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.     

Font tuning associated with expertise in letter perception

Font tuning (FT) occurs when observers recognize a sequence of letters presented in the same font faster than in different fonts (Sanocki 1987, 1988 Journal of Experimental Psychology. Human Perception and Performance 13 267-278; 14 472-480). Here, we test the hypothesis that FT is associated with expertise with a specific writing system. We developed a systematic search task allowing the measurement of FT over a large number of letters and generalized the finding of FT from English readers viewing Roman letters to Chinese readers viewing Chinese characters. Non-Chinese readers did not show evidence of FT for Chinese characters in this search task. We also used a simpler 3-letter identification task to directly compare novice and expert readers, and to explore FT for different aspects of font such as fill, slant, and aspect ratio. We found that experts tune to aspect ratio but not to the other font changes. These findings reveal that letters are not processed visually in the same manner as shapes, and suggest an explanation for the cortical specialization obtained in the visual system for letters.     

The time course of visual influences in letter recognition

This study builds on a specific characteristic of letters of the Roman alphabet—namely, that each letter name is associated with two visual formats, corresponding to their uppercase and lowercase versions. Participants had to read aloud the names of single letters, and event-related potentials (ERPs) for six pairs of visually dissimilar upper- and lowercase letters were recorded. Assuming that the end product of processing is the same for upper- and lowercase letters sharing the same vocal response, ERPs were compared backward, starting from the onset of articulatory responses, and the first significant divergence was observed 120 ms before response onset. Given that naming responses were produced at around 414 ms, on average, these results suggest that letter processing is influenced by visual information until 294 ms after stimulus onset. This therefore provides new empirical evidence regarding the time course and interactive nature of visual letter perception processes.     

Language and orthography as irrelevant features in colour-word and picture-word stroop interference

Based on evidence that Chinese yields more interference than English, Biederman and Tsao (1979) have suggested that the processes involved in reading Chinese are more similar to those involved in colour naming than are the processes involved in reading English. In three experiments conducted to evaluate the empirical foundation for this hypothesis it was found that: (1) Chinese yielded less interference than English (and French) in between-subjects comparisons involving Chinese-English bilinguals and English monolinguals or English-French bilinguals; (2) Chinese print did not yield more interference than English print in within-subjects comparisons involving the orthogonal combination of print language (Chinese or English) and naming language (Chinese or English) among Chinese-English bilinguals; and (3) compared with syntactic category, both language and orthography were relatively impotent variables in the object naming version of the Stroop task.     

ERP Correlates of Form and Rhyme Letter Tasks in Impaired Reading Children: A Critical Evaluation

Event-related potentials (ERPs) were obtained from 15 electrode sites in six average and six impaired reading children, 12 years of age, during visual letter discrimination tasks. Subjects responded to target letters with an enclosed area in the form task and to letters that rhymed with “e” in the rhyme task. Response accuracy was similar between the groups. Reaction time was relatively longer for the impaired group during the rhyme task. At lateral sites, condition differences were evident as greater negative shifts in the rhyme task than the form at 170 and 470 ms as well as a delayed late positivity for the rhyme. In terms of reading ability, the average readers’ ERPs were more negative than those of the impaired group at 270 and 450 ms. Interhemispheric variations were also seen between the groups, with the average readers more negative than the impaired readers at right hemisphere sites. Contrary to expectations, group differences in the ERP did not vary substantially as a function of condition, and task demands were evaluated in view of these findings.     

Familiarization effects for bilingual letter detection involving translation or exact text repetition.

In two experiments, English-Spanish bilinguals read passages, performing letter detection on some passages by circling target letters as they read. Detection passages were sometimes familiarized (primed) by prior reading of the same passage or a translation of it. Participants detected letters in English passages in Experiment 1 and in Spanish passages in Experiment 2. For both experiments, a missing letter effect occurred (depressed detection accuracy on frequent function words relative to less frequent content words). Familiarization promoted overall improvements in letter detection only for English passages, suggesting that reprocessing benefits depend on high language fluency. For Spanish passages, cognates engendered greater error rates than noncognates; the visual similarity of Spanish and English cognates apparently enabled faster identification of Spanish cognates in a way unaffected by familiarization of the whole text passage. Priming by familiarized text was significantly higher when the passages were in the same language than when they were in different languages, suggesting that the reprocessing benefits are at the word level instead of the semantic level. These results are consistent with the GO model of reading (Greenberg, Healy, Koriat, & Kreiner, 2004) but require an expanded consideration of attention redistribution processes in that model.     

A memory-based interference effect in midstream order deficit

People do not accurately recognize the relative order of a letter sequence displayed in a rapid serial visual presentation when the letter sequence is presented repeatedly and the exposure of the letters is very brief in the first half of the presentation. This phenomenon is known as midstream order deficit (MOD), and is considered to reflect the limitation of temporal resolution in segmentation processes. However, the results from three experiments revealed that MOD occurred even when the stimuli induced exogenous segmentation. Furthermore, a MOD-like effect could be observed when an irrelevant letter sequence was presented before the target letter sequence. We propose a new explanation for MOD, based on interference between the representations of order in memory and current perception.     

ERP correlates of form and rhyme letter tasks in impaired reading children: a critical evaluation.

Event-related potentials (ERPs) were obtained from 15 electrode sites in six average and six impaired reading children, 12 years of age, during visual letter discrimination tasks. Subjects responded to target letters with an enclosed area in the form task and to letters that rhymed with "e" in the rhyme task. Response accuracy was similar between the groups. Reaction time was relatively longer for the impaired group during the rhyme task. At lateral sites, condition differences were evident as greater negative shifts in the rhyme task than the form at 170 and 470 ms as well as a delayed late positivity for the rhyme. In terms of reading ability, the average readers' ERPs were more negative than those of the impaired group at 270 and 450 ms. Inter-hemispheric variations were also seen between the groups, with the average readers more negative than the impaired readers at right hemisphere sites. Contrary to expectations, group differences in the ERP did not vary substantially as a function of condition, and task demands were evaluated in view of these findings.     

Not All Visual Expertise Is Holistic, but It May Be Leftist: The Case of Chinese Character Recognition

ABSTRACT— We examined whether two purportedly face-specific effects, holistic processing and the left-side bias, can also be observed in expert-level processing of Chinese characters, which are logographic and share many properties with faces. Non-Chinese readers (novices) perceived these characters more holistically than Chinese readers (experts). Chinese readers had a better awareness of the components of characters, which were not clearly separable to novices. This finding suggests that holistic processing is not a marker of general visual expertise; rather, holistic processing depends on the features of the stimuli and the tasks typically performed on them. In contrast, results for the left-side bias were similar to those obtained in studies of face perception. Chinese readers exhibited a left-side bias in the perception of mirror-symmetric characters, whereas novices did not; this effect was also reflected in eye fixations. Thus, the left-side bias may be a marker of visual expertise.     

中-英双语者词汇语义通达的大脑功能偏侧化与合作效应

采用半视野速示术对48名英语专业硕士研究生进行词汇判别的语义启动实验,检查中一英双语者词汇语义通达可能存在的大脑功能偏侧化与合作效应.结果提示:(1)相对熟练的中一英双语者L1(中文)和L2(英文)均可直接通达一个共同的词汇语义概念表征系统,但L1可以通过两半球,而L2可能主要依赖于大脑右半球;(2)跨语言条件出现了半球间语义通达的合作优势效应.     

Recall and articulation of English and Chinese words by Chinese-English bilinguals

Three groups of subjects were tested to investigate the effect of language on the relationship between recall span and articulation rate. Native English-speaking monolinguals and native Chinese-speaking monolinguals recalled only English or Chinese words, respectively. Chinese-English bilinguals recalled both English and Chinese words. Articulation rates for English and Chinese monolinguals and Chinese-English bilinguals in each language were also obtained. When recall span was regressed on articulation rate, the slopes for Chinese and English words were significantly different for the Chinese-English bilinguals. This difference was not due to language proficiency but to phonological differences between English and Chinese.     

Immediate and delayed recognition of visual stimuli in poor and normal readers.

The present study investigated the hypothesis that specific reading disability is attributable to inadequate visual memory. Previous research had demonstrated that poor readers sustain no basic dysfunction in visual perception, but there was need to evaluate the possibility that deficiencies in letter and word recognition result from disorder in long-term visual storage. Adopting a format employed in a previous study, randomly arranged Hebrew letters were presented to poor and normal readers unfamiliar with Hebrew, and both groups were asked to demonstrate retention for these stimuli on three separate occasions: immediately after initial presentation, 24 hours later and 6 months later. As a control measure, the performance of the non-Hebrew subjects was compared with that of normal readers familiar with Hebrew letters. It was found that retention in the non-Hebrew groups was equivalent under all of the temporal conditions, but the performance of both was poorer than the Hebrew groups under the immediate and 24-hour conditions. However, none of the reader groups differed in the case of retention after a 6-month delay period. It was concluded that deficient visual memory is an unlikely source of specific reading disability, and alternative explanations of the disorder were considered.     

The involvement of letter names in the silent processing of isolated letters: A developmental perspective

This study was designed to clarify the nature of the mental representations underlying the processing of letters. A total of 96 Hebrew readers randomly recruited from three levels of education were asked to make rapid same/different judgments for Hebrew letter dyads with monosyllabic and bisyllabic names. The results obtained from the performance of participants under perceptual and conceptual processing conditions suggest that Hebrew readers access nominal letter representations in order to mediate letter processing in tasks that cannot be resolved on the basis of a sheer perceptual analysis of the letters?? visual properties. The finding that the retrieval of nominal letter representations was evident for participants who differed rather markedly in their letter-processing speeds highlights the central role of letter names in the processing of isolated letters.     

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.     

非熟练中-英双语者跨语言的错误记忆通道效应

采用DRM范式以112名非熟练中-英双语者为被试进行了跨语言的错误记忆通道效应实验。实验采用三因素混合设计,根据学习通道和测验通道的不同,把被试分为4组,用由汉语与英语单词组成的DRM词表进行学习和测验。结果发现,⑴在非熟练中-英双语被试中存在错误记忆的跨语言现象;⑵非熟练中-英双语者跨语言的错误记忆存在很强的语言特异性,表现为相同语言条件高于不同语言条件、汉语高于英语;⑶在学习与测验相同语言条件下运用校正的再认分数——敏感性指标Pr,进一步探讨错误记忆的通道效应,发现了跟西方不一致的结论：即无论汉语词表还是英语词表,非熟练中-英双语者在视觉通道上的错误记忆明显高于听觉通道     

Letter identification and lateral masking in dyslexic and average readers

Lateral masking and letter identification in dyslexic and average readers were investigated with a methodology that corrected for some of the weaknesses of the Geiger and Lettvin studies (1986, 1987). Target letters were presented alone or embedded within three-letter arrays at retinal locations from 0 degrees to 15 degrees to the right or left of a fixation point. A foveal letter, which was the same as or different from a target letter, appeared as a distractor, and comparisons were made between scaled and unscaled stimuli. Dyslexic readers were found to be better than average readers at detecting scaled letters embedded in an array in some of the peripheral locations tested. Unlike the results of Geiger and Lettvin, however, this finding of better letter detection in the periphery by dyslexics was limited to selected conditions of the study. Reading groups were also found to differ in responding to the foveal distractor in the letter task. Detection of letters by average readers was affected by the type of distractor, but this variable was not found to influence the dyslexic readers. These findings suggest some differences between dyslexic and average readers in attention to stimuli presented at multiple locations in the visual field.