Visual Line Bisection Task Research Articles

Spatial biases in deaf, blind, and deafblind individuals as revealed by a haptic line bisection task.

In this study, we investigated whether auditory deprivation leads to a more balanced bilateral control of spatial attention in the haptic space. We tested four groups of participants: early deaf, early blind, deafblind, and control (normally hearing and sighted) participants. Using a haptic line bisection task, we found that while normally hearing individuals (even when blind) showed a significant tendency to bisect to the left of the veridical midpoint (i.e., pseudoneglect), deaf individuals did not show any significant directional bias. This was the case of both deaf signers and non-signers, in line with prior findings obtained using a visual line bisection task. Interestingly, deafblind individuals also erred significantly to the left, resembling the pattern of early blind and control participants. Overall, these data critically suggest that deafness induces changes in the hemispheric asymmetry subtending the orientation of spatial attention also in the haptic modality. Moreover, our findings indicate that what counterbalances the right-hemisphere dominance in the control of spatial attention is not the lack of auditory input per se, nor sign language use, but rather the heavier reliance on visual experience induced by early auditory deprivation.

Related but different: Examining pseudoneglect in audition, touch and vision

Although researchers have consistently demonstrated a leftward attentional bias in visual and representational (e.g. tactile/mental number line) line bisection tasks, the results from audition have been mixed. Differences in methodology between auditory and visual bisection tasks, especially with regards to the location of stimuli of peripersonal versus extrapersonal space, have also meant that researchers have not been able to compare performance in visual, tactile and auditory line bisection directly. In this research, 39 neurologically typical individuals participated in standard visual and tactile line bisection tasks, together with a newly developed auditory line bisection task. Results demonstrated significant leftward bisection biases across all three modalities. Hence, we demonstrate auditory pseudoneglect in peripersonal space for the first time. Tactile and auditory line bisections showed a relatively small but statistically reliable correlation, but neither task correlated with visual line bisection. This suggests that the processes underlying auditory line bisection are not synonymous to those involved in visual perceptual bisection, and further we argue that this bias may be related to representational pseudoneglect.

Callosal disconnection neglect: reassessment after 34 years

ABSTRACTIn 1984, Watson and Heilman reported a patient with a partial callosal disconnection following an infarction of the anterior portion of her corpus callosum. This woman’s performance on line-bisection tasks revealed “callosal disconnection neglect.” The objective of this research is to reexamine this woman 34 years after her callosal disconnection to gain information about her recovery. The patient completed visual line-bisection tasks in which horizontal lines were placed in the right, left, and center hemispaces and she performed these bisections using her right or left hand. Unlike her performance 34 years ago in which each hand deviated to its ipsilateral hemispace, with greater deviation when lines were placed in the contralateral rather than ipsilateral hemispace, currently, there were no significant main effects for hand or spatial position. Thus, there were notable differences between this woman’s most recent performance on the line bisection and her previous performance 34 years ago. Unlike her prior testing 34 years back, this woman’s most recent performance resembled the performance of a previous tested healthy control group for whom differences in hand and hemispace were not found. It remains unclear whether her callosal disconnection neglect improved because each hemisphere learned to allocate ipsilateral spatial attention or because she learned a compensatory strategy in which she turned her body so that the lines placed in her right or left hemispace were now toward her midline.

Does gravity influence the visual line bisection task?

The visual line bisection task (LBT) is sensitive to perceptual biases of visuospatial attention, showing slight leftward (for horizontal lines) and upward (for vertical lines) errors in healthy subjects. It may be solved in an egocentric or allocentric reference frame, and there is no obvious need for graviceptive input. However, for other visual line adjustments, such as the subjective visual vertical, otolith input is integrated. We hypothesized that graviceptive input is incorporated when performing the LBT and predicted reduced accuracy and precision when roll-tilted. Twenty healthy right-handed subjects repetitively bisected Earth-horizontal and body-horizontal lines in darkness. Recordings were obtained before, during, and after roll-tilt (±45°, ±90°) for 5 min each. Additionally, bisections of Earth-vertical and oblique lines were obtained in 17 subjects. When roll-tilted ±90° ear-down, bisections of Earth-horizontal (i.e., body-vertical) lines were shifted toward the direction of the head (P < 0.001). However, after correction for vertical line-bisection errors when upright, shifts disappeared. Bisecting body-horizontal lines while roll-tilted did not cause any shifts. The precision of Earth-horizontal line bisections decreased (P ≤ 0.006) when roll-tilted, while no such changes were observed for body-horizontal lines. Regardless of the trial condition and paradigm, the scanning direction of the bisecting cursor (leftward vs. rightward) significantly (P ≤ 0.021) affected line bisections. Our findings reject our hypothesis and suggest that gravity does not modulate the LBT. Roll-tilt-dependent shifts are instead explained by the headward bias when bisecting lines oriented along a body-vertical axis. Increased variability when roll-tilted likely reflects larger variability when bisecting body-vertical than body-horizontal lines.

Music-induced changes in functional cerebral asymmetries

After decades of research, it remains unclear whether emotion lateralization occurs because one hemisphere is dominant for processing the emotional content of the stimuli, or whether emotional stimuli activate lateralised networks associated with the subjective emotional experience. By using emotion-induction procedures, we investigated the effect of listening to happy and sad music on three well-established lateralization tasks. In a prestudy, Mozart’s piano sonata (K. 448) and Beethoven’s Moonlight Sonata were rated as the most happy and sad excerpts, respectively. Participants listened to either one emotional excerpt, or sat in silence before completing an emotional chimeric faces task (Experiment 1), visual line bisection task (Experiment 2) and a dichotic listening task (Experiment 3 and 4). Listening to happy music resulted in a reduced right hemispheric bias in facial emotion recognition (Experiment 1) and visuospatial attention (Experiment 2) and increased left hemispheric bias in language lateralization (Experiments 3 and 4). Although Experiments 1–3 revealed an increased positive emotional state after listening to happy music, mediation analyses revealed that the effect on hemispheric asymmetries was not mediated by music-induced emotional changes. The direct effect of music listening on lateralization was investigated in Experiment 4 in which tempo of the happy excerpt was manipulated by controlling for other acoustic features. However, the results of Experiment 4 made it rather unlikely that tempo is the critical cue accounting for the effects. We conclude that listening to music can affect functional cerebral asymmetries in well-established emotional and cognitive laterality tasks, independent of music-induced changes in the emotion state.

Deaf Individuals Show a Leftward Bias in Numerical Bisection.

Consistent evidence suggests that deaf individuals conceive of numerical magnitude as a left-to-right-oriented mental number line, as typically observed in hearing individuals. When accessing this spatial representation of numbers, normally hearing individuals typically show an attentional bias to the left (pseudoneglect), resembling the attentional bias they show in physical space. Deaf individuals do not show pseudoneglect in representing external space, as assessed by a visual line bisection task. However, whether deaf individuals show attentional biases in representing numerical space has never been investigated before. Here we instructed groups of deaf and hearing individuals to quickly estimate (without calculating) the midpoint of a series of numerical intervals presented in ascending and descending order. Both hearing and deaf individuals were significantly biased toward lower numbers (i.e., the leftward side of the mental number line) in their estimations. Nonetheless, the underestimation bias was smaller in deaf individuals than in the hearing when bisecting pairs of numbers given in descending order. This result may depend on the use of different strategies by deaf and hearing participants or a less pronounced lateralization of deaf individuals in the control of spatial attention.

Visuospatial Attention Deficits in Developmental Dyslexia: Evidence from Visual and Mental Number Line Bisection Tasks

Previous research has shown that individuals with DD (developmental dyslexia) demonstrated a left mini neglect on visual line (VL) bisection tasks, which has been commonly referred to as right parietal dysfunction. However, insufficient reading experience characterizes dyslexia and may call into question the validity of this interpretation, since the VL bisection task has been found to be influenced by reading habits. The current study investigated whether altered performance of individuals with DD on bisection tasks may be attributed to impaired attentional mechanisms or to insufficient reading exposure. DD and control groups performed visual and mental number line bisection tasks, which have been shown to be modulated differently by reading habits. In both tasks, the magnitude of left bisection errors was significantly larger in the DD group compared with controls. This finding suggests attentional mechanisms act differently in dyslexia and supports evidence linking dyslexia to decreased function of the left hemisphere.

Right fronto-parietal dysfunction underlying spatial attention in bipolar disorder

Although the neural underpinning of bipolar disorder (BD) is still unknown, recent research suggests that the right fronto-parietal cortex is particularly affected in BD patients. If this were true, we would expect atypical functional cerebral asymmetries in allocation of visuospatial attention. To test this hypothesis, euthymic BD patients and age- and gender-matched healthy controls were compared on the visual line-bisection task, a reliable measure of visuospatial attention, associated with right parietal function. Line bisection performance (i.e. absolute and directional bias) was compared between groups as a function of response hand and line position. The results showed a typical hand-use effect in healthy controls involving a larger leftward bias (i.e. pseudoneglect) with the left hand than with the right hand. Although euthymic BD patients did not differ from healthy controls in the overall accuracy (i.e. absolute bias), they differed significantly in the directional line bisection bias. In contrast to healthy controls, BD patients did not significantly deviate from the veridical center, regardless of which hand was used to bisect horizontal lines. This finding indicates an atypical functional cerebral asymmetry in visuospatial attention in euthymic BD patients, supporting the idea of a dysfunction especially in the right fronto-parietal cortex.

Hemispatial neglect evaluated by visual line bisection task in schizophrenic patients and their unaffected siblings

Visuospatial attentional asymmetry has been investigated by the line bisection task in patients with schizophrenia, however, those studies are in small number and the results are controversial. The present study aimed to investigate hemispatial neglect in patients with schizophrenia (n=30), their healthy siblings (n=30) and healthy individuals (n=24) by a computerized version of the line bisection task. Deviation from the midline for both hemispaces (mean bisection error—MBE) were calculated and the effects of both hand and line length were controlled. Repeated measures ANOVA yielded a significant hemispace effect for the MBE scores, but no group or group×hemispace interaction effect, i.e., all three groups were inclined to a leftward bias in the left and a rightward bias in the right hemispace. MBEs were significantly different from “zero” only for the right hemispace in siblings and for the left hemispace in controls. Negative symptoms were significantly correlated with the bisection errors in the right hemispace. The results of the present study do not support aberrant hemispheric asymmetry, but bigger bisection errors in schizophrenia.

Oral contraceptive therapy modulates hemispheric asymmetry in spatial attention

Background Functional cerebral asymmetries (FCAs) are known to fluctuate across the menstrual cycle. The visual line-bisection task administered to normally cycling women showed different patterns of the interhemispheric interactions during menses and the midluteal cycle phase. However, the contribution of estrogens and progestins hormones to this phenomenon is still unclear. Study Design The aim of our study was to show a variation of FCAs in women administered oral contraceptives (OCs) using the visual line-bisection task. Visual line-bisection task with three horizontal lines was administered to 36 healthy women taking a 21-day OC. Twenty-nine patients were right handed. The task was administered during OC intake (day 10) and at the end of the pill-free period. Results The right-handed women showed a significant leftward bias of veridical center on the first and third lines during OC intake compared with an opposite rightward bias during the pill-free period. The same phenomenon of contralateral deviation was observed in left-handed women on day 10 of OC intake. Conclusions The results of this study confirm a hormonal modulation on interhemispheric interaction and suggest that OCs may improve the interhemispheric interaction reducing FCAs compared with the low hormone level period. This opens new insights in OC prescription and choice of administration schedule in order to improve cognitive performances.

Hemifield asymmetry in the potency of exogenous auditory and visual cues

Neurologically normal subjects misperceive the midpoints of lines (PSE) as reliably leftward of veridical center, a phenomenon known as pseudoneglect. This leftward bias reflects the dominance of the right cerebral hemisphere in deploying spatial attention. Transient visual cues, delivered to either the left or right endpoints of lines, modulate PSE such that leftward biases are increased by leftward cues, and are decreased by rightward cues, relative to a no-cue control condition. We ask whether lateralized auditory cues can similarly influence PSE in a tachistoscopic visual line bisection task, and describe how visual and auditory cues, in spatially synergistic or antagonistic combinations, jointly influence PSE. Our results demonstrate that whereas auditory and visual cues both modulate PSE, visual cues are overall more potent than auditory cues. Visual and auditory cues are weighted such that visual cues are significantly more potent than auditory cues when visual cues are delivered to left hemispace. Visual and auditory cues are equipotent when visual cues are delivered to right hemispace. These results are consistent with the existence of independent lateralized networks governing the deployment of visuospatial and audiospatial attention. An analysis of the weighting of unisensory visual and auditory cues which optimally predicts PSE in multisensory cue conditions shows that cues combine additively. There was no evidence for a superadditive multisensory cue combination.

Dissociation between visual line bisection and mental number line bisection in schizophrenia

Many studies of hemispatial neglect patients have indicated that spatial attention processes operate similarly in visual space and number space. However, some studies have indicated a dissociation of processing between visual line bisection and mental number bisection. A number of investigations have suggested that schizophrenic patients show a mild right pseudo-neglect on visual line bisection tasks. The present study was designed to determine if a functional link exists between performance of visual line and number line bisection in schizophrenic patients. Groups of 40 schizophrenic patients and 40 controls performed each bisection task. In the visual line bisection task, schizophrenic patients showed a significant leftward bias relative to the healthy controls for 9 different line lengths. No significant difference in bias was found between the 2 groups on the mental line bisection task. These results indicated that schizophrenic patients may exhibit attention deficit with respect to visual space but not number space, suggestive of the dissociation of processing between visual line bisection and mental number line bisection. These results provide more insight into the correlation between the visual line and number bisection tasks in schizophrenic patients.

Biases of spatial attention in vision and audition

Neurologically normal observers misperceive the midpoint of horizontal lines as systematically leftward of veridical center, a phenomenon known as pseudoneglect. Pseudoneglect is attributed to a tonic asymmetry of visuospatial attention favoring left hemispace. Whereas visuospatial attention is biased toward left hemispace, some evidence suggests that audiospatial attention may possess a right hemispatial bias. If spatial attention is supramodal, then the leftward bias observed in visual line bisection should also be expressed in auditory bisection tasks. If spatial attention is modality specific then bisection errors in visual and auditory spatial judgments are potentially dissociable. Subjects performed a bisection task for spatial intervals defined by auditory stimuli, as well as a tachistoscopic visual line bisection task. Subjects showed a significant leftward bias in the visual line bisection task and a significant rightward bias in the auditory interval bisection task. Performance across both tasks was, however, significantly positively correlated. These results imply the existence of both modality specific and supramodal attentional mechanisms where visuospatial attention has a prepotent leftward vector and audiospatial attention has a prepotent rightward vector of attention. In addition, the biases of both visuospatial and audiospatial attention are correlated.

Time-on-task effect in pseudoneglect

Neurologically normal subjects systematically misbisect space during visual line-bisection or similar tasks, generally erring to the left of the veridical center when bisecting horizontal lines, a phenomenon referred to as pseudoneglect. This phenomenon is usually interpreted as enhanced attention toward the left hemispace resulting in an overestimation of the leftward extent of a line. While most studies have examined the role of attention in spatial bias using spatial cueing methods in bisection tasks, Manly et al. (Neuropsychologia 43(12):1721-1728, 2005) proposed an original paradigm in which the participants' alertness was diminished by sleep deprivation or prolonged execution of a line-bisection task. The authors reported a significant rightward shift in attention related to declining alertness, but they did not control eye movements and, consequently, modifications of scanning and fixation strategies with fatigue cannot be ruled out in their study. Here we examine whether a diminution in alertness induced by a 60-min-long Landmark task would diminish (or even reverse) this attentional bias, when eye movements are absent. Participants performed a forced-choice judgment about the location of a transaction mark in relation to the veridical center of a horizontal line. The results confirmed a significant decrease in the leftward bias over the course of the session but, in contrast to the findings of Manly et al. (2005), we did not observe a reverse bias from the left to the right hemispace. The results are discussed within the context of the hemisphere-activation model.

The spatial representation of numerical and non-numerical sequences: Evidence from neglect

Psychophysical and neuropsychological studies have revealed that humans represent numbers along a continuous, left-to-right oriented mental line. However, it has been recently claimed that this format of representation is not special to numbers because non-numerical sequences would be spatially coded in the same way. To test this hypothesis, the present study investigated the effects of left neglect upon the bisection of numerical and non-numerical intervals. Eight patients with left neglect performed a visual line bisection task and three mental bisection tasks with number, letter, and month intervals. The error pattern in the number bisection task, indexed by the modulating effect of interval length, mirrored that of the visual task and confirmed the left-to-right spatial orientation of the mental number line. In contrast, the bisection of non-numerical intervals showed a very different pattern. The results suggest that the spatial layout characterizing numerical representations constitutes a specific property of numbers rather than a general characteristic of ordered sequences.

Children with developmental dyslexia show a left visual “minineglect”

We investigated the performance of children with developmental dyslexia on a visual line bisection task. Dyslexic children did not show the overestimation of the left visual field (pseudoneglect) characteristic of normal adult vision. These results suggest that children with developmental dyslexia present selective deficits in visual attention, probably involving neural structures located in the right posterior parietal cortex.

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.

Psychophysical Properties of Line Bisection and Body Midline Perception in Unilateral Neglect

Past research associated unilateral neglect with a systematic ipsilesional shift of the perceived position of the body midline; however, this was not confirmed by recent experiments. We used the constant stimuli method to control for potential artifacts intrinsic to the techniques used in previous studies. Body midline perception was measured in the visual and proprioceptive modalities in ten patients with left unilateral neglect, ten control patients and ten normal subjects and compared with a visual line bisection task, also using the constant stimuli method. Neglect patients showed a significant rightward bias in the line bisection task, but no consistent directional bias either in the proprioceptive or in the visual body midline task. These results clearly counter the association between neglect and an ipsilesional shift of the body midline. However, in the body midline tasks neglect patients made more errors in judgement on both sides of their subjective midline, both with respect to the control groups and with respect to the line bisection task. This may imply that a specific impairment of body-centered representations is indeed present and manifests as a non directional increase in response variability, rather than as a systematic shift. It is suggested that body- and object-related tasks (such as line bisection) may be processed by independent cognitive computations. This interpretation is discussed with reference to a recent neuroimaging study investigating the same kinds of tasks.

Vertical orienting control: evidence for attentional bias and "neglect" in the intact brain.

Unilateral neglect may be due to attentional bias: an exaggerated tendency to orient in an ipsilesional direction. Likewise, cases of vertical neglect suggest the existence of vertical attentional biases. This article reports evidence of upward biases in neurologically intact observers. In 5 experiments, observers performed a visual line-bisection task by judging the location of a gap along a tachistoscopically presented vertical line. The upward bias was influenced by attentional cues and was stronger in the right visual field than in the left visual field. Instructions designed to foster the use of an object-based, categorical encoding strategy were associated with an upward bias, whereas those fostering spatial, between-object comparisons were not. The results are discussed in terms of hemispheric differences in attention and specializations along the dorsal-ventral axis of the brain that influence directional orienting.

Effects of hand and spatial conditions on visual line bisection.

This study examined the effects of hand and spatial conditions on a visual line bisection task with normal right-handers and proposed a normal range of deviation for this task in middle and advanced age. Twenty-four normal dextrals in their fifties and sixties performed a visual line bisection task using either the left or right hand under three spatial conditions: at the midline and in the left and right hemispaces. Our results revealed that performance was significantly affected by the hand used but not spatial conditions: Left hand performance was significantly further leftward than right hand performance. There was no significant interaction between the hand and spatial conditions. The mean deviation of the right hand was 2.2% of the half line length to the right of the true center. The possibility of left unilateral spatial neglect should be considered if a patient bisects a line with a deviation greater than 10% of the half line length to the right.