We investigated the role of the visual eye-height (VEH) in the perception of affordance during short-term exposure to weightlessness. Sixteen participants were tested during parabolic flight (0g) and on the ground (1g). Participants looked at a laptop showing a room in which a doorway-like aperture was presented. They were asked to adjust the opening of the virtual doorway until it was perceived to be just wide enough to pass through (i.e., the critical aperture). We manipulated VEH by raising the level of the floor in the visual room by 25 cm. The results showed effects of VEH and of gravity on the perceived critical aperture. When VEH was reduced (i.e., when the floor was raised), the critical aperture diminished, suggesting that widths relative to the body were perceived to be larger. The critical aperture was also lower in 0g, for a given VEH, suggesting that participants perceived apertures to be wider or themselves to be smaller in weightlessness, as compared to normal gravity. However, weightlessness also had an effect on the subjective level of the eyes projected into the visual scene. Thus, setting the critical aperture as a fixed percentage of the subjective visual eye-height remains a viable hypothesis to explain how human observers judge visual scenes in terms of potential for action or “affordances”.

Idiopathic rapid-eye-movement sleep behavior disorder (iRBD) is becoming widely considered a prodromal symptom of Parkinson's disease (PD). Visuoperceptual deficits have been described in iRBD with still conflicting results. Since this cognitive domain is often impaired in PD, it appears of great interest to better describe visuoperceptual deficits in iRBD patients. Secondly, defining the neurophysiological correlates of these deficits would bring important data on the pathophysiology of iRBD. This study aimed to study the visual object processing in iRBD patients. High-density electroencephalograms were used to record event-related potential in fourteen iRBD patients and fourteen matched healthy volunteers during a fragmented images categorization task. The task consisted in categorizing “recognizable” images as real objects, and “unrecognizable” images as non-objects. The Ncl component (negativity associated with closure) was recorded and used as a marker of incomplete objects recognition processing. Behavioral results revealed no significant differences between the 2 groups in number of correct categorization and response time. The ERPs in the control group had significantly smaller amplitude for “recognizable” compared to “unrecognizable” images from 240 to 640 ms in the left posterior scalp regions. This relative negativity (Ncl) was absent in the iRBD patients group. This study provides neurophysiological data suggesting changes in the fragmented images processing in iRBD patients.

Neuroimaging studies have shown that faces exhibit a central visual field bias, as compared to buildings and scenes. With a saccadic choice task, Crouzet, Kirchner, and Thorpe (2010) demonstrated a speed advantage for the detection of faces with stimuli located 8° from fixation. We used the same paradigm to examine whether the face advantage, relative to other categories (animals and vehicles), extends across the whole visual field (from 10° to 80° eccentricity) or whether it is limited to the central visual field. Pairs of photographs of natural scenes (a target and a distractor) were displayed simultaneously left and right of central fixation for 1s on a panoramic screen. Participants were asked to saccade to a target stimulus (faces, animals, or vehicles). The distractors were images corresponding to the two other categories. Eye movements were recorded with a head-mounted eye tracker. Only the first saccade was measured. Experiment 1 showed that (a) in terms of speed of categorization, faces maintain their advantage over animals and vehicles across the whole visual field, up to 80° and (b) even in crowded conditions (an object embedded in a scene), performance was above chance for the three categories of stimuli at 80° eccentricity. Experiment 2 showed that, when compared to another category with a high degree of within category structural similarity (cars), faces keep their advantage at all eccentricities. These results suggest that the bias for faces is not limited to the central visual field, at least in a categorization task.

Un nombre croissant d’arguments mène à considérer les troubles du comportement en sommeil paradoxal dits idiopathiques (TCSPi) comme un symptôme « pré-moteur » de la maladie de Parkinson (MP). Des troubles visuo-perceptifs ont été décrits dans les TCSPi avec toutefois des résultats divergents. Ce domaine cognitif étant spécifiquement touché dans la MP, il semble intéressant de pouvoir décrire plus précisément ces troubles chez les patients avec TCSPi. Par ailleurs, l’étude des corrélats électrophysiologiques de ces troubles apporterait des données importantes sur la physiopathologie des TCSPi. L’objectif de cette étude était d’analyser le traitement perceptif de l’information visuelle chez les patients avec TCSPi. Des enregistrements électroencéphalographiques haute résolution ont été réalisés chez 14 patients avec TCSPi et 14 sujets contrôles afin d’analyser les potentiels évoqués cognitifs (PEc) engendrés par une tâche de catégorisation d’images fragmentées. La tâche consistait à catégoriser des images « reconnaissables » comme des objets réels et des images « non reconnaissables » comme des dessins aléatoires. La composante « Ncl » pour negativity associated with closure était analysée et utilisée comme un marqueur des processus de perception d’objets incomplets. Les résultats comportementaux n’ont mis en évidence aucune différence entre les deux groupes concernant le nombre de catégorisation correcte et le temps de réponse. Dans le groupe contrôle, le PEc avait une amplitude moyenne significativement plus faible pour les images « reconnaissables » que pour les images « non reconnaissables » dans la fenêtre de temps 240-640 ms. Cette différence concernait les régions postérieures gauches du scalp. Cette relative négativité (Ncl) était absente chez les patients avec TCSPi. Ces résultats vont dans le sens d’une modification des processus de traitement visuo-perceptif associée aux TCSPi. Les sources corticales de la Ncl ayant été décrites dans des régions de la voie ventrale de reconnaissance visuelle, nos résultats pourraient suggérer une atteinte corticale postérieure dans les TCSPi.

PURPOSE:To investigate the effect of age-related macular degeneration (AMD) on memory for spatial representations in realistic environments.METHODS:Participants were 19 patients with AMD and 13 age-matched observers. In a short-term spatial memory task, observers were first presented with one view of a scene (the prime view), and their task was to change the viewpoint forward or backward to match the prime view. Memory performance was measured as the number of snapshots between the selected view and the prime view.RESULTS:When selecting a match to the prime view, both people with AMD and those in the control group showed systematic biases toward the middle view of the range of snapshots. People with AMD exhibited a stronger middle bias after presentation of close and far prime views while navigating accurately after a middle prime view. No relation was found between visual acuity, visual field defect, or lesion size and the memory performance.CONCLUSIONS:Memory tasks using indoor scenes can be accomplished when central vision is impoverished, as with AMD. Stronger center bias for a scene location suggests that people with AMD rely more on their memory of a canonical view.

PURPOSE:To investigate the effect of contrast on scene perception in people with age-related macular degeneration (AMD) and to examine the relationship between task performance and macular function.METHODS:Nineteen patients with AMD and visual acuity below 20/50 were compared with 16 normally sighted, age-matched controls. Complete ophthalmologic examination (visual acuity, intraocular pressure measurement, and funduscopy) was performed in both patients and controls. In addition, Pelli-Robson contrast sensitivity, fluorescein angiography, and visual field size were assessed in the AMD study patients. The stimuli were photographs of natural scenes containing or lacking an animal (the target). For each scene, the contrast of the original photograph was divided by 2, 4, and 8 to yield versions with a residual contrast of 50, 25, and 12.5%, respectively. The four levels of contrast were presented randomly and participants were asked to press a key when they saw an animal.RESULTS:AMD patients exhibited a larger drop in target detection performance with the decrease in contrast than controls. We found a correlation between visual acuity and performance when the contrast was reduced to 50, 25, and 12.5% of the original value but not in the normal contrast condition. There were no correlations between letter contrast sensitivity, visual field lesion size, and performance.CONCLUSIONS:Our results suggest that optimal, stable contrast conditions would facilitate object recognition in everyday life for people with AMD.

Riccio and Stoffregen (1988) have suggested that task performance is the predominant constraint of change in postural control. To test this hypothesis, 12 healthy, young adults performed large lateral gaze shifts (left/right gaze shifts with a visual angle of 150° and at a frequency of 0.5Hz or 1Hz) and a control condition (looking at a stationary dot). Performance in the visual task was expected to be good under all conditions. In accordance with Riccio and Stoffregen’s hypothesis, the center of pressure sway variability (range or standard deviation) was expected to be similar in the three visual tasks when a destabilizing, narrow stance was adopted. Indeed, body sway had to be restrained in narrow stance to adequately perform the task. In standard and wide stance conditions, the center of pressure sway variability was expected to be larger when gaze shifts were performed. Indeed, in these more stable stance conditions, the task could be performed successfully in minimizing energy expenditure, that is, in letting body sway increase naturally. The results were consistent with these expectations. On a practical level, intentional, large gaze shifts may not cause postural instability per se, even though postural sway may increase significantly.

Many studies provided evidence that the emotional content of visual stimulations modulates behavioral performance and neuronal activity. Surprisingly, these studies were carried out using stimulations presented in the center of the visual field while the majority of visual events firstly appear in the peripheral visual field. In this study, we assessed the impact of the emotional facial expression of fear when projected in near and far periphery. Sixteen participants were asked to categorize fearful and neutral faces projected at four peripheral visual locations (15° and 30° of eccentricity in right and left sides of the visual field) while reaction times and event-related potentials (ERPs) were recorded. ERPs were analyzed by means of spatio-temporal principal component and baseline-to-peak methods. Behavioral data confirmed the decrease of performance with eccentricity and showed that fearful faces induced shorter reaction times than neutral ones. Electrophysiological data revealed that the spatial position and the emotional content of faces modulated ERPs components. In particular, the amplitude of N170 was enhanced by fearful facial expression. These findings shed light on how visual eccentricity modulates the processing of emotional faces and suggest that, despite impoverished visual conditions, the preferential neural coding of fearful expression of faces still persists in far peripheral vision. The emotional content of faces could therefore contribute to their foveal or attentional capture, like in social interactions.

PURPOSE:To investigate impairment in discriminating a figure from its background and to study its relation to visual acuity and lesion size in patients with neovascular age-related macular degeneration (AMD).METHODS:Seventeen patients with neovascular AMD and visual acuity <20/50 were included. Seventeen age-matched healthy subjects participated as controls. Complete ophthalmologic examination was performed on all participants. The stimuli were photographs of scenes containing animals (targets) or other objects (distractors), displayed on a computer monitor screen. Performance was compared in four background conditions: the target in the natural scene; the target isolated on a white background; the target separated by a white space from a structured scene; the target separated by a white space from a nonstructured, shapeless background. Target discriminability (d') was recorded.RESULTS:Performance was lower for patients than for controls. For the patients, it was easier to detect the target when it was separated from its background (under isolated, structured, and nonstructured conditions) than it was when located in a scene. Performance was improved in patients with increasing exposure time but remained lower in controls. Correlations were found between visual acuity, lesion size, and sensitivity for patients.CONCLUSIONS:Figure/ground segregation is impaired in patients with AMD. A white space surrounding an object is sufficient to improve the object's detection and to facilitate figure/ground segregation. These results may have practical applications to the rehabilitation of the environment in patients with AMD.

PURPOSE To assess the scene gist recognition in eyes with age-related macular degeneration (AMD) and to study the relationship between scene recognition and macular function. METHODS Twenty-seven patients with age-related macular degeneration with a visual acuity lower than 20/50 and 17 age-matched controls were included. All patients underwent a visual field test, fundus autofluorescence, and fluorescein angiography to assess the visual field defect and the lesion size. The stimuli were colored photographs of natural scenes displayed on a 30-inch screen. Two scene categorization tasks were performed: natural versus urban and indoor versus outdoor scenes. Participants were given a target (e.g., indoor scenes) and asked to press a key when they saw a picture corresponding to that target. Accuracy and response times were recorded. RESULTS Patients with AMD were able to accomplish both categorization tasks with a high correct detection rate (above 75% correct), though performance was lower than in controls for both natural/urban scenes and indoor/outdoor scenes. Patients with AMD were more accurate and faster for natural/urban scenes than for indoor/outdoor scenes, but performance did not differ between the two categories in controls. No significant correlation was found between performance for scene categorization and clinical variables such as visual acuity, type of AMD, size of the scotoma, and size of the lesion. CONCLUSIONS Scene gist recognition can be accomplished with the low spatial resolution of peripheral vision. These results support the "scene-centered approach" that initial scene recognition is based on the global scene properties and not on the objects it contains.

Age-related slowing is well documented but its origin remains unclear. A first validation study (Study 1) performed in 46 participants examined the effect of attention allocation (manipulated through a dual task) on various portions of individual simple reaction time (SRT) distribution (minimum, centile 5, centile 50, and centile 95 RTs). It showed that attention 'deprivation' due to a secondary task is not uniform throughout the distribution but impaired mainly the ability to produce a large number of fast responses. Study 2 investigated in 88 healthy participants age-related slowing of perceptual, motor, decision, and attentional processes using SRT and choice reaction time (CRT), finger tapping, and visual inspection time tests. It showed that the majority of SRT slowing after the age of 40 is due to lengthening of centile 5 RT, suggesting perceptuomotor slowing, an interpretation supported by longer visual inspection time and lower tapping frequency. After 60 years, SRT lengthening was due to a further lengthening of the centile 5-centile 50 SRT index, suggesting the participation of attentional decline. These findings support the hypothesis that age-related slowing in simple repetitive tasks is mainly related to slowing at the stage of perceptuomotor processes, and after 60 years, to additional decline of attention.

We tested rapid-categorization in a patient who was impaired in face and object recognition. Photographs of natural scenes were displayed for 100 ms. Participants had to press a key when they saw an animal among various objects as distractors or human faces among animal faces as distractors. Though the patient was impaired at figure/ground segregation, recognized very few objects and faces, she categorized animals and faces with a performance ranging between 70 and 86% correct. Displaying pictures in isolation did not improve performance. The results suggest that rapid categorization can be accomplished on the basis of coarse information without overt recognition.

Although complex hallucinations are extremely vivid, painful symptoms in schizophrenia, little is known about the underlying mechanisms of multisensory integration in such a phenomenon. We investigated the neural basis of these altered states of consciousness in a patient with schizophrenia, by combining state of the art neuroscientific exploratory methods like functional MRI, diffusion tensor imaging, cortical thickness analysis, electrical source reconstruction and trans-cranial magnetic stimulation. The results shed light on the functional architecture of the hallucinatory processes, in which unimodal information from different modalities is strongly functionally connected to higher-order integrative areas.

Peripheral vision has been the topic of few studies compared with central vision. Nevertheless, given that visual information covers all the visual field and that relevant information can originate from highly eccentric positions, the understanding of peripheral vision abilities for object perception seems essential. The poorer resolution of peripheral vision would first suggest that objects requiring large-scale feature integration such as buildings would be better processed than objects requiring finer analysis such as faces. Nevertheless, task requirements also determine the information (coarse or fine) necessary for a given object to be processed. We therefore investigated how task and eccentricity modulate object processing in peripheral vision. Three experiments were carried out requiring finer or coarser information processing of faces and buildings presented in central and peripheral vision. Our results showed that buildings were better judged as identical or familiar in periphery whilst faces were better categorised. We conclude that this superiority for a given stimulus in peripheral vision results (a) from the available information, which depends on the decrease of resolution with eccentricity, and (b) from the useful information, which depends on both the task and the semantic category.

Little is known about the ability of human observers to process objects in the far periphery of their visual field and nothing about its evolution in case of central vision loss. We investigated implicit and explicit recognition at two large visual eccentricities. Pictures of objects were centred at 30° or 50° eccentricity. Implicit recognition was tested through a priming paradigm. Participants (normally sighted observers and people with 10–20 years of central vision loss) categorized pictures as animal/transport both in a study phase (Block 1) and in a test phase (Block 2). In explicit recognition participants decided for each picture presented in Block 2 whether it had been displayed in Block 1 (“yes”/“no”). Both visual (identical) and conceptual/lexical (same-name) priming occurred at 30° and at 50°. Explicit recognition was observed only at 30°. In people with central vision loss testing was only performed at 50° eccentricity. The pattern of results was similar to that of normally sighted observers but global performance was lower. The results suggest that vision, at large eccentricity, is mainly based on nonconscious coarse representations. Moreover, after 10–20 years of central vision loss, no evidence was found for an increased ability to use peripheral information in object recognition.

Most studies on people with age-related macular degeneration (AMD) have been focused on investigations of low-level processes with simple stimuli like gratings, letters, and in perception of isolated faces or objects. We investigated the ability of people with low vision to analyze more complex stimuli like photographs of natural scenes. Fifteen participants with AMD and low vision (acuity on the better eye <20/200) and 11 normally sighted age-matched controls took part in the study. They were presented with photographs of either colored or achromatic gray level scenes in one condition and with photographs of natural scenes versus isolated objects extracted from these scenes in another condition. The photographs were centrally displayed for 300 ms. In both conditions, observers were instructed to press a key when they saw a predefined target (a face or an animal). The target was present in half of the trials. Color facilitated performance in people with low vision, while equivalent performance was found for colored and achromatic pictures in normally sighted participants. Isolated objects were categorized more accurately than objects in scenes in people with low vision. No difference was found for normally sighted observers. The results suggest that spatial properties that facilitate image segmentation (e.g., color and reduced crowding) help object perception in people with low vision.

INTRODUCTION:We examined the effect of attentional load on attentional capture in schizophrenia. On the basis of the ''resource limitations hypothesis'' in schizophrenia, we propose that attentional capture by an irrelevant distractor will be differentially affected by the attentional load for patients and healthy controls.METHOD:70 patients with schizophrenia, 15 schizotypals, and 54 controls were asked to attend to a central task while a lateral distractor moved. Participants were instructed either (i) to localise a black square (low-load condition), or (ii) to locate the larger number between two 1-digit numbers (medium-load condition), or (iii) to locate the larger number between two several-digit numbers (high-load condition). In the baseline condition, no distractor moved.RESULTS:All groups showed attentional capture in the low-load condition. Patients and schizotypals resisted interference from the distractor in the medium and highload conditions. Controls resisted interference in the high-load condition.CONCLUSION:The results suggest that attentional modulation is impaired in schizophrenia and in the schizophrenia spectrum.

Recent findings from event-related potentials (ERPs) studies provided strong evidence that cen- trally presented emotional pictures could be used to assess affective processing. Moreover, several studies showed that emotionally charged stimuli may automatically attract attention even if these are not consciously identified. Indeed, such perceptive conditions can be compared to those typical of the peripheral vision, particularly known to have low spatial resolution capacities. The aim of the present study was to characterize at behavioral and neural levels the impact of emotional visual scenes presented in peripheral vision. Eighteen participants were asked to categorize neutral and unpleasant pictures presented at central (0°) and peripheral eccentricities (−30 and +30°) while ERPs were recorded from 63 electrodes. ERPs were analysed by means of spatio-temporal principal component analyses (PCA) in order to evaluate influences of the emotional content on ERP components for each spatial position (central vs. peripheral). Main results highlight that affective modulation of early ERP components exists for both centrally and peripherally presented pictures. These findings suggest that, for far peripheral eccentricities as for central vision, the brain engages specific resources to process emotional information.