Bisection and perception of horizontal lines in normal children

A meta-analysis of the line bisection task in children

Meta-analyses have shown subtle, group-level asymmetries of spatial attention in adults favouring the left hemispace (pseudoneglect). However, no meta-analysis has synthesized data on children. We performed a random-effects meta-analysis of spatial biases in children aged ≤16 years. Databases (PsycINFO, Web of Science & Scopus) and pre-print servers (bioRxiv, medRxiv & PsyArXiv) were searched for studies involving typically developing children with a mean age of ≤16, who were tested using line bisection. Thirty-three datasets, from 31 studies, involving 2101 children, were included. No bias was identified overall, but there was a small leftward bias in a subgroup where all children were aged ≤16. Moderator analysis found symmetrical neglect, with right-handed actions resulting in right-biased bisections, and left-handed actions in left-biased bisections. Bisections were more leftward in studies with a higher percentage of boys relative to girls. Mean age, hand preference, and control group status did not moderate biases, and there was no difference between children aged ≤7 and ≥7 years, although the number of studies in each moderator analysis was small. There was no evidence of small study bias. We conclude that pseudoneglect may be present in children but is dependent on individual characteristics (sex) and/or task demands (hand used).Registration: Open Science Framework (https://osf.io/n68fz/).

Developmental changes in neural lateralization for visual-spatial function: Evidence from a line-bisection task

Studies of hemispheric specialization have traditionally cast the left hemisphere as specialized for language and the right hemisphere for spatial function. Much of the supporting evidence for this separation of function comes from studies of healthy adults and those who have sustained lesions to the right or left hemisphere. However, we know little about the developmental origins of lateralization. Recent evidence suggests that the young brain represents language bilaterally, with 4-6-year-olds activating the left-hemisphere regions known to support language in adults as well as homotopic regions in the right hemisphere. This bilateral pattern changes over development, converging on left-hemispheric activation in late childhood. In the present study, we ask whether this same developmental trajectory is observed in a spatial task that is strongly right-lateralized in adults-the line bisection (or "Landmark") task. We examined fMRI activation among children ages 5-11 years as they were asked to judge which end of a bisected vertical line was longer. We found that young children showed bilateral activation, with activation in the same areas of the right hemisphere as has been shown among adults, as well as in the left hemisphere homotopic regions. By age 10, activation was right-lateralized. This strongly resembles the developmental trajectory for language, moving from bilateral to lateralized activation. We discuss potential underlying mechanisms and suggest that understanding the development of lateralization for a range of cognitive functions can play a crucial role in understanding general principles of how and why the brain comes to lateralize certain functions.

Signatures of functional visuospatial asymmetries in early infancy

Adults present a large number of asymmetries in visuospatial behavior that are known to be supported by functional brain lateralization. Although there is evidence of lateralization for motor behavior and language processing in infancy, no study has explored visuospatial attention biases in the early stages of development. In this study, we tested for the presence of a leftward visuospatial bias (i.e., pseudoneglect) in 4- and 5-month-old infants using an adapted version of the line bisection task. Infants were trained to identify the center of a horizontal line (Experiment 1) while their eye gazes were monitored using a remote eye-tracking procedure to measure their potential gazing error. Infants exhibited a robust pseudoneglect, gazing leftward with respect to the veridical midpoint of the horizontal line. To investigate whether infants' pseudoneglect generalizes to any given object or is dependent on the horizontal dimension, in Experiment 2 we assessed infants' gaze deployment in vertically oriented lines. No leftward bias was found, suggesting that early visuospatial attention biases in infancy are constrained by the orientation of the visual plane in which the information is organized. The interplay between biological and cultural factors that might contribute to the early establishment of the observed leftward bias in the allocation of visuospatial attention is discussed.

Development of spatial biases in school-aged children

In the adult brain, biases in the allocation of spatial attention can be measured using a line bisection task and are directly relatable to neural attention signals in the fronto-parietal attention network. Behavioral studies on the development of spatial biases have yielded a host of inconsistent results, likely due to variance in sample size, definition of experimental groups, and motor confounds introduced by using a paper-and-pencil version of a line bisection task. Here, we used a perceptual, computerized version of this task and examined the development of spatial biases in 459 children from grades 1-8 and 61 college freshmen. We found that children in early elementary grades exerted a significant leftward bias that gradually diminished with advancing grade level. We further show that among children in early elementary school grades, the degree of leftward spatial bias predicted better performance on a rapid automatized naming test, a predictor of reading ability. Significant leftward biases in early elementary school grades may be due to reading experience, thereby reflecting an interaction of the attention network with the evolving reading network.

Examining handedness and sex-related effects on line-bisection in childhood

Eighty-eight Bulgarian children (range 5 – 7 years old), 40 left handers (18 boys) and 48 right handers (26 boys), completed line-bisection test one time with each hand. In accordance with previous studies the results show that the majority of children demonstrated deviation to the left of the true center with the left hand and to the right with the right hand, suggesting symmetrical neglect. Sex, handedness and their interaction had no main effect on mean percentage deviation scores at the group level, but only sex had a significant impact on the frequency of symmetrical neglect (p < .05), with higher one in girls than in boys.

Cognitive Mechanisms Underlying Directional and Non-directional Spatial-Numerical Associations across the Lifespan

There is accumulating evidence suggesting an association of numbers with physical space. However, the origin of such spatial-numerical associations (SNAs) is still debated. In the present study we investigated the development of two SNAs in a cross-sectional study involving children, young and middle-aged adults as well as the elderly: (1) the SNARC (spatial-numerical association of response codes) effect, reflecting a directional SNA; and (2) the numerical bisection bias in a line bisection task with numerical flankers. Results revealed a consistent SNARC effect in all age groups that continuously increased with age. In contrast, a numerical bisection bias was only observed for children and elderly participants, implying an U-shaped distribution of this bias across age groups. Additionally, individual SNARC effects and numerical bisection biases did not correlate significantly. We argue that the SNARC effect seems to be influenced by longer-lasting experiences of cultural constraints such as reading and writing direction and may thus reflect embodied representations. Contrarily, the numerical bisection bias may originate from insufficient inhibition of the semantic influence of irrelevant numerical flankers, which should be more pronounced in children and elderly people due to development and decline of cognitive control, respectively. As there is an ongoing debate on the origins of SNAs in general and the SNARC effect in particular, the present results are discussed in light of these differing accounts in an integrative approach. However, taken together, the present pattern of results suggests that different cognitive mechanisms underlie the SNARC effect and the numerical bisection bias.

Perceptual asymmetries and handedness: a neglected link?

Healthy individuals tend to weigh in more the left than the right side of visual space in a variety of contexts, ranging from pseudoneglect to perceptual asymmetries for faces. Among the common explanations proposed for the attentional and perceptual advantages of the left visual field, a link with the prevalence of right-handedness in humans has never been suggested, although some evidence seems to converge in favor of a bias of spatial attention toward the region most likely coincident with another person's right hand during a face-to-face interaction. Such a bias might imply an increased efficiency in monitoring both communicative and aggressive acts, the right limb being more used than the left in both types of behavior. Although attentional and perceptual asymmetries could be linked to right-handedness at the level of phylogeny because of the evolutionarily advantage of directing attention toward the region where others' dominant hand usually operates, it is also legitimate to question whether, at the ontogenetic level, frequent exposure to right-handed individuals may foster leftward biases. These views are discussed in the light of extant literature, and a number of tests are proposed in order to assess our hypotheses.

Hand preference, performance abilities, and hand selection in children

It is widely know that the pattern of human handedness is such that approximately 90% of the population is right handed with the remainder being left handed, at least in the adult population. What is less well understood is how handedness develops and at what age adult-like handedness patterns emerge. Quantified in terms of both preference and performance, a plethora of different behavioral assessments are currently in use with both children and adults. Handedness questionnaires are commonly used; however, these possess inherent limitations, considering their subjective nature. Hand performance measures have also been implemented; however, such tasks appear to measure different components of handedness. In addition to these traditional measures, handedness has been successfully assessed through observation of hand selection in reaching, which has proven to be a unique and effective manner in understanding the development of handedness in children. Research over the past several decades has demonstrated that young children display weak, inconsistent hand preference tendencies and are slower with both hands. Performance differences between the hands are larger for young children, and consistency improves with age. However, there remains some controversy surrounding the age at which hand preference and hand performance abilities can be considered fully developed. The following paper will provide a review of the literature pertaining to hand preference, performance abilities and hand selection in children in an attempt to ascertain the age at which adult-like patterns of hand preference and performance emerge.

Representational pseudoneglect: a review

Pseudoneglect, the tendency to be biased towards the left-hand side of space, is a robust and consistent behavioural observation best demonstrated on the task of visuospatial line bisection, where participants are asked to centrally bisect visually presented horizontal lines at the perceived centre. A number of studies have revealed that a representational form of pseudoneglect exists, occurring when participants are asked to either mentally represent a stimulus or explore a stimulus using touch in the complete absence of direct visuospatial processing. Despite the growing number of studies that have demonstrated representational pseudoneglect there exists no current and comprehensive review of these findings and no discussion of a theoretical framework into which these findings may fall. An important gap in the current representational pseudoneglect literature is a discussion of the developmental trajectory of the bias. The focus of the current review is to outline studies that have observed representational pseudoneglect in healthy participants, consider a theoretical framework for these observations, and address the impact of lifespan factors such as cognitive ageing on the phenomenon.

Spatial attention: differential shifts in pseudoneglect direction with time-on-task and initial bias support the idea of observer subtypes

Asymmetry in human spatial attention has long been documented. In the general population the majority of individuals tend to misbisect horizontal lines to the left of veridical centre. Nonetheless in virtually all previously reported studies on healthy participants, there have been subsets of people displaying rightward biases. In this study, we report differential time-on task effects depending on participants' initial pseudoneglect bias: participants with an initial left bias in a landmark task (in which they had to judge whether a transection mark appeared closer to the right or left end of a line) showed a significant rightward shift over the course of the experimental session, whereas participants with an initial right bias shifted leftwards. We argue that these differences in initial biases as well as the differential shifts with time-on task reflect genuine observer subtypes displaying diverging behavioural patterns. These observer subtypes could be driven by differences in brain organisation and/or lateralisation such as varying anatomical pathway asymmetries (Thiebaut de Schotten et al., 2011).

Left hand dominance affects supra-second time processing

Previous studies exploring specific brain functions of left- and right-handed subjects have shown variances in spatial and motor abilities that might be explained according to consistent structural and functional differences. Given the role of both spatial and motor information in the processing of temporal intervals, we designed a study aimed at investigating timing abilities in left-handed subjects. To this purpose both left- and right-handed subjects were asked to perform a time reproduction of sub-second vs. supra-second time intervals with their left and right hand. Our results show that during processing of the supra-second intervals left-handed participants sub-estimated the duration of the intervals, independently of the hand used to perform the task, while no differences were reported for the sub-second intervals. These results are discussed on the basis of recent findings on supra-second motor timing, as well as emerging evidence that suggests a linear representation of time with a left-to-right displacement.

The effects of reading-writing direction on the asymmetry of space perception and directional tendencies: A comparison between French and Tunisian children

We compared the influence of reading and writing habits on the asymmetry of space perception and the directional tendencies of French and Tunisian right-handers, aged 5, 7, and 9 years. By comparing two groups of children who use the opposite direction for writing (from left to right for French, from right to left for Arabic), before and after being taught to read in school, we evaluated the impact of writing direction on these asymmetries. A bisection task, a circle-drawing task, and a dot-filling task were used to assess spatial asymmetries and directional tendencies. On the bisection task, a group difference emerged at 9 years, with the French children bisecting the line to the left of the true centre, and the Tunisian children showing no bias. On the circle-drawing task, there was a group difference from 7 years on, as the French children, but not the Tunisian children, used increasing counterclockwise movements. Finally, on the dot-filling task performed with the right hand, the French children filled in significantly more dots when going from left to right from 7 years on, whereas Tunisian children filled in more dots when going from right to left. These results show the impact of basic tendencies in younger children (ipsilateral bias in line bisection, clockwise direction in circle drawing, outward tendency for horizontal displacement in dot filling), as well as the impact of writing direction on spatial asymmetries after learning to read. The results are also discussed in reference to the differences between the two languages, the closeness of the French direction of writing to spontaneous neural-based tendencies, and the influence of learning French at age 8 for the Tunisian children.

Corpus Callosum Maturation and Line Bisection Performance in Healthy Children

Line bisection performance in children has been hypothesized to be a measure of corpus callosum maturation. Several previous studies have shown that normal prepubescent children bisect lines to the right of true center with their right hand and to the left with their left hand (symmetrical neglect). In contrast, children entering puberty reportedly bisect lines to the left with both the right and left hands (pseudoneglect). The shift from symmetrical to pseudoneglect has been hypothesized to reflect corpus callosum maturation and its involvement in the transfer of attention-based visuospatial processes. In the current study, line bisection performance and MR quantitative corpus callosum volumes were examined in 46 healthy children ages 8-18 years. A linear relationship between corpus callosum volume and age was found. However, the expected age-contingent line bisection performance pattern was not observed. In addition to the expected two patterns of line bisection bias, pseudoneglect and symmetric neglect, two additional distinct patterns of line bisection were identified. These findings, and other findings in the literature, raise important questions about the reliability and validity of the line bisection test. No relationship was found between corpus callosum volume and amount or direction of line bisection deviation. Our findings do not support previous hypotheses regarding line bisection-corpus callosum relationship.

Differences in paper-and-pencil versus computerized line bisection according to ADHD subtype and hand-use

Two versions of the line bisection task, paper-and-pencil and computerized, were administered to non-medicated children (5-12 years) with and without Attention-Deficit/Hyperactivity Disorder (ADHD). Fifteen children were classified with ADHD-Inattentive type (ADHD-I), 15 were classified with ADHD-Combined or Hyperactive-Impulsive type (ADHD-C), and 15 children served as controls. During the paper-and-pencil task, and irrespective of hand-use, participants with ADHD-C bisected lines with a right bias, whereas participants with ADHD-I showed a leftwards bias. Interestingly, during the computerized version, an opposite pattern of hemineglect was observed with a leftwards bias for participants with ADHD-C and a rightwards bias for participants with ADHD-I. These findings suggest that different task demands are associated with the paper-and-pencil and computerized tasks. The findings also suggest that the two subtypes differ according to their cognitive profile, and possibly differ as to their underlying neural impairment.

Developmental changes in visual line bisection in women throughout adulthood

It has been suggested that some hemispheric asymmetries change in a systematic way from young adulthood to older age. However, little is known whether these changes are due to differential aging of a single hemisphere or based on age-related alterations of interhemispheric interactions. A sample of 281 right-handed neurologically healthy participants (151 women), ranging from age 20 to 79, was investigated with a line-bisection task. Previous studies indicate the midpoint estimation shows a consistent leftward bias from the veridical center, which is accentuated when the left hand is used to bisect lines. These findings support the view of a right hemispheric superiority in spatial attention. This study revealed this pattern to be stable in men throughout adulthood. However, women from 50 to 69 years of age showed a reduced leftward bias and a reduced hand effect compared to men and younger women. The results suggest that developmental changes in hemispheric asymmetry of spatial attention are more pronounced in women and support the view that neuromorphological changes during adulthood differ between sexes.

Peripersonal spatial attention in children with spina bifida: associations between horizontal and vertical line bisection and congenital malformations of the corpus callosum, midbrain, and posterior cortex

Horizontal and vertical line bisection was studied in 129 children and adolescents between 8 and 19 years of age, one group (n=32) of typically developing controls and one group (n=97) with spina bifida (SBM), a neurodevelopmental disorder associated with dysmorphology of the corpus callosum, posterior cortex, and midbrain. For each participant, structural brain MRIs were analyzed qualitatively to identify beaking of the midbrain tectum and corpus callosum agenesis and hypoplasia and quantitatively by segmentation and volumetric analyses of regional cortical white and gray matter. Each group showed the line length effect, whereby greater estimation errors are made with longer lines. The group with SBM differed from controls in terms of both accuracy and variability of line bisection. Children with SBM showed pseudoneglect, attending more than controls to left hemispace. The extent of rightward bisection bias was unrelated to right posterior brain volumes, although an intact corpus callosum during development moderated and normalized the exaggerated leftward line bisection bias. More children with SBM than controls attended to inferior hemispace. A normal midbrain and greater posterior cortex volume during development moderated and normalized the downward bias. Children with SBM showed more intra-subject variability than controls. Line bisection in children with SBM reflects three deficits: an exaggerated attentional bias to left hemispace, an abnormal attentional bias to inferior hemispace; and a larger zone of subjective uncertainty in bisection judgments.

Asymmetric deterioration of spatial awareness with diminishing levels of alertness in normal children and children with ADHD

BACKGROUND

There is growing literature suggesting that some children diagnosed with attention deficit hyperactivity disorder (ADHD) can show a significant bias in attention away from left space. Here we examine mechanisms that may underpin these effects in both clinical and non-clinical child populations. Unilateral spatial inattention (unilateral neglect) is a commonly reported consequence of stroke in adults. Although for most patients the problem is relatively transient, persistent forms of neglect are almost exclusively associated with right hemisphere lesions. It has been suggested that this chronicity may result from co-existing disruption to right hemisphere dominant systems that mediate alertness. Here we present two studies examining the relationship between sustained attention and left spatial awareness in childhood.

METHOD

In the first, normal children without the ADHD diagnosis were administered a non-spatial test of sustained attention/alertness. Children who performed poorly at this task, relative to their more attentive peers, showed a modest but reliable delay in awareness of left-sided visual information. Furthermore, attention towards the left declined for both groups as a function of time-on-task, suggesting a significant within-subject modulatory effect of alertness on spatial awareness. The second study examines this relationship in children referred to clinical services for attention problems. Irrespective of their final diagnosis, children were divided into two groups according to their performance in sustained attention/alertness tasks.

RESULTS

The results suggest that, regardless of the children's clinical diagnosis, diminished sustained attention/alertness levels formed the strongest predictor of relatively delayed awareness of information presented within left visual space. Two children within this group exhibited signs of hitherto undetected spatial neglect as severe as that observed in some brain-injured adults.

CONCLUSIONS

Clinical and theoretical implications are discussed.

Visual line bisection in sinistrals and dextrals as a function of hemispace, hand, and scan direction

Visual line bisection was investigated in 26 sinistral and 24 dextral subjects as a function of hemispace, hand and scan direction. An ANOVA revealed significant main effects for hand preference, due to the mean bisection errors of dextral subjects being significantly leftward of those of sinistral subjects; for hand, due to the bisection errors of the left hand being significantly to the left of the right hand; and for scan, due to the bisection errors following a left scan being significantly to the left of a right scan. One significant interaction was found, that between hand and direction of scan, due to a significant difference between left and right hands following a scan from the left but not following a scan from the right. For dextral subjects the leftward bisection errors of the left and right hands following a scan from the left, but not for a scan from the right, differed significantly from the midpoint. For sinistral subjects the leftward bisection errors following a scan from the left and rightward bisection errors following a scan from the right differed significantly from the midpoint for the left hand but not for the right hand. No significant main effect or interactions for hemispace were found. This confirms that both sinistral and dextral subjects display pseudoneglect when using their preferred hand and scanning from the left. However, sinistrals, but not dextrals, will display reversed pseudoneglect when using their preferred hand and adopting a scan direction from the right. These results are discussed in terms of the interaction between three factors, whose influence can jointly and severally produce misbisections, hemispheric specialisation for visuospatial function, hemispheric activation for a manual response, and the allocation of visual attention.

Hemispheric asymmetry in spatial attention across the menstrual cycle

Functional cerebral asymmetries (FCAs) are known to fluctuate across the menstrual cycle. The mechanisms of these sex hormonal modulations are poorly understood. It has been suggested that gonadal steroid hormones might suppress or specifically activate one hemisphere. However, recent studies suggest that high levels of gonadal steroid hormones reduce FCAs by its modulating effects on cortico-cortical transmission. To investigate the activating effects of gonadal steroid hormones on the interhemispheric interaction, a visual line-bisection task was administered to normally cycling women during menses and the midluteal cycle phase as well as to similar-aged healthy men. The results replicate previous findings of a sex difference in line-bisection as a function of hand-use and show that the hand-use effect fluctuates across the menstrual cycle. High levels of estradiol during the midluteal phase were related to a decrease of the hand-use effect. It is concluded that cycle-related fluctuations in levels of gonadal steroid hormones affect hemispheric asymmetry of spatial attention, presumably by interhemispheric spreading of neuronal activation.

Age and responding-hand related changes in performance of neurologically normal subjects on the line-bisection and chimeric-faces tasks

This study investigated age and responding-hand (left, right, and bimanual) related changes in visuospatial attention. Two tasks were completed by 107 neurologically normal right-handed subjects ranging in age from 5 to 70 years and distributed across four age groups. Task-specific differences between groups were apparent. In the line-bisection task, the younger and older groups displayed symmetrical neglect while the young and middle groups displayed pseudoneglect. In the chimeric-faces task the leftward bias was less pronounced in the older group and more susceptible to responding-hand effects in the middle and older groups. Whilst results, especially those of the bimanual method, provided strong support for an activation model, they imposed an age limitation on its appropriateness as an explanation for performance on the chimeric-faces task. Results are discussed as reflecting changes in the corpus callosum and right hemisphere.

Interaction of hand use and spatial selective attention in children

It has been argued that concurrent motor action can modulate visual spatial attention. The visual spatial biases of adult patients with unilateral neglect, for example, can be ameliorated by simultaneous use of the contralesional hand. Such improvements are most dramatic when the contralesional hand is moved within contralesional space. To date, evidence of such an interaction in neurologically healthy individuals has not been presented. Line bisection is a simple task that is sensitive to attentional spatial bias. When young children are asked to bisect horizontal lines using their right hands, they show a reliable, if small, bias that is consistent with the pattern seen in adult neglect. This bias is reversed when the left hand is used. Here, we show that these effects are significantly modulated by the location of the movements relative to the body mid-line - specifically that the conjunction of hand movements within ipsilateral space is necessary for the previously reported pattern to be observed. We further demonstrate that these effects are not present in the bisections of neurologically healthy adults. In a final study, we examined whether the hand movement effects seen in children's line bisections would persist in a purely visual task (that is when the movements were made irrelevant to the response). Again, significant modulation of children's perception by concurrent hand movements - and the relative location of those movements - was observed. The theoretical and clinical implications of the results are discussed.

Performance consistency of normal observers in forced-choice tachistoscopic visual line bisection

Pseudoneglect (PN) refers to the leftward error exhibited by normal observers on line bisection tasks (Bowers and Heilman, Neuropsychologia, 18, (1980) 491-8). Although a thorough review of the literature has shown PN to be relatively robust (Jewell and McCourt, Neuropsychologia, 38, (2000) 93-110), controversy remains concerning the reliability of the phenomenon, with some studies reporting a relatively high incidence of normal subjects with rightward bisection errors. The present experiment assesses the consistency of bisection performance in normal young observers. Right-handed subjects (N=22) participated in a tachistoscopic forced-choice line bisection task. Each subject participated in 7-16 experimental sessions separated by at least 24 h (total bisection measurements=317). Individual bisection performance could thus be evaluated with respect to within-subject variability measures. An eyetracker recorded gaze position during the task in one session. A highly significant mean group bisection error of -0.26 degrees (P<0.001) was obtained (left negative), and individual subject means ranged from -0.55 degrees to +0.03 degrees. Of the 317 total bisection measurements, 9% (28) deviated rightward. Significant (P<0.05) mean leftward errors occurred in 91% (20/22) of subjects. Mean bisection error in two subjects was not significantly different from zero. No subject possessed a significant rightward error. Mean gaze deviation from screen (and line) center ranged from +/-0.9 degrees, and was positively correlated (P<0.05) with bisection error. It is concluded that forced-choice tachistoscopic line bisection measures are highly reliable; a mean correlation of +0.87 exists between mean error based on 15 trials and means estimated from a random sample of only two trials. The incidence of true rightward bisection error in the population of normal right-handed subjects is thus estimated to be less than 5%.

The influence of unimanual response on pseudoneglect magnitude

Various factors influence the degree of leftward error (pseudoneglect) (Bowers & Heilman, 1980) that typifies the performance of normal subjects in line bisection tasks (Jewell & McCourt, 2000). The results of this experiment show that unimanual responding also exerts a subtle but significant modulating influence on spatial attention, as indexed by the differential magnitude of pseudoneglect. Using a forced-choice tachistoscopic line bisection protocol, 184 subjects (92 male and 92 female) bisected horizontally oriented lines (22.3 degrees wide x 0.39 degrees height) presented to central vision in two conditions, in which bisection responses were executed via button presses using the first two fingers of either the left (LH) or right (RH) hand. Perceived line midpoint deviated significantly leftward of veridical (p <.05) in both conditions. There was no significant influence of subject sex (p >.05). A significant influence of unimanual response was revealed (p <.05) where pseudoneglect magnitude was greater in the LH than the RH condition. The results are interpreted within the framework of the activation-orientation theory of attentional asymmetry.

Asymmetries of visuospatial attention are modulated by viewing distance and visual field elevation: pseudoneglect in peripersonal and extrapersonal space

Many factors influence the degree of leftward error (pseudoneglect) that typifies the line bisection performance of normal subjects. We find that viewing distance also exerts a modulating influence on spatial attention in normal subjects, as it appears to do in neglect syndrome. Using forced-choice tachistoscopic line bisection, 38 right-handed subjects (15 male, 23 female) bisected horizontal lines (13.7 degrees w x 0.24 degrees h) presented in the midsagittal plane as a function of line elevation (- 3.6 degrees, 0 degrees, and 3.6 degrees relative to horizontal midline) and viewing distance (45 and 90 cm). We find a significant main effect of viewing distance, F (1, 37) = 10.04, p = .003, where pseudoneglect is larger in peripersonal (45 cm) than in extrapersonal (90 cm) space. We replicate an effect of line elevation, F (2, 74) = 4.40, p = .016, where pseudoneglect is greatest in the superior visual field (McCourt and Jewell, 1999). The interaction was not significant, p > .05. Thus, we find evidence for independent spatiotopic (viewing distance) and retinotopic (line elevation) effects on line bisection performance in normal observers, suggesting that the allocation of visuospatial attention is modulated within multiple frameworks.

Line bisection performances of 650 normal children

When bisecting lines, an important number of brain damaged patients tend to place their bisection marks in the hemispace ipsilateral to their lesion. Biases have also been reported in normal adults. In vertical bisection both patients and normal subjects present with upward shifts, although a downward displacement may occur eventually. Surprisingly, little is known on line bisection (LB) in normal or brain damaged children. A total of 650 subjects, aged 7-12 years, performed a horizontal and vertical LB task with their preferred hand. Asymmetry indices (AIs) were used to measure directional bias. Unsigned AIs served to evaluate accuracy and mastery of the LB skill. In vertical bisection a general and significant upward bias was found, whereas in horizontal bisection subject (gender, handedness, utilized hand, age) and stimulus variables (orientation, length, position) yielded significantly different AIs. Although with increasing age significantly increasing accuracy was observed, none of the participating children mastered LB to mathematical precision. Differences in IQ-level and attention test score did not yield significantly different AIs. Impact from reading proficiency could not be demonstrated. It is suggested that stimulus length effect results are compatible with the Halligan and Marshall [Halligan, P., and Marshall, J. Toward a principled explanation of unilateral neglect. Cognitive Neuropsychology, 1994, 11, 167-206] model of hemispatial neglect. Moreover, data may support the hypothesis of greater hemispheric specialization of visuo-spatial skills in boys than in girls.

Pseudoneglect: a review and meta-analysis of performance factors in line bisection tasks

An exhaustive qualitative (vote-counting) review is conducted of the literature concerning visual and non-visual line bisection in neurologically normal subject populations. Although most of these studies report a leftward bisection error (i.e., pseudoneglect), considerable between-study variability and inconsistency characterize this literature. A meta-analysis of this same literature is performed in which the total quantitative data set, comprising 73 studies (or sub-studies) and 2191 subjects, is analyzed with respect to 26 performance factors. The meta-analytic results indicate a significant leftward bisection error in neurologically normal subjects, with an overall effect size of between -0.37 and -0.44 (depending on integration method), which is significantly modulated to varying degrees by a number of additional task or subject variables. For example, visual bisection tasks, midsagittal-pointing tasks and tactile bisection tasks all lead to leftward errors, while kinesthetic tasks result in rightward errors. Tachistoscopic forced-choice testing methods reveal much greater estimates of bisection error (effect size = -1.32) than do manual method-of-adjustment procedures (effect size= -0.40). Subject age significantly modulates line bisection performance such that older subjects err significantly rightward compared to younger subjects, and to veridical line midpoint. Male subjects make slightly larger leftward errors than do female subjects. Handedness has a small effect on bisection errors, with dextrals erring slightly further to the left than sinistral subjects. The hand used to perform manual bisection tasks modulated performance, where use of the left hand lead to greater leftward errors than those obtained using the right hand. One of the most significant factors modulating bisection error is the direction in which subjects initiate motor scanning (with either eye or hand), where a left-to-right scan pattern leads to large leftward errors while a right-to-left scan pattern leads to rightward errors.