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

Sex differences in line bisection as a function of hand

Validation of immersive virtual reality line and baguette bisection tasks for the assessment of unilateral spatial neglect.

Hemianopia patients have lost vision from the contralateral hemifield, but make behavioural adjustments to compensate for this field loss. As a result, their visual performance and behaviour contrast with those of hemineglect patients who fail to attend to objects contralateral to their lesion. These conditions differ in their ocular fixations and perceptual judgments. During visual search, hemianopic patients make more fixations in contralesional space while hemineglect patients make fewer. During line bisection, hemianopic patients fixate the contralesional line segment more and make a small contralesional bisection error, while hemineglect patients make few contralesional fixations and a larger ipsilesional bisection error. Hence, there is an attentional failure for contralesional space in hemineglect but a compensatory adaptation to attend more to the blind side in hemianopia. A challenge for models of visual attentional processes is to show how compensation is achieved in hemianopia, and why such processes are hindered or inaccessible in hemineglect. We used a neurophysiology-derived computational model to examine possible cortical compensatory processes in simulated hemianopia from a V1 lesion and compared results with those obtained with the same processes under conditions of simulated hemineglect from a parietal lesion. A spatial compensatory bias to increase attention contralesionally replicated hemianopic scanning patterns during visual search but not during line bisection. To reproduce the latter required a second process, an extrastriate lateral connectivity facilitating form completion into the blind field: this allowed accurate placement of fixations on contralesional stimuli and reproduced fixation patterns and the contralesional bisection error of hemianopia. Neither of these two cortical compensatory processes was effective in ameliorating the ipsilesional bias in the hemineglect model. Our results replicate normal and pathological patterns of visual scanning, line bisection, and differences between hemianopia and hemineglect, and may explain why compensatory processes that counter the effects of hemianopia are ineffective in hemineglect.

Objective:The prism adaptation (PA) with rightward shifting lenses is a promising rehabilitation technique for left hemispatial neglect. The PA has also been applied in healthy individuals to investigate cognitive mechanism(s) underlining such adaptation. Importantly, studies have suggested that PA may primarily impact the functions of the dorsal or the ventral attentional stream, and we have previously reported that PA to the upward and downward shifting lenses leads to a significant aftereffect in vertical line bisection task. However, this post-adaptation effect, similarly to that seen in the horizontal plane, might have been modified by the presence of the vertical pseudoneglect healthy participants often experience prior to PA. Thus, the aim of this study was to test this hypothesis.Participants and Methods:30 right-handed healthy adults (age M=22,4) performed a computerized line bisection (LB) in vertical and horizontal condition. The bisections were performed twice: before and after PA procedure. Participants took experimental procedure three times, each in at least 24 h of break, each time in one of three conditions of shifting lenses; down, up, control. Both LB tasks (vertical and horizontal) consisted of 24 lines, each centered on 23" touch screen. The participants were asked to find the middle of the line. Throughout the experiment, participants were comfortably seated with their head positioned on a chinrest. Participants were fitted with prismatic goggles that deviated their visual field by 10 degrees. For the adaptation we used the Peg-the-mole procedure consisting of 120 pointing movements.Results:To assess the effect of the vertical PA on landmark judgments we performed a repeated measures ANOVA with direction of PA (upward/downward), the condition of LB (vertical/ horizontal) and pre- vs post adaptation as a between-subjects factor. This analysis revealed a main effect of the direction of PA (p< 0.001) and a main effect of condition (p< 0.001). Overall, however, only adaptation in up-shifting lenses led to significant aftereffects (p<0.05). Further, when we excluded participants who did not exhibited horizontal pseudoneglect in preadaptation LB, the effect of PA in downshifting PA emerged in vertical LB (p<0.05). Further, this group also exhibited the aftereffect of PA in up-shifting lenses for the horizontal (p<0.01) and the vertical LB (p<0.05). Additionally, these participants exhibited a congruent tendency after upward and downward PA, and tended to allocate their attention more upward and rightward.Conclusions:The results of this study confirm that the vertical PA evokes a visuo-spatial bias. Moreover, the PA aftereffect seems to be modified by the presence of the pre-adaptation pseudoneglect. Whereas the mechanism inducing this bias is not fully known, it might be explained in light of the interhemispheric activation-inhibition balance. Both the upward and downward PA may primarily lead to activation of the posterior regions of the right hemisphere, and this activation may result with the upward and rightward bias in the LB task. However, future research with neuroimaging techniques is needed to test this hypothesis.

Unilateral neglect is a challenging disorder that pervades a range of behaviours following stroke and hampers recovery. Although a preponderance of clinical studies measure performance on a range of bedside...

Disturbed line bisection is associated with posterior brain lesions

To understand the nature of hemispatial attention allocation in virtual reality (VR), a line bisection task (LBT) was administered both in a real environment and a virtual environment to assess the rate of pseudoneglect. The mental construction of real and virtual environments was assumed to increase visuospatial activity in right hemisphere-related cognitive processes; an alteration in the activity that manifests in the direction and rate of line bisection lateral error. In the present study, fifty-one right-handed healthy college students were recruited. They performed a line bisection task in real and virtual environments. The obtained data showed that LBT errors in real and VR environments were correlated and individually consistent. Furthermore, a leftward LBT error was found in the physically real environment, however, in a VR the line bisection bias drifted towards the right hemispace. Participants with a lower right-handedness score showed a lower rate of left LBT bias in a real environment, but in VR, their LBT error showed a stronger rightwards error. Participants showed an individually consistent pattern in both real and VR environments, but VR-induced visuospatial reality construction was associated with rightward LBT bias in a virtual environment.

Music-induced changes in functional cerebral asymmetries

Previous research has indicated that rightward prism adaptation can reduce symptoms of spatial neglect following right brain damage. In addition, leftward prism adaptation can create "neglect-like" patterns of performance in healthy adults on tasks that measure attention and spatial biases. Although a great deal of research has focused on which behaviors are influenced by prism adaptation, very few studies have focused directly on how the magnitude of visual shift induced by prisms might be related to the observed aftereffects, or the effects of prisms on measures of attentional and spatial biases. In the current study, we examined these questions by having groups of healthy adult participants complete manual line bisection and landmark tasks prior to and following adaptation to either 8.5° (15 diopter; n=22) or 17° (30 diopter; n=25) leftward shifting prisms. Our results demonstrated a significantly larger rightward shift in straight-ahead pointing (a measure of prism aftereffect) following adaptation to 17°, compared to 8.5° leftward shifting prisms. In addition, only 17° leftward shifting prisms resulted in a significant rightward shift in line bisection following adaptation. However, there was a significant change in performance on the landmark task pre- versus post-adaptation in both the 8.5° and 17° leftward shifting prism groups. Interestingly, correlation analyses indicated that changes in straight-ahead pointing pre- versus post-adaptation were positively correlated with changes in performance on the manual line bisection task, but not the landmark task. These data suggest that larger magnitudes of prism adaptation seem to have a greater influence on tasks that require a response with the adapted hand (i.e., line bisection), compared to tasks that only require a perceptual judgment (i.e., the landmark task). In addition, these data provide further evidence that the effects of prisms on manual and perceptual responses are not related to one another.

It is generally accepted that visual illusions affect line bisection in the predicted direction. However, it has been reported an illusionary bias which seems questioning such general view. In a previous study, participants bisected lines flanked at both ends by two pairs of arrows, pointing in the same direction. The medialmost vertices of one pair converged on the line (converging arrows), whereas those of the other pair did not (non-converging arrows). Participants bisected lines toward the base of the arrows, i.e., toward the wider end of the stimulus and in the direction opposite to that predicted by the Baldwin illusion. However, the bisection bias was also directed away from the location of the converging arrows. We investigated what is the main factor affecting line bisection: arrows orientation, as previously suggested, or interference effects related to the location of converging arrows. In experiment 1, participants bisected lines flanked by converging versus non-converging arrows. Results confirmed the presence of a bisection bias directed not only toward the base of the converging arrows but also away from their location. In experiment 2, the arrows were located more internally, so that their medialmost vertices always converged on the line. Results showed that the bisection bias was directed away from the location of the arrows regardless of their orientation. It is suggested that the previously reported bisection bias did not depend on arrows orientation, but rather on interference effects related to converging arrows position. The theoretical implications of the results are discussed.

Mapping mental number line in physical space: Vertical and horizontal visual number line orientation in asymptomatic individuals with HIV

Does galvanic vestibular stimulation reduce spatial neglect? A negative study

1 Hz repetitive transcranial magnetic stimulation of the unaffected hemisphere ameliorates contralesional visuospatial neglect in humans

Line bisection error predicts the presence and severity of neglect dyslexia in paragraph reading

Meta-analysis of the visuospatial aftereffects of prism adaptation, with two novel experiments