Radial bisection of words and lines in right‐brain‐damaged patients with spatial neglect

The bisection of lines positioned radially (with the two ends of the line close and far, with respect to the participant's body) has been less investigated than that of lines placed horizontally (with their two ends left and right, with respect to the body's midsagittal plane). In horizontal bisection, patients with left neglect typically show a rightward bias for both lines and words, greater with longer stimuli. As for radial bisection, available data indicate that neurologically unimpaired participants make a distal error, while results from right‐brain‐damaged patients with left spatial neglect are contradictory. We investigated the bisection of radially oriented words, with the prediction that, during bisection, linguistic material would be recoded to its canonical left‐to‐right format in reading, with the performance of neglect patients being similar to that for horizontal words. Thirteen right‐brain‐damaged patients (seven with left spatial neglect) and fourteen healthy controls were asked to manually bisect 40 radial and 40 horizontal words (5–10 letters), and 80 lines, 40 radial and 40 horizontal, of comparable length. Right‐brain‐damaged patients with spatial neglect exhibited a proximal bias in the bisection of short radial words, with the proximal part corresponding to the final right part of horizontally oriented words. This proximal error was not found in patients without neglect and healthy controls. For bisection, short radial words may be recoded to the canonical orthographic horizontal format, unveiling the impact of left neglect on radially oriented stimuli.     

Small on the left,large on the right: numbers orient visual attention onto space in preverbal infants

Numbers are represented as ordered magnitudes along a spatially oriented number line. While culture and formal education modulate the direction of this number–space mapping, it is a matter of debate whether its emergence is entirely driven by cultural experience. By registering 8–9‐month‐old infants’ eye movements, this study shows that numerical cues are critical in orienting infants’ visual attention towards a peripheral region of space that is congruent with the number's relative position on a left‐to‐right oriented representational continuum. This finding provides the first direct evidence that, in humans, the association between numbers and oriented spatial codes occurs before the acquisition of symbols or exposure to formal education, suggesting that the number line is not merely a product of human invention.     

You never know where you are going until you know where you have been: Disorganized search after stroke

Disorders in spatial exploration can be expressed in a disorganized fashion of target cancellation. There is debate regarding whether disorganized search is related to stroke in general, to right brain damage or to unilateral spatial neglect (USN) in particular. In this study, 280 stroke patients and 37 healthy control subjects performed a computerized shape cancellation test. We investigated the number of perseverations and several outcome measures regarding disorganized search: Consistency of search direction (best r), distance between consecutive cancelled targets and intersections with paths between previous cancelled targets. We compared performance between patients with left and right brain damage (L, R) and with and without USN (USN+, USN?), resulting in four subgroups: LUSN?, RUSN?, LUSN+, and RUSN+. Higher numbers of intersections were found for the left brain‐ and right brain‐damaged patients with USN and for the right brain‐damaged patients without USN, compared to healthy control subjects. Furthermore, right brain‐damaged patients with USN showed a higher number of intersections compared to right brain‐damaged patients without USN and compared to left brain‐damaged patients with USN. To conclude, disorganized search was most strongly related to the neglect syndrome, and patients with more severe USN were even more impaired.     

Improving left spatial neglect through music scale playing

The study assessed whether the auditory reference provided by a music scale could improve spatial exploration of a standard musical instrument keyboard in right‐brain‐damaged patients with left spatial neglect. As performing music scales involves the production of predictable successive pitches, the expectation of the subsequent note may facilitate patients to explore a larger extension of space in the left affected side, during the production of music scales from right to left. Eleven right‐brain‐damaged stroke patients with left spatial neglect, 12 patients without neglect, and 12 age‐matched healthy participants played descending scales on a music keyboard. In a counterbalanced design, the participants' exploratory performance was assessed while producing scales in three feedback conditions: With congruent sound, no‐sound, or random sound feedback provided by the keyboard. The number of keys played and the timing of key press were recorded. Spatial exploration by patients with left neglect was superior with congruent sound feedback, compared to both Silence and Random sound conditions. Both the congruent and incongruent sound conditions were associated with a greater deceleration in all groups. The frame provided by the music scale improves exploration of the left side of space, contralateral to the right hemisphere, damaged in patients with left neglect. Performing a scale with congruent sounds may trigger at some extent preserved auditory and spatial multisensory representations of successive sounds, thus influencing the time course of space scanning, and ultimately resulting in a more extensive spatial exploration. These findings offer new perspectives also for the rehabilitation of the disorder.     

A mental number line in human newborns

Humans represent numbers on a mental number line with smaller numbers on the left and larger numbers on the right side. A left‐to‐right oriented spatial–numerical association, (SNA), has been demonstrated in animals and infants. However, the possibility that SNA is learnt by early exposure to caregivers’ directional biases is still open. We conducted two experiments: in Experiment 1, we tested whether SNA is present at birth and in Experiment 2, we studied whether it depends on the relative rather than the absolute magnitude of numerousness. Fifty‐five‐hour‐old newborns, once habituated to a number (12), spontaneously associated a smaller number (4) with the left and a larger number (36) with the right side (Experiment 1). SNA in neonates is not absolute but relative. The same number (12) was associated with the left side rather than the right side whenever the previously experienced number was larger (36) rather than smaller (4) (Experiment 2). Control on continuous physical variables showed that the effect is specific of discrete magnitudes. These results constitute strong evidence that in our species SNA originates from pre‐linguistic and biological precursors in the brain.     

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.     

When the whole is more than the sum of the parts: Evidence from visuospatial neglect

One possible pathological mechanism underlying the rightward bisection error of right‐brain‐damaged patients with left spatial neglect is a leftward relaxation of the spatial representational medium. This view was originally based on the finding that patients with left neglect, required to extend horizontal segments, in order to double their original length, may exhibit a relative left overextension of the drawn lines ( Bisiach et al., 1994 ). We investigated this putative distortion of representational space using a 16 cm ‘line segmentation’ task (Experiment 1). Were the representation of space relaxed contralesionally, a progressive increase from right to left of the size of the drawn segments would be expected. Right‐brain‐damaged patients with left unilateral neglect (N=12) performed the segmentation task with no left versus right differences, as right‐brain‐damaged patients without neglect (N=8), and neurologically unimpaired control subjects (N=10), did. Experiments 2 and 3 explored the effects of sample length (1, 2, 4, and 8 cm), by which the 16 cm lines had to be segmented. Neglect patients produced longer left‐sided segments only for the 8 cm sample (i.e. half of the length of the segment). This set of experiments suggests an impairment in the segmentation task only with the larger (8 cm) sample, when a more global level of processing may be involved. Experiment 4 assessed this hypothesis by a ‘part/whole’ bisection task, using 8 cm lines, presented either embedded in a longer 16 cm line or in isolation. Neglect patients made a larger rightward bisection error when the segment was not embedded. The suggestion is made that the lateral distortion of the representation of space in neglect patients (i.e. a leftward relaxation of the spatial medium) concerns tasks where a more ‘global’ representation of the visual stimulus has to be set up. The different demands of the segmentation and bisection tasks are discussed.     

Hemispatial neglect and serial order in verbal working memory

Working memory refers to our ability to actively maintain and process a limited amount of information during a brief period of time. Often, not only the information itself but also its serial order is crucial for good task performance. It was recently proposed that serial order is grounded in spatial cognition. Here, we compared performance of a group of right hemisphere-damaged patients with hemispatial neglect to healthy controls in verbal working memory tasks. Participants memorized sequences of consonants at span level and had to judge whether a target consonant belonged to the memorized sequence (item task) or whether a pair of consonants were presented in the same order as in the memorized sequence (order task). In line with this idea that serial order is grounded in spatial cognition, we found that neglect patients made significantly more errors in the order task than in the item task compared to healthy controls. Furthermore, this deficit seemed functionally related to neglect severity and was more frequently observed following right posterior brain damage. Interestingly, this specific impairment for serial order in verbal working memory was not lateralized. We advance the hypotheses of a potential contribution to the deficit of serial order in neglect patients of either or both (1) reduced spatial working memory capacity that enables to keep track of the spatial codes that provide memorized items with a positional context, (2) a spatial compression of these codes in the intact representational space.     

Neural connectivity patterns underlying symbolic number processing indicate mathematical achievement in children

In early childhood, humans learn culturally specific symbols for number that allow them entry into the world of complex numerical thinking. Yet little is known about how the brain supports the development of the uniquely human symbolic number system. Here, we use functional magnetic resonance imaging along with an effective connectivity analysis to investigate the neural substrates for symbolic number processing in young children. We hypothesized that, as children solidify the mapping between symbols and underlying magnitudes, important developmental changes occur in the neural communication between the right parietal region, important for the representation of non‐symbolic numerical magnitudes, and other brain regions known to be critical for processing numerical symbols. To test this hypothesis, we scanned children between 4 and 6 years of age while they performed a magnitude comparison task with Arabic numerals (numerical, symbolic), dot arrays (numerical, non‐symbolic), and lines (non‐numerical). We then identified the right parietal seed region that showed greater blood‐oxygen‐level‐dependent signal in the numerical versus the non‐numerical conditions. A psychophysiological interaction method was used to find patterns of effective connectivity arising from this parietal seed region specific to symbolic compared to non‐symbolic number processing. Two brain regions, the left supramarginal gyrus and the right precentral gyrus, showed significant effective connectivity from the right parietal cortex. Moreover, the degree of this effective connectivity to the left supramarginal gyrus was correlated with age, and the degree of the connectivity to the right precentral gyrus predicted performance on a standardized symbolic math test. These findings suggest that effective connectivity underlying symbolic number processing may be critical as children master the associations between numerical symbols and magnitudes, and that these connectivity patterns may serve as an important indicator of mathematical achievement.     

Selective spatial attention and length representation in normal subjects and in patients with unilateral spatial neglect

The aim of this study was to assess whether perceptual representation along the horizontal axis is affected by hemispace position of the stimulus or by orienting attention to one side. Ten control subjects and 10 right brain damaged patients with left unilateral spatial neglect (USN) were asked to bisect lines of five lengths in three space positions (left, center, right) and under three cueing conditions (no cue, left cue, right cue). Normal controls showed significant displacement of bisection opposite to the side of hemispace presentation and toward the side of cueing. USN patients showed a bisection error toward the right end which increased with lines placed in the left hemispace and decreased with lines placed in the right hemispace and when attention was oriented toward the left side. We conclude that (1) In absence of cues normal subjects tend to overestimate the portions of space closer to their body midline; (2) both normal and USN patients tend to overestimate portions of space that they direct their attention to; (3) USN patients' performance without cueing is consistent with an attentional shift toward the right hemispace implying a gradient of overestimation of the right-most portions of space. A common neural substratum for directing attention and space representation can explain these findings.     

Drawing perseveration in neglect: Effects of target density

In cancellation tasks, patients with unilateral spatial neglect typically fail to mark targets within the side of the sheet contralateral to the side of the lesion (contralesional). Moreover, they can show a perseverative behaviour, which consists in repeatedly cancelling stimuli, mainly in the side of the display ipsilateral to the side of the lesion (ipsilesional). We investigated in 13 right‐brain‐damaged patients with left spatial neglect and perseverative behaviour whether and how different densities of horizontal targets modulated omission and perseverative errors. We found that the density of targets modulated the patients’ distribution of neglect (area of omission), but not its extent, as indexed by the percentage of omissions. Specifically, the area of omissions tightened when target density increased leftwards. On the other hand, target density did not affect the distribution of perseverative behaviour (area of perseveration), as well as its extent, as indexed by the percentage of perseverations. Correlation analyses showed that both the extent and the distribution of omissions were positively correlated to clinical measures of spatial neglect. Conversely, perseverations did not show such a correlation. These findings support the view that two different pathological mechanisms might be involved in left spatial neglect and in ipsilesional perseverative behaviour.     

Testing conclusions from functional imaging of working memory with data from acute stroke

Functional imaging studies indicate that the left hemisphere mediates verbal working memory, while the right hemisphere mediates both verbal and spatial working memory. We evaluated acute stroke patients with working memory tests and imaging to identify whether unilateral dysfunction causes deficits in spatial and/or verbal working memory deficits. While left cortical stroke patients had verbal working memory impairments (p<0.003), right cortical stroke patients had both verbal p<0.007) and spatial working memory (p<0.03) impairments, confirming functional imaging results. Patients with transient ischemic stroke and patients with non-cortical stroke did not have significant deficits in working memory in either modality.     

Visual imagery and knowledge about the visual appearance of objects in patients with posterior cerebral artery lesions

The purpose of this study was to explore whether patients with left posterior cerebral artery (PCA) lesions have defective mental visual imagery and to differentiate whether such a deficit stems from a loss of knowledge about the visual appearance of objects or from an inability to create mental visual images out of preserved visual knowledge. Normal controls and patients with either left or right PCA lesions were asked to verify low- and high-imagery sentences and then to verify pictorial representations of the predicates of high-imagery sentences. High-imagery questions concerned either the shape or the color of objects. In addition, perceptual discrimination of shape and color was assessed. Patients with right PCA lesions were impaired on the perceptual discrimination tasks. Left PCA patients did not significantly differ from controls on low-imagery sentences but scored significantly lower on shape and color questions. Their impairment was distinctly more severe with the pictorial than with the verbal versions of shape and color questions. In comparison to patients with occipital left PCA lesions, patients with temporo-occipital left PCA lesions were selectively impaired on verbal and visual color questions. It is concluded that patients with left PCA lesions lack knowledge about shape and color of objects, but that their ability to convert visual knowledge into mental images is preserved.     

Functional asymmetry of human prefrontal cortex: encoding and retrieval of verbally and nonverbally coded information

There are several views about the organization of memory functions in the human prefrontal cortex. One view assumes a process-specific brain lateralization according to different memory subprocesses, that is, encoding and retrieval. An alternative view emphasizes content-specific lateralization of brain systems involved in memory processes. This study addresses this apparent inconsistency between process- and content-specific lateralization of brain activity by investigating the effects of verbal and nonverbal encoding on prefrontal activations during encoding and retrieval of environmental novel sounds using fMRI. An intentional memory task was applied in which subjects were required either to judge the sounds' loudness (nonverbal encoding task) or to indicate whether or not a sound can be verbally described (verbal encoding task). Retrieval processes were examined in a subsequent yes/no recognition test. In the study phase the right posterior dorsolateral prefrontal cortex (PFC) was activated in both tasks. During verbal encoding additional activation of the left dorsolateral PFC was obtained. Retrieval-related fMRI activity varied as a function of encoding task: For the nonverbal task we detected an activation focus in the right posterior dorsolateral PFC whereas an activation in the left dorsolateral PFC was observed for the verbal task. These findings indicate that the right dorsolateral PFC is engaged in encoding of auditory information irrespective of encoding task. The lateralization of PFC activity during retrieval was shown to depend on the availability of verbal codes, with left hemispheric involvement for verbally and right hemispheric activation for nonverbally coded information.     

Lateralization of egocentric and allocentric spatial processing after parietal brain lesions

The purpose of this paper was to verify whether left and right parietal brain lesions may selectively impair egocentric and allocentric processing of spatial information in near/far spaces. Two Right-Brain-Damaged (RBD), 2 Left-Brain-Damaged (LBD) patients (not affected by neglect or language disturbances) and eight normal controls were submitted to the Ego-Allo Task requiring distance judgments computed according to egocentric or allocentric frames of reference in near/far spaces. Subjects also completed a general neuropsychological assessment and the following visuospatial tasks: reproduction of the Rey-Osterreith figure, line length judgement, point position identification, mental rotation, mental construction, line length memory, line length inference, Corsi block-tapping task. LBD patients presented difficulties in both egocentric and allocentric processing, whereas RBD patients dropped in egocentric but not in allocentric judgements, and in near but not far space. Further, RBD patients dropped in perceptually comparing linear distances, whereas LBD patients failed in memory for distances. The overall pattern of results suggests that the right hemisphere is specialized in processing metric information according to egocentric frames of reference. The data are interpreted according to a theoretical model that highlights the close link between egocentric processing and perceptual control of action.     

Spatializing Emotion: No Evidence for a Domain‐General Magnitude System

People implicitly associate different emotions with different locations in left‐right space. Which aspects of emotion do they spatialize, and why? Across many studies people spatialize emotional valence, mapping positive emotions onto their dominant side of space and negative emotions onto their non‐dominant side, consistent with theories of metaphorical mental representation. Yet other results suggest a conflicting mapping of emotional intensity (a.k.a., emotional magnitude), according to which people associate more intense emotions with the right and less intense emotions with the left — regardless of their valence; this pattern has been interpreted as support for a domain‐general system for representing magnitudes. To resolve the apparent contradiction between these mappings, we first tested whether people implicitly map either valence or intensity onto left‐right space, depending on which dimension of emotion they attend to (Experiments 1a, b). When asked to judge emotional valence, participants showed the predicted valence mapping. However, when asked to judge emotional intensity, participants showed no systematic intensity mapping. We then tested an alternative explanation of findings previously interpreted as evidence for an intensity mapping (Experiments 2a, b). These results suggest that previous findings may reflect a left‐right mapping of spatial magnitude (i.e., the size of a salient feature of the stimuli) rather than emotion. People implicitly spatialize emotional valence, but, at present, there is no clear evidence for an implicit lateral mapping of emotional intensity. These findings support metaphor theory and challenge the proposal that mental magnitudes are represented by a domain‐general metric that extends to the domain of emotion.     

Post‐Learning Verbal Information Changes Visual and Motor Memory for Hand‐Manipulative Tasks

Many instructions of a motor task include visual and verbal information. However, verbal information presented after a visual event has been shown to influence memory. This study examined whether this effect applies for hand‐manipulative motor tasks such as knot tying. Eighty‐six naive participants learned to tie the archaic bowline. Subsequently, half of the participants received misleading verbal information about the cowboy bowline, which differs from the originally instructed archaic bowline in one central detail: At a certain point, the rope crosses from left to right instead of from right to left. The remaining half of the participants received no misinformation. Dependent variables measured visual and motor memory for the knot. Results showed that misleading verbal information influenced visual and motor memory for knot‐tying tasks. More specifically, the misleading information changed memory at exactly this point to which it referred. This study suggests new avenues for our understanding and design of learning environments. Copyright © 2014 John Wiley & Sons, Ltd.     

Attention,Memory, and Language after Pediatric Ischemic Stroke

A previous study evaluating receptive language after unilateral brain damage in childhood hypothesized lateralized attention and memory deficits without direct measurement. Our study directly measured attention, memory, and language in order to evaluate empirically the severity and laterality of sequelae. The performances of 11 individuals with a unilateral ischemic-lesion (7 right and 4 left hemisphere) were compared to controls matched on age, sex, and socioeconomic status. Results suggest subtle but persistent deficits in verbal memory, functional memory, and speed of processing after a lesion to either hemisphere. Lesions sustained before two years of age were associated with the lowest IQ scores. Our findings provide support for a configural representation of language that can to some extent compensate for inefficient or damaged components (Bates, 1994), and the middle-ground lateralization position (Thal et al., 1991) that asserts initial hemispheric specialization with the potential for reorganization.     

Dissociating mental transformations and visuo‐spatial storage in working memory: Evidence from representational neglect

A study is reported of visuo‐spatial working memory in two individuals suffering from a cognitive deficit known as unilateral spatial neglect, and seven healthy control participants. Both patients have difficulties reporting details on the left side of imaged representations, and one has an additional difficulty with perceptual input to the left of his body midline. All participants were asked to report the location and identity of objects presented in novel 2 × 2 arrays that were either present throughout or were described orally by the experimenter, with no visual input. On half of the trials, the report was to be made from the opposite perspective, requiring 180 degree mental rotation of the mentally represented array. The patients show an impaired ability to report details from the presented or the imagined left, but had no difficulty with mental rotation. Results point to a clear separation between the processes of perception and those of visuo‐spatial working memory. Results also suggest that the patients might be suffering from damage to the system used for holding visuo‐spatial representations rather than a difficulty with attending to elements of that representation.