Right Visual Field Research Articles

Further fMRI validation of the visual half field technique as an indicator of language laterality: A large-group analysis

The best established lateralized cerebral function is speech production, with the majority of the population having left hemisphere dominance. An important question is how to best assess the laterality of this function. Neuroimaging techniques such as functional Magnetic Resonance Imaging (fMRI) are increasingly used in clinical settings to replace the invasive Wada-test. We evaluated the usefulness of behavioral visual half field (VHF) tasks for screening a large sample of healthy left-handers. Laterality indices (LIs) calculated on the basis of the latencies in a word and picture naming VHF task were compared to the brain activity measured in a silent word generation task in fMRI (pars opercularis/BA44 and pars triangularis/BA45). Results confirmed the usefulness of the VHF-tasks as a screening device. None of the left-handed participants with clear right visual field (RVF) advantages in the picture and word naming task showed right hemisphere dominance in the scanner. In contrast, 16/20 participants with a left visual field (LVF) advantage in both word and picture naming turned out to have atypical right brain dominance. Results were less clear for participants who failed to show clear VHF asymmetries (below 20 ms RVF advantage and below 60 ms LVF advantage) or who had inconsistent asymmetries in picture and word naming. These results indicate that the behavioral tasks can mainly provide useful information about the direction of speech dominance when both VHF differences clearly point in the same direction.

Differential Hemispheric Processing in the Recognition of Chinese Characters with Different Structures in Foveal and Parafoveal Vision

Whether foveal representation in reading is initially split and contralaterally projected to different hemispheres or bilaterally projected remains a controversial issue. Here we examine visual field asymmetry effects in naming Chinese characters with different structures, with characters presented either to the left visual field or the right visual field (RVF), and either within or outside foveal vision (eccentricity). We show that overall the RVF advantage in naming characters was significant in both eccentricity conditions (fovea vs. parafovea), with a stronger effect in parafoveal vision. This suggests that foveal splitting may not be an all-or-none phenomenon but has a graded effect. When examining characters with different structures separately, this interaction between visual field and eccentricity was significant only in the dominant, right-heavy character structure type, but not in the minority left-heavy or symmetric structure types, suggesting a modulation of character structure or type frequency on the eccentricity effect. In addition, existence of a phonetic radical modulated the visual field asymmetry effect differentially in different character structure types; however this effect did not interact with eccentricity. This result thus suggests that character structure and existence of a phonetic radical have differential modulation on character processing in the foveal and parafoveal vision.

A right visual field advantage for tool-recognition in the visual half-field paradigm

Neuropsychological and brain imaging studies have shown that the identification and use of tools mainly involve areas of the left hemisphere. We investigate whether this dominance can be observed in a behavioral visual half-field (VHF) task as well. To make sure that the VHF-effect was due to laterality and not due to attentional bias, we made use of two tasks: tool recognition and object recognition. On the basis of the existing literature, we predicted a right visual field (RVF) advantage for tool recognition, but not for object recognition. Twenty right-handed participants made judgments about whether one of two bilaterally presented stimuli was an object/non-object or a tool/non-tool. No VHF/hemisphere advantage was found for object recognition, whereas a significant RVF/left hemisphere advantage was observed for tool recognition. These findings show that VHF-tasks can be used as a valid laterality measure of tool recognition.

Location, location, location: How it affects the neighborhood (effect)

Reaction times in lexical decision are more sensitive to a words’ length and orthographic-neighborhood density when the stimulus is presented to the left visual field (LVF) than to the right visual field (RVF). We claim that the length effect is equivalent to the neighborhood effect, and propose a novel explanation of why the LVF, but not the RVF, is sensitive to density, based on different firing rates of abstract-letter representations encoding letters falling in the LVF versus RVF. We support this proposal with a large-scale implemented model of lexical decision utilizing spiking units, which provides a reasonable fit to the data from the English Lexicon Project under simulated central presentation, while replicating the observed hemifield asymmetries under simulated lateralized presentation.

Lateralized neural mechanisms underlying the modulation of response inhibition processes

Functional cerebral asymmetries (FCAs) are an important modulator of cognitive functions. Here, we investigated the temporal and spectral dynamics as well as the cortical networks underlying the lateralized modulation of executive functions related to response inhibition. To this end, we recorded event-related potentials (ERPs) during tachistoscopic presentation of verbal ‘Go’ and ‘Nogo’ stimuli in the left (LVF) and the right visual field (RVF).Participants committed fewer false alarms to verbal Nogo stimuli presented in the RVF than to stimuli presented in the LVF. This asymmetry was paralleled by neurophysiological data. The Nogo-N2 and related delta frequency band power were stronger when response inhibition was driven by stimuli presented in the LVF, implying a stronger response conflict. This effect was mediated by stronger activations in bilateral medial-prefrontal and especially left parietal networks. This shows that asymmetries in behavioural performance do not necessarily reflect differences in the overall capability of one hemisphere to solve a task. Even though information is initially confined to one hemisphere after tachistoscopic presentation, this does not primarily cause behavioural asymmetries. Instead, hemispheric dominances in information processing can induce differences in demands on cognitive processes operating via bilateral networks that ultimately drive behavioural asymmetries.

Position of phonetic components may influence how written words are processed in the brain: Evidence from Chinese phonetic compound pronunciation

Previous studies have shown a right-visual-field (RVF)/left-hemisphere (LH) advantage in Chinese phonetic compound pronunciation. Here, we contrast the processing of two phonetic compound types: a dominant structure in which a semantic component appears on the left and a phonetic component on the right (SP characters), and a minority structure with the opposite arrangement (PS characters). We show that this RVF/LH advantage was observed only in SP character pronunciation, but not in PS character pronunciation. This result suggests that SP character processing is more LH lateralized than is PS character processing and is consistent with corresponding ERP N170 data. This effect may be due to the dominance of SP characters in the lexicon, which makes readers opt to obtain phonological information from the right of the characters. This study thus shows that the overall information distribution of word components in the lexicon may influence how written words are processed in the brain. Supplemental materials for this article may be downloaded from http://cabn.psychonomic-journals.org/content/supplemental.

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

Right-handed participants respond more quickly and more accurately to written words presented in the right visual field (RVF) than in the left visual field (LVF). Previous attempts to identify the neural basis of the RVF advantage have had limited success. Experiment 1 was a behavioral study of lateralized word naming which established that the words later used in Experiment 2 showed a reliable RVF advantage which persisted over multiple repetitions. In Experiment 2, the same words were interleaved with scrambled words and presented in the LVF and RVF to right-handed participants seated in an MEG scanner. Participants read the real words silently and responded “pattern” covertly to the scrambled words. A beamformer analysis created statistical maps of changes in oscillatory power within the brain. Those whole-brain maps revealed activation of the reading network by both LVF and RVF words. Virtual electrode analyses used the same beamforming method to reconstruct the responses to real and scrambled words in three regions of interest in both hemispheres. The middle occipital gyri showed faster and stronger responses to contralateral than to ipsilateral stimuli, with evidence of asymmetric channeling of information into the left hemisphere. The left mid fusiform gyrus at the site of the ‘visual word form area’ responded more strongly to RVF than to LVF words. Activity in speech-motor cortex was lateralized to the left hemisphere, and stronger to RVF than LVF words, which is interpreted as representing the proximal cause of the RVF advantage for naming written words.

Hemispheric asymmetries in categorical perception of orientation in infants and adults

Orientation CP is the faster or more accurate discrimination of two orientations from different categories (e.g., oblique1 and vertical1) compared to two orientations from the same category (e.g., oblique1 and oblique2), even when the degree of difference is equated across conditions. Here, we assess whether there are hemispheric asymmetries in this effect for adults and 5-month-old infants. Experiment 1 identified the location of the vertical–oblique category boundary. Experiment 2, using a visual search task with oriented lines found that adult search was more accurate when the target and distractors were from different orientation categories, compared to targets and distractors of an equivalent physical difference taken from the same category. This effect was stronger for targets lateralized to the left visual field (LVF) than the right visual field (RVF), indicating a right hemisphere (RH) bias in adult orientation CP. Experiment 3, replicated the RH bias using different stimuli and also investigated the impact of visual and verbal interference on the category effect. Experiment 4, using the same visual search task, found that infant search was also faster when the target and distractors were from different orientation categories than the same, yet this category effect was stronger for RVF than LVF lateralized targets, indicating a LH bias in orientation CP at 5 months. These findings are contrasted to equivalent studies on the lateralization of color CP (e.g., Gilbert, Regier, Kay, & Ivry, 2005). The implications for theories on the contribution of the left and right hemispheres of the infant and adult brain to categorical computations are discussed.

Language suppression effects on the categorical perception of colour as evidenced through ERPs

It is unclear how language influences colour perception so as to lead to the categorical perception of colour. This is particularly true when considering visual tasks that involve minimal memory requirements. In the present experiment we investigated this question by employing a “same–different” judgment task in which participants were asked to compare the colours of two presented visual features (a square and its surrounding frame), presented to the left visual field (LVF) or the right visual field (RVF), while event-related potentials (ERPs) were recorded. The “different” colour trials were of two types, including those consisting of within-category differences (e.g. two different shades of blue) and those consisting of between-category differences (i.e. blue vs. green), with matching hue differences for within-category comparisons and between-category comparisons. The ERP results show that, over the midline fronto-central scalp region, responses to the within-category stimuli presented in the RVF demonstrated a more negative N2 component (260–310ms post-stimulus) than either the responses to the between-category stimuli in the RVF, the between-category stimulus in the LVF, or the within-category stimulus in the LVF. Further, the responses for the within-category stimulus in the RVF resulted in a P3 component with a longer latency than that observed for the other three conditions. The results observed in this rapid colour discrimination task suggest that the categorical perception of colour stimuli presented in the RVF may result from an effect of language-related processes suppressing the capacity to discriminate two shades of colour within the same colour category.

Attention effects on motion processing are larger in the left vs. the right visual field

Purpose: Results from previous studies indicate that the magnitude of attention effects depends on stimulus features/task (e.g., Lee et al, 1997; Morrone et al, 2002). Here, we used a full/poor attention paradigm to investigate attention effects on two different stimuli/tasks: direction of motion and orientation discrimination. Data were obtained for central (CVF), left (LVF) and right visual field (RVF) to see if attention effects vary across space. Methods: On the motion task, subjects reported direction of a moving dot field (“left” vs. “right”). On the orientation task, subjects reported the tilt of a 0.8 cpd contrast grating (“clockwise” vs. “counterclockwise”). Stimuli subtended 5 degrees, and RVF and LVF stimuli were centered 5 degrees eccentric to fixation. Thresholds were obtained in two conditions: 1) Full Attention: Subjects performed a single-task, reporting direction (or orientation), and 2) Poor Attention: Subjects performed a dual-task, first counting the number of closed shapes at the fixation point, then reporting stimulus direction (or orientation). Attention effects were calculated as Thrpoor/Thrfull. Results: For orientation, attention effects were constant across space (LVF=1.29, CVF=1.45, RVF=1.20). However, for motion, attention effects varied across space (LVF=1.74, CVF=1.41, RVF=1.07; p=0.002). The difference between the LVF and RVF was driven by lower thresholds in the LVF under full attention (1.2-fold, p=0.045), yet higher thresholds in the LVF under poor attention (1.3-fold, p=0.006). Conclusions: The different attention effects for RVF vs. LVF motion suggest that attentional resources for motion may be enhanced in the RVF (perhaps from learning to read left-to-right, see Rayner 1998).

Crossmodal visual‐tactile extinction: Modulation by posture implicates biased competition in proprioceptively reconstructed space

Extinction is a common consequence of unilateral brain injury: contralesional events can be perceived in isolation, yet are missed when presented concurrently with competing events on the ipsilesional side. This can arise crossmodally, where a contralateral touch is extinguished by an ipsilateral visual event. Recent studies showed that repositioning the hands in visible space, or making visual events more distant, can modulate such crossmodal extinction. Here, in a detailed single-case study, we implemented a novel spatial manipulation when assessing crossmodal extinction. This was designed not only to hold somatosensory inputs and hand/arm-posture constant, but also to hold (retinotopic) visual inputs constant, yet while still changing the spatial relationship of tactile and visual events in the external world. Our right hemisphere patient extinguished left-hand touches due to visual stimulation of the right visual field (RVF) when tested in the usual default posture with eyes/head directed straight ahead. But when her eyes/head were turned to the far left (and any visual events shifted along with this), such that the identical RVF retinal stimulation now fell at the same external location as the left-hand touch, crossmodal extinction was eliminated. Since only proprioceptive postural cues could signal this changed spatial relationship for the critical condition, our results show for the first time that such postural cues alone are sufficient to modulate crossmodal extinction. Identical somatosensory and retinal inputs can lead to severe crossmodal extinction, or none, depending on current posture.

Absence of right visual field attentional bias in reading in dyslexic children.

A parafoveal word is better identified in the right visual field (RVF) than in the left visual field (LVF), in adults [4] and in school-age children [5]. Attention may play a role, at least partially, in this RVF superiority in reading. The hypothesis is that attention is not symmetrically distributed in the state of expectancy prior to the presentation of parafoveal words, and a bias in favor of the RVF exists. This attentional bias may be the consequence of the left hemispheric control when the subject is engaged in a linguistic task [2], and of scanning habits [1]. Many investigators have hypothesized a failure of left-hemisphere posterior brain systems to function properly during reading in dyslexia [6]. A possibility is that this hemispheric dysfunctioning may influence the distribution of spatial attention and affect the RVF bias in reading. We studied the distribution of attention when identifying parafoveal words in dyslexic children and agematched skilled readers. We compared performance in a condition in which a word was presented alone in the LVF or RVF, and a condition in which a distractor was simultaneously presented in the visual field opposite the word. The distribution of attention should be affected by the presence of the distractor, and the distractor effect is stronger in the LVF than in the RVF in normal

Right visual field attentional bias in reading in children and adults.

The identification of parafoveal words is better in the right visual field (RVF) than in the left visual field (LVF) [4]. In experiments using the identification of parafoveal words, attention is not necessarily distributed symmetrically in the state of expectancy prior to the presentation of each stimulus. The RVF superiority may be, at least partially, explained by an attentional bias in favour of the RVF [3], because of the activation of the left hemisphere when subjects are engaged in a linguistic task and because of the reading direction. Although several studies argue in favor of an early development of the RVF superiority for words in children [5], little is known on the development of this attentional bias. The goal of our study was to investigate the attentional bias in reading parafoveal words in school-age children and adults, using an identification task. Words were presented alone or with a distractor in the opposite visual field. The distractor was simultaneous with the word or was presented immediately before the word. Asimultaneous distractor may compete with the word for the allocation of attention [6,7]. A distractor appearing before the word may capture attention [2]. According to the attentional bias hypothesis we predicted a larger effect of the simultaneous distractor in the LVF,

Visual field asymmetries in attention vary with self-reported attention deficits

The purpose of this study was to determine whether an index of self-reported attention deficits predicts the pattern of visual field asymmetries observed in behavioral measures of attention. Studies of “normal” subjects do not present a consistent pattern of asymmetry in attention functions, with some studies showing better left visual field (LVF) performance, others showing no asymmetry or even a right visual field (RVF) advantage. Here we found that a participant variable (a measure of self-reported attention problems) may help to explain these inconsistencies. We used Conners’ Adult ADHD Rating Scales to measure self-reported attention problems in a group of 36 normal (non-ADHD) subjects, and we used two behavioral tasks to directly measure their attentional abilities: a lateralized Attention Network Task (ANT) and a visual search task. Comparing subjects with relatively Low versus High scores on the attention-deficit (AD) scale, we found that subjects with High scores were less efficient in orienting attention to the left visual field. When LVF targets were preceded by a valid spatial cue, response times were positively correlated with AD scores, indicating slower covert-attention shifts as attention-deficit scores increased. Right visual field data showed a different pattern of results. Subjects with High AD scores were at least as efficient as those with Low AD scores in orienting attention to the RVF. This study provides evidence that visual field asymmetries in orienting attention vary across individuals, and that level of self-reported attention problems correlates with behavioral deficiencies in orienting attention to the left visual field.

Re-examining format distortion and orthographic neighbourhood size effects in the left, central and right visual fields

Research has shown orthographic neighbourhood size effects (ONS) in the left visual field (LVF) but not in the right visual field (RVF). An earlier study examined the combined effects of ONS and font distortion in the LVF and RVF, but did not find an interaction. The current lexical decision experiment re-examined the interaction between ONS and format distortion at fixation and in the LVF and RVF with the addition of several methodological improvements. Main results replicated previous findings and extended them by indicating that (a) ONS effects in the LVF are immune to the putatively disruptive effects of format distortion, (b) format distortion revealed ONS effects in the RVF and (c) large orthographic neighbourhood size slowed pseudoword rejections regardless of format distortion or visual field presentation. Results are discussed within the context of relevant literature on the visual field laterality of visuoperceptual-orthographic processing.

Zeigarnik effect in Insight problem solving: Hemi-spheric difference in brain activities following problem solving and during hint presentation

People tend to exhibit enhanced memory performance for the unfinished tasks relative to the finished ones, which known as the Zeigarnik effect. Consistently, the impasse state in insightful problem solving were believevd to play an important role in maintaining the problem in one’s mind and in catching the critical clue to overcome the main obstacles. More importantly, through hemi-visual field presentation technology, studies on insight found the keynotes for the unsolved puzzle could be more efficient in catalyzing a breakthrough when presented to the left-visual field (i.e., the right hemisphere) than to the right-visual field, especially when there was a temporal delay between the disappearance of the puzzle and the presentation of keynotes. This observation implied that the right hemisphere, relative to the left one, might play a more important role in keeping the information of the unsolved problem online and might be more ready in processing the related clue for that problem. In order to testify this hypothesis, we compared the Event-Related Potentials (ERPs) between the solved and unsolved insightful chunk decomposition problems during (a) the moment when the subjects pressed a key to indicate whether or not they could solve the problem by themselves before seeing any external hint, and (b) the moment when subjects were given the hint. The ERPs results showed that, during the moment of subjects’ confirmation of their successful or unsuccessful problem solving, the unsolved problems were accompanied with a more positive P150 over the right frontal cortex, whereas the solved ones exhibited a more positive P150 over the left side. Consistently, during the moment of hints presentation, the hints to the unsolved problems also elicited a more positive P2 over the right hemisphere, whereas the the hints to the solved problems elicited a more positive P2 over the left side. These results confirmed the hypothesis that, after the failure in insight problem solving, the right hemisphere might be more positive in preserving the unsolved problem in mind and be more responsive to the external hint for problem solving.

Right visual field advantage in parafoveal processing: Evidence from eye-fixation-related potentials

Readers acquire information outside the current eye fixation. Previous research indicates that having only the fixated word available slows reading, but when the next word is visible, reading is almost as fast as when the whole line is seen. Parafoveal-on-foveal effects are interpreted to reflect that the characteristics of a parafoveal word can influence fixation on a current word. Prior studies also show that words presented to the right visual field (RVF) are processed faster and more accurately than words in the left visual field (LVF). This asymmetry results either from an attentional bias, reading direction, or the cerebral asymmetry of language processing. We used eye-fixation-related potentials (EFRP), a technique that combines eye-tracking and electroencephalography, to investigate visual field differences in parafoveal-on-foveal effects. After a central fixation, a prime word appeared in the middle of the screen together with a parafoveal target that was presented either to the LVF or to the RVF. Both hemifield presentations included three semantic conditions: the words were either semantically associated, non-associated, or the target was a non-word. The participants began reading from the prime and then made a saccade towards the target, subsequently they judged the semantic association. Between 200 and 280 ms from the fixation onset, an occipital P2 EFRP-component differentiated between parafoveal word and non-word stimuli when the parafoveal word appeared in the RVF. The results suggest that the extraction of parafoveal information is affected by attention, which is oriented as a function of reading direction.

Language regions of brain are operative in color perception.

The effect of language on the categorical perception of color is stronger for stimuli in the right visual field (RVF) than in the left visual field, but the neural correlates of the behavioral RVF advantage are unknown. Here we present brain activation maps revealing how language is differentially engaged in the discrimination of colored stimuli presented in either visual hemifield. In a rapid, event-related functional MRI study, we measured subjects' brain activity while they performed a visual search task. Compared with colors from the same lexical category, discrimination of colors from different linguistic categories provoked stronger and faster responses in the left hemisphere language regions, particularly when the colors were presented in the RVF. In addition, activation of visual areas 2/3, responsible for color perception, was much stronger for RVF stimuli from different linguistic categories than for stimuli from the same linguistic category. Notably, the enhanced activity of visual areas 2/3 coincided with the enhanced activity of the left posterior temporoparietal language region, suggesting that this language region may serve as a top-down control source that modulates the activation of the visual cortex. These findings shed light on the brain mechanisms that underlie the hemifield- dependent effect of language on visual perception.

Language status and hemispheric involvement in reading: Evidence from trilingual Arabic speakers tested in Arabic, Hebrew, and English.

This study explores the effects of language status on hemispheric involvement in lexical decision. The authors looked at the responses of native Arabic speakers in Arabic (L1 for reading) and in two second languages (L2): Hebrew, which is similar to L1 in morphological structure, and English, which is very different from L1. Two groups of Arabic speakers performed lateralized lexical decision tasks in the three languages, using unilateral presentations and bilateral presentations. These paradigms allowed us to infer both hemispheric specialization and interhemispheric communication in the three languages, and the effects of language status (native vs. nonnative) and similarity on hemispheric patterns of responses. In general the authors show an effect of language status in the right visual field (RVF), reflecting the greater facility of the left hemisphere (LH) in recognizing words in the participant's native Arabic than in their other languages. The participants revealed similar patterns of interhemispheric integration across the languages, with more integration occurring for words than for nonwords. Both hemispheres revealed sensitivity to morphological complexity, a pattern similar to that of native Hebrew readers and different from that of native English readers.

Lateralization of categorical perception of color changes with color term acquisition

Categorical perception (CP) of color is the faster and more accurate discrimination of two colors from different categories than two colors from the same category, even when same- and different-category chromatic separations are equated. In adults, color CP is lateralized to the left hemisphere (LH), whereas in infants, it is lateralized to the right hemisphere (RH). There is evidence that the LH bias in color CP in adults is due to the influence of color terms in the LH. Here we show that the RH to LH switch in color CP occurs when the words that distinguish the relevant category boundary are learned. A colored target was shown in either the left- or right-visual field on either the same- or different-category background, with equal hue separation for both conditions. The time to initiate an eye movement toward the target from central fixation at target onset was recorded. Color naming and comprehension was assessed. Toddlers were faster at detecting targets on different- than same-category backgrounds and the extent of CP did not vary with level of color term knowledge. However, for toddlers who knew the relevant color terms, the category effect was found only for targets in the RVF (LH), whereas for toddlers learning the color terms, the category effect was found only for targets in the LVF (RH). The findings suggest that lateralization of color CP changes with color term acquisition, and provide evidence for the influence of language on the functional organization of the brain.