Effect of a visual distractor on line bisection

Previous studies have shown that a flanking distractor produces a spatial bias during line bisection. In the present study, we investigated whether that bias depends on perceptual or motor components. Participants were asked to bisect a horizontal line, or to reach towards a dot, with or without vision of their hand. The line and the target could be flanked by a distractor. Movement trajectories and endpoints were consistently deviated away from the location of the distractor in the bisection task, but not in the reaching task, irrespectively of whether the participants had online visual feedback from their moving hand. It is suggested that flanking distractors influence perceptual localization of the subjective mid-point during line bisection.     

Line bisection performance in patients with generalized anxiety disorder and treatment-resistant depression

Background and Objectives The line bisection error to the left of the true center has been interpreted as a relative right hemisphere activation, which might relate to the subject''s emotional state. Considering that patients with generalized anxiety disorder (GAD) or treatment-resistant depression (TRD) often have negative emotions, we hypothesized that these patients would bisect lines significantly leftward. Methods We tried the line bisection task in the right-handed healthy volunteers (n = 56), GAD (n = 47) and TRD outpatients (n = 52). Subjects also completed the Zuckerman - Kuhlman Personality Questionnaire, the Zuckerman Sensation Seeking Scales, and the Plutchik-van Praag Depression Inventory. Results GAD patients scored highest on the Neuroticism-Anxiety trait, TRD patients scored highest on depression, and both patients scored lower on the Sociability trait. Patients with GAD also bisected lines significantly leftward compared to the healthy subjects. The Frequency of the bisection error was negatively correlated with Disinhibition-Seeking in the healthy subjects, and with Total sensation-seeking and Experience-Seeking in GAD patients, while the Magnitude of the line bisection error was negatively correlated with depression in TRD patients. Conclusions The study suggests a stronger right hemispheric activation, a weaker left activation, or both in the GAD, instead of TRD patients.     

Age-related differences in distractor interference on line bisection

Using a bisection paradigm, we investigated age-related differences in susceptibility to distractor interference. Older and younger participants were asked to bisect a horizontal line flanked by a pair of distractors, placed in either left or right hemispace. The results showed that (1) in both groups the distractors interfered with line bisection so that the localization of subjective midpoint was selectively shifted away from their position; (2) the shifting of subjective midpoint was greater in the older than in the younger group when the distractors were placed in the left hemispace. We suggest that the increase of the bisection bias in the older group depends on changes in attentional mechanisms involved in inhibiting irrelevant information.     

Emotion and space: lateralized emotional word detection depends on line bisection bias

There is converging evidence, from various independent areas of neuroscience, for a functional specialization of the left and right cerebral hemispheres for positive and negative emotions, respectively (“valence theory” of emotional processing). One subfield, however, has produced mixed results, i.e. work on the detection of parafoveally presented positively or negatively emotional words by healthy subjects. Right or left visual field advantages were described and interpreted as reflecting the superiority of either the left hemisphere (LH) for linguistic material, or of the right hemisphere (RH) for highly emotional stimuli. Here we show that 48 healthy, right-handed participants' performance on a lateralized lexical decision task depends on their individual inclination to bisect a line to the left or right of the objective center. Only those with a bisection bias to the right showed the LH advantage for word detection known from the neuropsychological literature. Negative emotional words were processed with comparable accuracy in the two visual fields. However, a recognition advantage for negative over positive emotional words was found exclusively for those participants with a leftward line bisection bias. These results suggest that in work on functional hemispheric differences state variables like stimulus lateralization and word emotionality may be less decisive than the trait variable of lateral hemispatial attention. We propose a cautious reconsideration of the concept of “hemisphericity,” which once emphasized individual differences in baseline hemispheric arousal, but was later dismissed in a reaction to oversimplifications in popular science accounts.     

Tactile and visual bisection tasks by sighted and blind children

Roeltgen and Roeltgen (1989) suggested that symmetrical patterns observed when young children bisect lines in a visuo‐manual task could be due to callosal immaturity. To further investigate this hypothesis, the present study compared performances of sighted children in visuo‐manual and tactile‐kinesthetic bisection tasks. In addition two groups of visually handicapped children were tested with the tactile‐kinesthetic bisection task. In the visuo‐manual task, a symmetrical pattern was observed, confirming previous findings. However, in the tactile‐kinesthetic task no symmetrical pattern was observed. Instead, sighted children bisected to the right of the midpoint with the left hand, totally blind children bisected to the left with both right and left hands, and no significant deviation was observed with partially blind children. The magnitude of the errors, irrespective of directionality, were not different between the three groups (sighted, totally blind, and partially blind children) in the tactile‐kinesthetic task. These results suggest that past visual experience is not crucial to tactile length representation but affects tactile directional space representation. Furthermore, because visual performance differed from tactile performance, commisural immaturity seems an inadequate explanation of the observed results in children's line bisection tasks.     

Multiple spatial representations of number: evidence for co-existing compressive and linear scales

Although the spatial representation of number (mental number line) is well documented, the scaling associated with this representation is less clear. Sometimes people appear to rely on compressive scaling, and sometimes on linear scaling. Here we provide evidence for both compressive and linear representations on the same numerical bisection task, in which adult participants estimate (without calculating) the midpoint between two numbers. The same leftward bias (pseudoneglect) shown on physical line bisection appears on this task, and was previously shown to increase with the magnitude of bisected numbers, consistent with compressive scaling (Longo and Lourenco in Neuropsychologia 45:1400–1407, 2007). In the present study, participants held either small (1–9) or large (101–109) number primes in memory during bisection. When participants remembered small primes, bisection responses were consistent with compressive scaling. However, when they remembered large primes, responses were more consistent with linear scaling. These results show that compressive and linear representations may be accessed flexibly on the same task, depending on the numerical context.     

Grasping at sticks: pseudoneglect for perception but not action

A current question in theories of visual cognition is whether distinct cognitive processes subserve perceptual judgments and perception for action. This paper examines bisection tasks which have previously been used to demonstrate a dissociation between perception and action in brain injured patients. Forty neurologically intact participants completed a standard line bisection task and a variant of this task—rod bisection. A typical leftwards bias was observed for line bisection but when asked to locate the centre of wooden rods using perceptual judgments, a distinct rightwards bias was shown. By contrast, when participants were asked to pick the rods up by the centre, their judgments showed no bias. The results are in line with theories suggesting that perception and action are independent; however, alternative explanations are also considered.     

Visual search pattern during the line quadrisection task in normal subjects

A common test for the assessment of hemispatial neglect is the line bisection test. A recent modification of the task has been reported wherein subjects place a mark at either 25% or 75% of line length (quadrisection). In a previous study, we suggested that line quadrisection might entail iteration of two steps involved in standard line bisection: (1) finding the midpoint of the entire line, and then (2) bisecting the half-line segment between the adjudged midpoint and the line end ipsilateral to the target quadrisection point. The present study investigated eye movement patterns during line quadrisection in order to test this hypothesis. Twenty normal volunteers determined the left or right quadrisection point of a horizontal line while their eye movements were recorded using two-dimensional video-oculography. Analysis revealed that, like the results of previous studies on bisection, most normal subjects fixate the central portion of the line segment before reaching the target area during the quadrisection task. Normal subjects eye movements during quadrisection performance share a number of features with line bisection and provide support for the two-step processing hypothesis.     

Delayed flanker effects on lateralized readiness potentials

When participants were required to respond to a relevant central target and ignore irrelevant flanking stimuli, the flankers produced a response compatibility effect. Electrophysiological studies have shown that irrelevant flanker stimuli can affect the motor system. The present experiments further examined the characteristics of flanker effects on the motor system. Sixty participants responded in the flanker task to arrows (experiment 1) or letters (experiment 2). To examine time and extent of flanker effects on the motor system, target onset was delayed with blocked or random stimulus-onset asynchronies (SOA). With SOA of 0 and 100 ms, flanker effects on behavioral measures were reduced in random as compared to blocked conditions, but enhanced with SOA of 400 ms. With SOA of 400 ms, flanker effects on the early lateralized readiness potentials (LRP) were reduced in blocked as compared to random conditions, indicating that the onset of flanker effects on the LRP was delayed. Response-locked LRPs suggest that flanker and target stimuli activate the motor system successively. Findings challenge current theories of the flanker compatibility effect.     

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.     

Tapping effects on numerical bisection

Numerical magnitude is believed to be represented along a mental number line (MNL), and there is evidence to suggest that the activation of the MNL affects the perception and representation of external space. In the present study, we investigated whether a spatial motor task affects numerical processing in the auditory modality. Blindfolded participants were presented with a numerical interval bisection task, while performing a tapping task with either their left or right hand, either in the fronto-central, fronto-left, or fronto-right peripersonal space. Results showed that tapping significantly influenced the participants’ numerical bisection, with tapping in the left side of space increasing the original tendency to err leftward, and tapping to the right reducing such bias. Importantly, the effect depended on the side of space in which the tapping activity was performed, regardless of which hand was used. Tapping with either the left or right hand in the fronto-central space did not affect the participants’ bias. These findings offer novel support for the existence of bidirectional interactions between external and internal representations of space.     

Line bisection by eye and by hand reveal opposite biases

The vision-for-action literature favours the idea that the motor output of an action—whether manual or oculomotor—leads to similar results regarding object handling. Findings on line bisection performance challenge this idea: healthy individuals bisect lines manually to the left of centre and to the right of centre when using eye fixation. In case that these opposite biases for manual and oculomotor action reflect more universal compensatory mechanisms that cancel each other out to enhance overall accuracy, one would like to observe comparable opposite biases for other material. In the present study, we report on three independent experiments in which we tested line bisection (by hand, by eye fixation) not only for solid lines, but also for letter lines; the latter, when bisected manually, is known to result in a rightward bias. Accordingly, we expected a leftward bias for letter lines when bisected via eye fixation. Analysis of bisection biases provided evidence for this idea: manual bisection was more rightward for letter as compared to solid lines, while bisection by eye fixation was more leftward for letter as compared to solid lines. Support for the eye fixation observation was particularly obvious in two of the three studies, for which comparability between eye and hand action was increasingly adjusted (paper–pencil versus touch screen for manual action). These findings question the assumption that ocular motor and manual output are always inter-changeable, but rather suggest that at least for some situations ocular motor and manual output biases are orthogonal to each other, possibly balancing each other out.     

Acute psychological stress promotes general alertness and attentional control processes: An ERP study

The current study investigated the influence of acute psychological stress on selective attention processes. After an acute stressor or a control condition, 20 participants performed an arrow-based version of the Eriksen flanker task, while ERPs (N1, N2, P3), reaction times, accuracy, subjective stress, and electrocardiogram signal were measured. Results showed elevated self-report stress, negative affect, state anxiety, heart rate, and reduced high-frequency heart rate variability in the stress block than in the control block, indicating that the flanker task was performed in a stressful situation. In the flanker task, faster response and larger flanker effect of accuracy were observed for the stress block relative to the control block, indicating increased arousal level and improved conflict detection under stress. Event-related potentials locked to target stimuli in the flanker task revealed that (a) frontal N1 was amplified in the stress block than in the control block, indicating elevated vigilance level under stress; (b) frontal N2 was increased in the stress block than in the control block for both congruent and incongruent trials, indicating more intensive attention control under stress; and (c) Increased P3 in the stress block than in the control block may reflect more allocation of neural resources as a consequence of improved attentional control under stress. These findings suggest that acute psychological stress increases general alertness and promotes attentional control in selective attention processes.     

Auditory deprivation affects biases of visuospatial attention as measured by line bisection

In this study, we investigated whether early deafness affects the typical pattern of hemispheric lateralization [i.e., right hemisphere (RH) dominance] in the control of spatial attention. To this aim, deaf signers, deaf non-signers, hearing signers, and hearing non-signers were required to bisect a series of centrally presented visual lines. The directional bisection bias was found to be significantly different between hearing and deaf participants, irrespective of sign language use. Hearing participants (both signers and non-signers) showed a consistent leftward bias, reflecting RH dominance. Conversely, we observed no evidence of a clear directional bias in deaf signers or non-signers (deaf participants overall showing a non-significant tendency to deviate rightward), suggesting that deafness may be associated to a more bilateral hemispheric engagement in visuospatial tasks.     

The spatial representation of numbers: evidence from neglect and pseudoneglect

The aim of the present paper is to provide an overview of the evidence that links spatial representation with representation of number magnitude. This aim is achieved by reviewing the literature concerning the number interval bisection task in patients with left hemispatial neglect and in healthy participants (pseudoneglect). Phenomena like the Spatial Numerical Association of Response Codes (SNARC) effect and the shifts of covert spatial attention caused by number processing are thought to support the notion that number magnitude is represented along a spatially organized mental number line. However, the evidence provided by chronometric studies is not univocal and is open to alternative, non-spatial interpretations. In contrast, neuropsychological studies have offered convincing evidence that humans indeed represent numbers on a mental number line oriented from left to right. Neglect patients systematically misplace the midpoint of a numerical interval they are asked to bisect (e.g., they say that 〈5〉 is halfway between 〈2〉 and 〈6〉) and their mistakes closely resemble the typical pattern found in bisection of true visual lines. The presence of dissociations between impaired explicit knowledge and spared implicit knowledge supports the notion that neglect produces a deficit in accessing an intact mental number line, rather than a distortion in the representation of that line. Other results show that the existence of a strong spatial connotation constitutes a specific property of number representations rather than a general characteristic of all ordered sequences.

Examining the influence of ‘noise’ on judgements of spatial extent

The line bisection task--commonly used as a clinical measure of unilateral neglect--requires participants to place a mark on a horizontal line to indicate where they think centre is. In general, results suggest that the allocation of attention mediates bisection. In addition, previous research shows that participants rarely explore the endpoints of lines, suggesting that peripheral visual information informs bisection. Here, we examined bisection performance under conditions in which differing levels of 'noise' were introduced to the line to examine the hypothesis that the fidelity and symmetry of peripheral information would inform performance. Contrary to our expectations, results showed that symmetrically introducing noise to the line biased bisection further leftward compared to a 'no-noise' condition. Furthermore, asymmetrical noise increased leftward bisection errors primarily when lines were presented in left space or when the greater amount of noise was on the left half of the line. These results indicate that the fidelity of peripheral visual information mediates bisection behaviour that is already biased leftwards probably due to right hemisphere attentional mechanisms.     

Does cerebral oxygenation affect cognitive function during exercise?

This study tested whether cerebral oxygenation affects cognitive function during exercise. We measured reaction times (RT) of 12 participants while they performed a modified version of the Eriksen flanker task, at rest and while cycling. In the exercise condition, participants performed the cognitive task at rest and while cycling at three workloads [40, 60, and 80% of peak oxygen uptake ( [(V)\dot]\textO ₂ \dot{V}{\text{O}}_{ 2} )]. In the control condition, the workload was fixed at 20 W. RT was divided into premotor and motor components based on surface electromyographic recordings. The premotor component of RT (premotor time) was used to evaluate the effects of acute exercise on cognitive function. Cerebral oxygenation was monitored during the cognitive task over the right frontal cortex using near-infrared spectroscopy. In the exercise condition, we found that premotor time significantly decreased during exercise at 60% peak [(V)\dot]\textO ₂ \dot{V}{\text{O}}_{ 2} relative to rest. However, this improvement was not observed during exercise at 80% peak [(V)\dot]\textO ₂ \dot{V}{\text{O}}_{ 2} . In the control condition, premotor time did not change during exercise. Cerebral oxygenation during exercise at 60% peak [(V)\dot]\textO ₂ \dot{V}{\text{O}}_{ 2} was not significantly different from that at rest, while cerebral oxygenation substantially decreased during exercise at 80% peak [(V)\dot]\textO ₂ \dot{V}{\text{O}}_{ 2} . The present results suggest that an improvement in cognitive function occurs during moderate exercise, independent of cerebral oxygenation.     

The course of visual searching to a target in a fixed location: Electrophysiological evidence from an emotional flanker task

The present study investigated the course of visual searching to a target in a fixed location, using an emotional flanker task. Event-related potentials (ERPs) were recorded while participants performed the task. Emotional facial expressions were used as emotion-eliciting triggers. The course of visual searching was analyzed through the emotional effects arising from these emotion-eliciting stimuli. The flanker stimuli showed effects at about 150–250 ms following the stimulus onset, while the effect of target stimuli showed effects at about 300–400 ms. The visual search sequence in an emotional flanker task moved from a whole overview to a specific target, even if the target always appeared at a known location. The processing sequence was “parallel” in this task. The results supported the feature integration theory of visual search.     

Locomoting-to-reach: information variables and control strategies for nested actions

Locomoting-to-reach is a basic perception/action behavior that requires visual information for the control of both locomotion and reaching components. We investigated the visual information and the control strategies used to guide both the head and the hand on approach to a target in a locomotion-to-reach task. In this study, participants were required to locomote in the dark to a lit target in three different conditions: monocular vision/target with image size, binocular vision/target with image size, and binocular vision/point-light target (without image size). In task one, participants brought their eyes to the target. In task two, participants brought their outstretched hand to the target. Movement trajectories for both tasks were analyzed. Results show that participants were significantly more accurate when binocular information was present. In both tasks, participants were found to use a proportional rate control strategy rather than a constant [(t)\dot] \dot{\tau} strategy. In the walk-to-reach task, they used monocular and/or binocular τ information to guide the head and then switched to using relative disparity τ to guide the hand to final target acquisition, switching when the hand centric τ became less than the head centric τ. Dynamical models of the information and control strategies were used to perform simulations that were found to fit the data well. The conclusion is that proportional rate control is used sequentially with head centric, then hand-centric τ-based information, using at each moment the τ with the smallest value.     

Pseudoneglect for mental alphabet lines is affected by prismatic adaptation

While patients with right parietal damage and spatial neglect bisect lines to the right, the general population bisects lines to the left; a phenomenon known as pseudoneglect. The leftward bias also occurs for mental representations, such as number and alphabet lines. Prismatic adaptation can have a dramatic effect on attentional bias and corrects neglect and pseudoneglect for physical and mental number lines. This study examined whether prismatic adaptation can correct leftward bisection biases for alphabet lines, which may have a different spatial arrangement compared to number lines. In pre-adaptation testing, students (n = 42) were shown letter trigrams (e.g. C H P) and judged whether the alphabetical distance before or after the inner-letter was larger. Participants were then split into three groups and were adapted to left-shifting, control or right-shifting prims. After adaptation, the mental alphabet bisection task was re-administered. The length of left side of the alphabet lines was overestimated by all three groups in the pre-adaptation phase. Right-shifting prisms and control spectacles had no effect on the leftward bias whereas exposure to left-shifting prisms corrected the bias. The results replicate an effect observed for mental number lines and demonstrate that low-level sensory-motor shifts can correct attentional biases associated with high-level representations, such as letters.