilingual reader was smaller in Arabic than in Hebrew. However, when only words in which migrations do not change letter form were counted, the rate was similar in Arabic and Hebrew. Hence, whereas orthographies with multiple letter forms for each letter might seem more difficult in some respects, these orthographies are in fact easier to read in some forms of dyslexia. Thus, the diagnosis of LPD in Arabic should consider the effect of letter forms on migration errors, and use only migratable words that do not require letter-form change. The theoretical implications for the reading model are that letter form (of the position-dependent type found in Arabic) is part of the information encoded in the abstract letter identity, and thus affects further word recognition processes, and that there might be a pre-lexical graphemic buffer in which the checking of orthographic well-formedness takes place.     

Contextual facilitation in children's oral reading in relation to grade and decoding skill

This research investigated children's use of context to facilitate word recognition and comprehension-monitoring processes in the oral reading of connected prose as a function of grade level and decoding skill. Results indicated no overall contextual facilitation of word recognition accuracy, even in less skilled decoders, although there was evidence that less skilled decoders were assisted by context in decoding some content words. Children read word lists 50% more slowly than comparable selections of prose. The adoption of different and compensatory reading speed strategies in children's reading of prose and word lists renders the oral reading task an insensitive test of the contextual facilitation of word recognition accuracy. A qualitative analysis of the errors made in reading the prose passage showed that skilled decoders made (relative to less skilled decoders) a lower proportion of reading errors which, as first uttered, violated prior context, and a higher rate of contextually obligatory self-corrections, thus making a higher overall rate of contextually acceptable oral reading errors. These data were interpreted as suggesting that children's oral reading incorporates processing that occurs after lexical access, and that skilled decoders use context more effectively to monitor comprehension. In an oral reading task, this may counteract the tendency of less skilled decoders to rely more on context in the process of word recognition.     

Chinese character recognition in mirror reading: evidence from event-related potential

As is well known, mirror reading in language requires recognition of words and letters in mirror-reversed pattern compared with normal reading, and the cognitive mechanism underlying the mirror reading may involve two critical processes: visuospatial transformation and linguistic regulation. Chinese characters, different from English, are characterized by some unique features in orthography and spelling. Using ERP techniques, the present study investigated neural correlates underlying the mirror reading of Chinese characters, and whether the cognitive processes underlying the recognition of mirrored Chinese characters is different from those of alphabetic words. Twelve native Chinese speakers participated in the experiment, during which they were instructed to make an animal/nonanimal distinction. The stimuli varied with the word category (animal vs nonanimal) and presentation format (normal vs mirror-reversed). The data analyses focused on three aspects: the reaction times (RT) for Chinese words of normal and mirror-reversed formats, peak latencies, and peak amplitudes of ERP components elicited by mirror-reversed and normal Chinese words. The results from implicit reading provide evidence for a mirror-reversed effect. The behavioural data showed that mirror-reversed words were more difficult to identify than normal words, with RTs delayed for mirror-reversed words over normal words. Moreover, a clear N2 component, with maximal activity occurring at 200-250ms interval (N2), was more negative for mirror-reversed words than for normal words at posterior regions. However, there were no latency differences between normal and mirror-reversed words. The occipital N2 might be closely related to abstract word form representation. Larger N2 amplitude in response to mirror-reversed Chinese words is interpreted as reflecting visuospatial transformation in order to compensate for impaired word form analysis. The result of no N2 latency delay indicated that word form analysis and visuospatial transformation might be processed in parallel.     

The influence of parafoveal preprocessing and linguistic context on the optimal landing position effect

Several experiments have shown the existence of an optimal landing position effect during isolated word recognition as well as during text reading; both the probability of refixating the test word and the gaze duration are smaller if the eye first fixates near the center of the word than if the eye first fixates other positions in the word. However, recent data indicate that the optimal landing position effect is weakened under normal reading conditions, when words are included in texts. The purpose of the present experiment was to test whether parafoveal preprocessing or linguistic context specific to the text reading situation could be responsible for this weakening. With a paradigm that approximates normal reading, albeit in a somewhat slower manner, it was shown that although the possibility of preprocessing words in parafoveal vision and of predicting them from preceding context globally affected refixation probability and gaze duration on the word, this did not strongly affect the optimal landing position effect. Since the global effects of these factors were comparable to those found by other authors in normal reading, it was concluded that the weakening of the optimal landing position effect during text reading results from the influence of other factors peculiar to this situation. Hypotheses are proposed as explanations of the effects of the manipulated factors on oculomotor behavior.     

From "logographic" to normal reading: the case of a deaf beginning reader

Visual word recognition of a profoundly deaf girl (AH) with developmental reading disorders was explored using an experimental technique that measures performance as a function of eye fixation within a word. AH's fixation-dependent word recognition profile revealed that she was inferring the identity of words using a "logographic" reading strategy (i. e., using salient visual features). Following this observation a special training program that enhances the understanding of grapheme-phoneme relations was applied. After few months of training, AH's reading skills improved, while her fixation-dependent performance changed to become like that of normal readers. We discuss the impact of our technique for the early diagnosis of reading impairments.