Biomedical subjects

Yann Coello

Publications and source records attributed to Yann Coello.

7 recordsLinked to original sources

PubMed2006

Effect of structuring the workspace on cognitive and sensorimotor distance estimation: no dissociation between perception and action.

Independent processing of visual information for perception and action is supported by studies about visual illusions, which showed that context information influences overtjudgment but not reaching attempts. The objection was raised, however, that these two types of performance are notdirectly comparable, since they generally focus on different properties of the visual input. The goal of the present study was to quantify the influence of context information (in the form of a textured background) on the cognitive and sensorimotor processing of egocentric distance. We found that the subjective area comprising reachable objects (probed with a cognitive task) decreased, whereas the amplitude of reaching movement (probed with a sensorimotor task) increased in the presence of the textured background with both binocular and monocular viewing. Directional motor performance was not affected by the experimental conditions, but there was a tendency for the kinematic parameters to mimic trajectory variations. The similar but opposite effects of the textured background in the cognitive and sensorimotor tasks suggested that in both tasks the visual targets were perceived as closer when they were presented in a sparse environment. A common explanation for the opposite effects was confirmed by the percentage of background influence, which was highly correlated in the two tasks. We conclude that visual processing for perception and action cannot be dissociated from context influence, since it does not differ when the tasks entail the processing of similar spatial characteristics.

Adolescent↗

PubMed2005

Effect of posture on the perception of verticality in neglect patients.

BACKGROUND AND PURPOSE: The anticlockwise (ACW) deviation of the visual and visuohaptic subjective verticals (SVs), known to occur in patients with right hemisphere lesion, is amplified by spatial neglect (N). These patients have only been assessed when sitting. We investigated the hypothesis that postural changes modulate visuohaptic SV deviation. METHODS: Eight patients presenting with a right hemisphere lesion and spatial N were compared with 6 matched control subjects (C). In the dark, they had to rotate a luminous rod to put it at the vertical in 4 conditions: (1) sitting with plantar sole support; (2) sitting without plantar sole support; (3) sitting with legs extended on a support; and (4) supine position. RESULTS: N patients showed a significant ACW deviation (-4.5 degrees) of the SV compared with C subjects (+0.01 degrees). The effect of body position depended on the group (P=0.022) because changes had definite effects in the N but not in the C group. In fact, the former showed a reduction of the ACW deviation, from the first to the fourth condition. CONCLUSIONS: Although the possible role of plantar and leg somaesthetic inputs remains to be thoroughly investigated, the modulation of gravitational inputs at trunk or vestibular level influences the SV deviation in N patients. This has to be put in relation with the modulation of N signs reported by other authors when passing from the sitting to the supine position.

Aged↗

PubMed2005

The visual vertical in the pusher syndrome: influence of hemispace and body position.

The subjective visual vertical (SVV) was investigated in right brain-damaged (RBD) patients with pusher syndrome (PS) which is thought to stem from an erroneous perception of body orientation. The participants, sitting or lying, had to align a luminous rod with gravity. The task was performed in darkness with the rod centred to the body, or placed in the left (neglected) or in the right hemispace. The error, negligible in the control group (+0.3 degrees; n = 6) and mild in the nonneglect non-pusher patients (-1.8 degrees; n = 6), was clearly clockwise in the pusher neglect patients (N+P+; +7.2 degrees; n = 4), but anticlockwise in the non-pusher neglect patients (-6.6 degrees; n = 6). In both neglect groups, error was greater when the rod was in the left space. In N+P+ patients, the performance was strongly affected by posture (lying: +5.2 degrees ; sitting: +9.2 degrees ). Intra-individual variability was also much greater in this group. This study confirms the contralesional deviation of SVV in RBD patients without PS and suggests the presence of an opposite bias in RBD patients affected by PS.

Adult↗

PubMed2005

Subjective visual vertical in pitch and roll in right hemispheric stroke.

BACKGROUND AND PURPOSE: Patients with right hemispheric stroke usually present an anticlockwise deviation of the subjective visual vertical (SVV) in the frontal (roll) plane. However, the occurrence of a similar disorder in the sagittal (pitch) plane has never been assessed. We investigated the subjective visual vertical in both planes in those patients. METHODS: Eight patients, 4 with spatial neglect (N+) and 4 without neglect (N-), were compared with 4 healthy participants (C). They sat facing a luminous bar adjustable in rotation, either in the roll or in the pitch plane, and had to orient it in a vertical position, in the dark. RESULTS: Compared with N- (-0.1 degrees) and C (+1.1 degrees) groups, N+ patients presented with a significant backward deviation (-4.5 degrees) of the SVV in pitch. In accordance with other studies, they also showed a significant anticlockwise deviation (-8.8 degrees) of the SVV in roll, as compared with N- (-1.9 degrees) and C (+0.4 degrees) subjects. This was associated with an opposite trunk deviation in both planes. CONCLUSIONS: While confirming the anticlockwise deviation already reported in the frontal plane, we showed for the first time to our knowledge a backward deviation of the SVV in neglect patients, which has to be put in relation with their balance disorders.

Adult↗

PubMed2003

Apparent motion cues distort object localisation in egocentric space.

The visual localisation of objects in space is thought to rely on retinal information defining the environmental context and non-retinal cues from proprioception and motor commands. Here, the influence of dynamic contextual cues on the perception of egocentric space in a reaching task was investigated. Compared to performances with realistic motion or static cues, target localisation was less accurate when apparent motion was used to provide contextual information about space between the hand and the target. This effect could not be explained by the 'presence' of motion, or a bias in depth perception. Since the distortion was connected with the reaching area it was concluded that cognitive factors can unconsciously influence the perception of egocentric space, in particular distance estimation. We propose a mechanism for this whereby signals from areas MT/MST (middle temporal/medial superior temporal) create a perceptual bias through cortico-cortical connections with posterior parietal cortex.

Adult↗

PubMed2002

Frame of reference and adaptation to directional bias in a video-controlled reaching task.

The present study (N=56) investigated spatio-temporal accuracy of horizontal reaching movements controlled visually through a vertical video monitor. Direct vision of the hand was precluded and the direction of hand trajectory, as perceived on the video screen, was varied by changing the angle of the camera. The orientation of the visual scene displayed on the fronto-parallel plane was thus congruent (0 degrees condition) or non-congruent (directional bias of 15 degrees, 30 degrees or 45 degrees counterclockwise) according to the horizontal working space. The goal of this study was to determine whether local learning of a directional bias can be transferred to other locations in the working space, but taking into account the magnitude of the directional bias (15 degrees, 30 degrees or 45 degrees ), and the position of the successive objectives (targets at different distances (TDD) or different azimuths (TDA)). Analysis of the spatial accuracy of pointing movements showed that when introducing a directional bias, terminal angular error was linearly related to the amount of angular perturbation (around 30%). Seven trials were, on average, necessary to eliminate this terminal error, whatever the magnitude of the directional bias and the position of the successive targets. When changing the location of the spatial objective, transfer of adaptation was achieved in the TDD condition but remained partial in the TDA condition. Furthermore, initial orientation of the trajectory suggested that some participants used a hand-centred frame of reference whereas others used an external one to specify movement vector. The adaptation process differed as a function of the frame of reference used, but only in the TDA condition. Adaptation for participants using a hand-centred frame of reference was more concerned with changes in the shape of the trajectory, whereas participants using an external frame of reference adapted their movement by up-dating the initial direction of hand trajectory. As a whole, these findings suggest that the processes involved in remote visual control of hand movement are complex with the result that tasks requiring video-controlled manipulation like video-controlled surgery require specific spatial abilities in actors and consequential plasticity of their visuo-motor system, in particular concerning the selection of the frame of reference for action.

Adaptation, Physiological↗

PubMed2002

Retinal and extra-retinal contribution to position coding.

Though considerable effort has been expended on demonstrating the importance of extraretinal cues in distance perception (e.g. state of vergence), recent studies have shown that enriching the visual image brings about a decrease of perceptual underestimation of distance as observed otherwise, providing that contextual information is situated in the proximal space with regard to target position. The fact that a similar effect was observed when viewing monocularly was suggesting a prevalence of retinal input in distance coding. The present study, investigating reaching movements performed monocularly or binocularly in three successive visual scenes (dark-structured-dark), gave evidence for this assumption. Whatever the vision condition, a dark environment gave rise to an underestimation of target distance, which disappeared instantaneously when a structured background was unexpectedly provided. The sudden return to the dark condition resulted in a progressive drift towards underestimation. These findings strongly suggest that structured retinal information influences widely the perception of target distance. They show in addition that retinal signals may contribute to the calibration of non-retinal sources of information. The putative implication of the posterior parietal cortex in this dual influence is discussed.

Adult↗