Vertical representational biases in healthy university students

In line bisection tasks neurologically intact individuals tend to bisect lines slightly left of their midpoint for horizontal lines, and above centre for vertical lines, a phenomenon known as perceptual pseudoneglect (Bowers & Heilman, 1980; Van Vugt, Fransen, Creten, & Paquiner, 2000). Recent investigations have demonstrated the leftward bias to extend to mental imagery, a finding known as representational pseudoneglect (McGeorge, Beschin, Colnaghi, Rusconi, & Della Sala, 2007). This paper examined whether the upward bias found in perceptual tasks extended to mental imagery in healthy individuals. University students studied a diagram depicting a central character and target objects that were located in six positions relative to the person in the diagram (left/right, up/down, and front/back). Following learning, participants recalled the locations of the objects from several imagined orientations. Performance on the recall task revealed faster response latencies for upward targets, providing evidence for vertical representational biases in healthy individuals.     

视觉空间伪忽视与表征伪忽视神经机制的异同

伪忽视（pseudoneglect）是指个体存在的轻微偏左的不对称空间注意,而视觉空间伪忽视（visuo-spatial pseudoneglect）和表征伪忽视(representational pseudoneglect)是其两种主要表现形式。研究初期,研究者认为两种伪忽视基于相同的注意定向左偏机制,但近年来研究发现,它们仍存在神经机制的差异。本文主要从两种伪忽视神经机制的异同出发,梳理分析近期研究结果,以期增进对伪忽视的理解。未来研究可以从认知时间进程角度或设计更为完善的研究范式进一步探讨这两种伪忽视神经机制的异同。     

Horizontal and vertical pseudoneglect in peri- and extrapersonal space

The present study investigates the influence of depth on pseudoneglect in healthy young participants (n = 18) within three-dimensional virtual space, by presenting a variation of the greyscales task and a landmark task, which were specifically matched for stimulus–response compatibility, as well as perceptual factors within and across the tasks. Tasks were presented in different depth locations (peripersonal, extrapersonal) and different orientations (horizontal, vertical) within three-dimensional virtual space, using virtual reality technique. A horizontal leftward bias (pseudoneglect) for both tasks was found, which was stronger in peripersonal than in extrapersonal space. For the vertical condition, an upward bias was observed in the greyscales task, but not in the landmark task. These results support the hypotheses of right hemispheric dominance for visual spatial attention and our study is the first to examine horizontal and vertical orienting biases with the greyscales task in peri- and extrapersonal space. Furthermore, the differences in attentional asymmetries with respect to depth suggest dissociable neural mechanisms for visual attentional processing in near and far space and the lack of significant correlations implies independence of horizontal and vertical stimulus processing.     

Representational neglect for words as revealed by bisection tasks

In the present study, we showed that a representational disorder for words can dissociate from both representational neglect for objects and neglect dyslexia. This study involved 14 brain-damaged patients with left unilateral spatial neglect and a group of normal subjects. Patients were divided into four groups based on presence of left neglect dyslexia and representational neglect for non-verbal material, as evaluated by the Clock Drawing test. The patients were presented with bisection tasks for words and lines. The word bisection tasks (with words of five and seven letters) comprised the following: (1) representational bisection: the experimenter pronounced a word and then asked the patient to name the letter in the middle position; (2) visual bisection: same as (1) with stimuli presented visually; and (3) motor bisection: the patient was asked to cross out the letter in the middle position. The standard line bisection task was presented using lines of different length. Consistent with the literature, long lines were bisected to the right and short lines, rendered comparable in length to the words of the word bisection test, deviated to the left (crossover effect). Both patients and controls showed the same leftward bias on words in the visual and motor bisection conditions. A significant difference emerged between the groups only in the case of the representational bisection task, whereas the group exhibiting neglect dyslexia associated with representational neglect for objects showed a significant rightward bias, while the other three patient groups and the controls showed a leftward bisection bias. Neither the presence of neglect alone nor the presence of visual neglect dyslexia was sufficient to produce a specific disorder in mental imagery. These results demonstrate a specific representational neglect for words independent of both representational neglect and neglect dyslexia.     

Right up there: hemispatial and hand asymmetries of altitudinal pseudoneglect

Background

Pseudoneglect is a normal left sided spatial bias observed with attempted bisections of horizontal lines and a normal upward bias observed with attempted bisections of vertical lines. Horizontal pseudoneglect has been attributed to right hemispheric dominance for the allocation of attention. The goal of this study was to test the hypothesis that the upward bias in vertical line bisection may also relate to right hemispheric dominance for the allocation of attention and/or action-intention.

Methods

Twenty right handed healthy adults were asked to bisect vertical lines presented in the midsagittal plane (center space) and in sagittal planes to the left and right of the midsagittal plane (left and right hemispace) when using a pen held in either the right or left hand.

Results

Vertical line bisections were biased upward in all three sagittal planes and higher in left than right hemispace. However, bisections made with the left hand were lower than those made with the right hand.

Discussion

Whereas these results suggest a left hemispace-right hemispheric visuospatial attentional upward bias and a relative left hemispheric-right hand upward action-intentional bias, further studies are needed to document this intentional versus attentional bias and to understand the brain mechanisms that produce these biases.     

Representational pseudoneglect in line bisection

"Representational pseudoneglect" refers to a bias toward the left side of space that occurs when visual information is remembered. Recently a number of demonstrations of such representational pseudoneglect have appeared. In the present article, we report an experiment in which we adopted the classic line bisection paradigm to study representational pseudoneglect. Participants bisected horizontal lines that were shown in extrapersonal space. When the lines were visible on the screen, there was no evidence of any leftward bias. However, when lines were bisected from memory, the participants demonstrated a clear bias to the left. This is the first demonstration of a leftward bias in the bisection of remembered visually presented lines.     

Blind individuals show pseudoneglect in bisecting numerical intervals

Neurologically normal individuals typically show a leftward bias--known as pseudoneglect--in bisecting physical lines as well as numerical intervals. The latter bias may reflect the spatial nature in which numbers are represented (i.e., the mental number line). In previous studies, we found that congenitally blind individuals show such leftward bias in haptic bisection. Here, we demonstrate that blind individuals also show a consistent leftward bias in numerical bisection. The leftward bias was greater when numbers were presented in descending rather than ascending order, and the magnitude of the leftward bias was comparable to that shown by a control group of blindfolded sighted participants. Our findings thus support the view that pseudoneglect operates at a mental representational level rather than being perceptually based. Moreover, the consistent leftward bias shown by blind individuals in both line and numerical bisection suggests that the right hemisphere dominance in spatial processing, resulting in an overestimation of the left side of space, develops even in the absence of any visual input.     

Pseudoneglect for the bisection of mental number lines

Patients with unilateral neglect of the left side bisect physical lines to the right whereas individuals with an intact brain bisect lines slightly to the left (pseudoneglect). Similarly, for mental number lines, which are arranged in a left-to-right ascending sequence, neglect patients bisect to the right. This study determined whether individuals with an intact brain show pseudoneglect for mental number lines. In Experiment 1, participants were presented with visual number triplets (e.g., 16, 36, 55) and determined whether the numerical distance was greater on the left or right side of the inner number. Despite changing the spatial configuration of the stimuli, or their temporal order, the numerical length on the left was consistently overestimated. The fact that the bias was unaffected by physical stimulus changes demonstrates that the bias is based on a mental representation. The leftward bias was also observed for sets of negative numbers (Experiment 2)--demonstrating not only that the number line extends into negative space but also that the bias is not the result of an arithmetic distortion caused by logarithmic scaling. The leftward bias could be caused by a rounding-down effect. Using numbers that were prone to large or small rounding-down errors, Experiment 3 showed no effect of rounding down. The task demands were changed in Experiment 4 so that participants determined whether the inner number was the true arithmetic centre or not. Participants mistook inner numbers shifted to the left to be the true numerical centre--reflecting leftward overestimation. The task was applied to 3 patients with right parietal damage with severe, moderate, or no spatial neglect (Experiment 5). A rightward bias was observed, which depended on the severity of neglect symptoms. Together, the data demonstrate a reliable and robust leftward bias for mental number line bisection, which reverses in clinical neglect. The bias mirrors pseudoneglect for physical lines and most likely reflects an expansion of the space occupied by lower numbers on the left side of the line and a contraction of space for higher numbers located on the right.     

Pseudoneglect for the bisection of mental number lines

Patients with unilateral neglect of the left side bisect physical lines to the right whereas individuals with an intact brain bisect lines slightly to the left (pseudoneglect). Similarly, for mental number lines, which are arranged in a left-to-right ascending sequence, neglect patients bisect to the right. This study determined whether individuals with an intact brain show pseudoneglect for mental number lines. In Experiment 1, participants were presented with visual number triplets (e.g., 16, 36, 55) and determined whether the numerical distance was greater on the left or right side of the inner number. Despite changing the spatial configuration of the stimuli, or their temporal order, the numerical length on the left was consistently overestimated. The fact that the bias was unaffected by physical stimulus changes demonstrates that the bias is based on a mental representation. The leftward bias was also observed for sets of negative numbers (Experiment 2)—demonstrating not only that the number line extends into negative space but also that the bias is not the result of an arithmetic distortion caused by logarithmic scaling. The leftward bias could be caused by a rounding-down effect. Using numbers that were prone to large or small rounding-down errors, Experiment 3 showed no effect of rounding down. The task demands were changed in Experiment 4 so that participants determined whether the inner number was the true arithmetic centre or not. Participants mistook inner numbers shifted to the left to be the true numerical centre—reflecting leftward overestimation. The task was applied to 3 patients with right parietal damage with severe, moderate, or no spatial neglect (Experiment 5). A rightward bias was observed, which depended on the severity of neglect symptoms. Together, the data demonstrate a reliable and robust leftward bias for mental number line bisection, which reverses in clinical neglect. The bias mirrors pseudoneglect for physical lines and most likely reflects an expansion of the space occupied by lower numbers on the left side of the line and a contraction of space for higher numbers located on the right.     

Pseudoneglect: evidence for both perceptual and attentional factors

When neurologically normal individuals bisect a horizontal line as accurately as possible, they reliably show a slight leftward error. This leftward inaccuracy is called pseudoneglect because errors made by neurologically normal individuals are directionally opposite to those made by persons with visuospatial neglect (Jewell & McCourt, 2000). In the current study, normal right-handed observers bisected horizontal lines that were altered to bias line length judgments either toward the right or the left side of the line. Non-target dots were placed on or near the line stimuli using principles derived from a theory of visual illusions of length called centroid extraction (Morgan, Hole, & Glennerster, 1990). This theory argues that the position of a visual target is calculated as the mean position of all stimuli in close proximity to the target stimulus. We predicted that perceptual alterations that shifted the direction of centroid extraction would also shift the direction of line bisection errors. Our findings confirmed this prediction and support the idea that both perceptual and attentional factors contribute to the pseudoneglect effect.     

Representational pseudoneglect and reference points both influence geographic location estimates

Our mental representation of the world is far from objective. For example, western Canadians estimate the locations of North American cities to be too far to the west. This bias could be due to a reference point effect, in which people estimate more space between places close to them than far from them, or to representational pseudoneglect, in which neurologically intact individuals favor the left side of space when asked to image a scene. We tested whether either or both of these biases influence the geographic world representations of neurologically intact young adults from Edmonton and Ottawa, which are in western and eastern Canada, respectively. Individuals were asked to locate North American cities on a two-dimensional grid. Both groups revealed effects of representational pseudoneglect in this novel paradigm, but they also each exhibited reference point effects. These results inform theories in both cognitive psychology and neuroscience.     

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.     

Hemispatial asymmetries in judgment of stimulus size

Recent research has demonstrated a leftward bias in judgments of size. In the present experiments, hemispatial size bias was measured through simultaneous presentation of a circle and an ellipse varying in horizontal or vertical extent. A consistent leftward bias of horizontal size judgments (but not vertical) was obtained; at the point of subjective equality, the width of the objects that were presented in left hemispace was smaller than the width of the objects that were presented in right hemispace. These data suggest that the horizontal extent of stimuli appear larger in left hemispace than in right hemispace. Results also indicated that symmetrical stimulus presentation, with respect to the vertical meridian, is required for the bias to emerge. Furthermore, increasing or decreasing stimulus eccentricity weakened the effect. Attenuation of this bias upon the manipulation of parameters indicates that this phenomenon is context specific and is affected by similar parameters that are known to influence the magnitude of error in pseudoneglect.     

Orientation-specific aftereffects to mentally generated lines

After staring at a pattern of tilted lines, subsequent lines appear to be tilted in the opposite direction (direct tilt aftereffect, TAE). In a previous fMRI study we have demonstrated a direct TAE solely induced by the mental imagination accompanied by adaptation of orientation-selective neurons located in the extrastriate cortex, supporting the assumption of a perception-like coding of mental images. In this study we enlarge and specify the evidence for a perception-like coding of orientation-imagination. First, we replicated the previously detected direct TAE induced by line imagination with altered design-variations to control possible perceptual task confounds. Second, we tried to induce two other orientation-specific aftereffects: indirect TAE and contrast-threshold elevation aftereffect by mental imagery. The results replicate a robust direct TAE by mental imagery and by visual stimulation, with no influence of attentional resource allocation or perceptual task confounds. We could not induce an indirect TAE, but observed a perception bias in the opposite direction of the indirect TAE. The mental imagery of lines induced no orientation-selective contrast-threshold elevation aftereffect. In general, mental imagery seems to influence visual perception, indicating that perceptual resources are used by mental imagery. However, the utilisation of visual resources seems to be somewhat different from utilisation by perception.     

Bisection of shapes and lines: analysis of the visual and motor aspects of pseudoneglect

This study examined the visual and motor components of pseudoneglect as expressed on horizontal bisection tasks. Ten participants were tested on bisection of lines and elliptical shapes and judgement of pretransected lines. Results showed the same magnitude of leftward error on all three tasks, in contrast to previous findings for patients with visuospatial neglect who are known to bisect ellipses and circles much more accurately than lines. Participants' mean line bisection error was significantly further to the left than the mean subjective midpoint found on the judgement task. The findings contradict the claim that the visual component of pseudoneglect is caused by the same mechanism that causes visuospatial neglect but support the hypothesis that the motor component of pseudoneglect is similar to directional hypometria.     

Colour, face, and visuospatial imagery abilities in low-vision individuals with visual field deficits

This study investigates to what extent visual perception integrity is necessary for visual mental imagery. Sixteen low-vision participants with severe peripheral visual field loss, 16 with severe central field loss, 6 left brain-damaged patients with right homonymous hemianopia, 6 right brain-damaged patients with left homonymous hemianopia, and 16 normally sighted controls performed perceptual and imagery tasks using colours, faces, and spatial relationships. Results showed that (a) the perceptual and mental image>ry disorders vary according to the type of visual field loss, (b) hemianopics had no more difficulties imagining spatial stimuli in their contralesional hemispace than in their ipsilesional one, and (c) the only hemianopic participant to have perceptual and mental imagery impairments suffered from attentional deficits. Results suggest that (a) visual memory is not definitively established, but rather needs perceptual practice to be maintained, and (b) that visual mental imagery may involve some of the attentional-exploratory mechanisms that are employed in visual behaviour.     

Colour,face, and visuospatial imagery abilities in low-vision individuals with visual field deficits

This study investigates to what extent visual perception integrity is necessary for visual mental imagery. Sixteen low-vision participants with severe peripheral visual field loss, 16 with severe central field loss, 6 left brain-damaged patients with right homonymous hemianopia, 6 right brain-damaged patients with left homonymous hemianopia, and 16 normally sighted controls performed perceptual and imagery tasks using colours, faces, and spatial relationships. Results showed that (a) the perceptual and mental image>ry disorders vary according to the type of visual field loss, (b) hemianopics had no more difficulties imagining spatial stimuli in their contralesional hemispace than in their ipsilesional one, and (c) the only hemianopic participant to have perceptual and mental imagery impairments suffered from attentional deficits. Results suggest that (a) visual memory is not definitively established, but rather needs perceptual practice to be maintained, and (b) that visual mental imagery may involve some of the attentional–exploratory mechanisms that are employed in visual behaviour.     

Bisecting the mental number line in near and far space

Much evidence suggests that common posterior parietal mechanisms underlie the orientation of attention in physical space and along the mental number line. For example, the small leftward bias (pseudoneglect) found in paper-and-pencil line bisection is also found when participants “bisect” number pairs, estimating (without calculating) the number midway between two others. For bisection of physical lines, pseudoneglect has been found to shift rightward as lines are moved from near space (immediately surrounding the body) to far space. We investigated whether the presentation of stimuli in near or far space also modulated spatial attention for the mental number line. Participants bisected physical lines or number pairs presented at four distances (60, 120, 180, 240 cm). Clear rightward shifts in bias were observed for both tasks. Furthermore, the rate at which this shift occurred in the two tasks, as measured by least-squares regression slopes, was significantly correlated across participants, suggesting that the transition from near to far distances induced a common modulation of lateral attention in physical and numerical space. These results demonstrate a tight coupling between number and physical space, and show that even such prototypically abstract concepts as number are modulated by our on-line interactions with the world.     

Computational model of enactive visuospatial mental imagery using saccadic perceptual actions

From the onset of cognitive revolution, the concept of mental imagery has been given different, many times opposing, theoretical accounts. Mental imagery appears to be a ubiquitous, yet wholly individual, easy to explain experience on the one hand, being hard to deal with scientifically on the other hand. The focus of this research is on an enactive approach to visuospatial mental imagery, inspired by Sima’s perceptual instantiation theory. We designed a hybrid computational model, composed of a forward model, an inverse model, both implemented as neural networks, and a memory/controller module, that grounds simple mental concepts, such as a triangle and a square, in perceptual actions, and is able to reimagine these objects by performing the necessary perceptual actions in a simulated humanoid robot. We tested the model on three tasks – salience-based object recognition, imagination-based object recognition and object imagination – and achieved very good results showing, as a proof of concept, that perceptual actions are a viable candidate for grounding the visuospatial mental concepts as well as the credible substrate of visuospatial mental imagery.