Tachistoscopic treatment of dyslexia changes the distribution of visual-spatial attention

Twelve children with developmental dyslexia underwent a four-month treatment with tachistoscopic presentation of words, according to Bakker's methodology. One group received standard lateral presentation of words on a PC screen, while the other group received the same stimuli in random lateral position. The spatial distribution of visual attention was measured by means of the Form-Resolving Field (FRF; ), which was administered along with reading tests, before and after treatment. The FRF of children who received random presentation widened at -12.5 degrees on the left side, while the FRF in the group that received standard lateral presentation narrowed at that position. Both groups significantly improved in reading accuracy for both words and nonwords. Some hypotheses are proposed concerning the mechanisms responsible for the changes in the FRF and their correlation with improvements in word and nonword reading. The results of the present study are also compared with data suggesting a left "minineglect" in dyslexia.     

Visual field differences in the processing of numerical stimuli

Twenty-four right-handed subjects received random presentations of the numbers 1-6 in the form of words, digits, and dot patterns, to the left and right visual fields. Accuracy and reaction time were recorded for an odd-even judgment requiring a manual response. A significant stimulus type of visual field interaction was obtained, with words showing a left-hemisphere advantage and digits and dot patterns showing a right-hemisphere advantage. This pattern supports Coltheart's (1980, Deep dyslexia: A right hemisphere hypothesis, In M. Coltheart, K. Patterson, & J.C. Marshall (Eds.), Deep dyslexia, London: Routledge & Kegan Paul) right hemisphere reading hypothesis, which suggests that the left hemisphere's general advantage in processing linguistic material may be specific to stimuli which involve phonological processing. When phonological processing is not possible (e.g., for arabic digits and other ideographic orthographies), the right hemisphere may have an advantage because of its superior visuospatial processing capabilities.     

Phonological processing of words in right- and left-handers

It is commonly accepted that phonology is the exclusive domain of the left hemisphere. However, this pattern of lateralization, which posits a right visual field advantage, has been questioned by several studies. In fact, certain factors such as characteristics of the stimuli and subjects' handedness can modulate the right visual field advantage. Thus, the goal of this study was to compare the hemispheric dynamics of right-handers and left-handers during a divided visual field presentation of words that varied in terms of their phonological transparency. For non-transparent words, the left hemisphere seems more competent in both handedness groups. With regard to transparent words, the right hemisphere of both groups also appears competent. Surprisingly, left-handers achieved optimal processing with a functionally isolated left hemisphere, whereas right-handers needed the participation of both hemispheres. The pattern of performance cannot be fully explained by either the callosal or the direct access model.     

Right-hemisphere reading in a case of developmental deep dyslexia

The right-hemisphere hypothesis of deep dyslexia has received support from functional imaging studies of acquired deep dyslexia following damage to the left cerebral hemisphere, but no imaging studies of cases of developmental deep dyslexia, in which brain damage is not suspected, have been reported. In this paper, we report the first evidence of right hyperactivation in an adult case of developmental deep dyslexia. Hyperactivation was observed in the right inferior frontal cortex during functional magnetic resonance imaging (fMRI) of the oral reading of imageable content words and nonwords to which imageable lexical responses were frequently made. No evidence of right hyperactivation was observed in the oral reading of function words, nor during the naming of imageable words in response to pictured objects. The results reveal strategic and selective use of right-hemisphere functions for particular types of written stimuli. We propose that children with developmental deep dyslexia compensate for their lack of phonological skills by accessing right-hemisphere imageable associations that provide a mnemonic for linking written forms to spoken names.     

Right-hemisphere reading in a case of developmental deep dyslexia

The right-hemisphere hypothesis of deep dyslexia has received support from functional imaging studies of acquired deep dyslexia following damage to the left cerebral hemisphere, but no imaging studies of cases of developmental deep dyslexia, in which brain damage is not suspected, have been reported. In this paper, we report the first evidence of right hyperactivation in an adult case of developmental deep dyslexia. Hyperactivation was observed in the right inferior frontal cortex during functional magnetic resonance imaging (fMRI) of the oral reading of imageable content words and nonwords to which imageable lexical responses were frequently made. No evidence of right hyperactivation was observed in the oral reading of function words, nor during the naming of imageable words in response to pictured objects. The results reveal strategic and selective use of right-hemisphere functions for particular types of written stimuli. We propose that children with developmental deep dyslexia compensate for their lack of phonological skills by accessing right-hemisphere imageable associations that provide a mnemonic for linking written forms to spoken names.     

Semantic priming effects for stimuli presented to the right and left visual fields

Studies that have addressed the possibility of hemispheric differences in semantic priming effects have yielded contradictory results. This paper reports the findings of two experiments intended to shed greater light on the issue of hemispheric differences in semantic priming. Experiment 1 used a hemiretinal paradigm and examined manual response latency and response accuracy to four types of word pairs; categorically related, syntactically related, unrelated, and pairs containing a nonword member. Experiment 2 examined the effects of unrecognized, disambiguating flank words on verbal responses to a centrally presented homograph. Experiment 1 yielded no significant visual field differences in magnitude of priming effects when response latency served as the dependent measure, although categorical relatedness facilitated response accuracy for left but not right visual field stimuli. In experiment 2, the disambiguating words had a significant effect on meaning interpretation of the homographs that was independent of visual field of presentation. Taken together, the results of these studies are interpreted as indicating that semantic aspects of linguistic input are automatically processed and can influence the content and latency of subsequent responses, whether presented to the left or right visual field.     

Lateral cerebral differences in the deaf in response to linguistic and nonlinguistic stimuli

Groups of deaf subjects, exposed to tachistoscopic bilateral presentation of English words and American Sign Language (ASL) signs, showed weaker right visual half-field (VHF) superiority for words than hearing comparison groups with both a free-recall and matching response. Deaf subjects showed better, though nonsignificant, recognition of left VHF signs with bilateral presentation of signs but shifted to superior right VHF response to signs when word-sign combinations were presented. Cognitive strategies and hemispheric specialization for ASL are discussed as possible factors affecting half-field asymmetry.     

Representational neglect for words as revealed by bisection tasks

In the present study, we showed that a representational disorder for words can dissociate from both representational neglect for objects and neglect dyslexia. This study involved 14 brain-damaged patients with left unilateral spatial neglect and a group of normal subjects. Patients were divided into four groups based on presence of left neglect dyslexia and representational neglect for non-verbal material, as evaluated by the Clock Drawing test. The patients were presented with bisection tasks for words and lines. The word bisection tasks (with words of five and seven letters) comprised the following: (1) representational bisection: the experimenter pronounced a word and then asked the patient to name the letter in the middle position; (2) visual bisection: same as (1) with stimuli presented visually; and (3) motor bisection: the patient was asked to cross out the letter in the middle position. The standard line bisection task was presented using lines of different length. Consistent with the literature, long lines were bisected to the right and short lines, rendered comparable in length to the words of the word bisection test, deviated to the left (crossover effect). Both patients and controls showed the same leftward bias on words in the visual and motor bisection conditions. A significant difference emerged between the groups only in the case of the representational bisection task, whereas the group exhibiting neglect dyslexia associated with representational neglect for objects showed a significant rightward bias, while the other three patient groups and the controls showed a leftward bisection bias. Neither the presence of neglect alone nor the presence of visual neglect dyslexia was sufficient to produce a specific disorder in mental imagery. These results demonstrate a specific representational neglect for words independent of both representational neglect and neglect dyslexia.     

Word valence, attention, and hemispheric activity in depressed, remitted, and nondepressed controls

Clinically depressed (n = 20), previously depressed (n = 28), and nondepressed control (n = 27) individuals, classified according to a structured clinical diagnostic interview, participated in a study employing a modified prior entry (Titchener, 1908) procedure to investigate interrelationships among word (adjective) valence, visual attention, and cerebral hemispheric activity. Overall, positive words were selected more quickly when presented to the right, versus left, visual field (RVF, LVF); the opposite pattern was observed for negative words. While there was no significant group X Valence X Visual Field interaction, planned comparisons revealed that the aforementioned Valence X Visual Field interaction was significant only for the nondepressed control group. Although the remitted group exhibited an overall pattern similar to the control group, the depressed group evinced a pattern in the opposite direction for positive words (i.e., quicker in the LVF than the RVF).     

An intrahemispheric integration deficit in dyslexia

In order to investigate the hypothesis that dyslexia may result from a failure of intrahemispheric integration between auditory-verbal and visual-verbal processing, a dichotic listening task and a parallel divided visual field task were administered to a group of dyslexic boys between the ages of 8 and 11 years, and a group of normal control subjects individually matched for age and WISC intelligence. The dyslexics were on average over two years retarded in reading and spelling. Dyslexics exhibited a normal right ear advantage on dichotic listening for digits although lesser right ear advantage was related to reading retardation. In the divided visual field task, the normal controls showed a left visual field advantage for digits which it is argued resulted from a failure in fixation linked to reading habits. Within the dyslexic group greater reading deficiency was associated with relative bilateralization for visual verbal processing. The results therefore support the hypothesis.     

Right hemisphere sensitivity to word- and sentence-level context: evidence from event-related brain potentials

Researchers using lateralized stimuli have suggested that the left hemisphere is sensitive to sentence-level context, whereas the right hemisphere (RH) primarily processes word-level meaning. The authors investigated this message-blind RH model by measuring associative priming with event-related brain potentials (ERPs). For word pairs in isolation, associated words elicited more positive ERPs than unassociated words with similar magnitudes and onset latencies in both visual fields. Embedded in sentences, these same pairs showed large sentential context effects in both fields. Small effects of association were observed, confined to incongruous sentences after right visual hemifield presentation but present for both congruous and incongruous sentences after left visual hemifield presentation. Results do not support the message-blind RH model but do suggest hemispheric asymmetries in the use of word and sentence context during real-time processing.     

Facial speech gestures: the relation between visual speech processing,phonological awareness,and developmental dyslexia in 10‐year‐olds

Successful communication in everyday life crucially involves the processing of auditory and visual components of speech. Viewing our interlocutor and processing visual components of speech facilitates speech processing by triggering auditory processing. Auditory phoneme processing, analyzed by event‐related brain potentials (ERP), has been shown to be associated with impairments in reading and spelling (i.e. developmental dyslexia), but visual aspects of phoneme processing have not been investigated in individuals with such deficits. The present study analyzed the passive visual Mismatch Response (vMMR) in school children with and without developmental dyslexia in response to video‐recorded mouth movements pronouncing syllables silently. Our results reveal that both groups of children showed processing of visual speech stimuli, but with different scalp distribution. Children without developmental dyslexia showed a vMMR with typical posterior distribution. In contrast, children with developmental dyslexia showed a vMMR with anterior distribution, which was even more pronounced in children with severe phonological deficits and very low spelling abilities. As anterior scalp distributions are typically reported for auditory speech processing, the anterior vMMR of children with developmental dyslexia might suggest an attempt to anticipate potentially upcoming auditory speech information in order to support phonological processing, which has been shown to be deficient in children with developmental dyslexia.     

A pilot investigation into unimpaired and dyslexic Persian children's word naming and spelling: Implications for models of reading and counselling

There is now a growing body of research examining developmental dyslexia in different languages and writing systems. The phonologically transparent Persian orthography is normally transcribed with two distinct spellings, words spelled with vowels (letters) transcribed as a fixed part of the spelling (transparent) and words spelled with vowels (diacritics) omitted (opaque). This peculiarity of Persian would enable one to examine the impact of transparency, as well as the possible psychological factors associated with verbal punishment in Persian schools on the development of reading and spelling. Twenty-nine Persian children (22 male and 7 female) classified as being developmentally dyslexic (mean age 9.4, SD?=?1.4) were compared with 49 unimpaired male children (mean age 9, SD?=?1.3) on two main aspects of reading Persian opaque and transparent spellings, namely: Spelling and word naming. The results showed an expected impairment on all aspects of reading between unimpaired and children with dyslexia. However, performance of both groups of participants was impaired when performing tasks with opaque as opposed to transparent spellings. There was also a strong correlation between the recorded number of times the dyslexic child was verbally punished and the number of errors on the spelling and naming of transparent and opaque words. These results are supportive of the impact of spelling transparency, as well as psychological variables as factors in the development of reading and spelling.     

Brain activation on pre-reading tasks reveals at-risk status for dyslexia in 6-year-old children

In this fMRI-study, 6-year-old children considered at risk for dyslexia were compared with an age-/gender-matched control group for differences in brain activation when presented with visual stimuli differing in demands for literacy processing. Stimuli were nameable pictures, brand logos familiar to children, and written words - these were either regularly spelled using early-acquired rules ("alphabetic") or more complex ("orthographic"). Brain responses distinguished between the presentation conditions, as a function of group, within many cortical areas. Activation in the alphabetic and orthographic conditions in the left angular gyrus correlated with individual at-risk index scores, and activation in inferior occipito-temporal regions further indicated differential activation for the two groups related to orthographic processing, especially. Since similar patterns are reported in adult dyslexics when processing written words, it appears that sensitivity to the cortical differentiation of reading networks is established prior to formal literacy training.     

Sex task and processing strategy effects in hemispheric alpha asymmetries for the recall and recognition of arousal words: results from perceptual and motor tasks in males and females

Hemispheric alpha asymmetries of males and females were observed during perceptual and motor tasks requiring recall and recognition of words controlled for level of arousal (positive, negative, and neutral). Verbal reports of individual processing strategy were collected and analyzed relative to hemispheric alpha ratios. Results showed greater alpha suppression in the left relative to right hemisphere for recall as compared to recognition tasks and for word presentation when contrasted with motor conditions. High positive correlations were found between narrative report of processing strategy and hemispheric alpha data. A separate analysis revealed that seven subjects identified as highly analytic processors showed greater alpha suppression in the left relative to right hemisphere across tasks, conditions, and stimuli than did seven highly visual processors who, in contrast, demonstrated greater right hemispheric alpha suppression. Task difficulty and individual differences in processing style that modify cerebral laterality effects are discussed.     

Repetition priming within and between the two cerebral hemispheres

Two experiments explored repetition priming benefits in the left and right cerebral hemispheres. In both experiments, a lateralized lexical decision task was employed using repeated target stimuli. In the first experiment, all targets were repeated in the same visual field, and in the second experiment the visual field of presentation was switched following repetition. Both experiments demonstrated hemispheric specialization for the task (a RVF advantage for word identification) and hemispheric interaction for word processing (lexicality priming from contralateral distracters). In the first experiment, words were identified more quickly and accurately following repetition, with repetition facilitating faster but fewer correct responses for non-words. Complex interactions between visual field of first and second presentation in the second experiment indicate asymmetric interhemispheric repetition priming effects. These results provide a broad picture of hemispheric asymmetries in word processing and of complex interaction between the hemispheres during word recognition.     

Investigating hemispheric specialization in a novel face-word Stroop task

We examined hemispheric specialization in a lateralized Stroop facial identification task. A 2 (presentation side: left or right visual field [LVF or RVF])x2 (picture emotion: happy or angry)x3 (emotion of distractor word: happy, angry, or blank) factorial design placed the right hemispheric specialization for emotional expression processing and the left hemispheric specialization for verbal processing in conflict. Faces (from ) and emotion words were briefly displayed, and participants responded with keypresses corresponding to the picture emotion. As predicted, greater Stroop interference in identification accuracy was found with incongruent displays of facial expression in the LVF and emotion words in the RVF, and females exhibited less Stroop interference. Reaction times were moderated by emotion and visual field.     

Hemispheric asymmetry in the processing of negative and positive words: a divided field study

Research on the lateralisation of brain functions for emotion has yielded different results as a function of whether it is the experience, expression, or perceptual processing of emotion that is examined. Further, for the perception of emotion there appear to be differences between the processing of verbal and nonverbal stimuli. The present research examined the hemispheric asymmetry in the processing of verbal stimuli varying in emotional valence. Participants performed a lexical decision task for words varying in affective valence (but equated in terms of arousal) that were presented briefly to the right or left visual field. Participants were significantly faster at recognising positive words presented to the right visual field/left hemisphere. This pattern did not occur for negative words (and was reversed for high arousal negative words). These results suggest that the processing of verbal stimuli varying in emotional valence tends to parallel hemispheric asymmetry in the experience of emotion.     

Hemispheric asymmetry in the processing of negative and positive words: A divided field study

Research on the lateralisation of brain functions for emotion has yielded different results as a function of whether it is the experience, expression, or perceptual processing of emotion that is examined. Further, for the perception of emotion there appear to be differences between the processing of verbal and nonverbal stimuli. The present research examined the hemispheric asymmetry in the processing of verbal stimuli varying in emotional valence. Participants performed a lexical decision task for words varying in affective valence (but equated in terms of arousal) that were presented briefly to the right or left visual field. Participants were significantly faster at recognising positive words presented to the right visual field/left hemisphere. This pattern did not occur for negative words (and was reversed for high arousal negative words). These results suggest that the processing of verbal stimuli varying in emotional valence tends to parallel hemispheric asymmetry in the experience of emotion.     

Sublexical ambiguity effect in reading Chinese disyllabic compounds

For Chinese compounds, neighbors can share either both orthographic forms and meanings, or orthographic forms only. In this study, central presentation and visual half-field (VF) presentation methods were used in conjunction with ERP measures to investigate how readers solve the sublexical semantic ambiguity of the first constituent character in reading a disyllabic compound. The sublexical ambiguity of the first character was manipulated while the orthographic neighborhood sizes of the first and second character (NS1, NS2) were controlled. Subjective rating of number of meanings corresponding to a character was used as an index of sublexical ambiguity. Results showed that low sublexical ambiguity words elicited a more negative N400 than high sublexical ambiguity words when words were centrally presented. Similar patterns were found when words were presented to the left VF. Interestingly, different patterns were observed for pseudowords. With left VF presentation, high sublexical ambiguity psudowords showed a more negative N400 than low sublexical ambiguity pseudowords. In contrast, with right VF presentation, low sublexical ambiguity pseudowords showed a more negative N400 than high sublexical ambiguity pseudowords. These findings indicate that a level of morphological representation between form and meaning needs to be established and refined in Chinese. In addition, hemispheric asymmetries in the use of word information in ambiguity resolution should be taken into account, even at sublexical level.