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.     

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.     

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

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

Free viewing perceptual asymmetries for judgment of brightness and quantity: dependence on stimulus orientation

Previous research has indicated that normals exhibit strong leftward biases during free-viewing perceptual judgments of brightness and quantity. When participants view two symmetrical objects and they are forced to choose which object appears darker or more numerous, participants usually select the stimulus with the relevant feature on the left side. The present study investigated the possibility that these perceptual asymmetries are dependent on scanning a stimulus horizontally across the midline by administering a task with two rectangular reversed stimuli presented either horizontally or vertically. When the stimuli were presented horizontally (crossing the midline), participants exhibited leftward biases, but these biases disappeared when the stimuli were presented vertically. This result supports the position that free-viewing perceptual asymmetries are dependent on scanning the stimuli across the midline.     

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.     

Effect of a directional cue on line bisection

Normal participants display a leftward bias when bisecting horizontal lines. It has been proposed that bisection errors can be affected by representational biases. We investigated the possibility that this effect could also be explained as the result of perceptual cueing. Participants bisected horizontal lines with identical arrows arranged around the lines, all pointing to the same end. The arrows significantly affected bisection placement, although participants bisected significantly away from the direction the arrows pointed to. The findings favor the hypothesis that cueing, rather than representation, can affect bisection errors.     

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.     

Perceptual asymmetries in normal children and children with attention deficit/hyperactivity disorder

Perceptual asymmetries in normal right-handed children (7-12 years of age) and children with attention deficit/hyperactivity disorder (ADHD), combined type, were investigated using various chimeric stimuli in free-viewing conditions. In the face-matching task, participants indicated which of two symmetrical face chimeras more closely resembled the original; in the chimeric faces task, participants indicated which of a pair of faces appeared happier; and in the grey scales task participants indicated which of two shaded rectangles appeared to be darker overall. Leftward biases were found for normal children with no effects of age. Contrary to expectations, normal leftward biases were also found for ADHD children in the face-matching and the chimeric faces tasks; however, a significant leftward bias was not observed in the grey scales task. The absence of anomalous perceptual bias in ADHD children on these purely perceptual tasks, suggests that anomalous perceptual asymmetries observed in other tasks (line bisection and cancellation tasks) may have been confounded by the motor response, and/or the explicit spatial components of those tasks.     

Cognitive biases in three prediction tasks: A test of the cognitive model of depression

Cognitive therapy for depression is based on an assumption that depressed individuals have inaccurate, negative biases. Whether this assumption is accurate remains unresolved. Thus, this study sought to examine the relationship between depressive symptoms and bias in three sets of predictions (i.e., predictions of future life events, how one would be rated by a significant other, and performance on a vocabulary test). Following study announcements made to a subset of people pre-screened for depressive symptoms, 85 participants with widely varying depressive symptoms (17 of whom met diagnostic criteria for depression) made predictions on three judgment tasks and the outcomes for these tasks were assessed. Optimistic/pessimistic biases were related to depressive symptoms for each of the three tasks. Participants with high levels of depressive symptoms and depressed participants exhibited substantial pessimistic bias. Those high in depressive symptoms exhibited significant pessimistic bias on all three tasks. Participants meeting diagnostic criteria for depression exhibited pessimistic bias on two of three tasks. There was no evidence that depressive symptoms were associated with greater accuracy in judgments. Results are largely consistent with cognitive models of depression which postulate that depression is associated with pessimistic biases.     

The modulation of haptic line bisection by a visual illusion and optokinetic stimulation

Research has shown that a variety of different sensory manipulations, including visual illusions, transcutaneous nerve stimulation, vestibular caloric stimulation, optokinetic stimulation, and prism adaptation, can all influence people's performance on spatial tasks such as line bisection. It has been suggested that these manipulations may act upon the 'higher-order' levels of representation used to code spatial information. We investigated whether we could influence haptic line bisection in normal participants crossmodally by varying the visual background that participants viewed. In experiment 1, participants haptically bisected wooden rods while looking at a variant of the Oppel - Kundt visual illusion. Haptic-bisection judgments were influenced by the orientation of the visual illusion (in line with previous unimodal visual findings). In experiment 2, haptic-bisection judgments were also influenced by the presence of a leftward or rightward moving visual background. In experiments 3 and 4, the position of the to-be-bisected stimuli was varied with respect to the participant's body midline. The results confirmed an effect of optokinetic stimulation, but not of the Oppel -Kundt illusion, on participants' tactile-bisection errors, suggesting that the two manipulations might differentially affect haptic processing. Taken together, these results suggest that the 'higher-order' levels of spatial representation upon which perceptual judgments and/or motor responses are made may have multisensory or amodal characteristics.     

Perceptual biases in the horizontal and vertical dimensions are driven by separate cognitive mechanisms

Perceptual attention in healthy participants is characterized by two biases, one operating in the horizontal plane, which draws attention leftward, and the other operating in the vertical plane, which draws attention upward. Given that these biases are reliably found in the same individual, and appear similar at a surface level, a number of researchers have investigated the relationship between horizontal and vertical attentional biases. To date, these investigations have failed to find an association, and this may be due to the fact that one-dimensional vertical and horizontal stimuli were presented separately rather than being measured from a single, two-dimensional stimulus. Across three experiments, two dimensional stimuli were presented, and participants marked the centre of the stimuli. In addition, the shapes of the stimuli were manipulated to determine whether this produced the same modulation of the two biases. Across 13 stimuli and three experiments there were no correlations between the vertical and horizontal biases. In addition, manipulations of stimulus shape, which affected biases in one dimension, did not affect biases in the other dimension. There were, however, consistent correlations between the degree of bias within each dimension across the different stimuli. This study has produced converging evidence that horizontal and vertical biases in spatial judgments rely on separate cognitive mechanisms. To account for these results we discuss a model whereby horizontal asymmetries rely more on space-based mechanisms whereas vertical asymmetries rely more on object-based mechanisms.     

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

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

Lateral biases in assumptions of lighting position

People presume that the light source in pictures comes from above, and there is some evidence that this phenomenon also demonstrates lateral biases. When investigators present multiple ambiguous stimuli or visually complex objects, people assume that the source of light is from above, and to the left. However, when single relatively simple stimuli are presented, this lateral bias is not readily observed. To investigate whether lateral bias is dependent on the number of stimuli presented, the present experiment employs a within-subjects design to present single spheres or pairs of spheres. Contrary to our expectations, leftward biases were exhibited in both the single-sphere condition and the paired-spheres condition. Single spheres that were lit from the left were more likely to be judged as convex than comparable spheres lit from the right. Similarly, when pairs of laterally lit spheres were presented and participants were asked to judge which sphere appeared to be more convex, participants chose spheres lit from the left regardless of the angle of illumination. Collectively, these results suggest that there are lateral biases in assumptions of illumination position and that these biases do not depend on the number of stimuli being perceived at any given time.     

Lateral biases in assumptions of lighting position

People presume that the light source in pictures comes from above, and there is some evidence that this phenomenon also demonstrates lateral biases. When investigators present multiple ambiguous stimuli or visually complex objects, people assume that the source of light is from above, and to the left. However, when single relatively simple stimuli are presented, this lateral bias is not readily observed. To investigate whether lateral bias is dependent on the number of stimuli presented, the present experiment employs a within-subjects design to present single spheres or pairs of spheres. Contrary to our expectations, leftward biases were exhibited in both the single-sphere condition and the paired-spheres condition. Single spheres that were lit from the left were more likely to be judged as convex than comparable spheres lit from the right. Similarly, when pairs of laterally lit spheres were presented and participants were asked to judge which sphere appeared to be more convex, participants chose spheres lit from the left regardless of the angle of illumination. Collectively, these results suggest that there are lateral biases in assumptions of illumination position and that these biases do not depend on the number of stimuli being perceived at any given time.     

Spatial biases in peripersonal space in sighted and blind individuals revealed by a haptic line bisection paradigm

Our representation of peripersonal space does not always accurately reflect the physical world. An example of this is pseudoneglect, a phenomenon in which neurologically normal individuals bisect to the left of the veridical midpoint, reflecting an overrepresentation of the left portion of space compared with the right one. Consistent biases have also been observed in the vertical and radial planes. It is an open question whether these biases depend on normal visual experience for their occurrence. Here we systematically investigated this issue by testing blindfolded sighted and early blind individuals in a haptic line bisection task. Critically, we found a robust leftward bias in all participants. In the vertical and radial planes, sighted participants showed a consistent downward and proximal bias. Conversely, the directional bias in blind participants was dependent on the final movement direction; thus, there was no general bias in either direction. These findings are discussed in terms of different reference frames adopted by sighted and blind participants when encoding space.     

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.     

Left to right: representational biases for numbers and the effect of visuomotor adaptation

Adaptation to right-shifting prisms improves left neglect for mental number line bisection. This study examined whether adaptation affects the mental number line in normal participants. Thirty-six participants completed a mental number line task before and after adaptation to either: left-shifting prisms, right-shifting prisms or control spectacles that did not shift the visual scene. Participants viewed 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. Participants demonstrated a leftward bias (i.e. overestimated the length occupied by numbers located on the left side of the number line) that was consistent with the effect of pseudoneglect. The leftward bias was corrected by a short period of visuomotor adaptation to left-shifting prisms, but remained unaffected by adaptation to right-shifting prisms and control spectacles. The findings demonstrate that a simple visuomotor task alters the representation of space on the mental number line in normal participants.     

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.     

Eye movements and bisection behavior in spatial neglect syndrome: representational biases induced by the segment length and spatial dislocation of the stimulus

The present study explored behavioral and eye-movement measures in unilateral neglect patients in response to online bisection task (unfilled gap line). Two different tasks supported the bisection performance, a pointing and a grasping strategy. It was explored whether these different strategies may influence subjects' behavioral and eye-movement measures in response to different segment features: segment length (from shorter to longer) and segment spatial dislocation (from right to left spatial location). Consistent spatial biases were found for both bisection responses, fixation count, and duration, as well as for the first fixation count in case of pointing task. An "extreme-left" gradient effect was suggested and discussed, with patients' behavioral and eye measures more impaired. On the contrary, the patients' performance overlaps with the controls' one in case a grasping task. The direct link of visual pointing and grasping strategy, respectively, with the two cortical ventral and dorsal pathways was adduced to explain our results.     

Eye movements and bisection behavior in spatial neglect syndrome: representational biases induced by the segment length and spatial dislocation of the stimulus

The present study explored behavioral and eye-movement measures in unilateral neglect patients in response to online bisection task (unfilled gap line). Two different tasks supported the bisection performance, a pointing and a grasping strategy. It was explored whether these different strategies may influence subjects’ behavioral and eye-movement measures in response to different segment features: segment length (from shorter to longer) and segment spatial dislocation (from right to left spatial location). Consistent spatial biases were found for both bisection responses, fixation count, and duration, as well as for the first fixation count in case of pointing task. An “extreme-left” gradient effect was suggested and discussed, with patients’ behavioral and eye measures more impaired. On the contrary, the patients’ performance overlaps with the controls’ one in case a grasping task. The direct link of visual pointing and grasping strategy, respectively, with the two cortical ventral and dorsal pathways was adduced to explain our results.