Perception Of Position Research Articles

Reducing the occurrence of falls in Parkinson's disease by modulating the internal model of verticality: a case study

We present a documented observation suggesting the existence of a biased representation of verticality in PD, tilted backward dramatically, which resulted in a severe retropulsion and recurrent falls. A rehabilitation program aimed to modulate verticality perception improved the postural perception of the vertical, trunk posture and balance abilities and reduced retropulsion as well as lastingly fall frequency. A 68 year-old patient with Parkinson's disease fall backward 3 times a day despite a severe camptocormia. No amyotrophy of posterior trunk muscles neither spinal canal stenosis could explain camptocormia (CT scan). The postural vertical (PV) was tilted backward at −9° (normally for this age −1.2 ± 1.4°). This strongly suggested that retropulsion was the consequence of a backward PV tilt, the patient aligning implicitly his erect posture onto a biased internal model of verticality. This induced a backward disequilibrium and led to recurrent falls. We assume that camptocormia was mainly compensatory. An intensive rehabilitation program was set including during 2 weeks: erectus spinae muscles strengthening, postural exercises in front of a mirror, postural and general exercises. More specifically, on the basis of theoretical arguments (synthesis of graviceptive vestibular and somatosensory information) and at the light of published experimental studies, we also implemented 3 techniques supposed to recalibrate the internal model of verticality, undergone daily: 30° forward tilted posture on a tilt table, walking on a treadmill suspended by a cable (bodyweight support), vibration of tibialis anterior's tendons during dynamic postural tasks. Drugs were kept unchanged during this rehabilitation program. After 2 weeks of intensive training, the results were spectacular: reduction of 35 mm in the C7 sagittal arrow, gain of 1 point on the Backward Disequilibrium Scale (BDS) and overall normalization of PV = 0.1° (gain 9°). At discharge, the patient was instructed to regularly perform exercises taught. He was interviewed 2 and 6 months later and was very satisfied with a feeling to stand better and a net reduction of fall frequency. This observation brings a new insight about the nature of some postural disorders in PD, in relation with retropulsion and backward falls, partially compensated by a camptocormia. It suggests the interest of a novel rehabilitation approach in PD showing these particular postural disorders.

The effect of hand position on perceived finger orientation in left- and right-handers

In the absence of visual feedback, the perceived orientation of the fingers is systematically biased. In right-handers these biases are asymmetrical between the left and right hands in the horizontal plane and may reflect common functional postures for the two hands. Here we compared finger orientation perception in right- and left-handed participants for both hands, across various hand positions in the horizontal plane. Participants rotated a white line on a screen optically superimposed over their hand to indicate the perceived position of the finger that was rotated to one of seven orientations with the hand either aligned with the body midline, aligned with the shoulder, or displaced by twice the shoulder-to-midline distance from the midline. We replicated the asymmetric pattern of biases previously reported in right-handed participants (left hand biased towards an orientation ~30° inward, right hand ~10° inward). However, no such asymmetry was found for left-handers, suggesting left-handers may use different strategies when mapping proprioception to body or space coordinates and/or have less specialization of function between the hands. Both groups’ responses rotated further outward as distance of the hand from the body midline increased, consistent with other research showing spatial orientation estimates diverge outward in the periphery. Finally, for right-handers, precision of responses was best when the hand was aligned with the shoulder compared to the other two conditions. These results highlight the unique role of hand dominance and hand position in perception of finger orientation, and provide insight into the proprioceptive position sense of the upper limbs.

Interpreting spatial dysgraphia after stroke: Straight ahead or straight above?

Spatial dysgraphia, frequently observed after a right hemisphere stroke, associates signs of spatial compression in relation to spatial neglect, and a tilted writing which remains to be explained. Here we present a case study suggesting that tilted writing is due to a tilted representation of the vertical. JW, a 75-year-old patient who underwent a right hemisphere hemorrhage showed a pusher syndrome and a writing tilted 11.1° upwardly, consistent through many tests, without other signs of spatial dysgraphia. We comprehensively assessed and followed most aspects of spatial cognition, until nine months post-stroke. For writing assessments, head and trunk were kept upright, and JW was instructed to write with the right (non-paretic) hand, on a paper sheet affixed onto a graphic tablet (to quantify writing orientation and time) positioned in front him on a slanted table (30°). The writing was tested with or without visual clues, and after a modulation of verticality perception. One month post-stroke, spatial neglect was severe with predominant signs of body neglect. Subjective straight-ahead was normal. Visual (VV) and postural (PV) perceptions of the vertical were tilted of 11°, counterclockwise. This transmodal tilt was similar both in direction and magnitude to the tilt found congruent on all features of writing: margin, lines, and letters. At 3 months the writing was found slower than a control subject when JW was instructed to write on blank paper (1.67 vs. 0.82 s/letter; P < 0.001), and faster when writing on lines inclined 24° upwardly (1.11 s/letter; P < 0.05). Then JW was himself tilted, in sitting for 10 min at 30° to right side, in the dark using the wheel paradigm. As expected this normalized PV for several min. This PV modulation significantly reduced the writing tilt, measured 20 min later (6.2°; P = 0.001) and increased the writing speed (0.89 s/letter; P = 0.002). Nine months post-stroke we found a dissociation between signs of spatial neglect, which disappeared, and a tilt remaining both in verticality perception and writing (5° and 8.8°, respectively). After a right hemisphere stroke, a tilted writing is likely a sign of a tilted verticality representation.

The internal representation of head orientation differs for conscious perception and balance control.

We tested perceived head-on-feet orientation and the direction of vestibular-evoked balance responses in passively and actively held head-turned postures. The direction of vestibular-evoked balance responses was not aligned with perceived head-on-feet orientation while maintaining prolonged passively held head-turned postures. Furthermore, static visual cues of head-on-feet orientation did not update the estimate of head posture for the balance controller. A prolonged actively held head-turned posture did not elicit a rotation in the direction of the vestibular-evoked balance response despite a significant rotation in perceived angular head posture. It is proposed that conscious perception of head posture and the transformation of vestibular signals for standing balance relying on this head posture are not dependent on the same internal representation. Rather, the balance system may operate under its own sensorimotor principles, which are partly independent from perception. Vestibular signals used for balance control must be integrated with other sensorimotor cues to allow transformation of descending signals according to an internal representation of body configuration. We explored two alternative models of sensorimotor integration that propose (1) a single internal representation of head-on-feet orientation is responsible for perceived postural orientation and standing balance or (2) conscious perception and balance control are driven by separate internal representations. During three experiments, participants stood quietly while passively or actively maintaining a prolonged head-turned posture (>10min). Throughout the trials, participants intermittently reported their perceived head angular position, and subsequently electrical vestibular stimuli were delivered to elicit whole-body balance responses. Visual recalibration of head-on-feet posture was used to determine whether static visual cues are used to update the internal representation of body configuration for perceived orientation and standing balance. All three experiments involved situations in which the vestibular-evoked balance response was not orthogonal to perceived head-on-feet orientation, regardless of the visual information provided. For prolonged head-turned postures, balance responses consistent with actual head-on-feet posture occurred only during the active condition. Our results indicate that conscious perception of head-on-feet posture and vestibular control of balance do not rely on the same internal representation, but instead treat sensorimotor cues in parallel and may arrive at different conclusions regarding head-on-feet posture. The balance system appears to bypass static visual cues of postural orientation and mainly use other sensorimotor signals of head-on-feet position to transform vestibular signals of head motion, a mechanism appropriate for most daily activities.

Sustainable reduction in the occurrence of falls in a Parkinson's patient who followed an intensive and specific rehabilitation program to recalibrate verticality perception

To take care of postural disorders is a major issue in Parkinson's disease (PD). We present a documented observation suggesting the existence of a biased representation of verticality in PD, resulting in a severe retropulsion and recurrent falls. A rehabilitation program aimed to modulate verticality perception dramatically improved the postural perception of the vertical, trunk posture and balance abilities, and reduced retropulsion as well as lastingly fall frequency. A 68 year-old patient with Parkinson's disease fall backward 3 times a day. He presented an important camptocormia. There were no spinal muscular amyotrophy neither spinal canal stenosis on the lumbar tomography. The postural vertical (PV) was tilted backward at –9 (normal PV for this age = –1.2 ± 1.4). Our interpretation was that retropulsion was due to a backward tilt of the internal model of verticality, which led to recurrent falls. Camptocormia was mainly compensatory. The patient underwent an intensive rehabilitation program of 15 days including: erectus spinae muscles strengthening, realization of postural exercises thanks to mirror, forward modulation of PV. On the basis of theoretical arguments (synthesis of graviceptive vestibular and somatosensory information) and on experimental studies, we also proposed techniques supposed to recalibrate the internal model of verticality: 30 forward tilted posture on a tilt table, bodyweight support walking, vibration of tibialis anterior's tendons. PV measurements during/just after these techniques confirmed the relevance of this approach. The results were spectacular: 35 mm gain in the measurement of C7 sagittal arrow, 1 point gain in backward disequilibrium scale (BDS) and overall normalization of PV = 0.1. The patient was questioned 2 months later then assessed 6 months later. He continued to daily perform auto-exercises taught, and was very satisfied because of a dramatic reduction of fall frequency, with a feeling to stand better. This observation brings a new insight about the nature of some postural disorders in PD, and suggests the interest of a novel rehabilitation dedicated to the sense of verticality.

Perceptual shrinkage of a one-way motion path with high-speed motion.

Back-and-forth motion induces perceptual shrinkage of the motion path, but such shrinkage is hardly perceived for one-way motion. If the shrinkage is caused by temporal averaging of stimulus position around the endpoints, it should also be induced for one-way motion at higher motion speeds. In psychophysical experiments with a high-speed projector, we tested this conjecture for a one-way motion stimulus at various speeds (4–100 deg/s) along a straight path. Results showed that perceptual shrinkage of the motion path was robustly observed in higher-speed motion (faster than 66.7 deg/s). In addition, the amount of the forwards shift at the onset position was larger than that of the backwards shift at the offset position. These results demonstrate that high-speed motion can induce shrinkage, even for a one-way motion path. This can be explained by the view that perceptual position is represented by the integration of the temporal average of instantaneous position and the motion representation.

Spécificité et évaluation de la proprioception du genou

Several procedures have been developed to measure the proprioceptive capacity of the knee joint. The methods are based on the perception of either movement or posture. Two validated tests are widely used to measure joint motion. Joint Position Sense (JPS) is used to measure passive or active capacity to detect limb position in space. Threshold for Detection Motion (TDT) is used to measure the capacity to detect motion with the knee starting in an immobile position. Data in the literature and our own experience suggest that the TDPM is the most pertinent monitoring tool. The proprioception platform is widely used for postural assessment and appears to be the most adequate tool available. Using data from several personal studies, we examine the test's reproducibility and redefine norms for bipodal and monopodal stance. We have also analyzed the impact of visual feedback on the results and have compared normal values observed in a healthy population with those recorded in an anterior cruciate ligament repair population. Reproducibility was satisfactory but variable depending on the parameters analyzed. It was shown that visual feedback could be used to establish an adaptation strategy to reduce the surface of displacement. Significantly different postural profiles were defined separating the healthy population from the anterior cruciate ligament surgery population. There was however no difference between the healthy knee and the operated knee, a finding that appears to confirm the hypothesis of alterations in central proprioception processing with bilateral impact of a unilateral injury. Proprioceptive rehabilitation protocols must focus on improving the proprioceptive capacity of the injured limb, but at the same time must not ignore the impact on the healthy side.

Cognitive empathy modulates the visual perception of human-like body postures without imitation

ABSTRACTTo examine the mechanism of visual perception of human-like body postures, we conducted a posture recognition task, a questionnaire survey, and the Interpersonal Reactivity Index (IRI). The majority of participants perceived the pseudo-posture as a human posture in the early stage (78%), but only approximately half of them reported the imagination of bodily movement (66%). These results suggest that the majority of observers perceive pseudo-postures as human postures in the early stage of perception, but this human posture perception does not necessarily lead to the visualisation of bodily movement. In a group of who received the pseudo posture as a human-posture regardless of the perception stages, the participants who imagined bodily movement (64%) showed significantly higher scores than those who did not on the Fantasy subscale of the IRI. Highly empathic participants are more likely to detect a kinematic relation between the pseudo-postures.

Postural and Perception Variations When Using Manually Adjustable and Programmable Sit–Stand Workstations in an Emergency Call Center

OCCUPATIONAL APPLICATIONSTwo styles of sit–stand workstations were tested in an emergency (911) call center to quantify postural stress and perception variations. The usual manually adjusted electrically controlled sit–stand workstation was compared with a programmable workstation that automatically changed between seated and standing heights, made forward–backward adjustments, and rotated around the user regularly during a 20-minute cycle. Over 2 working days, neck and seated trunk postures improved with the programmable workstation. Manually controlled sit–stand workstations were not adjusted with the regularity recommended to minimize musculoskeletal discomfort. While seven perceptual measures did not significantly vary between workstations, two others worsened with the programmable workstation: general discomfort and back pain. Participant comments suggested opportunities for design refinements. User training was not included here but would normally further improve results. The programmable workstation improved posture over the manually adjusted workstation, although design refinements and user training in office ergonomics are recommended to maximize benefits.TECHNICAL ABSTRACT Background: Call center workers have high musculoskeletal discomfort, and emergency (911) center workers are among the most affected. Despite many centers including manually controlled sit–stand workstations that facilitate postural changes, these are not typically adjusted with the regularity recommended to minimize musculoskeletal discomfort. Thus, underuse or improper use may be barriers to preventing musculoskeletal disorders and discomfort. Purpose: This study investigates posture and perception of physical factors when using a powered dual-surface manually adjustable workstation and a powered programmable adjustable workstation. Methods: Twelve 911 call-center operators participated. For each workstation, postures were recorded using video cameras over a working day. Nine perception factors were captured at the end of each day using a visual analog scale. Results: Programmable workstation use resulted in significantly lower incidence of at-risk postures in the neck and back and more frequent standing. Perception did not vary significantly between workstations except for an increase in back pain and general discomfort with the programmable workstation. Conclusions: This limited sample exposure to a programmable moving workstation concept should be pursued, though with refinements in larger populations to improve musculoskeletal health of workers in high-stress sedentary environments and should be combined with training. Current observations may be applied to improve programmable workstation aspects that are contributing to perceived discomforts.

Perceptual eye position and gaze stability of the children with amblyopia

Perceptual eye position and gaze stability of the children with amblyopia

The study of perceptual eye position and gaze stability of the children with normal visual acuity

The study of perceptual eye position and gaze stability of the children with normal visual acuity

Holistic processing of human body postures: evidence from the composite effect.

The perception of socially relevant stimuli (e.g., faces and bodies) has received considerable attention in the vision science community. It is now widely accepted that human faces are processed holistically and not only analytically. One observation that has been taken as evidence for holistic face processing is the face composite effect: two identical top halves of a face tend to be perceived as being different when combined with different bottom halves. This supports the hypothesis that face processing proceeds holistically. Indeed, the interference effect disappears when the two face parts are misaligned (blocking holistic perception). In the present study, we investigated whether there is also a composite effect for the perception of body postures: are two identical body halves perceived as being in different poses when the irrelevant body halves differ from each other? Both a horizontal (i.e., top-bottom body halves; Experiment 1) and a vertical composite effect (i.e., left-right body halves; Experiment 2) were examined by means of a delayed matching-to-sample task. Results of both experiments indicate the existence of a body posture composite effect. This provides evidence for the hypothesis that body postures, as faces, are processed holistically.

Postural sway and perception of affordances in children at risk for developmental coordination disorder

Gibson (The ecological approach to visual perception, Houghton Mifflin, Boston, 1979/1986) defined affordances as opportunities for motor behaviors, and highly emphasized the interaction between perception and action. Research on children with developmental coordination disorder commonly reports difficulties in judgments of affordances (perception) and in postural control (action). However, how perception and action are coupled has not been studied yet. The present study sought to evaluate the relationship between control of postural sway and perception of affordances in children at risk for developmental coordination disorder (RDCD) and typically developing children (TDC). We hypothesized that the relationship between perception and action would differ between groups. Participants made a series of judgments about their maximum sitting height (SHmax) while standing with and without wearing 10 cm blocks on feet. Postural sway and the judgment accuracy were recorded. Our findings showed that RDCD swayed more during judgment sessions and made less accurate judgments compared to TDC. In addition, TDC reduced postural sway from inter-judgment to judgment sessions, whereas the postural sway of RDCD remained identical between sessions. Last, while TDC reduced postural sway across judgment trials and revealed a learning effect of the judgments about SHmax in the block condition, RDCD never modulated postural sway and did not learn their SHmax in both non-block and block conditions. Overall, modulation of postural sway differed between groups during judgment sessions and between inter-judgment and judgment sessions, whereby their perceptual judgments about SHmax were differentially influenced. To summarize, this study demonstrated a difference in perception and action coupling between RDCD and TDC.

SPINAL REPOSITIONING DEFICIT. THE EFFECT OF PROLONGED FLEXED POSTURE

Flexed sitting posture is commonly adopted in daily sitting activities and when sustained has been proposed to affect biological properties of spinal tissues and act detrimentally on proprioception. The objective...

Impaired body but not face perception in patients with obsessive–compulsive disorder

Empirical evidence involving the processing of social information by patients with obsessive-compulsive disorder (OCD) has been relatively scarce. Our study investigated the perceptual abilities of patients with OCD to recognize human faces and bodies. Fifty-four drug-free or drug-naïve patients with OCD and 42 healthy controls performed discrimination tasks consisting of four types of stimuli: two sets of faces that were manipulated with regard to configuration and features, human bodies, and chairs. The stimuli were presented in upright and upside-down orientations. Patients with OCD were significantly less accurate in discriminating pairs of bodily postures implying actions. However, we found no significant differences between patient and control groups in the ability to recognize faces and chairs. The inversion effects for bodies and faces were also comparable between the two groups. The current findings suggest that patients with OCD experience difficulty in perceiving static forms of bodily postures, but are able to adequately recognize human faces. Our data indicate a selective deficit in the perception of bodily postures in those with OCD and suggest that this deficit is probably not related to the abnormal configurational processing of social objects.

Responses evoked by a vestibular implant providing chronic stimulation1

Patients with bilateral vestibular loss experience dehabilitating visual, perceptual, and postural difficulties, and an implantable vestibular prosthesis that could improve these symptoms would be of great benefit to these patients. In previous work, we have shown that a one-dimensional, unilateral canal prosthesis can improve the vestibulooccular reflex (VOR) in canal-plugged squirrel monkeys. In addition to the VOR, the potential effects of a vestibular prosthesis on more complex, highly integrative behaviors, such as the perception of head orientation and posture have remained unclear. We tested a one-dimensional, unilateral prosthesis in a rhesus monkey with bilateral vestibular loss and found that chronic electrical stimulation partially restored the compensatory VOR and also that percepts of head orientation relative to gravity were improved. However, the one-dimensional prosthetic stimulation had no clear effect on postural stability during quiet stance, but sway evoked by head-turns was modestly reduced. These results suggest that not only can the implementation of a vestibular prosthesis provide partial restitution of VOR but may also improve perception and posture in the presence of bilateral vestibular hypofunction (BVH). In this review, we provide an overview of our previous and current work directed towards the eventual clinical implementation of an implantable vestibular prosthesis.

3-D Posture and Gesture Recognition for Interactivity in Smart Spaces

Automatic perception of human posture and gesture from vision input has an important role in developing intelligent video systems. In this paper, we present a novel gesture recognition approach for human computer interactivity based on marker-less upper body pose tracking in 3-D with multiple cameras. To achieve the robustness and real-time performance required for practical applications, the idea is to break the exponentially large search problem of upper body pose into two steps: first, the 3-D movements of upper body extremities (i.e., head and hands) are tracked. Then using knowledge of upper body model constraints, these extremities movements are used to infer the whole 3-D upper body motion as an inverse kinematics problem. Since the head and hand regions are typically well defined and undergo less occlusion, tracking is more reliable and could enable more robust upper body pose determination. Moreover, by breaking the problem of upper body pose tracking into two steps, the complexity is reduced considerably. Using pose tracking output, the gesture recognition is then done based on longest common subsequence similarity measurement of upper body joint angles dynamics. In our experiment, we provide an extensive validation of the proposed upper body pose tracking from 3-D extremity movement which showed good results with various subjects in different environments. Regarding the gesture recognition based on joint angles dynamics, our experimental evaluation of five subjects doing six upper body gestures with average classification accuracies over 90% indicates the promise and feasibility of the proposed system.

Self-produced stimulation can elicit rubber hand illusion

10. I felt as if I were touching the hand on the display. –The RHI is known to reflect the role of multi-sensory interaction in coherent body representation. It has mainly been studied using tactile stimuli provided by an experimenter. – In the control condition, a participant repeatedly touched his/her invisible real left hand, again using the haptic device without a visible pointer. – In the self-produced-touch condition, a participant moved his/her right hand with the haptic device to repeatedly touch his/her invisible real left hand. A virtual left hand and visual cues were visible on the CRT display and the pointer of the haptic device touched this hand in perfect synchrony with the participant's right hand motions. – In the externally-produced-touch condition, an experimenter repeatedly touched a participant's invisible real left hand, using the haptic device with visual cues on the CRT display. – The RHI was induced in three six-minute sessions. After each session, the difference of the perceptual position of the left hand from that before was measured, and the participant completed a questionnaire. Average Ratings

Implicit influence of affective postures on the perception of others: You can't show me how I feel.

This study examined how one's own posture influences the perception of another's posture in a task with implicit affective information. In 2 experiments, participants assumed or viewed a body posture and then compared that posture with a viewed posture. They were not told that postures varied in affective valence: positive, negative, neutral-abstract, or neutral-meaningful. Posture affect influenced both accuracy and response time measures of posture discrimination. Participants were slower and less accurate for targets that matched an assumed posture, but only for affective postures. This pattern did not hold for matching affectively neutral postures (meaningful or not), nonmatching postures, or for purely visual comparisons. These results are consistent with both cognitive embodiment theories postulating that personal body posture influences the perception of other's postures and emotional embodiment theories postulating sensorimotor and emotional simulation processes that create correspondences between one's own and another's emotional postures. Nonetheless, these findings differ from studies finding facilitation for explicit emotional judgments of affective congruence. People use different information depending on task requirements. The assumption of an affective posture may activate simulations of personal emotional experiences that may, in turn, serve to differentiate personal posture perception from ostensibly the same posture in another person.

The movement of motion-defined contours can bias perceived position

Illusory position shifts induced by motion suggest that motion processing can interfere with perceived position. This may be because accurate position representation is lost during successive visual processing steps. We found that complex motion patterns, which can only be extracted at a global level by pooling and segmenting local motion signals and integrating over time, can influence perceived position. We used motion-defined Gabor patterns containing motion-defined boundaries, which themselves moved over time. This 'motion-defined motion' induced position biases of up to 0.5 degrees , much larger than has been found with luminance-defined motion. The size of the shift correlated with how detectable the motion-defined motion direction was, suggesting that the amount of bias increased with the magnitude of this complex directional signal. However, positional shifts did occur even when participants were not aware of the direction of the motion-defined motion. The size of the perceptual position shift was greatly reduced when the position judgement was made relative to the location of a static luminance-defined square, but not eliminated. These results suggest that motion-induced position shifts are a result of general mechanisms matching dynamic object properties with spatial location.