Radial bisection of words and lines in right‐brain‐damaged patients with spatial neglect

The bisection of lines positioned radially (with the two ends of the line close and far, with respect to the participant's body) has been less investigated than that of lines placed horizontally (with their two ends left and right, with respect to the body's midsagittal plane). In horizontal bisection, patients with left neglect typically show a rightward bias for both lines and words, greater with longer stimuli. As for radial bisection, available data indicate that neurologically unimpaired participants make a distal error, while results from right‐brain‐damaged patients with left spatial neglect are contradictory. We investigated the bisection of radially oriented words, with the prediction that, during bisection, linguistic material would be recoded to its canonical left‐to‐right format in reading, with the performance of neglect patients being similar to that for horizontal words. Thirteen right‐brain‐damaged patients (seven with left spatial neglect) and fourteen healthy controls were asked to manually bisect 40 radial and 40 horizontal words (5–10 letters), and 80 lines, 40 radial and 40 horizontal, of comparable length. Right‐brain‐damaged patients with spatial neglect exhibited a proximal bias in the bisection of short radial words, with the proximal part corresponding to the final right part of horizontally oriented words. This proximal error was not found in patients without neglect and healthy controls. For bisection, short radial words may be recoded to the canonical orthographic horizontal format, unveiling the impact of left neglect on radially oriented stimuli.     

How does reading direction modulate perceptual asymmetry effects?

Left-side bias effects refer to a bias towards the left side of the stimulus/space in perceptual/visuospatial judgments, and are argued to reflect dominance of right hemisphere processing. It remains unclear whether reading direction can also account for the bias effect. Previous studies comparing readers of languages read from left to right with those read from right to left (e.g., French vs. Hebrew) have obtained inconsistent results. As a language that can be read from left to right or from right to left, Chinese provides a unique opportunity for a within-culture examination of reading direction effects. Chinese participants performed a perceptual judgment task (with both face and Chinese character stimuli; Experiment 1) and two visuospatial attention tasks (the greyscales and line bisection tasks; Experiment 2) once before and once after a reading task, in which they read Chinese passages either from left to right or from right to left for about 20 min. After reading from right to left, participants showed significantly reduced left-side bias in Chinese character perceptual judgments but not in the other three tasks. This effect suggests that the role of reading direction on different forms of left-side bias may differ, and its modulation may be stimulus-specific.     

Lateral biases and reading direction: a dissociation between aesthetic preference and line bisection

Perceptual asymmetries for tasks involving aesthetic preference or line bisection can be affected by asymmetrical neurological mechanisms or left/right reading habits. This study investigated the relative contribution of these mechanisms in 100 readers of Japanese and English. Participants made aesthetic judgments between pairs of mirror-reversed pictures showing: (a) static objects, (b) moving objects and (c) landscapes. A line bisection task was also administered. There was a strong effect of reading direction for static and mobile objects whereby Japanese readers preferred objects with a right-to-left directionality (and vice versa for English readers). In contrast, similar patterns were observed for the Japanese and English readers for the landscape and line bisection tasks. The results show that reading habits affect aesthetic judgments for static and moving object tasks, but not the landscape and line bisection tasks. The difference between the tasks may be related to the horizontal/vertical geometry of the stimuli, which makes the landscape and line bisection tasks more prone to universal effects related to cerebral dominance.     

The effects of focal and global attentional systems on spatial biases

The background page on which a stimulus is presented can influence the allocation of attention to that stimulus. The purpose of this study was to learn if there are hemispheric asymmetries in how background distraction affects attentional processing. Asymmetries were investigated by having right eye dominant subjects perform line bisections and manipulating the side of background distraction (right versus left), the eye of regard (right versus left), and the type of attention allocated (focal versus global). Overall subjects bisected lines to the left of center (pseudoneglect) and when viewing with the right eye (versus left) deviated more to the left. Subjects had more background distraction when viewing symbol than solid lines. Although overall, bias did not differ with the side of background distraction or the line being on one side or the other, when subjects viewed symbol, but not solid lines, this leftward bias was increased when the line was displaced to the right, thereby increasing the size of the left sided background. These findings suggest that when engaging the left hemisphere by using focused attention and placing the line on the right side, there is more distraction than when the right hemisphere is engaged.     

Visual-perceptual abilities in healthy controls, depressed patients, and schizophrenia patients

Previous studies have suggested a right hemineglect in schizophrenia, however few assessed possible visual-perceptual implication in this lateralized anomaly. A manual line bisection without (i.e., lines presented on their own) or with a local cueing paradigm (i.e., a number placed at one or both ends of the line) and the Motor-free Visual Perceptual Test-Vertical format (MVPT-V) were used to assess the visual-perceptual abilities of healthy controls, schizophrenia and depressed patients. Whereas healthy controls and depressed patients showed a non-significant leftward bias in manual line bisection, schizophrenia patients bisected significantly to the left of the true centre of the line. Interestingly, the pattern of performances in response to the local cueing paradigm was similar in depressed and schizophrenia patients such that both groups demonstrated a significant change in their bisection performance only in response to a cue placed at the right extremity of the line (control performance was modified by cues at either end of the line). Finally, in the MVPT-V, schizophrenia patients were impaired relative to the other two groups, especially in the spatial working memory and visual closure categories. These results suggest that: 1/a deficit towards the right hemifield, consistent with a mild form of right hemineglect, can be observed in schizophrenia; 2/lateralized anomalies could also be observed in depression using an appropriate tool such as manual line bisection; 3/performances in the MVPT-V suggested that a simple visual-perceptual deficit could not explain the lateralized anomaly observed in the manual line bisection, as it is the case in the hemineglect syndrome.     

Crossover by Line Length and Spatial Location

It is well known that line length has a systematic influence on line bisection error in neglect. Most patients with neglect misbisect long lines on the same side of true center as their brain lesion but then cross over on short lines, misbisecting them on the opposite side (i.e., crossover by line length). What is less recognized is that the spatial location of lines relative to the viewer can similarly induce a crossover effect when one considers line bisection error scores that have been averaged across individual line lengths. Patients with right hemisphere injury and neglect classically make averaged line bisection errors that fall right of true center on lines located either at midline or to the left of the viewer; however, we observed that the averaged line bisection error can fall left of true center when lines are located to the right of the viewer (i.e., crossover by spatial location). We hypothesized that crossover by both line length and spatial location stem from systematic errors in magnitude estimation, i.e., perceived line length. We tested predictions based on this hypothesis by examining how the crossover effect by line length is altered by the spatial location of lines along a horizontal axis relative to the viewer. Participants included patients with unilateral lesions of the right and left cerebral hemispheres and age-appropriate normal subjects. All groups demonstrated a crossover effect by line length at the midline location but the effect was altered by placing lines to the right and left of the viewer. In particular, patients with right hemisphere injury and neglect crossed-over across a broader range of line lengths when the lines were located to the right of the viewer rather than at either midline or left of the viewer. It is proposed that mental representations of stimulus magnitude are altered in neglect, in addition to mental representations of space, and that traditional accounts of neglect can be enhanced by including the psychophysical concept of magnitude estimation.     

Mental representation of a line when patients with left unilateral spatial neglect bisect it: A study with an endpoint reproduction task

Patients with left unilateral spatial neglect (USN) typically place the subjective midpoint to the right of the objective centre. Based on the previous findings (e.g., Ishiai et al. 1989, Brain, 112, 1485), we hypothesized that the patients with left USN may see the representational image of a line that extends equally towards either side of the subjective midpoint depending not upon the information about the leftward extent. The present study tested whether patients with left USN would place the subjective midpoint at the centre of their mental representation of the line. The participants were 10 patients with left USN and 10 neurologically healthy controls. We devised a new ‘endpoint reproduction task’ using a computer display with a touch panel to seek the representational image when patients with left USN bisect lines and asked the participants to reproduce the location of the right or left endpoint after bisecting lines. The results showed that the representational image of the bisected line depends primarily on the location of the objective right endpoint, not on the location of the objective left endpoint in space. The analyses of the estimated right and left representational extents confirmed our hypotheses that patients with left USN would bisect a line seeing the representational line image that centred across their subjective midpoint. We believe that the findings of the present study with the use of the endpoint reproduction task will contribute to a better understanding of the visuospatial process underlying line bisection of patients with left USN.     

Directional bias in the mental representation of spatial events: nature or culture?

Previous research has shown a tendency for people to imagine simple sentences as evolving from left to right, with the sentence subject being located to the left of the object. In two cross-cultural studies comparing Italian and Arab participants, we investigated whether this bias is a function of hemispheric specialization or of directionality of written language (left to right in Italian, right to left in Arabic). Both studies found a reversal of directional bias in Arabs. Italians tended to position the subject to the left of the object, and Arabs tended to position the subject to the right of the object (Experiment 1); both groups were facilitated in a sentence-picture matching task when the subject was drawn in the position that it would usually occupy in the written language (left for Italians, right for Arabs; Experiment 2). In Experiment 2, an additional, language-independent facilitation was observed when action evolved from left to right, suggesting that both hemispheric specialization and scanning habit affect visual imaging.     

Order information in verbal working memory shifts the subjective midpoint in both the line bisection and the landmark tasks

A largely substantiated view in the domain of working memory is that the maintenance of serial order is achieved by generating associations of each item with an independent representation of its position, so-called position markers. Recent studies reported that the ordinal position of an item in verbal working memory interacts with spatial processing. This suggests that position markers might be spatial in nature. However, these interactions were so far observed in tasks implying a clear binary categorization of space (i.e., with left and right responses or targets). Such binary categorizations leave room for alternative interpretations, such as congruency between non-spatial categorical codes for ordinal position (e.g., begin and end) and spatial categorical codes for response (e.g., left and right). Here we discard this interpretation by providing evidence that this interaction can also be observed in a task that draws upon a continuous processing of space, the line bisection task. Specifically, bisections are modulated by ordinal position in verbal working memory, with lines bisected more towards the right after retrieving items from the end compared to the beginning of the memorized sequence. This supports the idea that position markers are intrinsically spatial in nature.     

The influence of emotional faces on the spatial allocation of attention

Background objectives: Studies suggest that the right hemisphere is dominant for emotional facial recognition. In addition, whereas some studies suggest the right hemisphere mediates the processing of all emotions (dominance hypothesis), other studies suggest that the left hemisphere mediates positive emotions the right mediates negative emotions (valence hypothesis). Since each hemisphere primarily attends to contralateral space, the goals of this study was to learn if emotional faces would induce a leftward deviation of attention and if the valence of facial emotional stimuli can influence the normal viewer’s spatial direction of attention. Methods: Seventeen normal right handed participants were asked to bisect horizontal lines that had all combinations of sad, happy or neutral faces at ends of these lines. During this task the subjects were never requested to look at these faces and there were no task demands that depended on viewing these faces. Results: Presentation of emotional faces induced a greater leftward deviation compared to neutral faces, independent of where (spatial position) these faces were presented. However, faces portraying negative emotions tended to induce a greater leftward bias than positive emotions. Conclusions: Independent of location, the presence of emotional faces influenced the spatial allocation of attention, such that normal subjects shift the direction of their attention toward left hemispace and this attentional shift appears to be greater for negative (sad) than positive faces (happy).     

Effects of visual complexity and sublexical information in the occipitotemporal cortex in the reading of Chinese phonograms: a single-trial analysis with MEG

We employ a linear mixed-effects model to estimate the effects of visual form and the linguistic properties of Chinese characters on M100 and M170 MEG responses from single-trial data of Chinese and English speakers in a Chinese lexical decision task. Cortically constrained minimum-norm estimation is used to compute the activation of M100 and M170 responses in functionally defined regions of interest. Both Chinese and English participants’ M100 responses tend to increase in response to characters with a high numbers of strokes. English participants’ M170 responses show a posterior distribution and only reflect the effect of the visual complexity of characters. On the other hand, the Chinese participants’ left hemisphere M170 is increased when reading characters with high number of strokes, and their right hemisphere M170 is increased when reading characters with small combinability of semantic radicals. Our results suggest that expertise with words and the decomposition of word forms underlies processing in the left and right occipitotemporal regions in the reading of Chinese characters by Chinese speakers.     

The relationship between vertical stimulation and horizontal attentional asymmetries

The original aim was to examine the effect of perceived distance, induced by the Ponzo illusion, on left/right asymmetries for line bisection. In Experiment 1, university students (n?=?29) made left/right bisection judgements for lines presented in the lower or upper half of the screen against backgrounds of the Ponzo stimuli, or a baseline. While the Ponzo illusion had relatively little effect on line bisection, elevation in the baseline condition had a strong effect, whereby the leftward bias was increased for upper lines. Experiment 2 (n?=?17) eliminated the effect of elevation by presenting the line in the middle and moving the Ponzo stimuli relative to the line. Despite this change, the leftward bias was still stronger in the upper condition in the baseline condition. The final experiment (n?=?17) investigated whether upper/lower visual stimulation, which was irrelevant to the task, affected asymmetries for line bisection. The results revealed that a rectangle presented in the upper half of the screen increased the leftward line bisection bias relative to a baseline and lower stimulation condition. These results corroborate neuroimaging research, showing increased right parietal activation associated with shifts of attention into the upper hemispace. This increased right parietal activation may increase the leftward attentional bias—resulting in a stronger leftward bias for line bisection.     

Hemispheric specialization for reading

Behavioral laterality tasks with linguistic stimuli were used to assess the differential processing efficiencies of the cerebral hemispheres in right- and left-handed adults. Findings from a lateralized lexical decision task with concrete nouns supported Zaidel's (1983) "direct access" model of hemispheric functioning. A dual task consisting of oral and silent reading indicated that the right hand was significantly more disrupted than the left during unimanual finger tapping; however, some bilateral interference was observed. Taken together the findings suggest that although the left hemisphere was relatively more efficient, the right hemisphere was dynamically involved in the reading process.     

Hemispheric Differences in the Recognition of Environmental Sounds

ABSTRACT— Recent work has found support for two dissociable and parallel neural subsystems underlying object and shape recognition in the visual domain: an abstract-category subsystem that operates more effectively in the left cerebral hemisphere than in the right, and a specific-exemplar subsystem that operates more effectively in the right hemisphere than in the left. Evidence of this asymmetry has been observed for linguistic stimuli (words, pseudoword forms) and nonlinguistic stimuli (objects). In the auditory domain, we previously found hemispheric asymmetries in priming effects using linguistic stimuli (spoken words). In the present study, we conducted four long-term repetition-priming experiments to investigate whether such hemispheric asymmetries would be observed for nonlinguistic auditory stimuli (environmental sounds) as well. The results support the dissociable-subsystems theory. Specificity effects were obtained when sounds were presented to the left ear (right hemisphere), but not when sounds were presented to the right ear (left hemisphere). Theoretical implications are discussed.     

Right hemisphere participation in reading

This study examined whether the right hemisphere's contribution to lexical semantic processing is greatest when it is "disinhibited." Skilled reading may require the controlled modulation of interhemispheric interaction: the left hemisphere (or some other control mechanism) may regulate the subprocesses of reading by selectively "inhibiting" and "disinhibiting" right hemisphere function. Right-handed undergraduates concurrently performed two tasks: a lateralized semantic or rhyme task and a verbal memory task. It was hypothesized that right hemisphere reading processes would be disinhibited when the left hemisphere was "occupied" with the memory task. This hypothesis was supported for a subgroup of subjects who showed evidence of inhibition of right hemisphere function (i.e., left hemisphere dominance for lexical processing) when the lateralized semantic task was performed alone. Across subjects, there was a strong correlation between the degree of left hemisphere dominance in the single-task semantic conditions and the degree of disinhibition of right hemisphere function in the dual-task semantic condition.     

Spoken syntax in children with acquired unilateral hemisphere lesions

The spoken syntax of eight left hemisphere lesioned and eight right hemisphere lesioned children were compared to matched controls. The children's lesions were acquired between 0.08 and 6.17 years of age (mean = 1.33 years), and at the time of testing they were between 1.67 and 8.15 years of age (mean = 4.19). Based on analyses of spontaneous language samples, left hemisphere lesioned subjects performed more poorly than did their controls on most measures of simple and complex sentence structure. In contrast right lesioned subjects performed similarly to their controls on these measures, except for a tendency to make more errors in simple sentence structures. These findings provide further evidence that the left and right hemispheres are not comparable in supporting syntactic abilities.     

Written language acquisition after left or right hemidecortication in infancy

When written language is acquired in only one hemisphere because of hemidecortication in infancy, the left hemisphere is superior to the right at using morphophonemic rules to read and spell unfamiliar words, and at exploiting the structure of sentence units to achieve rapid reading of meaning in prose. The ability to learn names for logographs, however, is better in the right hemisphere than in the left. The greater mastery of written language in the left hemisphere is a result, not of an enhanced facility for making cross-modal associations between sounds and signs, but of a superior access to the morphophonemic rule system and the higher-order textual constraints of English.     

Perceptual-attentional and motor-intentional bias in near and far space

Spatial bias demonstrated in tasks such as line-bisection may stem from perceptual-attentional (PA) "where" and motor-intentional (MI) "aiming" influences. We tested normal participants' line bisection performance in the presence of an asymmetric visual distracter with a video apparatus designed to dissociate PA from MI bias. An experimenter stood as a distractor to the left or right of a video monitor positioned in either near or far space, where participants viewed lines and a laser point they directed under (1) natural and (2) mirror-reversed conditions. Each trial started with the pointer positioned at either the top left or top right corner of the screen, and alternated thereafter. Data analysis indicated that participants made primarily PA leftward errors in near space, but not in far space. Furthermore, PA, but not MI, bias increased bilaterally in the direction of distraction. In contrast, MI, but not PA, bias was shifted bilaterally in the direction of startside. Results support the conclusion that a primarily PA left sided bias in near space is consistent with right hemisphere spatial attentional dominance. A bottom-up visual distractor specifically affected PA "where" spatial bias while top-down motor cuing influenced MI "aiming" bias.     

Extra‐powerful on the visuo‐perceptual space,but variable on the number space: Different effects of optokinetic stimulation in neglect patients

We studied the effects of optokinetic stimulation (OKS; leftward, rightward, control) on the visuo‐perceptual and number space, in the same sample, during line bisection and mental number interval bisection tasks. To this end, we tested six patients with right‐hemisphere damage and neglect, six patients with right‐hemisphere damage but without neglect, and six neurologically healthy participants. In patients with neglect, we found a strong effect of leftward OKS on line bisection, but not on mental number interval bisection. We suggest that OKS influences the number space only under specific conditions.