Biomedical subjects

Yves Rossetti

Publications and source records attributed to Yves Rossetti.

At least 19 recordsLinked to original sources

PubMed2006

Pointing at targets by children with congenital and transient blindness.

The study investigated pointing at memorized targets in reachable space in congenitally blind (CB) and blindfolded sighted (BS) children (6, 8, 10 and 12 years; ten children in each group). The target locations were presented on a sagittal plane by passive positioning of the left index finger. A go signal for matching the target location with the right index finger was provided 0 or 4 s after demonstration. An age effect was found only for absolute distance errors and the surface area of pointing was smaller for the CB children. Results indicate that early visual experience and age are not predictive factors for pointing in children. The delay was an important factor at all ages and for both groups, indicating distinct spatial representations such as egocentric and allocentric frames of reference, for immediate and delayed pointing, respectively. Therefore, the CB like the BS children are able to use both ego- and allocentric frames of reference.

Age Factors↗

PubMed2006

Exaggerated leftward bias in the mental number line of patients with schizophrenia.

Several visuo-motor tasks can be used to demonstrate biases towards left hemispace in schizophrenic patients, suggesting a minor right hemineglect. Recent studies in neglect patients used a new number bisection task to highlight a lateralized defect in their visuo-spatial representation of numbers. To test a possible lateralized representational deficit in schizophrenia, we used the number bisection task in 11 schizophrenic patients compared to 11 healthy controls. Participants were required to orally indicate the central number of an interval orally presented. Whereas healthy subjects showed no significant bias, schizophrenic patients presented a significant leftward bias. Therefore, these results suggest an impairment in higher order representations of the number space in patients with schizophrenia, an impairment that is qualitatively similar to the deficit described in neglect patients.

Adult↗

PubMed2006

Visuo-spatial neglect: a systematic review of current interventions and their effectiveness.

Left visuo-spatial neglect is a well-recognized predictor of poor functional outcome following right hemisphere stroke. Over the past 60 years, 18 different methods have been described and evaluated aimed at reducing the effects of this impairment. Although there are some grounds for optimism particularly in terms of short-term impairment-based effects, the range and degree of disability borne by many patients remain high and the clinical effectiveness of the different methods viewed in terms of long-lasting functional improvement (i.e. improvement of disabilities or handicap) is not clear. A systematic review of the available clinically relevant literature, using comparative and stringent levels of evidence, indicates that visual scanning training (VST), trunk rotation (TR) or repeated neck muscle vibrations (NMV) when associated with an extensive training program, mental imagery training, video feedback training and prism adaptation (PA) can be recommended for the rehabilitation of patients with left neglect. More studies however are needed to determine the optimal paradigm of limb activation (LA) eliciting a sustained functional improvement. Sensory stimulations alone and Fresnel prisms do not appear to be functionally relevant. For the other methods, the actual literature is not sufficient to conclude whether or not a long-term functional improvement can be achieved.

Functional Laterality↗

PubMed2006

Long lasting aftereffect of a single prism adaptation: Directionally biased shift in proprioception and late onset shift of internal egocentric reference frame.

We aimed to dissociate components in prism adaptation and its aftereffect by using prism adaptation training in healthy humans. Arm proprioceptive aftereffects are usually measured by indicating the subjective straight ahead direction with eyes closed (S). This measure however could be affected by other components besides proprioception, such as an efferent motor component and internal egocentric reference frame. Here we report a very long lasting proprioceptive shift, detected by two measuring methods, that is a component of the adaptation aftereffects to left wedge prism glasses. In order to minimize possible active motor components, arm passive proprioceptive midsagittal judgment was measured (P). The subject's arm was passively brought from the right or left lateral position, and stopped by subjects' verbal order. The results from these different measurements of midsagittal judgment were compared for 7 days after prism adaptation. Surprisingly, we found two distinctly separate aftereffects of proprioceptive shift depending on the directions of the passive arm movement. The shift of the midsagittal plane appeared only when tested from the left (Pl). This indicates that our strong prism adaptation procedure affected proprioception in a directionally biased way and not a spatially ubiquitous way. Further, the early aftereffect seen in active straight ahead pointing (S) was mostly similar to this biased shift in proprioception (Pl). However the long lasting aftereffect in straight ahead pointing was independently maintained up to day 7, when the passive proprioception had returned to pretest level. These results indicate that active straight ahead pointing (S) involves other components in addition to the passively measurable proprioceptive component. We suggest a late onset shift in the internal egocentric reference frame is involved in S. Possible neural mechanisms for these phenomena are discussed.

Adaptation, Physiological↗

PubMed2006

Long-lasting aftereffect of a single prism adaptation: shifts in vision and proprioception are independent.

After a single adaptation session to prisms with gradually incremented shift magnitude, the prism adaptation aftereffect was measured by open loop mid-sagittal pointing (O) to a visual target without visual feedback. This aftereffect corresponded to the summation of the shift in proprioception, measured by straight ahead pointing without vision (S), and the visual straight ahead judgement (V), measured by verbal stopping of an LED moving from two opposite directions. However, the measurement of the aftereffects made over a period of 7 days revealed significantly different decay curves in V, O and S. Surprisingly the S shift was still present up to 7 days after the training, while V had returned to the original level by 2 h, which was the first measurement after subjects returned to a normal visual environment. O had returned to pre-test level after 1 day. After 3 days Wilkinson's (J Exp Psychol 89:250-257, 1971) additive hypothesis (O=S-V) no longer fit the data. Rather "O=Pl-V", where Pl (Pr) is the shift in proprioception measured by passive lateral arm movements from left (right), fitted better during the whole 7 days of aftereffect in our study. Therefore, the aftereffect of our strong prism adaptation revealed, firstly, that classical open loop pointing consisted of aftereffect shifts equal to the summation of the shifts in the two passively measurable aftereffect components, vision (V) and proprioception (Pl), rather than with active straight ahead pointing (S). Secondly, the decay of the shift in visual perception and in passively measurable proprioception is independent. The former decays fast, and the latter decays slowly with two separate waves. Thirdly, we suggest that the use of visual perception-dependent spatial codes for visual-manual transformation and the vision-independent internal egocentric reference frame are mutually exclusive. We proposed a model to explain these possible mechanisms.

Adaptation, Physiological↗

PubMed2006

Interaction between space and number representations during motor preparation in manual aiming.

The existence of a spatial component in the representation of number magnitude has been repeatedly supported by the demonstration that the left hand responds faster to smaller numbers, whereas the right hand responds faster to larger numbers. These results support the view that the 'mental number line' is oriented such that smaller numbers are associated with the left side of space while larger numbers are associated with the right side. We investigated whether the link between spatial and number processing arises from a continuous or categorical mapping between space and number representations. The investigation was designed to study all aspects of the motor act, including both planning and execution phases. For this purpose we measured reaction times (RTs), movement times (MTs), spatial accuracy, and endpoint pressure of manual aiming, while subjects reached with the right hand towards the location of a visual digit target. Five different digits were equiprobably presented at five positions along the horizontal axis. A GO/NO-GO choice task paradigm was used to ensure that digit parity (i.e., odd/even) was being processed. Analyses of MT, accuracy, and pressure data showed no digit effects. However, two number-related effects were observed on RTs. First, shorter RTs were obtained for smaller digits independent of target location, despite the use of the right hand. Second, an interaction was observed between target location and number magnitude whereby relative RTs were shortest when there was a congruity between target magnitude and location. These results imply that motor preparation is contaminated both by the direct activation of number magnitude and by the congruity between the spatial location of a target number and its magnitude. We conclude that continuous mapping intervenes between mental number representation and physical space.

Computer Graphics↗

PubMed2006

Effects of visual deprivation on space representation: immediate and delayed pointing toward memorised proprioceptive targets.

Congenitally blind, late-blind, and blindfolded-sighted participants performed a pointing task at proximal memorised proprioceptive targets. The locations to be memorised were presented on a sagittal plane by passively positioning the left index finger. A 'go' signal for matching the target location with the right index finger was given 0 or 8 s after left-hand demonstration. Absolute distance errors were smaller in the blind groups, with both delays pooled together; signed distance and direction errors were underestimated with the longer delay, and were overestimated by blind groups, whereas the blindfolded-sighted group underestimated them. Elongation of the scatters was stretched but not affected by delay or group. The surface scatter was greater with the longer delay; and orientation of the main axis of the pointing ellipses shows the use of an egocentric frame of reference by the congenitally blind group for both delays, the use of egocentric (0 s) and exocentric (8 s) frame of reference by the blindfolded-sighted group, with the late-blind group using an intermediate frame of reference for both delays. Therefore, early and late visual-deprivation effects are distinguished from transient visual-deprivation effects as long-term deprivation leads to increased capabilities (absolute distance estimations), unaltered organisation (for surface and elongation), and altered organisation (amplitude and direction estimations, orientation of pointing distribution) of the spatial representation with proprioception. Besides providing an extensive exploration of pointing ability and mechanisms in the visually deprived population, the results show that cross-modal plasticity applies not only to neural bases but extends to spatial behaviour.

Adult↗

PubMed2005

Parietal rTMS distorts the mental number line: simulating 'spatial' neglect in healthy subjects.

Patients with left-sided visuospatial neglect, typically after damage to the right parietal lobe, show a systematic bias towards larger numbers when asked to bisect a numerical interval. This has been taken as further evidence for a spatial representation of numbers, perhaps akin to a mental number line with smaller numbers represented to the left and larger numbers to the right. Previously, contralateral neglect-like symptoms in physical line bisection have been induced in healthy subjects with repetitive transcranial magnetic stimulation (rTMS) over right posterior parietal lobe. Here we used rTMS over parietal and occipital sites in healthy subjects to investigate spatial representations in a number bisection task. Subjects were asked to name the midpoint of numerical intervals without calculating. On control trials subjects' behaviour was similar to performance reported in physical line bisection experiments. Subjects underestimated the midpoint of the numerical interval. Repetitive transcranial magnetic stimulation produced representational neglect-like symptoms in number bisection when applied over right posterior parietal cortex (right PPC). Repetitive TMS over right PPC shifted the perceived midpoint of the numerical interval significantly to the right while occipital TMS had no effect on bisection performance. Our study therefore provides further evidence that subjects use spatial representations, perhaps akin to a mental number line, in basic numerical processing tasks. Furthermore, we showed that the right posterior parietal cortex is crucially involved in spatial representation of numbers.

Adult↗

PubMed2005

Blindsight in action: what can the different sub-types of blindsight tell us about the control of visually guided actions?

Blindsight broadly refers to the paradoxical neurological condition where patients with a visual field defect due to a cortical lesion nevertheless demonstrate implicit residual visual sensitivity within their field cut. The aim of this paper is twofold. First, through a selective review of the blindsight literature we propose a new taxonomy for the subtypes of residual abilities described in blindsight. Those patients able to accurately act upon blind field stimuli (e.g. by pointing or saccading towards them) are classified as having 'action-blindsight', those whose residual functions can be said to rely to some extent upon attentive processing of blind field stimuli are classified as demonstrating 'attention-blindsight', while finally, patients who have somewhat accurate perceptual judgements for blind field stimuli despite a complete lack of any conscious percept, are classified as having 'agnosopsia'--literally meaning 'not knowing what one sees'. We also address the possible neurological substrates of these residual sensory processes. Our second aim was to investigate the most striking subtype of blindsight, action-blindsight. We review the data relevant to this subtype and the hypotheses proposed to account for it, before speculating on how action-blindsight may inform our normal models of visuomotor control.

Attention↗

PubMed2005

Impairment of gaze-centered updating of reach targets in bilateral parietal-occipital damaged patients.

Recent studies have suggested that internal updating of visuospatial targets in humans occurs in gaze-centered coordinates and takes place in the parietal and extrastriate cortices. We explored how information for reaching is updated in two patients with bilateral lesions in these areas. Subjects performed two visuomotor tasks: (i) a fixation reaching task, which began with the appearance of one of five fixation positions (varying eye positions) followed by a central reaching target. Subjects reached to the target while fixating on the presented fixation position (relative to gaze the target was always presented in the periphery); and (ii) a saccade reaching task, in which subjects foveated on the central reaching target, then made a saccade to the presented fixation position before reaching to the central target. In both tasks, subjects reached to targets after a 500 or 5000 ms delay. Gaze-centered updating predicts similarities in reaching errors between fixation and saccade trials. Control subjects showed evidence for gaze-centered updating during both 500 and 5000 ms delay conditions. In contrast, patient AT, who had extensive occipital-parietal damage, only showed signs of gaze-centered representation after 5 s. Patient IG, with a more focal lesion in the parietal cortices, showed partial updating in gaze-centered coordinates when reaching with the small memory delay but recovered a complete gaze-centered representation after the longer delay. This suggests that patients with bilateral occipital-parietal lesions may rely on non-gaze-centered frames to store immediate target locations in reaching space but, given enough time, this information may be rerouted to access other gaze-centered motor cortical mechanisms.

Adult↗

PubMed2005

Applications of prism adaptation: a tutorial in theory and method.

Data and theory from prism adaptation are reviewed for the purpose of identifying control methods in applications of the procedure. Prism exposure evokes three kinds of adaptive or compensatory processes: postural adjustments (visual capture and muscle potentiation), strategic control (including recalibration of target position), and spatial realignment of various sensory-motor reference frames. Muscle potentiation, recalibration, and realignment can all produce prism exposure aftereffects and can all contribute to adaptive performance during prism exposure. Control over these adaptive responses can be achieved by manipulating the locus of asymmetric exercise during exposure (muscle potentiation), the similarity between exposure and post-exposure tasks (calibration), and the timing of visual feedback availability during exposure (realignment).

Adaptation, Physiological↗

PubMed2005

Interference between number processing and line bisection: a methodology.

It is usually thought that numbers are represented on a "mental number line" on which the progression of smaller to larger numbers occurs from left to right suggesting a spatial representation of numbers. Reciprocally, number processing has been shown to influence space representation [Fischer, M. (2001). Number processing induces spatial performance biases. Neurology, 822-826]. Specifically, it was found that when bisecting a string of numbers made up of smaller digits (1 or 2), the bisection was shifted to the left compared to bisecting a larger digit-string (8 or 9). In order to avoid any effect of physical difference in stimuli Here, we provide a simple methodology to investigate this relationship using a task involving the bisection of French number words (e.g."DEUX", "NEUF"). Results showed that subjects bisected strings more towards the left for smaller number words ("DEUX", 2) than for larger number words ("NEUF", 9), confirming that automatic number processing can influence visuo-motor aspects of behaviour. Similar results have been obtained with mirror versus canonical presentation, indicating that the reading direction is not the crucial factor of this number-induced bias. In addition, our sample of subjects showed a larger effect for number word strings than for Arabic number strings. It is therefore concluded that the implicit activation of the left/right side depends on the magnitude of the number being embedded within the stimulus lines, irrespective of its actual presentation format.

Adult↗

PubMed2004

Automatic avoidance of obstacles is a dorsal stream function: evidence from optic ataxia.

When we reach out to pick something up, our arm is directed to the target by visuomotor networks in the cortical dorsal stream. However, our reach trajectories are influenced also by nontarget objects, which might be construed as potential obstacles. We tested two patients with bilateral dorsal-stream (parietal lesions, both of whom were impaired at pointing to visual stimuli (optic ataxia). We asked them to reach between two cylinders, which varied in location from trial to trial. We found that the patients' reaches remained invariant with changes in obstacle location. In a control task when they were asked to point midway between the two objects, however, their responses shifted in an orderly fashion. We conclude that the dorsal stream provides the visual guidance we automatically build into our movements to avoid potential obstacles, as well as that required to ensure arrival at the target.

Adult↗

PubMed2004

Geographic information has to be spatialized to be neglected: a representational neglect case.

A patient with unilateral neglect had to evoke mentally the map of France in two different conditions. In the first condition, he was asked to build an iconic representation of the map of France and to list all the towns that he could 'see' on this mental image within two minutes. In the second condition, he had to remember and name as many French towns as possible within two minutes, without being instructed to form a mental image. Left representational neglect was observed in the first condition only, i.e., when an iconic representation was required. These findings, which were replicated four months later, suggest a dual mode of coding, retrieval, or both, of geographic information and show that, although topographic, geographic data has to be spatialized to be neglected.

Aged↗

PubMed2003

Optic ataxia revisited: visually guided action versus immediate visuomotor control.

Optic ataxia and visual agnosia have been proposed to constitute a double dissociation which provides the main argument for the assimilation of the anatomical distinction between a dorsal and a ventral visual stream to the functional distinction between perception and action. In the present review, we argue that insufficient evidence has been collected to argue for this double dissociation. Several criteria are reviewed: (1) exploration of the visuomotor behavior in central versus peripheral vision has not been matched for the two types of patients; (2) the temporal constraints of visual processes that are impaired in the two neurological conditions appear to play a crucial role in the apparent dissociation; (3) the necessary reductionism of experimental conditions used to study action has led to an overconsideration of optic ataxia as a global deficit for action. Altogether optic ataxia appears to result from a specific impairment of immediate visuomotor control rather than of visually guided action as a whole. These results are discussed in the light of recent research on optic ataxia and on motor control, and directions for future research are proposed.

Agnosia↗

PubMed2003

Ocular scanning and perceptual size distortion in hemispatial neglect: effects of prism adaptation and sequential stimulus presentation.

When asked to compare two lateralized shapes for horizontal size, neglect patients often indicate the left stimulus to be smaller. Gainotti and Tiacci (1971) hypothesized that this phenomenon might be related to a rightward bias in the patients' gaze. This study aimed to assess the relation between this size underestimation and oculomotor asymmetries. Eye movements were recorded while three neglect patients judged the horizontal extent of two rectangles. Two experimental manipulations were performed to increase the likelihood of symmetrical scanning of the stimulus display. The first manipulation entailed a sequential, rather than simultaneous presentation of the two rectangles. The second required adaptation to rightward displacing prisms, which is known to reduce many manifestations of neglect. All patients consistently underestimated the left rectangle, but the pattern of verbal responses and eye movements suggested different underlying causes. These include a distortion of space perception without ocular asymmetry, a failure to view the full leftward extent of the left stimulus, and a high-level response bias. Sequential presentation of the rectangles and prism adaptation reduced ocular asymmetries without affecting size underestimation. Overall, the results suggest that leftward size underestimation in neglect can arise for a number of different reasons. Incomplete leftward scanning may perhaps be sufficient to induce perceptual size distortion, but it is not a necessary prerequisite.

Adaptation, Physiological↗

PubMed2003

Abstraction from a sensori-motor perspective: can we get a quick hold on simple perception?

Two main types of dissociation can be considered in order to articulate action and abstraction. Vision for action and vision for perception are often described as dissociated systems at both anatomical and functional levels. Within this framework, abstraction should be specific to perceptual representation, whereas the action system would simply analyse the objective metric of space. By contrast, one may focus on dissociations within the action system. In this case, one will accept that action may involve abstract representations, at least during movement preparation. But a specific visuomotor level of processing can be described that appears to comply with the spatial properties of the relationship between the actor and the environment. This system would be specialized for fast movement guidance towards pre-defined goals. Such an automatic piloting system would thus be free of abstraction.

Concept Formation↗

PubMed2003

Simulating unilateral neglect in normals using prism adaptation: implications for theory.

Rightward deviation on line bisection is considered one of the most classic clinical signs of unilateral visual neglect--a cognitive disorder of spatial processing that commonly follows right brain damage. Recently, short-term adaptation to wedge prisms has been shown to significantly reduce neglect on this and other conventional diagnostic tasks. Our previous study has shown that visuomotor adaptation in normals produces a similar pattern of directional bias on a line bisection task. Based on the good working knowledge of how neglect patients perform on different versions of the standard diagnostic task, we showed here that using leftward-deviating prisms in normals, it is possible to produce: (1) a reliable bias on line bisection, (2) a rightward specific deviation, (3) a modulation of rightward deviation, which depends on the relative spatial location of the target lines and (4) a line length effect. A final experiment confirmed that these after-effects are specific to prism adaptation rather than passive prism exposure. Collectively, these findings confirm that adaptation to left-deviating prisms in normals produces a reliable right-sided bias and as shown by a previous visuospatial judgement task, these findings cannot be adequately explained by the symmetric sensori-motor effects of prism adaptation. Taken together with the improvement of spatial neglect shown by right-deviating prisms only, the present study suggests that low level sensori-motor adaptations play a greater role in right hemisphere organisation for spatial cognition than previously thought.

Adaptation, Physiological↗