It is challenging to recover local optic axis orientation from samples probed with fiber-based po... more It is challenging to recover local optic axis orientation from samples probed with fiber-based polarization-sensitive optical coherence tomography (PS-OCT). In addition to the effect of preceding tissue layers, the transmission through fiber and system elements, and imperfect system alignment, need to be compensated. Here, we present a method to retrieve the required correction factors from measurements with depth-multiplexed PS-OCT, which accurately measures the full Jones matrix. The correction considers both retardation and diattenuation and is applied in the wavenumber domain, preserving the axial resolution of the system. The robustness of the method is validated by measuring a birefringence phantom with a misaligned system. Imaging ex-vivo lamb trachea and human bronchus demonstrates the utility of reconstructing the local optic axis orientation to assess smooth muscle, which is expected to be useful in the assessment of airway smooth muscle thickness in asthma, amongst other fiber-based applications.
Studies on audiovisual interactions in sound localization have primarily focused on the relations... more Studies on audiovisual interactions in sound localization have primarily focused on the relations between the spatial position of sounds and their perceived visual source, as in the famous ventriloquist effect. Much less work has examined the effects on sound localization of seeing aspects of the visual environment. In this study, we took advantage of an innovative method for the study of spatial hearing-based on real sounds, virtual reality and real-time kinematic tracking-to examine the impact of a minimal visual spatial frame on sound localization. We tested sound localization in normal hearing participants (N = 36) in two visual conditions: a uniform gray scene and a simple visual environment comprising only a grid. In both cases, no visual cues about the sound sources were provided. During and after sound emission, participants were free to move their head and eyes without restriction. We found that the presence of a visual spatial frame improved hand-pointing in elevation. In addition, it determined faster first-gaze movements to sounds. Our findings show that sound localization benefits from the presence of a minimal visual spatial frame and confirm the importance of combining kinematic tracking and virtual reality when aiming to reveal the multisensory and motor contributions to spatial-hearing abilities.
Supplemental Digital Content is available in the text. Objectives: The aim of this study was to a... more Supplemental Digital Content is available in the text. Objectives: The aim of this study was to assess three-dimensional (3D) spatial hearing abilities in reaching space of children and adolescents fitted with bilateral cochlear implants (BCI). The study also investigated the impact of spontaneous head movements on sound localization abilities. Design: BCI children (N = 18, aged between 8 and 17) and age-matched normal-hearing (NH) controls (N = 18) took part in the study. Tests were performed using immersive virtual reality equipment that allowed control over visual information and initial eye position, as well as real-time 3D motion tracking of head and hand position with subcentimeter accuracy. The experiment exploited these technical features to achieve trial-by-trial exact positioning in head-centered coordinates of a single loudspeaker used for real, near-field sound delivery, which was reproducible across trials and participants. Using this novel approach, broadband sounds were delivered at different azimuths within the participants’ arm length, in front and back space, at two different distances from their heads. Continuous head-monitoring allowed us to compare two listening conditions: “head immobile” (no head movements allowed) and “head moving” (spontaneous head movements allowed). Sound localization performance was assessed by computing the mean 3D error (i.e. the difference in space between the X-Y-Z position of the loudspeaker and the participant’s final hand position used to indicate the localization of the sound’s source), as well as the percentage of front–back and left–right confusions in azimuth, and the discriminability between two nearby distances. Several clinical factors (i.e. age at test, interimplant interval, and duration of binaural experience) were also correlated with the mean 3D error. Finally, the Speech Spatial and Qualities of Hearing Scale was administered to BCI participants and their parents. Results: Although BCI participants distinguished well between left and right sound sources, near-field spatial hearing remained challenging, particularly under the “ head immobile” condition. Without visual priors of the sound position, response accuracy was lower than that of their NH peers, as evidenced by the mean 3D error (BCI: 55 cm, NH: 24 cm, p = 0.008). The BCI group mainly pointed along the interaural axis, corresponding to the position of their CI microphones. This led to important front–back confusions (44.6%). Distance discrimination also remained challenging for BCI users, mostly due to sound compression applied by their processor. Notably, BCI users benefitted from head movements under the “head moving” condition, with a significant decrease of the 3D error when pointing to front targets (p < 0.001). Interimplant interval was correlated with 3D error (p < 0.001), whereas no correlation with self-assessment of spatial hearing difficulties emerged (p = 0.9). Conclusions: In reaching space, BCI children and adolescents are able to extract enough auditory cues to discriminate sound side. However, without any visual cues or spontaneous head movements during sound emission, their localization abilities are substantially impaired for front–back and distance discrimination. Exploring the environment with head movements was a valuable strategy for improving sound localization within individuals with different clinical backgrounds. These novel findings could prompt new perspectives to better understand sound localization maturation in BCI children, and more broadly in patients with hearing loss.
Fast, online control of movement is an essential component of human motor skills, as it allows au... more Fast, online control of movement is an essential component of human motor skills, as it allows automatic correction of inaccurate planning. The present study explores the role of two types of concurrent signals in error correction: predicted visual reafferences coming from an internal representation of the hand, and actual visual feedback from the hand. While the role of sensory feedback in these corrections is well-established, much less is known about sensory prediction. The relative contributions of these two types of signals remain a subject of debate, as they are naturally interconnected. We address the issue in a study that compares online correction of an artificially induced, undetected planning error. Two conditions are tested, which only differ with respect to the accuracy of predicted visual reafferences. In the first, "Prism" experiment, a planning error is introduced by prisms that laterally displace the seen hand prior to hand movement onset. The prism-induced conflict between visual and proprioceptive inputs of the hand also generates an erroneous prediction of visual reafferences of the moving hand. In the second, "Jump" experiment, a planning error is introduced by a jump in the target position, during the orienting saccade, prior to hand movement onset. In the latter condition, predicted reafferences of the hand remained intact. In both experiments, after hand movement onset, the hand was either visible or hidden, which enabled us to manipulate the presence (or absence) of visual feedback during movement execution. The Prism experiment highlighted late and reduced correction of the planning error, even when natural visual feedback of the moving hand was available. In the Jump experiment, early and automatic corrections of the planning error were observed, even in the absence of visual feedback from the moving hand. Therefore, when predicted reafferences were accurate (the Jump experiment), visual feedback was processed rapidly and automatically. When they were erroneous (the Prism experiment), the same visual feedback was less efficient, and required voluntary, and late, control. Our study clearly demonstrates that in natural environments, reliable prediction is critical in the preprocessing of visual feedback, for fast and accurate movement.
Visuo-motor adaptation has been classically studied using movements aimed at visual targets with ... more Visuo-motor adaptation has been classically studied using movements aimed at visual targets with visual feedback. In this type of experimental design, the respective roles of the different error signals cannot be fully disentangled. Here, we show that visuo-motor adaptation occurs despite the terminal success of the action and the compensation of the external error by a jump of the visual target. By using three grasping task conditions we manipulated the retinal error signal between the seen hand and the target (external error) and the conflict between the hand's visual reafference and either the proprioceptive or the efference copy signal (internal error), in order to estimate their respective roles in prism adaptation. In all conditions, subjects were asked to rapidly grasp an object. In the classical 'Prism' condition the object was stationary, which provided both external and internal errors. In the 'Prism & Jump' condition, at movement onset the object was suddenly displaced (jump) toward its virtual image location (visually displaced by the prism) which also corresponded to the location where the movement was planned to and executed through prisms. This jump therefore cancelled the external error (between the seen target and the seen hand), whereas the internal error (between the seen hand and the expected visual reafference of the hand, or between the seen hand and the hand felt by proprioception) was unchanged (because it is independent of the presence of the goal). In the 'Jump' condition, the movement was planned and executed without prismatic goggles and consequently with no internal error (no difference between where the hand visual reafference is expected to be and where it actually is), but the object was suddenly displaced at movement onset by a displacement equivalent to a prism shift which provided an external error. The 'Prism' and 'Prism & Jump' conditions exhibited similar aftereffects, whereas no aftereffect was observed in the 'Jump' condition. These results suggest that successful actions can be subjected to adaptation and that internal error is the only signal necessary to elicit true visuomotor adaptation characterized by context-independent generalization.
When reaching to an object, information about the target location as well as the initial hand pos... more When reaching to an object, information about the target location as well as the initial hand position is required to program the motor plan for the arm. The initial hand position can be determined by proprioceptive information as well as visual information, if available. Bayes-optimal integration posits that we utilize all information available, with greater weighting on the sense that is more reliable, thus generally weighting visual information more than the usually less reliable proprioceptive information. The criterion by which information is weighted has not been explicitly investigated; it has been assumed that the weights are based on task- and effector-dependent sensory reliability requiring an explicit neuronal representation of variability. However, the weights could also be determined implicitly through learned modality-specific integration weights and not on effector-dependent reliability. While the former hypothesis predicts different proprioceptive weights for left an...
Annals of physical and rehabilitation medicine, Jan 18, 2018
After a coma, one major challenge is the detection of awareness in patients with disorders of con... more After a coma, one major challenge is the detection of awareness in patients with disorders of consciousness. In some patients, the only manifestation indicative of awareness is an appropriate emotional response. Preferred music is a powerful medium to elicit emotions and autobiographical memory. Furthermore, music has been shown to improve cognitive functions both in healthy subjects and patients with neurological impairment. We hypothesized that signs of awareness could be enhanced in some patients with disorders of consciousness under appropriate emotional stimulation such as preferred music and also probably preferred odors. To investigate an objective, easily recordable marker of emotions at the patients' bedside, electrodermal activity (skin conductance level, SCL) was assessed with stimulations in auditory and olfactory modalities, notably with preferred music, neutral sound, preferred odors, and neutral odors. The study was conducted in 11 patients with disorders of consc...
Sensorimotor Foundations of Higher Cognition, 1993
ABSTRACT Lesions of the dorsal posterior parietal cortex (PPC) typically result in optic ataxia (... more ABSTRACT Lesions of the dorsal posterior parietal cortex (PPC) typically result in optic ataxia (OA)—a disorder in which patients have difficulty reaching toward and grasping objects presented in peripheral vision, in the absence of primary sensory or motor deficits. It is therefore considered as a human model of the PPC involvement in visuo-manual control. In the early twentieth century, OA was described as part of the Bálint–Holmes syndrome. The main aim of most analyses of OA in the second part of the twentieth century was then to isolate a pure visuo-motor symptomatology from the complex Bálint&#39;s syndrome (e.g. Garcin et al., 1967; Rondot et al., 1977). In addition, OA has been used over the last 15 years to argue in favor of dissociable functions within the dorsal (&#39;How&#39;) and ventral (&#39;What&#39;) streams of visual information processing and visuo-manual guidance (Jeannerod and Rossetti, 1993; Milner and Goodale, 1995; Rossetti and Pisella, 2002). In these contexts, research on OA has focused primarily on visuo-motor functions (&#39;How&#39;) and has largely ignored visuo-spatial functions (&#39;Where&#39;). In this chapter, we will review recent accounts on the nature of the well-established visuo-motor deficits in OA and present original data revealing visuo-perceptual deficits in patients with OA. The possibility of a functional relationship between the visuo-motor deficits of OA patients and their perceptual deficits will be put forward and discussed. History OA is part of the Bálint syndrome &#39;Optische Ataxie&#39;—a defect of visually guided hand movements—was initially defined by Bálint (1909) as one of the three components of a clinical entity comprised of a set of complex spatial behavior disorders following bilateral damage to the parieto-occipital junction (POJ), known as &#39;Bálint&#39;s syndrome&#39; . The syndrome is a triad of spatial deficits including &#39;optische Ataxie&#39;, &#39;Seelenlähmung des Schauens&#39;—often referred to as psychic paralysis of gaze (probably corresponding to simultanagnosia)—and &#39;räumlische Storung der Aufmerksamkeit&#39;—lateralized spatial disorder of attention (probably corre-sponding to neglect) (Pisella et al., 2007). A related &#39;visual disorientation&#39; syndrome was described a few years later by Holmes (Smith and Holmes, 1916; Holmes, 1918).
We address three issues that might be important in evaluating the validity of the planning-contro... more We address three issues that might be important in evaluating the validity of the planning-control model: (1) It could be artificial to distinguish between control and planning when control involves the re-planning of a new corrective submovement that overlaps with the initial response; (2) experiments involving illusions are not totally compelling; (3) selectively implicating the superior parietal lobe in movement control and the basal ganglia in movement planning, appears questionable. In this interesting article, Glover reviews evidence for a dichotomy between the planning and on-line control of actions. Although we Commentary/Glover: Separate visual representations in the planning and control of action
We briefly address three issues that might be important to evaluate the validity of the “emulatio... more We briefly address three issues that might be important to evaluate the validity of the “emulation theory”: (1) Does it really say something new? (2) Are similar processes engaged in action, imagery, and perception? (3) Does a brain amodal emulator exist?
Movement accuracy depends crucially on the ability to detect errors while actions are being perfo... more Movement accuracy depends crucially on the ability to detect errors while actions are being performed. When inaccuracies occur repeatedly, both an immediate motor correction and a progressive adaptation of the motor command can unfold. Of all the movements in the motor repertoire of humans, saccadic eye movements are the fastest. Due to the high speed of saccades, and to the impairment of visual perception during saccades, a phenomenon called ''saccadic suppression'', it is widely believed that the adaptive mechanisms maintaining saccadic performance depend critically on visual error signals acquired after saccade completion. Here, we demonstrate that, contrary to this widespread view, saccadic adaptation can be based entirely on visual information presented during saccades. Our results show that visual error signals introduced during saccade execution-by shifting a visual target at saccade onset and blanking it at saccade offset-induce the same level of adaptation as error signals, presented for the same duration, but after saccade completion. In addition, they reveal that this processing of intra-saccadic visual information for adaptation depends critically on visual information presented during the deceleration phase, but not the acceleration phase, of the saccade. These findings demonstrate that the human central nervous system can use short intra-saccadic glimpses of visual information for motor adaptation, and they call for a reappraisal of current models of saccadic adaptation.
doi: 10.3389/fnhum.2014.00880 Visuomotor adaptation needs a validation of prediction error by fee... more doi: 10.3389/fnhum.2014.00880 Visuomotor adaptation needs a validation of prediction error by feedback error
To foveate a visual target, subjects usually execute a primary hypometric saccade (S1) bringing t... more To foveate a visual target, subjects usually execute a primary hypometric saccade (S1) bringing the target in perifoveal vision, followed by a corrective saccade (S2) or by more than one S2. It is still debated to what extent these S2 are pre-programmed or dependent only on post-saccadic retinal error. To answer this question, we used a visually-triggered saccade task in which target position and target visibility were manipulated. In one-third of the trials, the target was slightly displaced at S1 onset (so-called double step paradigm) and was maintained until the end of S1, until the start of the first S2 or until the end of the trial. Experiments took place in two visual environments: in the dark and in a dimly lit room with a visible random square background. The results showed that S2 were less accurate for shortest target durations. The duration of post-saccadic visual integration thus appears as the main factor responsible for corrective saccade accuracy. We also found that the visual context modulates primary saccade accuracy, especially for the most hypometric subjects. These findings suggest that the saccadic system is sensitive to the visual properties of the environment and uses different strategies to maintain final gaze accuracy.
Annals of Physical and Rehabilitation Medicine, 2011
Objectifs.-Une escarre est une lésion cutanée d'origine ischémique liée à une compression prolong... more Objectifs.-Une escarre est une lésion cutanée d'origine ischémique liée à une compression prolongée des tissus mous entre un plan dur et les saillies osseuses. Cette complication est particulièrement dévastatrice dans la population des blessés médullaires en raison des troubles sensitifs et moteurs, mais aussi de la
The gain of reactive saccades was manipulated in 17 subjects using a target-jump paradigm. Follow... more The gain of reactive saccades was manipulated in 17 subjects using a target-jump paradigm. Following adaptation three sub-groups were formed: (1) rest 15 min in the dark, eyes closed; (2) perform self-generated saccades for 15 min; (3) perform reactive saccades for 15 min. The series of saccades were the same in groups 2 and 3 (amplitude, sequence), except that group 3 performed fewer saccades (same number as the lowest number of saccades performed by one subject in group 2). Neither the rest period nor the series of self-generated saccades affected the adapted gain. The series of reactive saccades generated, by contrast, quick de-adaptation. These results support the conclusion that the gain of self-generated and reactive saccades is independently controlled.
The processes underlying short-term plasticity induced by visuomotor adaptation to a shifted visu... more The processes underlying short-term plasticity induced by visuomotor adaptation to a shifted visual field are still debated.Two main sources of error can induce motor adaptation: reaching feedback errors, which correspond to visually perceived discrepancies between hand and target positions, and errors between predicted and actual visual reafferences of the moving hand. These two sources of error are closely intertwined and difficult to disentangle, as both the target and the reaching limb are simultaneously visible. Accordingly, the goal of the present study was to clarify the relative contributions of these two types of errors during a pointing task under prism-displaced vision. In "terminal feedback error" condition, viewing of their hand by subjects was allowed only at movement end, simultaneously with viewing of the target. In "movement prediction error" condition, viewing of the hand was limited to movement duration, in the absence of any visual target, and error signals arose solely from comparisons between predicted and actual reafferences of the hand. In order to prevent intentional corrections of errors, a subthreshold, progressive stepwise increase in prism deviation was used, so that subjects remained unaware of the visual deviation applied in both conditions. An adaptive aftereffect was observed in the "terminal feedback error" condition only. As far as subjects remained unaware of the optical deviation and self-assigned pointing errors, prediction error alone was insufficient to induce adaptation. These results indicate a critical role of hand-to-target feedback error signals in visuomotor adaptation; consistent with recent neurophysiological findings, they suggest that a combination of feedback and prediction error signals is necessary for eliciting aftereffects. They also suggest that feedback error updates the prediction of reafferences when a visual perturbation is introduced gradually and cognitive factors are eliminated or strongly attenuated.
A saccade is a rapid shift of the position of the eyes (o 100 ms). Saccades are generally conside... more A saccade is a rapid shift of the position of the eyes (o 100 ms). Saccades are generally considered too quick to be in£uenced by retinal signals. To address this idea, we displaced the visual target of a rightward horizontal saccade at eye movement onset (when there is suppression of conscious perception). To prevent adaptive and learning e¡ects to occur, jump saccades were always followed by a random series of 10 no-jump saccades. Results indicated that the target jump in£uenced signi¢cantly the amplitude and the peak velocity of the ongoing saccade (opposite e¡ects were found for rightward and leftward jumps). Changes in saccade kinematics occurred as early as 50 ms after the target jump. These results show that retinal information is processed quickly during eye movements, presumably through sub-cortical pathways.
It is challenging to recover local optic axis orientation from samples probed with fiber-based po... more It is challenging to recover local optic axis orientation from samples probed with fiber-based polarization-sensitive optical coherence tomography (PS-OCT). In addition to the effect of preceding tissue layers, the transmission through fiber and system elements, and imperfect system alignment, need to be compensated. Here, we present a method to retrieve the required correction factors from measurements with depth-multiplexed PS-OCT, which accurately measures the full Jones matrix. The correction considers both retardation and diattenuation and is applied in the wavenumber domain, preserving the axial resolution of the system. The robustness of the method is validated by measuring a birefringence phantom with a misaligned system. Imaging ex-vivo lamb trachea and human bronchus demonstrates the utility of reconstructing the local optic axis orientation to assess smooth muscle, which is expected to be useful in the assessment of airway smooth muscle thickness in asthma, amongst other fiber-based applications.
Studies on audiovisual interactions in sound localization have primarily focused on the relations... more Studies on audiovisual interactions in sound localization have primarily focused on the relations between the spatial position of sounds and their perceived visual source, as in the famous ventriloquist effect. Much less work has examined the effects on sound localization of seeing aspects of the visual environment. In this study, we took advantage of an innovative method for the study of spatial hearing-based on real sounds, virtual reality and real-time kinematic tracking-to examine the impact of a minimal visual spatial frame on sound localization. We tested sound localization in normal hearing participants (N = 36) in two visual conditions: a uniform gray scene and a simple visual environment comprising only a grid. In both cases, no visual cues about the sound sources were provided. During and after sound emission, participants were free to move their head and eyes without restriction. We found that the presence of a visual spatial frame improved hand-pointing in elevation. In addition, it determined faster first-gaze movements to sounds. Our findings show that sound localization benefits from the presence of a minimal visual spatial frame and confirm the importance of combining kinematic tracking and virtual reality when aiming to reveal the multisensory and motor contributions to spatial-hearing abilities.
Supplemental Digital Content is available in the text. Objectives: The aim of this study was to a... more Supplemental Digital Content is available in the text. Objectives: The aim of this study was to assess three-dimensional (3D) spatial hearing abilities in reaching space of children and adolescents fitted with bilateral cochlear implants (BCI). The study also investigated the impact of spontaneous head movements on sound localization abilities. Design: BCI children (N = 18, aged between 8 and 17) and age-matched normal-hearing (NH) controls (N = 18) took part in the study. Tests were performed using immersive virtual reality equipment that allowed control over visual information and initial eye position, as well as real-time 3D motion tracking of head and hand position with subcentimeter accuracy. The experiment exploited these technical features to achieve trial-by-trial exact positioning in head-centered coordinates of a single loudspeaker used for real, near-field sound delivery, which was reproducible across trials and participants. Using this novel approach, broadband sounds were delivered at different azimuths within the participants’ arm length, in front and back space, at two different distances from their heads. Continuous head-monitoring allowed us to compare two listening conditions: “head immobile” (no head movements allowed) and “head moving” (spontaneous head movements allowed). Sound localization performance was assessed by computing the mean 3D error (i.e. the difference in space between the X-Y-Z position of the loudspeaker and the participant’s final hand position used to indicate the localization of the sound’s source), as well as the percentage of front–back and left–right confusions in azimuth, and the discriminability between two nearby distances. Several clinical factors (i.e. age at test, interimplant interval, and duration of binaural experience) were also correlated with the mean 3D error. Finally, the Speech Spatial and Qualities of Hearing Scale was administered to BCI participants and their parents. Results: Although BCI participants distinguished well between left and right sound sources, near-field spatial hearing remained challenging, particularly under the “ head immobile” condition. Without visual priors of the sound position, response accuracy was lower than that of their NH peers, as evidenced by the mean 3D error (BCI: 55 cm, NH: 24 cm, p = 0.008). The BCI group mainly pointed along the interaural axis, corresponding to the position of their CI microphones. This led to important front–back confusions (44.6%). Distance discrimination also remained challenging for BCI users, mostly due to sound compression applied by their processor. Notably, BCI users benefitted from head movements under the “head moving” condition, with a significant decrease of the 3D error when pointing to front targets (p < 0.001). Interimplant interval was correlated with 3D error (p < 0.001), whereas no correlation with self-assessment of spatial hearing difficulties emerged (p = 0.9). Conclusions: In reaching space, BCI children and adolescents are able to extract enough auditory cues to discriminate sound side. However, without any visual cues or spontaneous head movements during sound emission, their localization abilities are substantially impaired for front–back and distance discrimination. Exploring the environment with head movements was a valuable strategy for improving sound localization within individuals with different clinical backgrounds. These novel findings could prompt new perspectives to better understand sound localization maturation in BCI children, and more broadly in patients with hearing loss.
Fast, online control of movement is an essential component of human motor skills, as it allows au... more Fast, online control of movement is an essential component of human motor skills, as it allows automatic correction of inaccurate planning. The present study explores the role of two types of concurrent signals in error correction: predicted visual reafferences coming from an internal representation of the hand, and actual visual feedback from the hand. While the role of sensory feedback in these corrections is well-established, much less is known about sensory prediction. The relative contributions of these two types of signals remain a subject of debate, as they are naturally interconnected. We address the issue in a study that compares online correction of an artificially induced, undetected planning error. Two conditions are tested, which only differ with respect to the accuracy of predicted visual reafferences. In the first, "Prism" experiment, a planning error is introduced by prisms that laterally displace the seen hand prior to hand movement onset. The prism-induced conflict between visual and proprioceptive inputs of the hand also generates an erroneous prediction of visual reafferences of the moving hand. In the second, "Jump" experiment, a planning error is introduced by a jump in the target position, during the orienting saccade, prior to hand movement onset. In the latter condition, predicted reafferences of the hand remained intact. In both experiments, after hand movement onset, the hand was either visible or hidden, which enabled us to manipulate the presence (or absence) of visual feedback during movement execution. The Prism experiment highlighted late and reduced correction of the planning error, even when natural visual feedback of the moving hand was available. In the Jump experiment, early and automatic corrections of the planning error were observed, even in the absence of visual feedback from the moving hand. Therefore, when predicted reafferences were accurate (the Jump experiment), visual feedback was processed rapidly and automatically. When they were erroneous (the Prism experiment), the same visual feedback was less efficient, and required voluntary, and late, control. Our study clearly demonstrates that in natural environments, reliable prediction is critical in the preprocessing of visual feedback, for fast and accurate movement.
Visuo-motor adaptation has been classically studied using movements aimed at visual targets with ... more Visuo-motor adaptation has been classically studied using movements aimed at visual targets with visual feedback. In this type of experimental design, the respective roles of the different error signals cannot be fully disentangled. Here, we show that visuo-motor adaptation occurs despite the terminal success of the action and the compensation of the external error by a jump of the visual target. By using three grasping task conditions we manipulated the retinal error signal between the seen hand and the target (external error) and the conflict between the hand's visual reafference and either the proprioceptive or the efference copy signal (internal error), in order to estimate their respective roles in prism adaptation. In all conditions, subjects were asked to rapidly grasp an object. In the classical 'Prism' condition the object was stationary, which provided both external and internal errors. In the 'Prism & Jump' condition, at movement onset the object was suddenly displaced (jump) toward its virtual image location (visually displaced by the prism) which also corresponded to the location where the movement was planned to and executed through prisms. This jump therefore cancelled the external error (between the seen target and the seen hand), whereas the internal error (between the seen hand and the expected visual reafference of the hand, or between the seen hand and the hand felt by proprioception) was unchanged (because it is independent of the presence of the goal). In the 'Jump' condition, the movement was planned and executed without prismatic goggles and consequently with no internal error (no difference between where the hand visual reafference is expected to be and where it actually is), but the object was suddenly displaced at movement onset by a displacement equivalent to a prism shift which provided an external error. The 'Prism' and 'Prism & Jump' conditions exhibited similar aftereffects, whereas no aftereffect was observed in the 'Jump' condition. These results suggest that successful actions can be subjected to adaptation and that internal error is the only signal necessary to elicit true visuomotor adaptation characterized by context-independent generalization.
When reaching to an object, information about the target location as well as the initial hand pos... more When reaching to an object, information about the target location as well as the initial hand position is required to program the motor plan for the arm. The initial hand position can be determined by proprioceptive information as well as visual information, if available. Bayes-optimal integration posits that we utilize all information available, with greater weighting on the sense that is more reliable, thus generally weighting visual information more than the usually less reliable proprioceptive information. The criterion by which information is weighted has not been explicitly investigated; it has been assumed that the weights are based on task- and effector-dependent sensory reliability requiring an explicit neuronal representation of variability. However, the weights could also be determined implicitly through learned modality-specific integration weights and not on effector-dependent reliability. While the former hypothesis predicts different proprioceptive weights for left an...
Annals of physical and rehabilitation medicine, Jan 18, 2018
After a coma, one major challenge is the detection of awareness in patients with disorders of con... more After a coma, one major challenge is the detection of awareness in patients with disorders of consciousness. In some patients, the only manifestation indicative of awareness is an appropriate emotional response. Preferred music is a powerful medium to elicit emotions and autobiographical memory. Furthermore, music has been shown to improve cognitive functions both in healthy subjects and patients with neurological impairment. We hypothesized that signs of awareness could be enhanced in some patients with disorders of consciousness under appropriate emotional stimulation such as preferred music and also probably preferred odors. To investigate an objective, easily recordable marker of emotions at the patients' bedside, electrodermal activity (skin conductance level, SCL) was assessed with stimulations in auditory and olfactory modalities, notably with preferred music, neutral sound, preferred odors, and neutral odors. The study was conducted in 11 patients with disorders of consc...
Sensorimotor Foundations of Higher Cognition, 1993
ABSTRACT Lesions of the dorsal posterior parietal cortex (PPC) typically result in optic ataxia (... more ABSTRACT Lesions of the dorsal posterior parietal cortex (PPC) typically result in optic ataxia (OA)—a disorder in which patients have difficulty reaching toward and grasping objects presented in peripheral vision, in the absence of primary sensory or motor deficits. It is therefore considered as a human model of the PPC involvement in visuo-manual control. In the early twentieth century, OA was described as part of the Bálint–Holmes syndrome. The main aim of most analyses of OA in the second part of the twentieth century was then to isolate a pure visuo-motor symptomatology from the complex Bálint&#39;s syndrome (e.g. Garcin et al., 1967; Rondot et al., 1977). In addition, OA has been used over the last 15 years to argue in favor of dissociable functions within the dorsal (&#39;How&#39;) and ventral (&#39;What&#39;) streams of visual information processing and visuo-manual guidance (Jeannerod and Rossetti, 1993; Milner and Goodale, 1995; Rossetti and Pisella, 2002). In these contexts, research on OA has focused primarily on visuo-motor functions (&#39;How&#39;) and has largely ignored visuo-spatial functions (&#39;Where&#39;). In this chapter, we will review recent accounts on the nature of the well-established visuo-motor deficits in OA and present original data revealing visuo-perceptual deficits in patients with OA. The possibility of a functional relationship between the visuo-motor deficits of OA patients and their perceptual deficits will be put forward and discussed. History OA is part of the Bálint syndrome &#39;Optische Ataxie&#39;—a defect of visually guided hand movements—was initially defined by Bálint (1909) as one of the three components of a clinical entity comprised of a set of complex spatial behavior disorders following bilateral damage to the parieto-occipital junction (POJ), known as &#39;Bálint&#39;s syndrome&#39; . The syndrome is a triad of spatial deficits including &#39;optische Ataxie&#39;, &#39;Seelenlähmung des Schauens&#39;—often referred to as psychic paralysis of gaze (probably corresponding to simultanagnosia)—and &#39;räumlische Storung der Aufmerksamkeit&#39;—lateralized spatial disorder of attention (probably corre-sponding to neglect) (Pisella et al., 2007). A related &#39;visual disorientation&#39; syndrome was described a few years later by Holmes (Smith and Holmes, 1916; Holmes, 1918).
We address three issues that might be important in evaluating the validity of the planning-contro... more We address three issues that might be important in evaluating the validity of the planning-control model: (1) It could be artificial to distinguish between control and planning when control involves the re-planning of a new corrective submovement that overlaps with the initial response; (2) experiments involving illusions are not totally compelling; (3) selectively implicating the superior parietal lobe in movement control and the basal ganglia in movement planning, appears questionable. In this interesting article, Glover reviews evidence for a dichotomy between the planning and on-line control of actions. Although we Commentary/Glover: Separate visual representations in the planning and control of action
We briefly address three issues that might be important to evaluate the validity of the “emulatio... more We briefly address three issues that might be important to evaluate the validity of the “emulation theory”: (1) Does it really say something new? (2) Are similar processes engaged in action, imagery, and perception? (3) Does a brain amodal emulator exist?
Movement accuracy depends crucially on the ability to detect errors while actions are being perfo... more Movement accuracy depends crucially on the ability to detect errors while actions are being performed. When inaccuracies occur repeatedly, both an immediate motor correction and a progressive adaptation of the motor command can unfold. Of all the movements in the motor repertoire of humans, saccadic eye movements are the fastest. Due to the high speed of saccades, and to the impairment of visual perception during saccades, a phenomenon called ''saccadic suppression'', it is widely believed that the adaptive mechanisms maintaining saccadic performance depend critically on visual error signals acquired after saccade completion. Here, we demonstrate that, contrary to this widespread view, saccadic adaptation can be based entirely on visual information presented during saccades. Our results show that visual error signals introduced during saccade execution-by shifting a visual target at saccade onset and blanking it at saccade offset-induce the same level of adaptation as error signals, presented for the same duration, but after saccade completion. In addition, they reveal that this processing of intra-saccadic visual information for adaptation depends critically on visual information presented during the deceleration phase, but not the acceleration phase, of the saccade. These findings demonstrate that the human central nervous system can use short intra-saccadic glimpses of visual information for motor adaptation, and they call for a reappraisal of current models of saccadic adaptation.
doi: 10.3389/fnhum.2014.00880 Visuomotor adaptation needs a validation of prediction error by fee... more doi: 10.3389/fnhum.2014.00880 Visuomotor adaptation needs a validation of prediction error by feedback error
To foveate a visual target, subjects usually execute a primary hypometric saccade (S1) bringing t... more To foveate a visual target, subjects usually execute a primary hypometric saccade (S1) bringing the target in perifoveal vision, followed by a corrective saccade (S2) or by more than one S2. It is still debated to what extent these S2 are pre-programmed or dependent only on post-saccadic retinal error. To answer this question, we used a visually-triggered saccade task in which target position and target visibility were manipulated. In one-third of the trials, the target was slightly displaced at S1 onset (so-called double step paradigm) and was maintained until the end of S1, until the start of the first S2 or until the end of the trial. Experiments took place in two visual environments: in the dark and in a dimly lit room with a visible random square background. The results showed that S2 were less accurate for shortest target durations. The duration of post-saccadic visual integration thus appears as the main factor responsible for corrective saccade accuracy. We also found that the visual context modulates primary saccade accuracy, especially for the most hypometric subjects. These findings suggest that the saccadic system is sensitive to the visual properties of the environment and uses different strategies to maintain final gaze accuracy.
Annals of Physical and Rehabilitation Medicine, 2011
Objectifs.-Une escarre est une lésion cutanée d'origine ischémique liée à une compression prolong... more Objectifs.-Une escarre est une lésion cutanée d'origine ischémique liée à une compression prolongée des tissus mous entre un plan dur et les saillies osseuses. Cette complication est particulièrement dévastatrice dans la population des blessés médullaires en raison des troubles sensitifs et moteurs, mais aussi de la
The gain of reactive saccades was manipulated in 17 subjects using a target-jump paradigm. Follow... more The gain of reactive saccades was manipulated in 17 subjects using a target-jump paradigm. Following adaptation three sub-groups were formed: (1) rest 15 min in the dark, eyes closed; (2) perform self-generated saccades for 15 min; (3) perform reactive saccades for 15 min. The series of saccades were the same in groups 2 and 3 (amplitude, sequence), except that group 3 performed fewer saccades (same number as the lowest number of saccades performed by one subject in group 2). Neither the rest period nor the series of self-generated saccades affected the adapted gain. The series of reactive saccades generated, by contrast, quick de-adaptation. These results support the conclusion that the gain of self-generated and reactive saccades is independently controlled.
The processes underlying short-term plasticity induced by visuomotor adaptation to a shifted visu... more The processes underlying short-term plasticity induced by visuomotor adaptation to a shifted visual field are still debated.Two main sources of error can induce motor adaptation: reaching feedback errors, which correspond to visually perceived discrepancies between hand and target positions, and errors between predicted and actual visual reafferences of the moving hand. These two sources of error are closely intertwined and difficult to disentangle, as both the target and the reaching limb are simultaneously visible. Accordingly, the goal of the present study was to clarify the relative contributions of these two types of errors during a pointing task under prism-displaced vision. In "terminal feedback error" condition, viewing of their hand by subjects was allowed only at movement end, simultaneously with viewing of the target. In "movement prediction error" condition, viewing of the hand was limited to movement duration, in the absence of any visual target, and error signals arose solely from comparisons between predicted and actual reafferences of the hand. In order to prevent intentional corrections of errors, a subthreshold, progressive stepwise increase in prism deviation was used, so that subjects remained unaware of the visual deviation applied in both conditions. An adaptive aftereffect was observed in the "terminal feedback error" condition only. As far as subjects remained unaware of the optical deviation and self-assigned pointing errors, prediction error alone was insufficient to induce adaptation. These results indicate a critical role of hand-to-target feedback error signals in visuomotor adaptation; consistent with recent neurophysiological findings, they suggest that a combination of feedback and prediction error signals is necessary for eliciting aftereffects. They also suggest that feedback error updates the prediction of reafferences when a visual perturbation is introduced gradually and cognitive factors are eliminated or strongly attenuated.
A saccade is a rapid shift of the position of the eyes (o 100 ms). Saccades are generally conside... more A saccade is a rapid shift of the position of the eyes (o 100 ms). Saccades are generally considered too quick to be in£uenced by retinal signals. To address this idea, we displaced the visual target of a rightward horizontal saccade at eye movement onset (when there is suppression of conscious perception). To prevent adaptive and learning e¡ects to occur, jump saccades were always followed by a random series of 10 no-jump saccades. Results indicated that the target jump in£uenced signi¢cantly the amplitude and the peak velocity of the ongoing saccade (opposite e¡ects were found for rightward and leftward jumps). Changes in saccade kinematics occurred as early as 50 ms after the target jump. These results show that retinal information is processed quickly during eye movements, presumably through sub-cortical pathways.
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Papers by Valérie Gaveau