Flanker interference effects in a line bisection task

Previous studies have shown that flanking distractors influence line bisection. In the present study, we examined if reaching the flanker after bisecting the line resulted in a variation of flanker interference on line bisection. Right- and left-handed participants were asked to bisect a horizontal line flanked by a dot (bisection task, B-task) or to bisect the line and then to reach the dot (bisection plus reaching task, BR-task). The dot was placed laterally to, and above or below, the line edge. The results showed that in both tasks the subjective midpoint was shifted away from the position of the dot. However, this effect was greater in the BR-task than in the B-task. We suggest that the requirement to perform an action to the flanker in the BR-task induced participants to pay more attention to the dot, enhancing its salience and distorting effects on line bisection.     

Development of attention in normal children: A possible corpus callosum effect

Two tests designed to examine the ability of young children to move their hands into contralateral hemispace were given to 60 normal, right‐handed 2‐ to 5‐year‐olds. Results from these tasks, line bisection and letter cancellation, indicated that the older children's performances were similar to adults’. However, on the line bisection task, the younger children did not cross the midline as well as the older children, deviating to the left with the left hand and to the right with the right hand. On letter cancellation, a similar effect was seen for the left hand, but not for the right hand. This failure to cross the midline adequately is similar to that seen in patients with lesions of the corpus callosum. Therefore, it was concluded that performance by the younger children indicated a relative immaturity of callosal function that may correspond to the normal lack of callosal myelination in young children.     

Exploring the syndrome of spatial unilateral neglect through an illusion of length

Both a neuropsychological syndrome (unilateral spatial neglect) and a visual illusion of length (the Brentano version of the Müller-Lyer illusion) bring about a misjudgement of the subjective centre of a horizontal line, with a unilateral shift. In experiment 1 we investigated, in patients with left unilateral neglect, illusory effects of horizontal length, with the aim of exploring the functional and neural basis of horizontal space perception, and the role of visual processing in shaping the patients' bisection performance. Fourteen right-brain-damaged patients with left spatial unilateral neglect, seven with and seven without left visual half-field deficits (assessed by confrontation, perimetry, and visual event-related potentials), entered this study. Two conditions of manual line bisection were assessed: setting the mid-point of a horizontal line, and of the shaft of the Brentano-Müller-Lyer illusion, with either a left- or a right-sided expansion. Both groups of patients set the subjective midpoint to the right of the objective centre of the line, consistent with the presence of left neglect. Patients with neglect and left hemianopia showed no illusory effects and a greater bisection error. The effects of the illusion, by contrast, were fully present in neglect patients without hemianopia, in both illusory conditions, adding to, or subtracting from, the rightward bisection bias. Anatomoclinical correlations revealed an association of damage to the occipital regions with the lack of illusory effects. Conversely, more anterior damage, sparing these regions, did not disrupt the illusion, revealing a dissociation between visual and spatial processing of extension. These findings suggest that processing of the Müller-Lyer illusion of length is likely to occur in the occipital cortex, at a retinotopic level of representation. In neglect patients with left homonymous hemianopia the visual deficit adds to the spatial bias, yielding a greater error in line bisection, but not in other visual exploratory tasks, such as cancellation, where the contribution of retinotopic frames is likely to be comparatively minor. Experiment 2 showed preserved illusory effects in patients with homonymous visual field defects without spatial unilateral neglect, suggesting that preserved spatial processing may compensate for unilateral visual field defects.     

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.     

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.     

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.     

Pseudoneglect and embryonic light stimulation in the avian brain

A bias to allocate attention to the left hemispace, similar to the well-known pseudoneglect phenomenon shown by humans, has been recently reported in domestic chicks and other species of birds. Asymmetrical light exposure of the embryo of the domestic chick in a critical period before hatching is known to be responsible for a structural asymmetry in the visual ascending projections of the thalamofugal pathway and for lateralization of some visual behaviors. Thus the animal model provided by the chick makes possible investigation of the prenatal factors that may influence asymmetry in spatial attention. Here chicks coming from eggs exposed to light (light incubated, Li-chicks) and chicks incubated in darkness (dark incubated, Di-chicks) were tested in a task in which they were required to explore an area in front of them and to sample grains of food. The results showed that Li-chicks attended more to target stimuli located in the left hemispace, whereas no asymmetry was shown by Di-chicks. When grains of food were presented with small novel pebbles as distractors, both Li- and Di-chicks tended to allocate attention toward the left hemispace. When, however, chicks were tested after familiarization with pebbles, no bias was shown by either Li- and Di-chicks. Hence it seems that cerebral lateralization associated with right hemispheric involvement in response to novelty, interacts with the modulatory effect of asymmetric embryonic light stimulation on preferential allocation of spatial attention in the left hemispace (right hemisphere) and right eye (left hemisphere) control of visual discrimination during feeding.     

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.     

Emotional influences on spatial attention

The relationships between the anterior-posterior and left-right regions of the brain have been characterized as mutually inhibitory. Whereas the left hemisphere attends to right proximal hemispace and is associated with positive emotions, the right hemisphere attends to left distal hemispace and is associated with negative emotions. Because of the excitatory and inhibitory influences between the left and right frontal and posterior regions of the brain, the expression of emotion will result in an ipsilateral attentional bias. Given these functional systems, we hypothesized that positive emotions would be associated with a bias for left distal hemispace and negative emotions would be associated with a bias for right proximal hemispace. We tested these hypotheses by having 138 undergraduate students place emotionally labeled pegs on a large board. Our results indicated that the positively labeled pegs were placed in left distal hemispace and the relative placement of negatively labeled pegs was rightward and proximally. Whereas numerous research investigations have examined how attention is biased for emotional stimuli, ours is the first investigation to provide evidence that emotions can bias attentional allocation.     

The middle range of the number line orients attention to the left side of visual space

Mental representation of numbers is believed to be spatial in nature, with small numbers occupying the left and large numbers the right side of a putative mental number line. Consistent with this, presentation of numbers from the low and high ends of the mental number line induces covert shifts of spatial attention to the left and right side of visual space, respectively. However, the effect of the presentation of the middle range (containing numbers below and above the midpoint) of the number line on visual perception has so far not been studied. Here we show in two experiments, using a line bisection task and a simple target detection task, that processing of middle-range numbers affects allocation of visuospatial attention in a similar way as processing of small numbers, with attention shifted to the left side of space. We suggest that this pattern of results arises due to “anchoring” heuristics that participants use in number processing.     

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.     

Development and evaluation of a new instrument to measure visual exploration behavior

Effective visual exploration is required for many activities of daily living and instruments to assess visual exploration are important for the evaluation of the visual and the oculomotor system. In this article, the development of a new instrument to measure central and peripheral target recognition is described. The measurement setup consists of a hemispherical projection which allows presenting images over a large area of ±90° horizontal and vertical angle. In a feasibility study with 14 younger (21–49 years) and 12 older (50–78 years) test persons, 132 targets and 24 distractors were presented within naturalistic color photographs of everyday scenes at 10°, 30°, and 50° eccentricity. After the experiment, both younger and older participants reported in a questionnaire that the task is easy to understand, fun and that it measures a competence that is relevant for activities of daily living. A main result of the pilot study was that younger participants recognized more targets with smaller reaction times than older participants. The group differences were most pronounced for peripheral target detection. This test is feasible and appropriate to assess the functional field of view in younger and older adults.     

Distinct mechanisms for the impact of distraction and interruption on working memory in aging

Interference is known to negatively impact the ability to maintain information in working memory (WM), an effect that is exacerbated with aging. Here, we explore how distinct sources of interference, i.e., distraction (stimuli to-be-ignored) and interruption (stimuli requiring attention), differentially influence WM in younger and older adults. EEG was recorded while participants engaged in three versions of a delayed-recognition task: no interference, a distracting stimulus, and an interrupting stimulus presented during WM maintenance. Behaviorally, both types of interference negatively impacted WM accuracy in older adults significantly more than younger adults (with a larger deficit for interruptions). N170 latency measures revealed that the degree of processing both distractors and interruptors predicted WM accuracy in both populations. However, while WM impairments could be explained by excessive attention to distractors by older adults (a suppression deficit), impairment induced by interruption were not clearly mediated by age-related increases in attention to interruptors. These results suggest that distinct underlying mechanisms mediate the impact of different types of external interference on WM in normal aging.     

The rubber hand illusion modulates pseudoneglect

The rubber hand illusion (RHI) refers to the illusory perception of ownership of a rubber hand that may occur when covert tactile stimulation of a participant's hand co-occurs with overt corresponding stimulation of a rubber hand. It is proposed that integrating the rubber hand into one's body image may shift the subjective body midline away from the rubber hand. The present study investigated the influence of the RHI on pseudoneglect on the line bisection task, i.e. the leftward bias when marking the centre of horizontal lines, in 79 neurologically healthy adults. Overall, pseudoneglect was reduced after RHI application. Importantly, this effect was specific for individuals who reported having vividly experienced the illusion (high responders) as opposed to individuals who did not (low responders). Moreover, pseudoneglect was eliminated only after RHI application to the left hand. This pattern of results is consistent with functional hemispheric asymmetry for spatial processing and suggests that integrating the left sided rubber hand into one's body image shifts the subjective body midline to the right, thus counteracting pseudoneglect.     

The relation between polysomnography and subjective sleep and its dependence on age – poor sleep may become good sleep

Women complain more about sleep than men, but polysomnography (PSG) seems to suggest worse sleep in men. This raises the question of how women (or men) perceive objective (PSG) sleep. The present study sought to investigate the relation between morning subjective sleep quality and PSG variables in older and younger women. A representative sample of 251 women was analysed in age groups above and below 51.5 years (median). PSG was recorded at home during one night. Perceived poor sleep was related to short total sleep time (TST), long wake within total sleep time (WTSP), low sleep efficiency and a high number of awakenings. The older women showed lower TST and sleep efficiency and higher WTSP for a rating of good sleep than did the younger women. For these PSG variables the values for good sleep in the older group were similar to the values for poor sleep in the young group. It was concluded that women perceive different levels of sleep duration, sleep efficiency and wake after sleep onset relatively well, but that older women adjust their objective criteria for good sleep downwards. It was also concluded that age is an important factor in the relation between subjective and objective sleep.     

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.     

The effects of multisensory targets on saccadic trajectory deviations: eliminating age differences

The present study had two aims. First, to determine if bimodal audio–visual targets allow for greater inhibition of visual distractors, which in turn may lead to greater saccadic trajectory deviations away from those distractors. Second, to determine if bimodal targets can reduce age differences in the ability to generate deviations away, as older adults tend to benefit more from multisensory integration than younger adults. The results show that bimodal targets produced larger deviations away than unimodal targets, but only when the distractor preceded the target, and this effect was comparable across age groups. Furthermore, in contrast to previous research, older adults in this study showed similar deviations away from distractors to those of younger adults. These findings suggest that age differences in the production of trajectory deviations away are not inevitable and that multisensory integration may be an important means for increasing top–down inhibition of irrelevant distraction.     

Pseudoneglect in schizophrenia: A line bisection study with cueing

Introduction. Numerous authors have reported the existence of lateralised abnormalities towards the right side in patients with schizophrenia.

Methods. In the present study, a manual line bisection task was used to assess the existence of a visuospatial bias in patients with schizophrenia as compared to healthy subjects and left unilateral neglect patients. In addition, we used a local cueing paradigm (consisting of a number placed on the right, on the left, or at both ends of the line).

Results. Healthy subjects showed a leftwards trend in the “no cue” condition (known as pseudoneglect) and neglect patients showed a right bias in all cue conditions. In contrast, patients with schizophrenia placed their manual estimation of the centre further to the left than healthy subjects in all cue conditions, reflecting neglect of the right side of the line. Moreover, like healthy subjects and neglect patients, patients with schizophrenia were affected by the local cueing.

Conclusion. Hence, patients with schizophrenia show a bias in their spatial representation, which does not interfere with local context processing.     

Line bisection as a neural marker of approach motivation

Approach motivation has been reliably associated with relative left prefrontal brain activity as measured with electroencephalography (EEG). Motivation researchers have increasingly used the line bisection task, a behavioral measure of relative cerebral asymmetry, as a neural index of approach motivation‐related processes. Despite its wide adoption, however, the line bisection task has not been confirmed as a valid measure of the precise pattern of activity linked to approach motivation. In two studies, we demonstrate that line bisection bias is specifically related to baseline, approach‐related, prefrontal EEG alpha asymmetry (Study 1) and is heightened by the same situational factors that heighten the same approach‐related prefrontal EEG alpha asymmetry (Study 2). Results support the line bisection task as an efficient and unobtrusive behavioral neuroscience measure of approach motivation.     

Analyses of preschool children's task choices based on the objective and subjective task difficulty levels

In this experiment, younger (4-year-olds) and older (6-year-olds) preschool children's task choices were analyzed based on the objective and subjective task difficulty levels. First, preschool children's understanding of the objective task difficulty levels was examined. While most older children understood the objective task difficulty levels, younger children did not. No understandable children's subjective task difficulty levels were checked. Next, younger and older children's task choices were analyzed respectively based on the objective task difficulty levels. As a result, there was no difference between an easy task choice and a moderate or a difficult task choice in both of them. Then, understandable children's task choices were reanalyzed based on the objective task difficulty levels and no understandable children's task choices were reanalyzed based on their subjective task difficulty levels. As a result, younger children chose an easy task more than a moderate or a difficult task. On the other hand, older children chose a moderate or a difficult task more than an easy one.