Finding faces, animals, and vehicles in far peripheral vision.

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.

Space representation in age-related macular degeneration.

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.

Scene perception in age-related macular degeneration: the effect of contrast.

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.

Rapid categorization of faces and objects in a patient with impaired object recognition.

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.

Age-related slowing: perceptuomotor, decision, or attention decline?

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.

Neural functional organization of hallucinations in schizophrenia: multisensory dissolution of pathological emergence in consciousness.

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.

Does context or color improve object recognition in patients with low vision?

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.

Recognition of facial emotion in low vision: a flexible usage of facial features.

Age-related macular degeneration (AMD) is a major cause of visual impairment in people older than 50 years in Western countries, affecting essential tasks such as reading and face recognition. Here we investigated the mechanisms underlying the deficit in recognition of facial expressions in an AMD population with low vision. Pictures of faces displaying different emotions with the mouth open or closed were centrally displayed for 300 ms. Participants with AMD with low acuity (mean 20/200) and normally sighted age-matched controls performed one of two emotion tasks: detecting whether a face had an expression or not (expressive/non expressive (EXNEX) task) or categorizing the facial emotion as happy, angry, or neutral (categorization of expression (CATEX) task). Previous research has shown that healthy observers are mainly using high spatial frequencies in an EXNEX task while performance at a CATEX task was preferentially based on low spatial frequencies. Due to impaired processing of high spatial frequencies in central vision, we expected and observed that AMD participants failed at deciding whether a face was expressive or not but categorized normally the emotion of the face (e.g., happy, angry, neutral). Moreover, we observed that AMD participants mostly identified emotions using the lower part of the face (mouth). Accuracy did not differ between the two tasks for normally sighted observers. The results indicate that AMD participants are able to identify facial emotion but must base their decision mainly on the low spatial frequencies, as they lack the perception of finer details.

Children with benign epilepsy with centrotemporal spikes (BECTS) show impaired attentional control: evidence from an attentional capture paradigm.

Children with epilepsy often have attention deficits, even when epilepsy is idiopathic and benign. The mechanisms underlying attention deficits are still unknown and appear to be different between focal and generalized epilepsy. In this study, an attentional capture paradigm was used to study and compare one aspect of attentional control, the resistance to interference from distractors, in 18 children with benign epilepsy with centrotemporal spikes (BECTS), 18 children with idiopathic generalized epilepsy and 18 controls aged 7-12 years. The results showed longer response times (RT) and more omissions in the two groups with epilepsy compared to controls. Attentional capture with longer response times in trials with a moving distractor compared to baseline condition with stationary distractors was found in both controls and children with epilepsy. The magnitude of interference from moving distractors was greater in the BECTS group than in the idiopathic generalized epilepsy group and in the controls group. These results suggest an impact of epilepsy on resistance to interference from distractors in children with BECTS.

Colour recognition at large visual eccentricities in normal observers and patients with low vision.

When we look at our spatial environment we have the feeling that the whole visual field is coloured, yet the density of cone photoreceptors decreases considerably as eccentricity increases. We investigated colour perception (coloured/noncoloured), colour naming and whether colour helps object recognition at eccentricities varying from 0 degrees to 80 degrees in healthy observers and patients with low vision. We found that colours can be perceived and even identified above chance at very large eccentricities (60 degrees). When asked to categorize coloured and grey level objects as edible/nonedible, both healthy observers and patients with low vision showed better performance for coloured edible objects at 50 degrees suggesting that colour is used for object recognition in conditions of degraded form perception.

Perception of Affordance during Short-Term Exposure to Weightlessness in Parabolic Flight.

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".

Large lateral head movements and postural control.

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 0.5 Hz or 1 Hz) 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.

Figure ground discrimination in age-related macular degeneration.

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.

Fearful faces impact in peripheral vision: behavioral and neural evidence.

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.

Scene perception in age-related macular degeneration.

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.

Face or building superiority in peripheral vision reversed by task requirements.

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.

Attentional capture in schizophrenia and schizotypy: effect of attentional load.

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.

Peripherally presented emotional scenes: a spatiotemporal analysis of early ERP responses.

Recent findings from event-related potentials (ERPs) studies provided strong evidence that centrally 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 degrees ) and peripheral eccentricities (-30 and +30 degrees ) 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.

Self awareness and speech processing: an fMRI study.

Language production and perception imply motor system recruitment. Therefore, language should obey the theory of shared motor representation between self and other, by means of mirror-like systems. These mirror-like systems (referring to single-unit recordings in animals) show the property to be recruited both when accomplishing and when perceiving a goal-directed action, whatever the sensory modality may be. This hypothesis supposes that a neural network for self-awareness is involved to distinguish speech production from speech listening. We used fMRI to test this assumption in 12 healthy subjects, who performed two different block-design experiments. The first experiment showed involvement of a lateral mirror-like network in speech listening, including ventral premotor cortex, superior temporal sulcus and the inferior parietal lobule (IPL). The activity of this mirror-like network is associated with the perception of an intelligible speech. The second experiment looked at a self-awareness network. It showed involvement of a medial resting-state network, including the medial parietal and medial prefrontal cortices, during the 'self-generated voice' condition, as opposed to passive speech listening. Our results support the fact that deactivation of this medial network, in association with modulation of the activity of the IPL (part of the mirror-like network previously described), is linked to self-awareness in speech processing. Overall, these results support the idea that self-awareness is present when distinguishing between speech production and speech listening situations, and may depend on these two different parieto-frontal networks.