Vertical bias in neglect: A question of time?

Neglect is defined as the failure to attend and to orient to the contralesional side of space. A horizontal bias towards the right visual field is a classical finding in patients who suffered from a right-hemispheric stroke. The vertical dimension of spatial attention orienting has only sparsely been investigated so far. The aim of this study was to investigate the specificity of this vertical bias by means of a search task, which taps a more pronounced top-down attentional component. Eye movements and behavioural search performance were measured in thirteen patients with left-sided neglect after right hemispheric stroke and in thirteen age-matched controls. Concerning behavioural performance, patients found significantly less targets than healthy controls in both the upper and lower left quadrant. However, when targets were located in the lower left quadrant, patients needed more visual fixations (and therefore longer search time) to find them, suggesting a time-dependent vertical bias.

Moving along the mental number line: Interactions between whole-body motion and numerical cognition

Active head turns to the left and right have recently been shown to influence numerical cognition by shifting attention along the mental number line. In the present study, we found that passive whole-body motion influences numerical cognition. In a random-number generation task (Experiment 1), leftward and downward displacement of participants facilitated small number generation, whereas rightward and upward displacement facilitated the generation of large numbers. Influences of leftward and rightward motion were also found for the processing of auditorily presented numbers in a magnitude-judgment task (Experiment 2). Additionally, we investigated the reverse effect of the number-space association (Experiment 3). Participants were displaced leftward or rightward and asked to detect motion direction as fast as possible while small or large numbers were auditorily presented. When motion detection was difficult, leftward motion was detected faster when hearing small number and rightward motion when hearing large number. We provide new evidence that bottom-up vestibular activation is sufficient to interact with the higher-order spatial representation underlying numerical cognition. The results show that action planning or motor activity is not necessary to influence spatial attention. Moreover, our results suggest that self-motion perception and numerical cognition can mutually influence each other.

Self-motion perception influences number processing: evidence from a parity task

We investigated the role of horizontal body motion on the processing of numbers. We hypothesized that leftward self-motion leads to shifts in spatial attention and therefore facilitates the processing of small numbers, and vice versa, we expected that rightward self-motion facilitates the processing of large numbers. Participants were displaced by means of a motion platform during a parity judgment task. We found a systematic influence of self-motion direction on number processing, suggesting that the processing of numbers is intertwined with the processing of self-motion perception. The results differed from known spatial numerical compatibility effects in that self-motion exerted a differential influence on inner and outer numbers of the given interval. The results highlight the involvement of sensory body motion information in higher-order spatial cognition.

A novel computer test to assess driving-relevant cognitive functions - a pilot study

BACKGROUND: The assessment of driving-relevant cognitive functions in older drivers is a difficult challenge as there is no clear-cut dividing line between normal cognition and impaired cognition and not all cognitive functions are equally important for driving. METHODS: To support decision makers, the Bern Cognitive Screening Test (BCST) for older drivers was designed. It is a computer-assisted test battery assessing visuo-spatial attention, executive functions, eye-hand coordination, distance judgment, and speed regulation. Here we compare the performance in BCST with the performance in paper and pencil cognitive screening tests and the performance in the driving simulator testing of 41 safe drivers (without crash history) and 14 unsafe drivers (with crash history). RESULTS: Safe drivers performed better than unsafe drivers in BCST (Mann-Whitney U test: U = 125.5; p = 0.001) and in the driving simulator (Student's t-test: t(44) = -2.64, p = 0.006). No clear group differences were found in paper and pencil screening tests (p > 0.05; ns). BCST was best at identifying older unsafe drivers (sensitivity 86%; specificity 61%) and was also better tolerated than the driving simulator test with fewer dropouts. CONCLUSIONS: BCST is more accurate than paper and pencil screening tests, and better tolerated than driving simulator testing when assessing driving-relevant cognition in older drivers.

Structural Organization of the Corpus Callosum Predicts Attentional Shifts after Continuous Theta Burst Stimulation

Repetitive transcranial magnetic stimulation (rTMS) applied over the right posterior parietal cortex (PPC) in healthy participants has been shown to trigger a significant rightward shift in the spatial allocation of visual attention, temporarily mimicking spatial deficits observed in neglect. In contrast, rTMS applied over the left PPC triggers a weaker or null attentional shift. However, large interindividual differences in responses to rTMS have been reported. Studies measuring changes in brain activation suggest that the effects of rTMS may depend on both interhemispheric and intrahemispheric interactions between cortical loci controlling visual attention. Here, we investigated whether variability in the structural organization of human white matter pathways subserving visual attention, as assessed by diffusion magnetic resonance imaging and tractography, could explain interindividual differences in the effects of rTMS. Most participants showed a rightward shift in the allocation of spatial attention after rTMS over the right intraparietal sulcus (IPS), but the size of this effect varied largely across participants. Conversely, rTMS over the left IPS resulted in strikingly opposed individual responses, with some participants responding with rightward and some with leftward attentional shifts. We demonstrate that microstructural and macrostructural variability within the corpus callosum, consistent with differential effects on cross-hemispheric interactions, predicts both the extent and the direction of the response to rTMS. Together, our findings suggest that the corpus callosum may have a dual inhibitory and excitatory function in maintaining the interhemispheric dynamics that underlie the allocation of spatial attention. SIGNIFICANCE STATEMENT: The posterior parietal cortex (PPC) controls allocation of attention across left versus right visual fields. Damage to this area results in neglect, characterized by a lack of spatial awareness of the side of space contralateral to the brain injury. Transcranial magnetic stimulation over the PPC is used to study cognitive mechanisms of spatial attention and to examine the potential of this technique to treat neglect. However, large individual differences in behavioral responses to stimulation have been reported. We demonstrate that the variability in the structural organization of the corpus callosum accounts for these differences. Our findings suggest novel dual mechanism of the corpus callosum function in spatial attention and have broader implications for the use of stimulation in neglect rehabilitation.

Dynamic gamma frequency feedback coupling between higher and lower order visual cortices underlies perceptual completion in humans

To perceive a coherent environment, incomplete or overlapping visual forms must be integrated into meaningful coherent percepts, a process referred to as ?Gestalt? formation or perceptual completion. Increasing evidence suggests that this process engages oscillatory neuronal activity in a distributed neuronal assembly. A separate line of evidence suggests that Gestalt formation requires top-down feedback from higher order brain regions to early visual cortex. Here we combine magnetoencephalography (MEG) and effective connectivity analysis in the frequency domain to specifically address the effective coupling between sources of oscillatory brain activity during Gestalt formation. We demonstrate that perceptual completion of two-tone ?Mooney? faces induces increased gamma frequency band power (55?71 Hz) in human early visual, fusiform and parietal cortices. Within this distributed neuronal assembly fusiform and parietal gamma oscillators are coupled by forward and backward connectivity during Mooney face perception, indicating reciprocal influences of gamma activity between these higher order visual brain regions. Critically, gamma band oscillations in early visual cortex are modulated by top-down feedback connectivity from both fusiform and parietal cortices. Thus, we provide a mechanistic account of Gestalt perception in which gamma oscillations in feature sensitive and spatial attention-relevant brain regions reciprocally drive one another and convey global stimulus aspects to local processing units at low levels of the sensory hierarchy by top-down feedback. Our data therefore support the notion of inverse hierarchical processing within the visual system underlying awareness of coherent percepts.

A recuperação da informação da memória de trabalho: evidências baseadas em tarefas de imagem mental e de memória visual

A imagem mental e a memória visual têm sido consideradas como componentes distintos na codificação da informação, e associados a processos diferentes da memória de trabalho. Evidências experimentais mostram, por exemplo, que o desempenho em tarefas de memória baseadas na geração de imagem mentais (imaginação visual) sofre a interferência do ruído visual dinâmico (RVD), mas não se observa o mesmo efeito em tarefas de memória visual baseadas na percepção visual (memória visual). Embora várias evidências mostrem que tarefas de imaginação e de memória visual sejam baseadas em processos cognitivos diferentes, isso não descarta a possibilidade de utilizarem também processos em comum e que alguns resultados experimentais que apontam diferenças entre as duas tarefas resultem de diferenças metodológicas entre os paradigmas utilizados para estuda-las. Nosso objetivo foi equiparar as tarefas de imagem mental visual e memória visual por meio de tarefas de reconhecimento, com o paradigma de dicas retroativas espaciais. Sequências de letras romanas na forma visual (tarefa de memória visual) e acústicas (tarefa de imagem mental visual) foram apresentadas em quatro localizações espaciais diferentes. No primeiro e segundo experimento analisou-se o tempo do curso de recuperação tanto para o processo de imagem quanto para o processo de memória. No terceiro experimento, comparou-se a estrutura das representações dos dois componentes, por meio da apresentação do RVD durante a etapa de geração e recuperação. Nossos resultados mostram que não há diferenças no armazenamento da informação visual durante o período proposto, porém o RVD afeta a eficiência do processo de recuperação, isto é o tempo de resposta, sendo a representação da imagem mental visual mais suscetível ao ruído. No entanto, o processo temporal da recuperação é diferente para os dois componentes, principalmente para imaginação que requer mais tempo para recuperar a informação do que a memória. Os dados corroboram a relevância do paradigma de dicas retroativas que indica que a atenção espacial é requisitada em representações de organização espacial, independente se são visualizadas ou imaginadas.

"mind the gap": The size-distance dissociation in visual neglect is a cueing effect

There is a growing body of evidence that the processes mediating the allocation of spatial attention within objects may be separable from those governing attentional distribution between objects. In the neglect literature, a related proposal has been made regarding the perception of (within-object) sizes and (between-object) distances. This proposal follows observations that, in size-matching and bisection tasks, neglect is more strongly expressed when patients are required to attend to the sizes of discrete objects than to the (unfilled) distances between objects. These findings are consistent with a partial dissociation between size and distance processing, but a simpler alternative must also be considered. Whilst a neglect patient may fail to explore the full extent of a solid stimulus, the estimation of an unfilled distance requires that both endpoints be inspected before the task can be attempted at all. The attentional cueing implicit in distance estimation tasks might thus account for their superior performance by neglect patients. We report two bisection studies that address this issue. The first confirmed, amongst patients with left visual neglect, a reliable reduction of rightward error for unfilled gap stimuli as compared with solid lines. The second study assessed the cause of this reduction, deconfounding the effects of stimulus type (lines vs. gaps) and attentional cueing, by applying an explicit cueing manipulation to line and gap bisection tasks. Under these matched cueing conditions, all patients performed similarly on line and gap bisection tasks, suggesting that the reduction of neglect typically observed for gap stimuli may be attributable entirely to cueing effects. We found no evidence that a spatial extent, once fully attended, is judged any differently according to whether it is filled or unfilled.

Marqueurs électrophysiologiques des dysfonctions attentionnelles et de leur récupération suite à un traumatisme craniocérébral léger

L’objectif principal de cette thèse était d’obtenir, via l’électrophysiologie cognitive, des indices de fonctionnement post-traumatisme craniocérébral léger (TCCL) pour différents niveaux de traitement de l’information, soit l’attention sélective, les processus décisionnels visuoattentionnels et les processus associés à l’exécution d’une réponse volontaire. L’hypothèse centrale était que les mécanismes de production des lésions de même que la pathophysiologie caractérisant le TCCL engendrent des dysfonctions visuoattentionnelles, du moins pendant la période aiguë suivant le TCCL (i.e. entre 1 et 3 mois post-accident), telles que mesurées à l’aide d’un nouveau paradigme électrophysiologique conçu à cet effet. Cette thèse présente deux articles qui décrivent le travail effectué afin de rencontrer ces objectifs et ainsi vérifier les hypothèses émises. Le premier article présente la démarche réalisée afin de créer une nouvelle tâche d’attention visuospatiale permettant d’obtenir les indices électrophysiologiques (amplitude, latence) et comportementaux (temps de réaction) liés aux processus de traitement visuel et attentionnel précoce (P1, N1, N2-nogo, P2, Ptc) à l’attention visuelle sélective (N2pc, SPCN) et aux processus décisionnels (P3b, P3a) chez un groupe de participants sains (i.e. sans atteinte neurologique). Le deuxième article présente l’étude des effets persistants d’un TCCL sur les fonctions visuoattentionelles via l’obtention des indices électrophysiologiques ciblés (amplitude, latence) et de données comportementales (temps de réaction à la tâche et résultats aux tests neuropsychologiques) chez deux cohortes d’individus TCCL symptomatiques, l’une en phase subaigüe (3 premiers mois post-accident), l’autre en phase chronique (6 mois à 1 an post-accident), en comparaison à un groupe de participants témoins sains. Les résultats des articles présentés dans cette thèse montrent qu’il a été possible de créer une tâche simple qui permet d’étudier de façon rapide et peu coûteuse les différents niveaux de traitement de l’information impliqués dans le déploiement de l’attention visuospatiale. Par la suite, l’utilisation de cette tâche auprès d’individus atteints d’un TCCL testés en phase sub-aiguë ou en phase chronique a permis d’objectiver des profils d’atteintes et de récupération différentiels pour chacune des composantes étudiées. En effet, alors que les composantes associées au traitement précoce de l’information visuelle (P1, N1, N2) étaient intactes, certaines composantes attentionnelles (P2) et cognitivo-attentionnelles (P3a, P3b) étaient altérées, suggérant une dysfonction au niveau des dynamiques spatio-temporelles de l’attention, de l’orientation de l’attention et de la mémoire de travail, à court et/ou à long terme après le TCCL, ceci en présence de déficits neuropsychologiques en phase subaiguë surtout et d’une symptomatologie post-TCCL persistante. Cette thèse souligne l’importance de développer des outils diagnostics sensibles et exhaustifs permettant d’objectiver les divers processus et sous-processus cognitifs susceptible d’être atteints après un TCCL.

Marqueurs électrophysiologiques des dysfonctions attentionnelles et de leur récupération suite à un traumatisme craniocérébral léger

L’objectif principal de cette thèse était d’obtenir, via l’électrophysiologie cognitive, des indices de fonctionnement post-traumatisme craniocérébral léger (TCCL) pour différents niveaux de traitement de l’information, soit l’attention sélective, les processus décisionnels visuoattentionnels et les processus associés à l’exécution d’une réponse volontaire. L’hypothèse centrale était que les mécanismes de production des lésions de même que la pathophysiologie caractérisant le TCCL engendrent des dysfonctions visuoattentionnelles, du moins pendant la période aiguë suivant le TCCL (i.e. entre 1 et 3 mois post-accident), telles que mesurées à l’aide d’un nouveau paradigme électrophysiologique conçu à cet effet. Cette thèse présente deux articles qui décrivent le travail effectué afin de rencontrer ces objectifs et ainsi vérifier les hypothèses émises. Le premier article présente la démarche réalisée afin de créer une nouvelle tâche d’attention visuospatiale permettant d’obtenir les indices électrophysiologiques (amplitude, latence) et comportementaux (temps de réaction) liés aux processus de traitement visuel et attentionnel précoce (P1, N1, N2-nogo, P2, Ptc) à l’attention visuelle sélective (N2pc, SPCN) et aux processus décisionnels (P3b, P3a) chez un groupe de participants sains (i.e. sans atteinte neurologique). Le deuxième article présente l’étude des effets persistants d’un TCCL sur les fonctions visuoattentionelles via l’obtention des indices électrophysiologiques ciblés (amplitude, latence) et de données comportementales (temps de réaction à la tâche et résultats aux tests neuropsychologiques) chez deux cohortes d’individus TCCL symptomatiques, l’une en phase subaigüe (3 premiers mois post-accident), l’autre en phase chronique (6 mois à 1 an post-accident), en comparaison à un groupe de participants témoins sains. Les résultats des articles présentés dans cette thèse montrent qu’il a été possible de créer une tâche simple qui permet d’étudier de façon rapide et peu coûteuse les différents niveaux de traitement de l’information impliqués dans le déploiement de l’attention visuospatiale. Par la suite, l’utilisation de cette tâche auprès d’individus atteints d’un TCCL testés en phase sub-aiguë ou en phase chronique a permis d’objectiver des profils d’atteintes et de récupération différentiels pour chacune des composantes étudiées. En effet, alors que les composantes associées au traitement précoce de l’information visuelle (P1, N1, N2) étaient intactes, certaines composantes attentionnelles (P2) et cognitivo-attentionnelles (P3a, P3b) étaient altérées, suggérant une dysfonction au niveau des dynamiques spatio-temporelles de l’attention, de l’orientation de l’attention et de la mémoire de travail, à court et/ou à long terme après le TCCL, ceci en présence de déficits neuropsychologiques en phase subaiguë surtout et d’une symptomatologie post-TCCL persistante. Cette thèse souligne l’importance de développer des outils diagnostics sensibles et exhaustifs permettant d’objectiver les divers processus et sous-processus cognitifs susceptible d’être atteints après un TCCL.

Effects of spoken cues on decision-making in netball: An eye movement study

Thirteen international netballers viewed static images of scenarios taken from netball open play. Two ‘team mates’, each marked by one opponent, could be seen in each image; each team mate-opponent pair was located on opposite sides of the vertical meridian, such that a binary response was required (‘left’ or ‘right’) from the participant, in order to select a team mate to whom they would pass the ball. For each trial, a spoken word (“left”/“right”) was presented monaurally at the onset of the visual image. Spatially invalid auditory cues (i.e., in the ear contralateral to the correct passing option), reduced performance accuracy relative to valid ones. Semantically invalid cues (e.g., a call of “left” when the target was right-located), increased response times relative to valid ones. However, there were no accompanying changes in visual attention to the team mates and their markers. The effects of auditory cues on covert attentional shifts and decision-making are discussed.

Functional heterogeneity of medial posterior parietal cortex of macaque monkey

The posterior parietal cortex (PPC) of primates represents a remarkable platform that has evolved over time to solve some of the computational challenges that we face in the everyday life, such as sensorimotor integration, spatial attention, and motor planning. With the aim of further investigating the multifaceted functional characteristics of medial PPC, we conducted three studies to explore the visuomotor, somatic, visual, and attention-related properties of two PPC areas: V6A, a visuomotor area part of the dorsomedial visual stream, and PE, an area strongly dominated by somatomotor input, residing mainly on the exposed surface of the superior parietal lobule. In the first study, we tested the impact of visual feedback on V6A grasp-related activity during arm movements towards objects of different shapes. Our results demonstrate that V6A is modulated by both grip type and visual information during grasping preparation and execution, with a predominance of cells influenced by grip type. In the second study, we explored the influence of depth and direction information on reach-related activity of neurons in the so far largely neglected medial part of area PE. We observed a remarkable trend in medial PPC, going from the joint coding of depth and direction signals caudally, in area V6A, to a largely segregated processing of the two signals rostrally, in area PE. In the third study, we used a combined fMRI-electrophysiology experiment to investigate the neuronal mechanisms underlying covert shift of attention processes in area V6A. Our preliminary results reveal that half of the cells showed shift-selective activity when the monkey covertly shifted its attention towards the receptive field. All together these findings highlight the role of the medial PPC in integrating information coming from different sources (vision, somatosensory and motor) and emphasize the involvement of action-related regions of the dorsomedial visual stream in higher level cognitive functions.

Spatial representation and attention in toddlers with Williams syndrome and Down syndrome

The nature of the spatial representations that underlie simple visually guided actions early in life was investigated in toddlers with Williams syndrome (WS), Down syndrome (DS), and healthy chronological age- and mental age-matched controls, through the use of a "double-step" saccade paradigm. The experiment tested the hypothesis that, compared to typically developing infants and toddlers, and toddlers with DS, those with WS display a deficit in using spatial representations to guide actions. Levels of sustained attention were also measured within these groups, to establish whether differences in levels of engagement influenced performance on the double-step saccade task. The results showed that toddlers with WS were unable to combine extra-retinal information with retinal information to the same extent as the other groups, and displayed evidence of other deficits in saccade planning, suggesting a greater reliance on sub-cortical mechanisms than the other populations. Results also indicated that their exploration of the visual environment is less developed. The sustained attention task revealed shorter and fewer periods of sustained attention in toddlers with DS, but not those with WS, suggesting that WS performance on the double-step saccade task is not explained by poorer engagement. The findings are also discussed in relation to a possible attention disengagement deficit in WS toddlers. Our study highlights the importance of studying genetic disorders early in development. (C) 2002 Elsevier Science Ltd. All rights reserved.

The influence of naturalistic, directionally non-specific motion on the spatial deployment of visual attention in right-hemispheric stroke

An impairment of the spatial deployment of visual attention during exploration of static (i.e., motionless) stimuli is a common finding after an acute, right-hemispheric stroke. However, less is known about how these deficits: a) are modulated through naturalistic motion (i.e., without directional, specific spatial features); and, b) evolve in the subacute/chronic post-stroke phase. In the present study, we investigated free visual exploration in three patient groups with subacute/chronic right-hemispheric stroke and in healthy subjects. The first group included patients with left visual neglect and a left visual field defect (VFD), the second patients with a left VFD but no neglect, and the third patients without neglect or VFD. Eye movements were measured in all participants while they freely explored a traffic scene without (static condition) and with (dynamic condition) naturalistic motion, i.e., cars moving from the right or left. In the static condition, all patient groups showed similar deployment of visual exploration (i.e., as measured by the cumulative fixation duration) as compared to healthy subjects, suggesting that recovery processes took place, with normal spatial allocation of attention. However, the more demanding dynamic condition with moving cars elicited different re-distribution patterns of visual attention, quite similar to those typically observed in acute stroke. Neglect patients with VFD showed a significant decrease of visual exploration in the contralesional space, whereas patients with VFD but no neglect showed a significant increase of visual exploration in the contralesional space. No differences, as compared to healthy subjects, were found in patients without neglect or VFD. These results suggest that naturalistic motion, without directional, specific spatial features, may critically influence the spatial distribution of visual attention in subacute/chronic stroke patients.

Evidence for divided automatic attention

A long-standing debate in the literature is whether attention can form two or more independent spatial foci in addition to the well-known unique spatial focus. There is evidence that voluntary visual attention divides in space. The possibility that this also occurs for automatic visual attention was investigated here. Thirty-six female volunteers were tested. In each trial, a prime stimulus was presented in the left or right visual hemifield. This stimulus was characterized by the blinking of a superior, middle or inferior ring, the blinking of all these rings, or the blinking of the superior and inferior rings. A target stimulus to which the volunteer should respond with the same side hand or a target stimulus to which she should not respond was presented 100 ms later in a primed location, a location between two primed locations or a location in the contralateral hemifield. Reaction time to the positive target stimulus in a primed location was consistently shorter than reaction time in the horizontally corresponding contralateral location. This attentional effect was significantly smaller or absent when the positive target stimulus appeared in the middle location after the double prime stimulus. These results suggest that automatic visual attention can focus on two separate locations simultaneously, to some extent sparing the region in between.