Naïve chicks do not prefer objects with stable body orientation, though they may prefer behavioural variability.

Domestic chicks (Gallus gallus domesticus) have been widely used as a model to study the motion cues that allow visually naïve organisms to detect animate agents shortly after hatching/birth. Our previous work has shown that chicks prefer to approach agents whose main body axis and motion direction are aligned (a feature typical of creatures whose motion is constrained by a bilaterally symmetric body plan). However, it has never been investigated whether chicks are also sensitive to the fact that an agent maintains a stable front-back body orientation in motion (i.e. consistency in which end is leading and which trailing). This is another feature typical of bilateria, which is also associated with the detection of animate agents in humans. The aim of the present study was to fill this gap. Contrary to our initial expectations, after testing 300 chicks across 3 experimental conditions, we found a recurrent preference for the agent which did not maintain a stable front-back body orientation. Since this preference was limited to female chicks, the results are discussed also in relation to sex differences in the social behaviour of this model. Overall, we show for the first time that chicks can discriminate agents based on the stability of their front-back orientation. The unexpected direction of the effect could reflect a preference for agents' whose behaviour is less predictable. Chicks may prefer agents with greater behavioural variability, a trait which has been associated with animate agents, or have a tendency to explore agents performing "odd behaviours".

CAMSAP3 facilitates basal body polarity and the formation of the central pair of microtubules in motile cilia.

Synchronized beating of cilia on multiciliated cells (MCCs) generates a directional flow of mucus across epithelia. This motility requires a "9 + 2" microtubule (MT) configuration in axonemes and the unidirectional array of basal bodies of cilia on the MCCs. However, it is not fully understood what components are needed for central MT-pair assembly as they are not continuous with basal bodies in contrast to the nine outer MT doublets. In this study, we discovered that a homozygous knockdown mouse model for MT minus-end regulator calmodulin-regulated spectrin-associated protein 3 (CAMSAP3), Camsap3tm1a/tm1a , exhibited multiple phenotypes, some of which are typical of primary ciliary dyskinesia (PCD), a condition caused by motile cilia defects. Anatomical examination of Camsap3tm1a/tm1a mice revealed severe nasal airway blockage and abnormal ciliary morphologies in nasal MCCs. MCCs from different tissues exhibited defective synchronized beating and ineffective generation of directional flow likely underlying the PCD-like phenotypes. In normal mice, CAMSAP3 localized to the base of axonemes and at the basal bodies in MCCs. However, in Camsap3tm1a/tm1a , MCCs lacked CAMSAP3 at the ciliary base. Importantly, the central MT pairs were missing in the majority of cilia, and the polarity of the basal bodies was disorganized. These phenotypes were further confirmed in MCCs of Xenopus embryos when CAMSAP3 expression was knocked down by morpholino injection. Taken together, we identified CAMSAP3 as being important for the formation of central MT pairs, proper orientation of basal bodies, and synchronized beating of motile cilia.

Attenuated spontaneous postural sway enhances diastolic blood pressure during quiet standing.

PURPOSE: Spontaneous postural sway during quiet standing has been considered a simple output error of postural control. However, as postural sway and inherent body orientation evoke compensatory activity of the plantar flexors, they might contribute to blood circulation under gravitational stress via the muscle pump. Hence, the present study employed an external support device to attenuate the plantar flexor activity in supported standing (SS), to experimentally identify its physiological impact on blood circulation. METHODS: Eight healthy young subjects performed two 5-min quiet standing trials (i.e., normal standing (NS) and SS), and the beat-to-beat interval (RRI) and blood pressure (BP) were compared between trials. We confirmed that postural sway and corresponding plantar flexor activity, quantified by the anteroposterior displacement of the foot center of pressure and lower back position with respect to the wall, and by the amplitude of electromyography and mechanomyography, respectively, were attenuated in SS, while mean body orientation angle and relative position of the BP sensor were comparable to NS. RESULTS: The 5-min averages of diastolic BP and mean arterial pressure during SS were significantly higher than during NS, while RRI and systolic BP did not change. These could be interpreted as an increase in peripheral vascular resistance; meanwhile, in NS, this effect was replaced by the muscle pump of the plantar flexors. CONCLUSION: The muscle contractions related to spontaneous postural sway and body orientation produce substantial physiological impact on blood circulation during quiet standing.

Feeling addressed! The neural processing of social communicative cues in patients with major depression.

The feeling of being addressed is the first step in a complex processing stream enabling successful social communication. Social impairments are a relevant characteristic of patients with major depressive disorder (MDD). Here, we investigated a mechanism which-if impaired-might contribute to withdrawal or isolation in MDD, namely, the neural processing of social cues such as body orientation and gesture. During funtional magnetic resonance imaging (fMRI) data acquisition, 33 patients with MDD and 43 healthy control subjects watched video clips of a speaking actor: one version with a gesture accompanying the speech and one without gesture. Videos were filmed simultaneously from two different viewpoints: one with the actor facing the viewer head-on (frontal) and one side-view (lateral). After every clip, the participants were instructed to evaluate whether they felt addressed or not. Despite overall comparable addressment ratings and a large overlap in activation patterns in MDD and healthy subjects for gesture processing, the anterior cingulate cortex, bilateral superior/middle frontal cortex, and right angular gyrus were more strongly activated in patients than in healthy subjects for the frontal conditions. Our analyses revealed that patients showed specifically higher activation than healthy subjects for the frontal condition without gesture in regions including the posterior cingulate cortex, left prefrontal cortex, and the left hippocampus. We conclude that MDD patients can recognize and interpret social cues such as gesture or body orientation; however, they seem to require more neural resources. This additional effort might affect successful communication and contribute to social isolation in MDD.

Gesture's body orientation modulates the N400 for visual sentences primed by gestures.

Body orientation of gesture entails social-communicative intention, and may thus influence how gestures are perceived and comprehended together with auditory speech during face-to-face communication. To date, despite the emergence of neuroscientific literature on the role of body orientation on hand action perception, limited studies have directly investigated the role of body orientation in the interaction between gesture and language. To address this research question, we carried out an electroencephalography (EEG) experiment presenting to participants (n = 21) videos of frontal and lateral communicative hand gestures of 5 s (e.g., raising a hand), followed by visually presented sentences that are either congruent or incongruent with the gesture (e.g., "the mountain is high/low…"). Participants underwent a semantic probe task, judging whether a target word is related or unrelated to the gesture-sentence event. EEG results suggest that, during the perception phase of handgestures, while both frontal and lateral gestures elicited a power decrease in both the alpha (8-12 Hz) and the beta (16-24 Hz) bands, lateral versus frontal gestures elicited reduced power decrease in the beta band, source-located to the medial prefrontal cortex. For sentence comprehension, at the critical word whose meaning is congruent/incongruent with the gesture prime, frontal gestures elicited an N400 effect for gesture-sentence incongruency. More importantly, this incongruency effect was significantly reduced for lateral gestures. These findings suggest that body orientation plays an important role in gesture perception, and that its inferred social-communicative intention may influence gesture-language interaction at semantic level.

How do hoverflies use their righting reflex?

When taking off from a sloping surface, flies have to reorient themselves dorsoventrally and stabilize their body by actively controlling their flapping wings. We have observed that righting is achieved solely by performing a rolling manoeuvre. How flies manage to do this has not yet been elucidated. It was observed here for the first time that hoverfly reorientation is entirely achieved within 6 wingbeats (48.8 ms) at angular roll velocities of up to 10×103 deg s-1 and that the onset of their head rotation consistently follows that of their body rotation after a time lag of 16 ms. The insects' body roll was found to be triggered by the asymmetric wing stroke amplitude, as expected. The righting process starts immediately with the first wingbeat and seems unlikely to depend on visual feedback. A dynamic model for the fly's righting reflex is presented, which accounts for the head/body movements and the time lag recorded in these experiments. This model consists of a closed-loop control of the body roll, combined with a feedforward control of the head/body angle. During the righting manoeuvre, a strong coupling seems to exist between the activation of the halteres (which measure the body's angular speed) and the gaze stabilization reflex. These findings again confirm the fundamental role played by the halteres in both body and head stabilization processes.

Multi-Person Pose Estimation Using an Orientation and Occlusion Aware Deep Learning Network.

Image based human behavior and activity understanding has been a hot topic in the field of computer vision and multimedia. As an important part, skeleton estimation, which is also called pose estimation, has attracted lots of interests. For pose estimation, most of the deep learning approaches mainly focus on the joint feature. However, the joint feature is not sufficient, especially when the image includes multi-person and the pose is occluded or not fully visible. This paper proposes a novel multi-task framework for the multi-person pose estimation. The proposed framework is developed based on Mask Region-based Convolutional Neural Networks (R-CNN) and extended to integrate the joint feature, body boundary, body orientation and occlusion condition together. In order to further improve the performance of the multi-person pose estimation, this paper proposes to organize the different information in serial multi-task models instead of the widely used parallel multi-task network. The proposed models are trained on the public dataset Common Objects in Context (COCO), which is further augmented by ground truths of body orientation and mutual-occlusion mask. Experiments demonstrate the performance of the proposed method for multi-person pose estimation and body orientation estimation. The proposed method can detect 84.6% of the Percentage of Correct Keypoints (PCK) and has an 83.7% Correct Detection Rate (CDR). Comparisons further illustrate the proposed model can reduce the over-detection compared with other methods.

Feeling addressed! The role of body orientation and co-speech gesture in social communication.

During face-to-face communication, body orientation and coverbal gestures influence how information is conveyed. The neural pathways underpinning the comprehension of such nonverbal social cues in everyday interaction are to some part still unknown. During fMRI data acquisition, 37 participants were presented with video clips showing an actor speaking short sentences. The actor produced speech-associated iconic gestures (IC) or no gestures (NG) while he was visible either from an egocentric (ego) or from an allocentric (allo) position. Participants were asked to indicate via button press whether they felt addressed or not. We found a significant interaction of body orientation and gesture in addressment evaluations, indicating that participants evaluated IC-ego conditions as most addressing. The anterior cingulate cortex (ACC) and left fusiform gyrus were stronger activated for egocentric versus allocentric actor position in gesture context. Activation increase in the ACC for IC-ego>IC-allo further correlated positively with increased addressment ratings in the egocentric gesture condition. Gesture-related activation increase in the supplementary motor area, left inferior frontal gyrus and right insula correlated positively with gesture-related increase of addressment evaluations in the egocentric context. Results indicate that gesture use and body-orientation contribute to the feeling of being addressed and together influence neural processing in brain regions involved in motor simulation, empathy and mentalizing.

Mitigating the squash effect: sloths breathe easily upside down.

Sloths are mammals renowned for spending a large proportion of time hanging inverted. In this position, the weight of the abdominal contents is expected to act on the lungs and increase the energetic costs of inspiration. Here, we show that three-fingered sloths Bradypus variegatus possess unique fibrinous adhesions that anchor the abdominal organs, particularly the liver and glandular stomach, to the lower ribs. The key locations of these adhesions, close to the diaphragm, prevent the weight of the abdominal contents from acting on the lungs when the sloth is inverted. Using ventilation rate and body orientation data collected from captive and wild sloths, we use an energetics-based model to estimate that these small adhesions could reduce the energy expenditure of a sloth at any time it is fully inverted by almost 13%. Given body angle preferences for individual sloths in our study over time, this equates to mean energy saving of 0.8-1.5% across individuals (with individual values ranging between 0.01 and 8.6%) per day. Given the sloth's reduced metabolic rate compared with other mammals and extremely low energy diet, these seemingly innocuous adhesions are likely to be important in the animal's energy budget and survival.

Improving orientation with respect to gravity enhances balance and gait recovery after stroke: DOBRAS cohort.

BACKGROUND: Lateropulsion is a deficit in body orientation with respect to gravity, frequent after stroke. Although it is a primary factor affecting mobility, the impact of its attenuation on balance and gait recovery has never been investigated. Moreover, most studies on the lateropulsion time-course focus on severe forms suspected to have a poor recovery, which is not proven. OBJECTIVES: To investigate lateropulsion attenuation and test 2 hypotheses: 1) lateropulsion attenuation greatly contributes to balance and gait recovery and 2) severe forms of lateropulsion recover slower than moderate forms. METHODS: This longitudinal study involved individuals included in the Determinants of Balance Recovery After Stroke (DOBRAS) cohort, after a first-ever hemispheric stroke, with data collected on day 30 (D30), D60 and D90 post-stroke. Body orientation with respect to gravity was assessed using the Scale for Contraversive Pushing (both scores and severity grouping), in parallel with balance (Postural Assessment Scale for Stroke) and gait (modified Fugl-Meyer Gait Assessment). RESULTS: Among the 106 eligible individuals (mean age 66.5 [SD 9.7] years), on D30, 43 (41%) were considered upright and 63 (59%) showed lateropulsion: 30 (28%) moderate and 33 (31%) severe. Most individuals with lateropulsion (73%) improved their body orientation, progressing from severe to moderate lateropulsion, or becoming upright. However, half were still not upright on D90. The improvement in body orientation had a large impact on mobility, especially in individuals with severe lateropulsion, in whom it explained about 50% of balance and gait recovery between D30 and D60, then 20% (D60-D90). For moderate lateropulsion, its attenuation explained about 20% of balance and gait recovery until D90. Lateropulsion attenuation was not slower in individuals with severe forms. CONCLUSIONS: Lateropulsion attenuation enhances balance and gait recovery in individuals after stroke suggesting that specific rehabilitation of body orientation with respect to gravity might help to recover mobility. REGISTRATION: NCT03203109.

Physical Body Orientation Impacts Virtual Navigation Experience and Performance.

Most human navigation studies in MRI rely on virtual navigation. However, the necessary supine position in MRI makes it fundamentally different from daily ecological navigation. Nonetheless, until now, no study has assessed whether differences in physical body orientation (BO) affect participants' experienced BO during virtual navigation. Here, combining an immersive virtual reality navigation task with subjective BO measures and implicit behavioral measures, we demonstrate that physical BO (either standing or supine) modulates experienced BO. Also, we show that standing upright BO is preferred during spatial navigation: participants were more likely to experience a standing BO and were better at spatial navigation when standing upright. Importantly, we report that showing a supine virtual agent reduces the conflict between the preferred BO and physical supine BO. Our study provides critical, but missing, information regarding experienced BO during virtual navigation, which should be considered cautiously when designing navigation studies, especially in MRI.

A wireless physiological parameter monitoring system with a treatment feedback function during neonatal phototherapy.

Objective. Neonatal jaundice is a common condition in the early stages of newborns, and phototherapy is a fast, safe and effective method that is used to treat it. However, recent studies have shown that phototherapy may elicit side effects in infants, such as hypothermia, hyperthermia and dehydration. To improve the quality of phototherapy and the prognosis of patients, the changes in neonatal physiological parameters during phototherapy should be monitored to give better feedback to pediatricians or the phototherapy system. However, the current standard of clinical care during neonatal phototherapy with hard-wired devices limits this realization.Approach. Here, we developed a prototype of a neonatal wearable device, which can wirelessly potentially monitor the jaundice value, transepidermal water loss, skin wettedness factor and body orientation during phototherapy, and conducted prototype validation experiments. We also set up user-friendly interfaces and an analysis system on custom software, all designed to make the future addition of data interfaces for treatment feedback functions easier.Main results. The preliminaryin vitroexperiment demonstrated the effectiveness of simultaneous monitoring of the required physiological parameters. And further suggestions and specific operations are discussed in terms of optimization of the treatment of neonatal jaundice.Significance. It is believed that the established system has the potential to provide a basis for future phototherapy nursing guidelines and physiological monitoring standards.

Body Pose Estimation Integrated With Notational Analysis: A New Approach to Analyze Penalty Kicks Strategy in Elite Football.

Body orientation of football players has proven to be an informative resource related to successful penalty kicks. OpenPose is one of the most popular open-source pose estimation technologies. This study aims: (i) to verify whether OpenPose can detect relevant body orientation angles from video data of penalty kicks in elite football and (ii) to investigate the relationship between these body angles and observable behaviors analyzed via an observational system for penalty kick analysis in football (OSPAF) with the penalty taker and goalkeeper strategy. A total of 34 penalty videos, with standardized viewing angle, from the main European leagues (2017-2020) were analyzed. Relevant body orientation variables were selected for penalty kicks analysis and were extracted from video data through OpenPose technique. The OSPAF, previously validated by experts, was used. The mean confidence score of OpenPose measures was 0.80 ± 0.14. OpenPose Retest reliability values was 0.976 ± 0.03. Logistic regressions were performed to investigate the relationship between OpenPose investigated variables (penalty taker: shoulder, hips, and nonkicking foot orientation; goalkeeper: right and left foot, anticipation), observable behaviors (OSPAF variables), and the strategy (penalty taker: goalkeeper dependent or independent; goalkeeper: shooter dependent or independent) in penalty kicks. The selected body orientation angle (goalkeeper anticipation) measured through OpenPose correlated significantly with the goalkeeper strategy. The prediction model of the goalkeeper's strategy had its accuracy increased to 97% when the variable goalkeeper anticipation was included [ χ ( 35 ) 2 = 49.648, p < 0.001]. Lower degrees of goalkeeper anticipation, the goalkeeper tactical action (awaiting), and run up speed (slow) were associated with a kicker-dependent strategy. Regarding the penalty taker, the selected body angles measured through OpenPose did not associate significantly with the shooter strategy. Body orientation analysis by using OpenPose has shown sufficient reliability and provides practical applications for analyzing the strategies adopted by goalkeepers in penalty kicks in elite football.

Modeling the associations between internal body orientation, body appreciation, and intuitive eating among early-adult and middle-adult men and women: A multigroup structural invariance analysis.

This cross-sectional study investigated the associations among internal body orientation, body appreciation, intuitive eating, age, and BMI in men and women between 30 and 70 years old as delineated in the acceptance model of intuitive eating. Self-report measures were administered to a final sample of 522 individuals consisting of early-adult men (ages 30-44; n = 153), middle-adult men (ages 45-70; n = 108), early-adult women (ages 30-44; n = 135), and middle-adult women (ages 45-70; n = 126). Overall mean age was 45.03 (SD = 10.95). Structural equation modeling evidenced that, for both age groups of men and women, internal body orientation was positively associated with body appreciation and body appreciation was positively associated with intuitive eating. Internal body orientation was positively associated with intuitive eating in each group, except early-adult women. The associations among age and BMI with the aforementioned variables were inconsistent. Although evidencing measurement non-invariance among a number of parameters, multigroup structural invariance analyses showed that the associations among internal body orientation, body appreciation, intuitive eating, age, and BMI were invariant across each gender and age. These results further confirm components of the acceptance model of intuitive eating among men and women in early-adulthood and middle-adulthood.

Automatic Detection of Gaze and Body Orientation in Elementary School Classrooms.

Detecting the direction of the gaze and orientation of the body of both teacher and students is essential to estimate who is paying attention to whom. It also provides vital clues for understanding their unconscious, non-verbal behavior. These are called "honest signals" since they are unconscious subtle patterns in our interaction with other people that help reveal the focus of our attention. Inside the classroom, they provide important clues about teaching practices and students' responses to different conscious and unconscious teaching strategies. Scanning this non-verbal behavior in the classroom can provide important feedback to the teacher in order for them to improve their teaching practices. This type of analysis usually requires sophisticated eye-tracking equipment, motion sensors, or multiple cameras. However, for this to be a useful tool in the teacher's daily practice, an alternative must be found using only a smartphone. A smartphone is the only instrument that a teacher always has at their disposal and is nowadays considered truly ubiquitous. Our study looks at data from a group of first-grade classrooms. We show how video recordings on a teacher's smartphone can be used in order to estimate the direction of the teacher and students' gaze, as well as their body orientation. Using the output from the OpenPose software, we run Machine Learning (ML) algorithms to train an estimator to recognize the direction of the students' gaze and body orientation. We found that the level of accuracy achieved is comparable to that of human observers watching frames from the videos. The mean square errors (RMSE) of the predicted pitch and yaw angles for head and body directions are on average 11% lower than the RMSE between human annotators. However, our solution is much faster, avoids the tedium of doing it manually, and makes it possible to design solutions that give the teacher feedback as soon as they finish the class.

Force-velocity profile changes with forearm wearable resistance during standing start sprinting.

Abstract Horizontal force-velocity (F-V) profiling is a strategy to assess athletes' individual performance capabilities during sprinting. This study investigated the acute changes in F-V profiles during sprinting of fourteen collegiate male sprinters with a mean 100-m sprint time of 11.40 ± 0.39 s, from a split-stance starting position. The subjects sprinted 30-m with, and without, wearable resistance (WR) equivalent to 2% body mass, attached to their forearms. Sprinting time at 5, 10, 20, and 30-m was assessed using laser technology. External horizontal F-V relationships were calculated via velocity-time signals. Maximal theoretical velocity (V 0), theoretical relative and absolute horizontal force (F 0), and horizontal power (P max) were determined from the F-V relationship. Paired t-tests were used to determine statistical differences (p ≤ 0.05) in variables across conditions with Cohen's d as effect sizes (ES) calculated to assess practical changes. Sprint times at 10-m and beyond were significantly increased (1.9-3.3%, p 0.01-0.03, ES 0.46-0.60) with WR compared to unloaded sprinting. The only significant change in F-V with the WR condition was found in relative P max system (-6.1%, p 0.01, ES 0.66). A small decrease was reported in V 0 (-1.0%, p 0.11, ES 0.27), with small to medium ES decreases reported in F 0 (-4.8% to -6.1%, p 0.07-0.21, ES 0.25-0.51) and P max (-4.3% to -4.6%, p 0.06-0.08, ES 0.32-0.45). The greater changes to F 0 and P max suggest that forearm WR may be a possible training tool for athletes who wish to focus on force and power adaptation during sprint acceleration from a standing start.

A novel setup for 3D chasing behavior analysis in free flying flies.

BACKGROUND: Insects catching prey or mates on the wing perform one of the fastest behaviours observed in nature. Some dipteran flies are aerial acrobats specialized to detect, chase and capture their targets within the blink of an eye. Studies of aerial pursuits and its underlying sensorimotor control have been a long-standing subject of interest in neuroethology research. NEW METHOD: We designed an actuated dummy target to trigger chasing flights in male blowflies. Our setup generates arbitrary 2D target trajectories in the horizontal plane combining translation up to 1 m/s and angular rotation up to 720°/s. RESULTS: Using stereovision methods we reconstructed target and pursuer positions every 5 ms with a maximum 3D error of 5 mm. The pursuer's body pitch and yaw angles were resolved within an error range of 6deg. An embedded observation point provides a close-up view of the pursuer's final approach and enables us to measure its body roll angle. We observed banked turns and sideslip which have not been reported for chasing blowflies in the past. COMPARISON WITH EXISTING METHOD(S): Previous studies focused on pursuit along circular paths or interception of translating targets while our method allows us to generate more complex target trajectories. Measurements of body orientation in earlier accounts were limited to the heading direction while we extended the analysis to include the full body orientation during pursuit. CONCLUSIONS: Our setup offers an opportunity to investigate kinematics and governing visual parameters of chasing behaviour in species up to the size of blowflies under a large variety of experimental conditions.

Perceptual reversals and time-response analyses within the scope of decoding a bistable image / Análisis de reversibilidades perceptuales y de tiempos de respuesta en el marco de la decodificación de una imagen biestable

Abstract A bistable image admits two possible interpretations, so that the observer can recognize the two percepts, but never at the same time. The alternations between percepts are called "perceptual reversals". When the observer's position is different from the upright position, the ability to make perceptual alternations may be impaired. Besides, the recognition of the percepts of a bistable image can be a complex reaction time visual task, if it involves recognizing two different conceptual units, added to the fact of having to make a subsequent report. A visual task was performed by 88 people in order to establish whether the perception of Boring's bistable image My girlfriend or my mother-in-law is associated with areas that condition its interpretation. It was assumed that decoding the image and reporting the perceived percept implied a complex reaction time. The task itself was done in front of a fixed 120 Hz eye-tracker, in two opposite body positions. Analyses were made reviewing the association of the percepts with bottom-up modulation areas of the image, and considering ocular fixations made 200 and 250 milliseconds before the time of the report. The records of these fixations were obtained so as to establish which of the two reaction times (200 ms or 250 ms) was involved in the bottom-up modulation process from the moment of ocular fixation to the reports given by the participants. It was concluded that perceptual reversals decrease significantly when head idiotropic axis points in the gravity vector direction, in comparison to the upright position. Likewise, associations between visual percepts and bottom-up modulating areas of the image were found when analyses were done by considering ocular fixations made 250 ms before the moment of the report. Interpreting Boring's bistable image implies a complex visual task in accordance with the results obtained.

Resumen Una imagen biestable admite dos interpretaciones, de modo que el observador reconoce cada percepto, pero nunca los dos al mismo tiempo. Cada alternancia entre uno y otro percepto se conoce con el nombre de "reversibilidad perceptual". Este tipo de percepción, denominada también "biestable", puede implicar dos tipos de modulación, una mediada por las características físicas del estímulo visual y por las áreas de fijación ocular, y otra por información contextual o por conocimiento almacenado en memoria. En ese sentido, las alternancias perceptuales que se manifiestan durante la observación de una imagen biestable pueden estar condicionadas por la manera en que el observador recorre con su mirada el estímulo biestable, de manera tal que es manifiesta una asociación entre específicas áreas de la imagen y el percepto que se reconoce. En efecto, para la imagen biestable de Boring Mi novia o mi suegra, se han establecido áreas de fijación ocular que favorecen los dos posibles perceptos (una mujer joven y una mujer de edad). Algunas de estas zonas elicitan más la interpretación de uno de los perceptos, otras de los dos indistintamente, como se reconoce en estudios precedentes. Por otra parte, se ha encontrado evidencia de que cuando la posición corporal del observador es distinta a la posición erguida (el tronco y la cabeza alineados con la vertical), puede dificultarse la capacidad para hacer las alternancias perceptuales. La rotación del eje idiotrópico de la cabeza con respecto al vector que apunta verticalmente hacia el cénit tiene repercusiones en los procesos perceptuales visuales y también en la manifestación de las reversibilidades perceptuales inherentes a la observación de imágenes biestables. El reconocimiento de los perceptos de un estímulo visual biestable puede suponer una tarea visual de tiempo de reacción complejo (superior a 230 milisegundos), dado que esta implica reconocer dos unidades conceptuales diferentes. A esto se suma el hecho de tener que hacer un reporte posterior que implique eferencias motoras. A los efectos de establecer si la percepción de la imagen biestable Mi novia o mi suegra está asociada a las áreas del estímulo que condicionan su interpretación cuando se asume que su decodificación más su reporte implican un tiempo de reacción complejo, se hicieron análisis de tareas visuales realizadas por 88 personas frente a un eye-tracker fijo de 120 Hz en dos posiciones corporales opuestas (una, con el tronco erguido y el eje idiotrópico de la cabeza apuntando hacia el cénit, y otra con el vector idiotrópico de la cabeza apuntando hacia el suelo en paralelo al eje gravitacional). Se revisó la asociación de los perceptos con las áreas de modulación de la imagen y considerando las fijaciones oculares realizadas 200 y 250 milisegundos antes del momento del reporte, el cual fue realizado por cada participante mediante el uso de los botones de un dispositivo conectado al registrador de datos. Los registros de fijaciones oculares, tomados en dos momentos previos al momento del reporte de los perceptos identificados, fueron considerados para establecer cuál de los dos tiempos de reacción (200 ms o 250 ms) está implicado en el proceso de modulación bottom-up desde el momento de la fijación ocular hasta el reporte dado por los participantes. Se concluyó que las reversibilidades perceptuales disminuyen significativamente cuando el eje idiotrópico de la cabeza apunta en el sentido del vector gravitacional en comparación con la posición erguida. Se encontraron asociaciones entre los perceptos y las áreas de modulación cuando en el análisis se consideran las fijaciones oculares registradas, 250 milisegundos antes de los reportes. La interpretación de la imagen analizada supone una tarea visual compleja de conformidad con los resultados, pues el análisis de asociación entre perceptos reportados y áreas moduladoras que arroja significancia es el que se hace revisando las fijaciones oculares hechas 250 ms antes del registro del reporte de cada percepto.

The Influence of Human Body Orientation on Distance Judgments.

People maintain larger distances to other peoples' front than to their back. We investigated if humans also judge another person as closer when viewing their front than their back. Participants watched animated virtual characters (avatars) and moved a virtual plane toward their location after the avatar was removed. In Experiment 1, participants judged avatars, which were facing them as closer and made quicker estimates than to avatars looking away. In Experiment 2, avatars were rotated in 30 degree steps around the vertical axis. Observers judged avatars roughly facing them (i.e., looking max. 60 degrees away) as closer than avatars roughly looking away. No particular effect was observed for avatars directly facing and also gazing at the observer. We conclude that body orientation was sufficient to generate the asymmetry. Sensitivity of the orientation effect to gaze and to interpersonal distance would have suggested involvement of social processing, but this was not observed. We discuss social and lower-level processing as potential reasons for the effect.

Maintaining Trunk and Head Upright Optimizes Visual Vertical Measurement After Stroke.

BACKGROUND: Visual vertical (VV) measurement provides information about spatial cognition and is now part of postural disorders assessment. Guidelines for clinical VV measurement after stroke remain to be established, especially regarding the orientation settings for patients who do not sit upright. OBJECTIVES: We analyzed the need to control body orientation while patients estimate the VV. METHODS: VV orientation and variability were assessed in 20 controls and 36 subacute patients undergoing rehabilitation after a first hemisphere stroke, in 3 settings: body not maintained (trunk and head free), partially maintained (trunk maintained, head free), or maintained (trunk and head). VV was analyzed as a function of trunk and head tilt, also quantified. RESULTS: Trunk and head orientations were independent. The ability to sit independently was affected by a tilted trunk. The setting had a strong effect on VV orientation and variability in patients with contralesional trunk tilt (n = 11; trunk orientation -18.4 ± 11.7°). The contralesional VV bias was severe and consistent under partially maintained (-8.4 ± 5.2°) and maintained (-7.8 ± 3.5°) settings, whereas various individual behaviors reduced the mean bias under the nonmaintained setting (-3.6 ± 9.3°, P < .05). VV variability was lower under the maintained (1.5 ± 0.2°) than nonmaintained (3.7 ± 0.4°, P < .001) and partially maintained (3.6 ± 0.2°, P < .001) settings. In contrast, setting had no effect in patients with satisfactory postural control in sitting. CONCLUSION: Subject setting improves VV measurement in stroke patients with postural disorders. Maintaining the trunk upright enhances the validity of VV orientation, and maintaining the head upright enhances the validity of within-subject variability. Measuring VV without any body maintaining is valid in patients with satisfactory balance abilities.