The processing of multiple letters and multiple words in deaf adults.

The non-contribution of attentional biases to visual field asymmetries for temporal discrimination

Words presented to the right visual field (RVF) are recognised more readily than those presented to the left visual field (LVF). This RVF advantage could reflect: (a) the direct connection between the RVF and left hemisphere, (b) an attentional bias directed towards the RVF, or (c) an attentional advantage, where the left hemisphere is able to recognise words using less attention than the right hemisphere. The attentional bias and advantage models were tested in 20 dextral adults during a divided visual field word-naming task. Spatial attention was manipulated with valid, invalid, or neutral central cues. Error and reaction time measures revealed a RVF advantage for word recognition. If the attentional bias model is correct, the RVF advantage should have been attenuated for valid and invalid cues compared to neutral cues. Instead of this, an interaction emerged whereby the cueing effect was stronger for words in the LVF than the RVF. This interaction has been reported previously in studies using peripheral spatial cues. The interaction suggests that the RVF requires less attention to process words than the LVF. This left hemisphere attentional advantage may reflect asymmetries between the hemispheres in their word processing styles.

We investigated the extent to which accuracy in word identification in foveal and parafoveal vision is determined by variations in the visibility of the component letters of words. To do so we measured word identification accuracy in displays of three three-letter words, one on fixation and the others to the left and right of the central word. We also measured accuracy in identifying the component letters of these words when presented at the same location in a context of three three-letter nonword sequences. In the word identification block, accuracy was highest for central targets and significantly greater for words to the right compared with words to the left. In the letter identification block, we found an extended W-shaped function across all nine letters, with greatest accuracy for the three central letters and for the first and last letter in the complete sequence. Further analyses revealed significant correlations between average letter identification per nonword position and word identification at the corresponding position. We conclude that letters are processed in parallel across a sequence of three three-letter words, hence enabling parallel word identification when letter identification accuracy is high enough.

When two targets are presented in a rapid serial visual presentation (RSVP), recognition of the second target (T2) is usually reduced when presented 150-500 ms after the first target, demonstrating an attentional blink (AB). Previous studies have shown a left visual-field (LVF) advantage in T2 recognition, when T2 was embedded in one of two streams, demanding top-down attention for its recognition. Here, we explored the impact of bottom-up saliency on spatial asymmetry in the AB. When T2 was spatially shifted outside from the RSVP, creating an abrupt onset of T2, right T2s showed a right visual-field (RVF) advantage. In lag-1 trials, right T2s were not only better recognized, but also showed a low T1-T2 order error rate. In contrast, recognized left T2s exhibited high order error rate. Without abrupt onset, symmetrical AB was found and order error rate was similarly low in both sides. Follow-up experiments showed that, while RVF advantage was related to bottom-up saliency, order errors were affected by T1 mask. The discrepancy between LVF and RVF advantage in the AB could be resolved in terms of two mechanisms of attentional gating: top-down attentional gating, which is biased towards LVF, and bottom-up attentional gating, which is biased towards RVF.

Lateralization patterns of event-related potential and performance indices in schizophrenia: relationship to clinical state and neuroleptic treatment

Hemispheric Memory for Surrealistic Versus Realistic Paintings

Information about object-associated manipulations is lateralized to left parietal regions, while information about the visual form of tools is represented bilaterally in ventral occipito-temporal cortex. It is unknown how lateralization of motor-relevant information in left-hemisphere dorsal stream regions may affect the visual processing of manipulable objects. We used a lateralized masked priming paradigm to test for a right visual field (RVF) advantage in tool processing. Target stimuli were tools and animals, and briefly presented primes were identical to or scrambled versions of the targets. In Experiment 1, primes were presented either to the left or to the right of the centrally presented target, while in Experiment 2, primes were presented in one of eight locations arranged radially around the target. In both experiments, there was a RVF advantage in priming effects for tool but not for animal targets. Control experiments showed that participants were at chance for matching the identity of the lateralized primes in a picture-word matching experiment and also ruled out a general RVF speed-of-processing advantage for tool images. These results indicate that the overrepresentation of tool knowledge in the left hemisphere affects visual object recognition and suggests that interactions between the dorsal and ventral streams occurs during object categorization.

In recognition of the ecological importance of processing the talking face and its potential role in the development of right hemisphere specialization for face processing, descriptive studies examined the effects of concurrent speech on hemispheric lateralization for face recognition. To explore the potentially special nature of the face-speech concurrence, the effect of speech on inverted face recognition was also examined. Separate groups of right-handed participants took part in each of 4 studies. In Study 1, participants were asked to identify which of 4 male faces was presented in tachistoscopic fashion via computer. Correct recognition of faces was significantly faster in the left visual field (LVF) than in the right visual field (RVF), and the majority of participants exhibited a LVF processing-speed advantage (ADV). However, those participants whose responses to faces were faster in the RVF (RVF ADV) were more accurate at recognizing faces. In Study 2, a spoken word was incidentally presented simultaneously with each face. This altered hemispheric lateralization for face recognition. There was no longer evidence for LVF responses being faster than RVF ones or for participants with a RVF ADV being better at recognizing faces. However, these participants were superior at an unannounced speech recognition test. Unexpectedly, concurrent processing did not diminish performance on face recognition. Good memory for the incidental speech was also evident during an unannounced speech recognition test, indicating that participants successfully did 2 things at once. It was hypothesized that the special nature of the face-speech combination was responsible for this. Concurrent processing of the nonecological combination of inverted faces and speech provided no evidence in support of this hypothesis.

Hemispheric priming was examined in 3 language-trained chimpanzees (Pan troglodytes) using a simple reaction time paradigm. Subjects were required to hold down a response button until the occurrence of a response cue. A warning stimulus was presented to either the left visual field (LVF) or the right visual field (RVF) before the response cue occurred. No warning stimulus was presented on control trials. The warning stimuli were geometric communicative symbols from two semantic categories: foods and tools. A third set of warning stimuli were familiar geometric symbols. Dependent measures included reaction time and the number of false-positive responses. Reaction-time data indicated an RVF advantage in priming when the warning stimuli were food or tool symbols. No significant visual half-field differences were found for familiar symbols, but a trend toward an RVF advantage was observed. These effects were enhanced when subjects responded with their left hand. False-positive data also indicated an RVF advantage for the food and tool warning stimuli. The data indicate that hemispheric asymmetries for processing communicative symbols are present in language-trained chimpanzees.

Hemispheric Asymmetry in Lexical Decisions: The Effects of Grammatical Class and Imageability

Non-verbal IQ is correlated with visual field advantages for short duration coherent motion detection in deaf signers with varied ASL exposure and etiologies of deafness

Two experiments were conducted to examine laterality differences and practice effects under various central backward masking conditions. Critical stimulus onset asynchrony (SOA) was determined for subjects on 3 consecutive days using single letters as target stimuli (TS) and a pattern masking stimulus (MS). There was a right visual field (RVF) advantage on Day 1 but no difference between the visual fields on following days. The decline in the RVF advantage appeared to be dependent upon prior experience with laterally located letters, to be independent of initial experience with a particular set of letters, and to be more pronounced for females than for males. In addition, large improvements in performance were found, particularly between the first and second testing sessions. These practice effects were discussed in terms of the possible development of strategies for enhancing TS features or attenuating MS features.

The first steps in the process of reading a printed word belong to the domain of visual object perception. They culminate in a representation of letter strings as an ordered set of abstract letter identities, a representation known as the Visual Word Form (VWF). Brain lesions in patients with pure alexia and functional imaging data suggest that the VWF is subtended by a restricted patch of left-hemispheric fusiform cortex, which is reproducibly activated during reading. In order to determine whether the operation of this Visual Word Form Area (VWFA) depends exclusively on the visual features of stimuli, or is influenced by language-dependent parameters, brain activations induced by words, consonant strings and chequerboards were compared in normal subjects using functional MRI (fMRI). Stimuli were presented in the left or right visual hemifield. The VWFA was identified in both a blocked-design experiment and an event-related experiment as a left-hemispheric inferotemporal area showing a stronger activation to alphabetic strings than to chequerboards, and invariant for the spatial location of stimuli. In both experiments, stronger activations of the VWFA to words than to strings of consonants were observed. Considering that the VWFA is equally activated by real words and by readable pseudowords, this result demonstrates that the VWFA is initially plastic and becomes attuned to the orthographic regularities that constrain letter combination during the acquisition of literacy. Additionally, the use of split-field stimulation shed some light on the cerebral bases of the classical right visual field (RVF) advantage in reading. A left occipital extrastriate area was found to be activated by RVF letter strings more than by chequerboards, while no symmetrical region was observed in the right hemisphere. Moreover, activations in the precuneus and the left thalamus were observed when subjects were reading RVF versus left visual field (LVF) words, and are likely to reflect the attentional component of the RVF advantage.

This study investigated the ability of auditory and visual temporal processing measured before school entry (mean age 5.36 years) to predict early reading development in an unselected sample of children. There were 142 children at the first phase (Preschool), 125 at the second phase 6 - 8 months later (early Grade 1; mean age 5.94 years), and 105 at the third phase12 months later (Grade 2; mean age 6.94 years). There were similar numbers of males and females. Visual and auditory temporal order judgement (TOJ) and Temporal Dot accuracy (rapid visual sequencing task) measured at Preschool explained a significant percentage of the variance in letter identification (an important pre-reading skill) measured concurrently. These measures also predicted a significant percentage of the variance in letter and word identification (word reading accuracy) and reading rate (fluency) measured in early Grade 1, even after controlling for the effects of age, environment, memory, attentional vigilance, non-verbal ability, and speech and language problems. They also significantly discriminated between groups of children at Grade 1 who could and could not use phonological decoding to read non-words. By Grade 2, these Preschool measures accounted for significant variance in word reading accuracy and fluency and in non-word decoding. Only Preschool auditory temporal processing accounted for significant unique variance in the reading measures at Preschool or Grade 1, but by Grade 2, visual temporal processing (Temporal Dot) also accounted for significant unique variance. Temporal Dot accuracy also explained unique variance in the rate of growth in these reading measures across this period. These changes in predictive ability by the auditory and visual temporal processing measures were interpreted as reflecting developmental changes in their roles in reading as reading develops. Auditory temporal processing was important in early pre-reading and reading and remained important throughout. Visual temporal processing only became important in the later phase, possibly because of increasing need to analyse letter sequences. Preschool temporal and phonological processing measures accounted for approximately equal percentages of variance in the reading measures at Preschool and Grade 1, but by Grade 2, the Preschool phonological processing measures accounted for significantly more variance in all reading measures, except Pseudohomophone Choice (orthographic processing). Very little of the variance that was explained in the reading measures was common to temporal and phonological processing. The variance that each uniquely explained in reading was more important than the variance they explained in common. Therefore, utilising both temporal and phonological processing predictors optimised prediction of early reading skills. The study also showed there was significant linear development occurring in temporal processing from Preschool to Grade 2. The correlations of scores on the temporal measures from Preschool to Grade 1 were moderate. The relative position of children within the distribution on these skills showed moderate stability over the short-term, but less stability over the long-term. The majority of children who fell in the bottom quartile on the temporal and phonological processing measures at Preschool remained in the bottom half of the distribution on those measures by Grade 2. These children may represent those who are at most risk for reading difficulties. Letter Word Identification showed high stability from Preschool to Grade 2. There was little difference in the percentage of variance explained in subsequent reading between temporal processing measures obtained at Preschool or Grade 1. However, performance on the Visual temporal order judgement task was more likely to account for significant unique variance in reading when measured after school entry than before. This was consistent with the expected developmental changes in reading. When measured after school-entry, phonological processing measures accounted for greater percentages of variance in the reading measures than when measured before. There were also developmental changes in which phonological processing measures were important predictors of reading skills. When measured at Grade 1, rhyme and alliteration detection and phonemic segmentation were the most important predictors. However, when measured at Grade 2, performance on the Rhyme and Alliteration task had reached ceiling, so would no longer be a useful predictor of later reading. These results were consistent with developmental models of reading and of phonological processing. The results provided support for a causal role of temporal processing in reading development. They also showed that measures of visual and auditory temporal processing obtained close to school-entry would be a useful addition to predicting risk of early reading difficulties. However, additional work is needed to determine the most suitable temporal processing measures for this younger age group.

The neural basis of the right visual field advantage in reading: An MEG analysis using virtual electrodes