The Modulation of Visual and Task Characteristics of a Writing System on Hemispheric Lateralization in Visual Word Recognition—A Computational Exploration

Through computational modeling, here we examine whether visual and task characteristics of writing systems alone can account for lateralization differences in visual word recognition between different languages without assuming influence from left hemisphere (LH) lateralized language processes. We apply a hemispheric processing model of face recognition to visual word recognition; the model implements a theory of hemispheric asymmetry in perception that posits low spatial frequency biases in the right hemisphere and high spatial frequency (HSF) biases in the LH. We show two factors that can influence lateralization: (a) Visual similarity among words: The more similar the words in the lexicon look visually, the more HSF/LH processing is required to distinguish them, and (b) Requirement to decompose words into graphemes for grapheme‐phoneme mapping: Alphabetic reading (involving grapheme‐phoneme conversion) requires more HSF/LH processing than logographic reading (no grapheme‐phoneme mapping). These factors may explain the difference in lateralization between English and Chinese orthographic processing.     

Reading through a noisy channel: why there's nothing special about the perception of orthography

The goal of research on how letter identity and order are perceived during reading is often characterized as one of "cracking the orthographic code." Here, we suggest that there is no orthographic code to crack: Words are perceived and represented as sequences of letters, just as in a dictionary. Indeed, words are perceived and represented in exactly the same way as other visual objects. The phenomena that have been taken as evidence for specialized orthographic representations can be explained by assuming that perception involves recovering information that has passed through a noisy channel: the early stages of visual perception. The noisy channel introduces uncertainty into letter identity, letter order, and even whether letters are present or absent. We develop a computational model based on this simple principle and show that it can accurately simulate lexical decision data from the lexicon projects in English, French, and Dutch, along with masked priming data that have been taken as evidence for specialized orthographic representations.     

The primacyof visual information inthe analysis of letter strings

In Experiment 1, orthographic and phonetic information were separated by using artificial letters to represent English pseudowords and random letter strings. Subjects could learn to distinguish combinations of artificial letters on the basis of (1) orthographic, but not phonetic, information, (2) orthographic and phonetic information, (3) paired-associate verbal labels without orthographic information, and (4) neither orthographic nor phonetic information. By imposing a variety of response deadlines it appeared that subjects quickly exploited orthographic information without any contribution from phonetic correspondences. The only suggestion of a phonetic effect occurred in the absence of orthographic information and at longer latencies. Experiment 3 (using English letters) also suggested that phonetic information influenced the analysis of letter string pairs at only longer latencies, after visual analysis. Experiment 2 provided a demonstration that orthographic rules similar to those exploited in Experiment 1 were useful in visual discriminations regardless of the particular letter position affected by those rules. The results strain phonetic mediation models of performance in word-related tasks (e. g., Spoehr & Smith, 1975)and support models that emphasize visual analysis(Barron & Baron, 1977; Massaro, 1975; Pollatsek, Well, & Schindler, 1975).     

Graphemes are perceptual reading units

Graphemes are commonly defined as the written representation of phonemes. For example, the word 'BREAD' is composed of the four phonemes /b/, /r/, /e/ and /d/, and consequently, of the four graphemes 'B', 'R', 'EA', and 'D'. Graphemes can thus be considered the minimal 'functional bridges' in the mapping between orthography and phonology. In the present study, we investigated the hypothesis that graphemes are processed as perceptual units by the reading system. If the reading system processes graphemes as units, then detecting a letter in a word should be harder when this letter is embedded in a multi-letter grapheme than when it corresponds to a single-letter grapheme. In Experiment 1A, done in English, participants were slower to detect a target letter in a word when the target letter was embedded in multi-letter grapheme (i.e. 'A' in 'BEACH') than when it corresponded to a single-letter grapheme (i.e. 'A' in 'PLACE'). In Experiment 1B, this effect was replicated in French. In Experiment 2, done in English, this grapheme effect remained when phonemic similarity between the target letter alone and the target letter inside the word was controlled. Together, the results are consistent with the assumption that graphemes are processed as perceptual reading units in alphabetic writing systems such as English or French.     

Silent letters and phonological priming

Many written English words contain silent letters. Omitting them produces nonwords pronounced identically to the original words, for example, SALM for PSALM and COLUM for COLUMN. We report two naming and two lexical decision experiments in which targets of 4–11 letters followed primes exposed for 100 ms in mask-prime-mask-target sequences. Priming in SALM-psalm and COLUM-column pairs exceeded priming in orthographic control pairs such as ASTA-pasta and COUSI-cousin, pairs in which pronounced letters are omitted to form the primes. SALM and COLUM, however, were less effective primes than PSALM and COLUMN. Results were discussed in terms of the phonological coherence hypothesis, the role of orthographic codes in filtering phonologically activated representations, and graphemes as reading units.     

A meta-analysis of executive functioning in dyslexia with consideration of the impact of comorbid ADHD

Grapheme coding was examined in French Grade 6 and Grade 8 children and adults who learned English as a second language (L2). In Experiments 1 and 2, three conditions were compared in a letter detection task in L2: (1) simple grapheme (i.e., detect “a” in black); (2) complex language-shared grapheme (i.e., “a” in brain) and (3) complex L2-specific grapheme (i.e., “a” in beach). The data indicated that graphemes in L2 words were functional sub-lexical orthographic units for these L2 learners. Moreover, L2-specific graphemes took longer to process than language-shared complex graphemes. Using the same task, Experiment 3 examined phonological influences by manipulating the cross-language congruency of grapheme-to-phoneme mappings (detect “a” in have [congruent] vs. take [incongruent]). The outcome of this study offers preliminary evidence of graphemic coding during L2 word recognition both at the orthographic and the orthography-to-phonology mapping levels.     

Tracking the transition from sublexical to lexical processing: On the creation of orthographic and phonological lexical representations

Participants read aloud nonword letter strings, one at a time, which varied in the number of letters. The standard result is observed in two experiments; the time to begin reading aloud increases as letter length increases. This result is standardly understood as reflecting the operation of a serial, left-to-right translation of graphemes into phonemes. The novel result is that the effect of letter length is statistically eliminated by a small number of repetitions. This elimination suggests that these nonwords are no longer always being read aloud via a serial left-to-right sublexical process. Instead, the data are taken as evidence that new orthographic and phonological lexical entries have been created for these nonwords and are now read at least sometimes by recourse to the lexical route. Experiment 2 replicates the interaction between nonword letter length and repetition observed in Experiment 1 and also demonstrates that this interaction is not seen when participants merely classify the string as appearing in upper or lower case. Implications for existing dual-route models of reading aloud and Share's self-teaching hypothesis are discussed.     

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.     

The effects of length and transposed‐letter similarity in lexical decision: Evidence with beginning,intermediate, and adult readers

Do length and transposed‐letter effects reflect developmental changes on reading acquisition in a transparent orthography? Can computational models of visual word recognition accommodate these changes? To answer these questions, we carried out a masked priming lexical decision experiment with Spanish beginning, intermediate, and adult readers (N=36, 44, and 39; average age: 7, 11, and 22 years, respectively). Target words were either short or long (6.5 vs. 8.5 letters), and transposed‐letter primes were formed by the transposition of two letters (e.g. aminal–ANIMAL) or by the substitution of two letters (orthographic control: arisal–ANIMAL). Children showed a robust length effect (i.e. long words were read slower than short words) that vanished in adults. In addition, both children and young adults showed a transposed‐letter priming effect relative to the control condition. A robust transposed‐letter priming effect was also observed in non‐word reading, which strongly suggests that this effect occurs at an early prelexical level. Taken together, the results reveal that children evolve from a letter‐by‐letter reading to a direct lexical access and that the lexical decision task successfully captures the changing strategies used by beginning, intermediate, and adult readers. We examine the implications of these findings for the recent models of visual word recognition.     

A case study of an English-Japanese bilingual with monolingual dyslexia

We report the case of AS, a 16 year-old English/Japanese bilingual boy, whose reading/writing difficulties are confined to English only. AS was born in Japan to a highly literate Australian father and English mother, and goes to a Japanese selective senior high school in Japan. His spoken language at home is English. AS's reading in logographic Japanese Kanji and syllabic Kana is equivalent to that of Japanese undergraduates or graduates. In contrast, his performance in various reading and writing tests in English as well as tasks involving phonological processing was very poor, even when compared to his Japanese contemporaries. Yet he has no problem with letter names or letter sounds, and his phoneme categorisation is well within the normal range of English native speakers. In order to account for our data that show a clear dissociation between AS's ability to read English and Japanese, we put forward the ‘hypothesis of granularity and transparency'. It is postulated that any language where orthography-to-phonology mapping is transparent, or even opaque, or any language whose orthographic unit representing sound is coarse (i.e. at a whole character or word level) should not produce a high incidence of developmental phonological dyslexia.     

A developmental, interactive activation model of the word superiority effect

Parallel distributed processing (PDP) models of reading developed out of an appreciation of the role that context plays in letter and word perception. Adult readers can more accurately identify letters in a word than alone or in other random display contexts, a phenomenon known as the Word Superiority Effect (WSE). We examined the effects of orthographic context on the letter recognition skills of dyslexic children, comparing their performance to adults, and chronological- and reading-age matched groups. Consistent with previous studies, results showed adults better able to identify letters in the context of words and pseudowords than in random letter strings. Young normal readers demonstrated the WSE, but their pseudoword advantage was less than adults. The dyslexic children showed no WSE at all. PDP computer simulations for the experimental data using the Interactive Activation model (IA) suggested that the orthographic components of the lexical system of normal children are interactive and distributed as they are in adults but provide less bottom-up activation. In addition, top-down processing increases with age and reading skill, but may be absent for dyslexic readers.     

Processing complex graphemes in handwriting production

Recent studies on handwriting production and neuropsychological data have suggested that orthographic representations are multilevel structures that encode information on letter identity and order, but also on intermediate-grained processing units such as syllables and morphemes. This study on handwriting production examined whether orthographic representations also include a graphemic-processing level. French adults wrote words containing an embedded one-, two-, or three-letter grapheme (e.g., a in clavier, ai in prairie, ain in plainte) on a digitizer. The results for letter duration revealed that the timing of movement processing depends on grapheme length (e.g., the duration of a for one-letter graphemes was shorter than that for two-letter graphemes, which, in turn, was shorter than that for three-letter graphemes). Two- and three-letter graphemes start to be processed before we start to write them. The results therefore revealed that orthographic representations also encode information on grapheme complexity.     

Units of English spelling‐to‐sound mapping: a rational approach to reading instruction

In this paper a rationale for choosing how many and what types of spelling‐to‐sound units of English to teach children to learn to read is introduced. The rationale is based on an analysis of the frequency with which various units of spelling‐to‐sound mapping occur in monosyllabic words of the English language. Analysis of spelling‐to‐sound mappings at three levels (whole words, onsets and rimes and graphemes) reveals that the distribution of these mappings in English text approximates Zipf's Law. Further analyses reveal that a substantial proportion of text can be read if knowledge of the most frequent mappings at each level is assumed. It is suggested that viewing reading from this perspective can be useful in developing reading instruction so that children are taught information that is most useful in achieving the endpoint of learning to read. Copyright © 2007 John Wiley & Sons, Ltd.     

Developmental letter position dyslexia

Letter position dyslexia (LPD) is a peripheral dyslexia that causes errors of letter order within words. So far, only cases of acquired LPD have been reported. This study presents selective LPD in its developmental form, via the testing of 11 Hebrew‐speaking individuals with developmental dyslexia. The study explores the types of errors and effects on reading in this dyslexia, using a variety of tests: reading aloud, lexical decision, same‐different decision, definition and letter naming. The findings indicate that individuals with developmental LPD have a deficit in the letter position encoding function of the orthographic visual analyser, which leads to underspecification of letter position within words. Letter position errors occur mainly in adjacent middle letters, when the error creates another existing word. The participants did not show an output deficit or phonemic awareness deficit. The selectivity of the deficit, causing letter position errors but no letter identity errors and no migrations between words, supports the existence of letter position encoding function as separate from letter identification and letter‐to‐word binding.     

A comparative quantitative analysis of Greek orthographic transparency

Orthographic transparency refers to the systematicity in the mapping between orthographic letter sequences and phonological phoneme sequences in both directions, for reading and spelling. Measures of transparency previously used in the analysis of orthographies of other languages include regularity, consistency, and entropy. However, previous reports have typically been hampered by severe restrictions, such as using only monosyllables or only word-initial phonemes. Greek is sufficiently transparent to allow complete sequential alignment between graphemes and phonemes, therefore permitting full analyses at both letter and grapheme levels, using every word in its entirety. Here, we report multiple alternative measures of transparency, using both type and token counts, and compare these with estimates for other languages. We discuss the problems stemming from restricted analysis sets and the implications for psycholinguistic experimentation and computational modeling of reading and spelling.     

Rapid processing of letters,digits and symbols: what purely visual‐attentional deficit in developmental dyslexia?

Visual‐attentional theories of dyslexia predict deficits for dyslexic children not only for the perception of letter strings but also for non‐alphanumeric symbol strings. This prediction was tested in a two‐alternative forced‐choice paradigm with letters, digits, and symbols. Children with dyslexia showed significant deficits for letter and digit strings but not for symbol strings. This finding is difficult to explain for visual‐attentional theories of dyslexia which postulate identical deficits for letters, digits and symbols. Moreover, dyslexics showed normal W‐shaped serial position functions for letter and digit strings, which suggests that their deficit is not due to an abnormally small attentional window. Finally, the size of the deficit was identical for letters and digits, which suggests that poor letter perception is not just a consequence of the lack of reading. Together then, our results show that symbols that map onto phonological codes are impaired (i.e. letters and digits), whereas symbols that do not map onto phonological codes are not impaired. This dissociation suggests that impaired symbol‐sound mapping rather than impaired visual‐attentional processing is the key to understanding dyslexia.     

Reading Ability and the Use of Context in Orthographic Information Processing

Reading ability and context use in orthographic processing during silent reading were investigated. Poor readers and reading-level matched controls were presented target words containing a letter substitution in two contrasting context conditions. The hypothesis was that presenting a word in a highly predictable context would induce readers to proceed through the text without completely processing orthographic units at lower processing levels in the hierarchy (e.g., constituent letters). This general context effect was found. Normal and poor readers did not differ in context dependency. Poor readers more often missed substitutions, regardless of context. Poor readers also processed orthographic information less accurately. Target letters located in final word position were missed most often. Substitutions located in high bigram-frequency letter clusters were more often missed, and this effect was independent of intraword location. The implications of these results for understanding poor readers' basic reading problems are discussed.     

Friends in Low-Entropy Places: Orthographic Neighbor Effects on Visual Word Identification Differ Across Letter Positions

Visual word recognition is facilitated by the presence of orthographic neighbors that mismatch the target word by a single letter substitution. However, researchers typically do not consider where neighbors mismatch the target. In light of evidence that some letter positions are more informative than others, we investigate whether the influence of orthographic neighbors differs across letter positions. To do so, we quantify the number of enemies at each letter position (how many neighbors mismatch the target word at that position). Analyses of reaction time data from a visual word naming task indicate that the influence of enemies differs across letter positions, with the negative impacts of enemies being most pronounced at letter positions where readers have low prior uncertainty about which letters they will encounter (i.e., positions with low entropy). To understand the computational mechanisms that give rise to such positional entropy effects, we introduce a new computational model, VOISeR (Visual Orthographic Input Serial Reader), which receives orthographic inputs in parallel and produces an over-time sequence of phonemes as output. VOISeR produces a similar pattern of results as in the human data, suggesting that positional entropy effects may emerge even when letters are not sampled serially. Finally, we demonstrate that these effects also emerge in human subjects' data from a lexical decision task, illustrating the generalizability of positional entropy effects across visual word recognition paradigms. Taken together, such work suggests that research into orthographic neighbor effects in visual word recognition should also consider differences between letter positions.