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P Vuilleumier

Publications and source records attributed to P Vuilleumier.

At least 19 recordsLinked to original sources
PubMed2002

Perceived gaze direction in faces and spatial attention: a study in patients with parietal damage and unilateral neglect.

Perceived gaze in faces is an important social signal that may influence orienting of attention in normal observers. Would such effects of gaze still occur in patients with right parietal damage and left neglect who usually fail to attend to contralesional space? Two experiments tested for effects of perceived gaze on visual extinction. Face or shape stimuli were presented in the right, left, or both hemifields, with faces looking either straight ahead or toward the opposite field. On bilateral trials, patients extinguished a left shape much less often when a concurrent right face looked leftward rather than straight ahead. This occurred, even though gaze was not relevant to the task and processing of facial signals implied attention to a competing ipsilesional stimulus. By contrast, rightward gaze in faces presented on the left side had no effect on extinction, suggesting that gaze cues are not extracted without attention. Two other experiments examined effects of perceived gaze on the detection of peripheral targets. Targets appeared at one of four possible locations to the right or left of a central face looking either toward the target location, another location on the same side, the opposite side, or straight ahead. Face and gaze were not relevant to the task and not predictive of target location. Patients responded faster when the face looked toward the target on both the contralesional and ipsilesional sides. In contralesional space, gaze allowed shifting of attention in a specific quadrant direction, but only to the first target along the scan path when there were different possible locations on the same side. By contrast, in intact ipsilesional space, attention was selectively directed to one among different eccentric locations. Control experiments showed that symbolic arrow cues did not produce similar effects. These results indicate that even though parietal damage causes spatial neglect and impairs the representation of location on the contralesional side, perceived gaze in faces can still trigger automatic shifts of attention in the contralesional direction, suggesting the existence of specific and anatomically distinct attentional mechanisms.

Aged↗
PubMed2002

Multiple levels of visual object constancy revealed by event-related fMRI of repetition priming.

We conducted two event-related functional magnetic resonance imaging (fMRI) experiments to investigate the neural substrates of visual object recognition in humans. We used a repetition-priming method with visual stimuli recurring at unpredictable intervals, either with the same appearance or with changes in size, viewpoint or exemplar. Lateral occipital and posterior inferior temporal cortex showed lower activity for repetitions of both real and non-sense objects; fusiform and left inferior frontal regions showed decreases for repetitions of only real objects. Repetition of different exemplars with the same name affected only the left inferior frontal cortex. Crucially, priming-induced decreases in activity of the right fusiform cortex depended on whether the three-dimensional objects were repeated with the same viewpoint, regardless of whether retinal image size changed; left fusiform decreases were independent of both viewpoint and size. These data show that dissociable subsystems in ventral visual cortex maintain distinct view-dependent and view-invariant object representations.

Adult↗
PubMed2001

Modulation of visual perception by eye gaze direction in patients with spatial neglect and extinction.

Parietal neurons have retinotopic receptive fields whose response is modulated by eye gaze signals. We examined the role of eye position and eye movement direction on visual extinction in three patients with parietal damage and left neglect, characterized by impaired perception of contralesional field stimuli despite intact visual cortex. Patients tracked a horizontally moving fixation point, while discriminating fine changes at the fixated point and detecting more salient targets flashed on either side of fixation. Eye position modulated extinction, with worse detection of left field targets during eccentric fixation towards the left. Direction of eye movement also modulated extinction, with worse detection of left targets during rightward scanning. These results demonstrate that extinction in contralesional field is influenced by extra-retinal factors related to eye position and eye movements, consistent with a convergence of these signals in parietal cortex.

Aged↗
PubMed2001

Beware and be aware: capture of spatial attention by fear-related stimuli in neglect.

Stimuli with threat significance may be privileged in summoning attention, allowing fast detection even outside the field of attention. We studied patients with unilateral neglect and visual extinction, who usually remain unaware of contralesional stimuli presented together with concurrent ipsilesional stimuli, to learn whether emotional stimuli might differentially be affected by contralesional extinction. Pictures of spiders or flowers with similar features were presented in right, left, or both fields. On bilateral trials, the patients detected emotional stimuli (spiders) on the left side much more often than neutral pictures (flowers). While mechanisms of spatial attention are impaired after parietal damage in neglect patients, intact visual pathways to the ventral temporal lobe and amygdala might still mediate distinct mechanisms of emotional attention.

Amygdala↗
PubMed2001

Neural fate of seen and unseen faces in visuospatial neglect: a combined event-related functional MRI and event-related potential study.

To compare neural activity produced by visual events that escape or reach conscious awareness, we used event-related MRI and evoked potentials in a patient who had neglect and extinction after focal right parietal damage, but intact visual fields. This neurological disorder entails a loss of awareness for stimuli in the field contralateral to a brain lesion when stimuli are simultaneously presented on the ipsilateral side, even though early visual areas may be intact, and single contralateral stimuli may still be perceived. Functional MRI and event-related potential study were performed during a task where faces or shapes appeared in the right, left, or both fields. Unilateral stimuli produced normal responses in V1 and extrastriate areas. In bilateral events, left faces that were not perceived still activated right V1 and inferior temporal cortex and evoked nonsignificantly reduced N1 potentials, with preserved face-specific negative potentials at 170 ms. When left faces were perceived, the same stimuli produced greater activity in a distributed network of areas including right V1 and cuneus, bilateral fusiform gyri, and left parietal cortex. Also, effective connectivity between visual, parietal, and frontal areas increased during perception of faces. These results suggest that activity can occur in V1 and ventral temporal cortex without awareness, whereas coupling with dorsal parietal and frontal areas may be critical for such activity to afford conscious perception.

Aged↗
PubMed2001

Emotional facial expressions capture attention.

OBJECTIVE: To determine whether the emotional significance of stimuli can influence spatial attention. BACKGROUND: Motivational and emotional factors may affect attention toward stimuli. However, this has never been examined in brain-damaged patients who present with unilateral inattention due to left spatial neglect. METHODS: The authors studied three patients with chronic left neglect and visual extinction after right parietal stroke. Shapes or faces with neutral, happy, or angry expressions were briefly presented in the right, left, or both visual fields. On unilateral trials, the patients detected all stimuli equally on both sides. On bilateral trials, they extinguished faces in the contralesional field much less often than shapes, and faces with happy or angry facial expressions much less than faces with a neutral expression. CONCLUSION: Facial features and emotional expressions can be analyzed despite lying on the unattended side, and may influence the spatial distribution of attention. These findings support the view that attention is controlled by neural mechanisms involving not only frontoparietal areas but also limbic components in cingulate cortex and amygdala, which may interact with ventral visual areas in the temporal lobe to detect affective value and prioritize attention to salient stimuli.

Aged↗
PubMed2001

Pure representational neglect after right thalamic lesion.

After a right thalamic stroke, an 86-year-old man presented an acute pure left representational neglect in the absence of any perceptual neglect. On spatial mental imagery tasks, the patient systematically omitted items located on his left side, but only when a vantage point was given. This suggests that (1) pure representational neglect is not just a residual finding after recovery from global (perceptual and representational) neglect; (2) space representation can be coded by two independent processes: in viewer-centered or world-based (allocentric) coordinates; and (3) the right thalamus serves as a relay in the processing of spatial visual imagery.

Aged↗
PubMed2001

Functional magnetic resonance imaging and evoked potential correlates of conscious and unconscious vision in parietal extinction patients.

We describe recent functional magnetic resonance imaging (fMRI) and event-related potential (ERP) studies of visual extinction in patients with right parietal damage who can detect isolated visual stimuli on either side, yet often miss contralesional (left) stimuli during bilateral stimulation. We consider the neural fate of such extinguished visual stimuli and how neural responses differ for consciously detected versus extinguished stimuli. fMRI findings indicate that extinguished stimuli evoke activity in striate and ventral extrastriate visual cortex, despite escaping awareness. Activations for extinguished stimuli can be found even in category-specific (face-responsive) areas of the fusiform gyrus. On the other hand, activations in visual cortex are stronger for consciously detected versus extinguished stimuli, with parietal and frontal areas of the intact left hemisphere also implicated in this comparison. Recent ERP data likewise suggest differential neural responses for consciously detected versus extinguished stimuli. We discuss these findings in relation to current speculations about the neural basis of conscious and unconscious perception.

Attention↗
PubMed2001

Perceptual awareness and its loss in unilateral neglect and extinction.

We review recent evidence from studies of patients with unilateral neglect and/or extinction, who suffer from a loss of awareness for stimuli towards the affected side of space. We contrast their deficit with the effects of damage to primary sensory areas, noting that such areas can remain structurally intact in neglect, with lesions typically centred on the right inferior parietal lobe. In keeping with preservation of initial sensory pathways, many recent studies have shown that considerable residual processing can still take place for neglected or extinguished stimuli, yet without reaching the patient's awareness. This ranges from preserved visual grouping processes through to activation of identity, semantics and emotional significance. Similarly to 'preattentive' processing in normals, such residual processing can modulate what will enter the patient's awareness. Recent studies have used measures such as ERPs and fMRI to determine the neural correlates of conscious versus unconscious perception in the patients, which in turn can be related to the anatomy of their lesions. We relate the patient findings to neurophysiological data from areas in the monkey parietal lobe, which indicate that these serve as cross-modal and sensorimotor interfaces highlighting currently relevant locations as targets for intentional action. We speculate on the special role such brain regions may play in perceptual awareness, seeking to explain how damage to a system which appears primarily to code space could eliminate awareness even for non-spatial stimulus properties at affected locations. This may relate to the extreme nature of 'winner-takes-all' functions within the parietal lobe, and their correspondingly strong influence on other brain areas.

Awareness↗
PubMed2001

Explicit and implicit perception of illusory contours in unilateral spatial neglect: behavioural and anatomical correlates of preattentive grouping mechanisms.

Studies of hemispatial neglect suggest that some perceptual processes still operate on contralesional stimuli independent from spatial attention or awareness. Here we examined whether preattentive processing in extrastriate areas may group unconnected elements inducing illusory contours despite neglect. While it has been debated whether illusory contours arise from preattentive grouping or higher cognitive processes, neurophysiological studies show that neurones in secondary visual cortex (V2) can code for illusory contours. Twelve patients with right hemisphere damage and left neglect were tested for implicit and explicit detection of illusory contours using, respectively: (1) a bisection task where patients were not explicitly required to attend to lateral elements and judged the midpoint of Kanizsa illusory stimuli, as well as other physically connected or unconnected stimuli of the same length; (2) a matching task where patients had to overtly attend to lateral elements and made same/different judgements on pairs of illusory stimuli with identical or different inducers on the right or left side. In some patients, bisection judgements were consistently similar on Kanizsa stimuli with illusory contours and connected stimuli with real contours but different on unconnected gap figures, regardless of their length, suggesting implicit grouping of inducing elements prior to processing stages where a spatial attentional bias arose. Their lesions centred on the inferior parietal cortex or thalamus. Other patients did not show a systematic bisection pattern and had lesions extending posteriorly in the lateral occipital cortex. However, both groups of patients failed to detect left-side inducers in explicit matching judgements, even though errors often revealed unconscious processing, and they showed similar neglect severity on other standard tests. These findings suggest that grouping by illusory contours can occur preattentively and influence bisection independently from the ability to detect contralateral inducers explicitly, severity of inattention, and other forms of unconscious processing. Implicit grouping may depend on the sparing of lateral occipital areas involved in figure-ground segmentation at early stages of visual processing.

Aged↗
PubMed2001

Two eyes make a pair: facial organization and perceptual learning reduce visual extinction.

We examined a patient with left spatial neglect and visual extinction due to right parietal damage in tasks where identical stimuli were presented before and after they were primed so as to be perceived as the eyes of schematic faces. In a first block, we presented alphanumeric stimuli (+, o, T, 6) on the right, left, or both sides of fixation on a blank background, and established that the patient could perceive unilateral stimuli on either side but extinguished most of the left-sided ones in the bilateral trials. In a second block, some of these stimuli (+, o) were presented again, but now in the position of eyes within the context of an oval frame which created the impression of a schematic face. Other stimuli (T, 6) were presented as previously on a blank background for an equal number of trials. In the third critical block, all stimuli were presented once again on a blank background, as in the first block. Now the patient extinguished very few of those left-sided stimuli primed to be seen as a pair of eyes in face configuration (+, o), but still extinguished most of the other stimuli (T, 6). A second control experiment showed no effect of repeatedly exposing stimuli in a common region of space defined by meaningless shape boundaries. These results suggest that facial organization can group eye features before the level where attentional selection or extinction occurs, and that such grouping may be influenced by rapid perceptual learning.

Facial Expression↗
PubMed2001

Effects of attention and emotion on face processing in the human brain: an event-related fMRI study.

We used event-related fMRI to assess whether brain responses to fearful versus neutral faces are modulated by spatial attention. Subjects performed a demanding matching task for pairs of stimuli at prespecified locations, in the presence of task-irrelevant stimuli at other locations. Faces or houses unpredictably appeared at the relevant or irrelevant locations, while the faces had either fearful or neutral expressions. Activation of fusiform gyri by faces was strongly affected by attentional condition, but the left amygdala response to fearful faces was not. Right fusiform activity was greater for fearful than neutral faces, independently of the attention effect on this region. These results reveal differential influences on face processing from attention and emotion, with the amygdala response to threat-related expressions unaffected by a manipulation of attention that strongly modulates the fusiform response to faces.

Adult↗
PubMed2001

Functional neuroanatomical correlates of hysterical sensorimotor loss.

Hysterical conversion disorders refer to functional neurological deficits such as paralysis, anaesthesia or blindness not caused by organic damage but associated with emotional "psychogenic" disturbances. Symptoms are not intentionally feigned by the patients whose handicap often outweighs possible short-term gains. Neural concomitants of their altered experience of sensation and volition are still not known. We assessed brain functional activation in seven patients with unilateral hysterical sensorimotor loss during passive vibratory stimulation of both hands, when their deficit was present and 2-4 months later when they had recovered. Single photon emission computerized tomography using (99m)Tc-ECD revealed a consistent decrease of regional cerebral blood flow in the thalamus and basal ganglia contralateral to the deficit. Independent parametric mapping and principal component statistical analyses converged to show that such subcortical asymmetries were present in each subject. Importantly, contralateral basal ganglia and thalamic hypoactivation resolved after recovery. Furthermore, lower activation in contralateral caudate during hysterical conversion symptoms predicted poor recovery at follow-up. These results suggest that hysterical conversion deficits may entail a functional disorder in striatothalamocortical circuits controlling sensorimotor function and voluntary motor behaviour. Basal ganglia, especially the caudate nucleus, might be particularly well situated to modulate motor processes based on emotional and situational cues from the limbic system. Remarkably, the same subcortical premotor circuits are also involved in unilateral motor neglect after organic neurological damage, where voluntary limb use may fail despite a lack of true paralysis and intact primary sensorimotor pathways. These findings provide novel constraints for a modern psychobiological theory of hysteria.

Adolescent↗
PubMed2000

Faces call for attention: evidence from patients with visual extinction.

Three patients with left spatial neglect and visual extinction from right brain damage were studied to determine whether faces are privileged in summoning attention. In a first experiment, either a face, a name, or a meaningless shape were briefly presented in the right, left or both visual hemifields. On bilateral trials, all patients extinguished a left-side face much less often than a left-side name or a left-side shape. Conversely, they extinguished a left-side shape more often when it was accompanied by a right-side face rather than a right-side name. In a second experiment, either a face or a scrambled face could appear in the right, left or both hemifields. Again, on bilateral trials, a left-side face was less likely to be missed than a scrambled one. These results suggest an advantage of faces in capturing attention and overcoming extinction, which may be related to their special biological and social value, or to the very efficient and automatic operation of specific perceptual processses that extract facial organization in extrastriate visual areas. These findings also demonstrate that the distribution of spatial attention and extinction can be modulated by the relevance of visual stimuli. This implies that substantial analysis and categorization may take place in the visual system before information from the contralesional field is selected for, or excluded from, attentive vision.

Aged↗
PubMed2000

Distinct behavioral and EEG topographic correlates of loss of consciousness in absences.

PURPOSE: To describe the behavioral and EEG topographic correlates of absences with 3-Hz generalized spike-waves and partitioned impairment of consciousness. METHODS: Two adult women had so-called "phantom" absences, characterized by brief and mild impairments of consciousness that were previously inconspicuous to both patient and physician. Neuropsychological examination was performed under video-EEG monitoring during absence status. EEG topographic mapping of spike-wave discharges was obtained in the two cases. RESULTS: Only mild attentional and executive disturbances were observed during absence status despite prolonged discharges. Spike-wave bursts were associated with selective impairment in the initiation of response and self-generated action, whereas short-term storage of external information during discharges was fully preserved. This is consistent with a predominant involvement of frontomesial cortex demonstrated by topographic mapping of spike-wave discharges in the two cases. By contrast, in two other patients with typical absences and a complete lack of retention for information given during the discharges, topographic mapping found a more lateral frontal involvement by spike-wave activity. CONCLUSIONS: Different types of absence seizures may impair distinct components of conscious behavior. A predominant involvement of frontomesial thalamocortical circuitry may underlie an "inconspicuous" disorder of consciousness as seen in phantom absences with selective loss of initiation and goal-oriented behavior, whereas involvement of more lateral frontal areas in typical absences may additionally disrupt working memory processes.

Adult↗
PubMed1999

Semantically-triggered reading epilepsy: an experimental case study.

Primary reading epilepsy (PRE) is a rare syndrome in which epileptic seizures are electively provoked by reading. Cognitive neuropsychology has demonstrated the existence of at least two pathways for reading, the sublexical pathway involved in converting graphemes to phonemes, and the lexical pathway used when meaning is conveyed. Which of these specific pathways is relevant in triggering epileptic discharges remains largely unknown. We report the case of a patient suffering from PRE in which the two routes were distinguished on the basis of the reading material employed. Significantly less epileptic discharges were observed when the patient read non-words than words. In view of our findings, we tentatively contrast a lexical form of PRE, triggered by the activation of semantic knowledge structures, with a sublexical form, triggered by non-word reading. Evidence from the literature suggests that the former is characterized by bilateral EEG activating patterns, whereas the latter involves preferentially the left hemisphere.

Electroencephalography↗
PubMed1999

To see better to the left when looking more to the right: effects of gaze direction and frames of spatial coordinates in unilateral neglect.

Unilateral spatial neglect entails a failure to detect or respond to stimuli in the space opposite to a brain lesion. However, the contralesional hemispace can be determined by different frames of spatial coordinates, such as eyes-, head-, body-, or environment-centered coordinates. We observed 2 patients with a right hemisphere stroke whose left spatial neglect was modulated by distinct coordinates systems depending on the task. Four tasks were given in different conditions of central gaze and either the eyes or the head rotated 30 degrees to the right or 30 degrees to the left. While the 2 patients had a retinotopic defect in 1 visual field quadrant that remained the same irrespective of gaze direction (upper or lower quadrant in 1 case each), the other quadranopic field defect improved with eyes rotation to the right but not with head rotation, suggesting a head-centered spatiotopic deficit. Performance on line bisection was influenced both by eyes and head rotation, as well as by the position of the lines with respect to the trunk midline, suggesting the involvement of both head-centered and body-centered coordinates. Visual imagery and auditory extinction were not modified by changing the eyes or head position. These findings suggest that distinct spatial coordinates are brought into play depending on the tasks demands.

Aged↗