Sébastien Szaffarczyk

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.

The contribution of body weight distribution and center of pressure location in the control of mediolateral stance

The study investigated the mediolateral control of upright stance in 16 healthy, young adults. The model analyzed the body weight distribution and center of pressure location mechanisms under three stance width conditions (feet close, under standard condition, and apart). Our first objective was to discuss some methodological requirements to investigate the contribution of both mechanisms by means of two platforms. It is proposed that both the amplitude contribution (in variability analyses) and active contribution (in cross-correlation analyses) need to be studied distinctively. These analyses may be concerned with the strength and the degree of active contributions, respectively. Based on this theoretical proposition, we expected and found that the amplitude contribution of both mechanisms was higher and lower in wide and narrow stances compared with that in the standard stance, respectively. Indeed, the closer the two reaction forces, the lower their mechanical contribution. As expected, the active contribution of both mechanisms was significantly lower and higher in wide and narrow stances, respectively. Indeed, the further the feet apart, the less active both mechanisms needed to be to control mediolateral stance. Overall, only the center of pressure location mechanism really changed its significant contribution to control mediolateral stance under the three conditions. The result is important because this mechanism is known to be secondary, weaker than the body weight distribution mechanism to control mediolateral stance. In practical terms, these findings may explain why the mediolateral variability of center of pressure displacement was significantly higher in narrow stance but not lower in wide stance.

Impaired mediolateral postural control at the ankle in healthy, middle-aged adults.

ABSTRACT Elderly adults sway more than young adults. Based on the literature, the authors expected the mediolateral ankle postural control mechanism to be affected before age 60 years. Twelve healthy young adults (24.21 ± 2.50 years) and 12 middle-aged adults (51.13 ± 6.09 years) participated in the study. To challenge mediolateral stance, the conditions modified the mediolateral distance among the feet (narrow and standard distances), mandibular position (rest position, left and right laterality occlusion positions), and the occlusion with clenching (intercuspal occlusion, left and right maximal voluntary clenches). As we expected, middle-aged adults exhibited significantly reduced contribution of the ankle mechanism. It was so both in narrow and standard stances. A second objective was to show a greater contribution of the 2 mechanisms in narrow than in standard stances. The results confirmed our hypothesis. As we expected, mandibular conditions only had a significant effect on center of pressure sway. Unexpectedly, middle-aged adults did not increase their range of center of pressure sway in narrow stance. They may have overconstrained their center of pressure sway because of their ankle impairments. On the practical level, our results suggest that older adults should increase their stance width to relieve their hip and ankle control mechanisms and to stabilize their mediolateral posture.

Implicit processing of scene context in macular degeneration.

PURPOSE For normally sighted people, there is a general consensus that objects that appear in a congruent context (e.g., a hair dryer in a bathroom) are processed more accurately and/or more quickly than objects in an incongruent context (e.g., a hair dryer in a corn field). We investigated whether people with AMD, who have impairments in recognizing objects embedded in complex scenes, can nevertheless take advantage of contextual information for object detection. METHODS TWENTY-TWO PEOPLE WITH AMD AND 18 AGE-MATCHED, NORMALLY SIGHTED CONTROLS TOOK PART IN THE STUDY. THEY WERE TESTED IN TWO TASKS: (1) an object detection task in which a foreground target object was set within a congruent background or an incongruent background, with no information being given to the participants as to the relationship between the target and its background, and (2) a task in which the participant had to explicitly state whether or not the foreground object was congruent with its background. A go/no-go paradigm was used in both tasks (i.e., a key press when the target is present and no key press when it is absent). The same participants, stimuli, and presentation conditions were used in both tasks. RESULTS In the context task, the people with AMD exhibited higher sensitivity when the target object was consistent with its background; however, they performed no better than chance in the explicit task. Normally sighted controls benefited from the congruent context in both tasks. CONCLUSIONS Our results suggest that when central vision is impaired (as in AMD), the contextual information captured by peripheral vision provides cues for object categorization.

Animal spotting in Alzheimer's disease: an eye tracking study of object categorization.

We investigated rapid object categorization and, more specifically, the ability to detect a target object within a natural scene in people with mild Alzheimers disease (AD) using a saccadic choice task. It has been suggested that the anatomical pathway likely used to initiate rapid oculomotor responses in the saccadic choice task could involve the Frontal Eye Field, a structure that is part of the dorsal attentional network, in which connectivity is disrupted in AD. Seventeen patients with mild AD and 23 healthy age-matched controls took part in the study. A group of 24 young healthy observers was included as it has been reported that normal aging affects eye movements. Participants were presented with pairs of colored photographs of natural scenes, one containing an animal (the target) and one containing various objects (distracter), displayed for 1 s left and right of fixation. They were asked to saccade to the scene containing an animal. Neither pathology nor age affected temporal (saccade latencies and durations) and spatial (saccade amplitude) parameters of eye movements. Patients with AD were significantly less accurate than age-matched controls, and older participants were less accurate than young observers. The results are interpreted in terms of noisier sensory information and increased uncertainty in relation to deficits in the magnocellular pathway. The results suggest that, even at a mild stage of the pathology, people exhibit difficulties in selecting relevant objects.

Impact of Peripheral Field Loss on the Execution of Natural Actions: A Study With Glaucomatous Patients and Normally Sighted People.

Purpose:We investigated the visuomotor behavior of people with reduced peripheral field due to glaucoma while they accomplished natural actions. Methods:Twelve participants with glaucoma and 13 normally sighted controls were included. Participants were asked to accomplish a familiar sandwich-making task and a less familiar model-building task with a children’s construction set while their eye movements were recorded. Both scene layouts contained task-relevant and task-irrelevant objects. There was no time constraint. Results:Participants with glaucoma were slower to perform the task than were the normal observers, but the slower performance was confined to the unfamiliar model-building task. Patients and controls were equally efficient in the more familiar sandwich-making task. On initial exposure, before the first reaching movement was initiated, patients scanned the objects longer than did controls, particularly in the unfamiliar model-building task, and controls fixated irrelevant objects less than did patients. During the working phase fixations were on average longer for patients than for controls and patients made more saccades than did controls. Patients did not grasp more irrelevant objects compared with controls. Conclusions:The results provide evidence that, although slower than controls, patients with glaucoma were able to accomplish natural actions efficiently even when the task required discrimination of small structurally similar objects (nuts and screws in the model-building task). Their difficulties were reflected in longer fixation times and more head and eye movements compared with controls, presumably to compensate for lower visibility when objects fell in the part of their visual field where sensitivity was reduced.

Functional Synergy Between Postural and Visual Behaviors When Performing a Difficult Precise Visual Task in Upright Stance

Previous works usually report greater postural stability in precise visual tasks (e.g., gaze-shift tasks) than in stationary-gaze tasks. However, existing cognitive models do not fully support these results as they assume that performing an attention-demanding task while standing would alter postural stability because of the competition of attention between the tasks. Contrary to these cognitive models, attentional resources may increase to create a synergy between visual and postural brain processes to perform precise oculomotor behaviors. To test this hypothesis, we investigated a difficult searching task and a control free-viewing task. The precise visual task required the 16 young participants to find a target in densely furnished images. The free-viewing task consisted of looking at similar images without searching anything. As expected, the participants exhibited significantly lower body displacements (linear, angular) and a significantly higher cognitive workload in the precise visual task than in the free-viewing task. Most important, our exploration showed functional synergies between visual and postural processes in the searching task, that is, significant negative relationships showing lower head and neck displacements to reach more expended zones of fixation. These functional synergies seemed to involve a greater attentional demand because they were not significant anymore when the cognitive workload was controlled (partial correlations). In the free-viewing task, only significant positive relationships were found and they did not involve any change in cognitive workload. An alternative cognitive model and its potential subtended neuroscientific circuit are proposed to explain the supposedly cognitively grounded functional nature of vision-posture synergies in precise visual tasks.

Impact of age-related macular degeneration on object searches in realistic panoramic scenes: Age-related macular degeneration

This study investigated whether realistic immersive conditions with dynamic indoor scenes presented on a large, hemispheric panoramic screen covering 180° of the visual field improved the visual search abilities of participants with age‐related macular degeneration (AMD).

The Stationary-Gaze Task Should Not Be Systematically Used as the Control Task in Studies of Postural Control

ABSTRACT In studies of postural control, a control task is often used to understand significant effects obtained with experimental manipulations. This task should be the easiest task and (therefore) engage the lowest behavioral variability and cognitive workload. Since 1983, the stationary-gaze task is considered as the most relevant control task. Instead, the authors expected that free looking at small targets (white paper or images; visual angle: 12°) could be an easier task. To verify this assumption, 16 young individuals performed stationary-gaze, white-panel, and free-viewing 12° tasks in steady and relaxed stances. The stationary-gaze task led to significantly higher cognitive workload (mean score in the National Aeronotics and Space Administration Task Load Index questionnaire), higher interindividual body (head, neck, and lower back) linear variability, and higher interindividual body angular variability—not systematically yet—than both other tasks. There was more cognitive workload in steady than relaxed stances. The authors also tested if a free-viewing 24° task could lead to greater angular displacement, and hence greater body sway, than could the other tasks in relaxed stance. Unexpectedly, the participants mostly moved their eyes and not their body in this task. In the discussion, the authors explain why the stationary-gaze task may not be an ideal control task and how to choose this neutral task.

Categorization Task over a Touch Screen in Age-Related Macular Degeneration.

Purpose In our modern society, many touch screen applications require hand-eye coordination to associate an icon with its specific contextual unit on phones, on computers, or in public transport. We assessed the ability of patients with age-related macular degeneration (AMD) to explore scenes and to associate a target (animal or object) with a unique congruent scene (e.g., to match a fish with the sea) presented between three other distractors on a touch screen computer. Methods Twenty-four patients with AMD (64 to 90 years) with best-corrected visual acuity between 20/40 and 20/400 as well as 17 age-matched (60 to 94 years) and 15 young (22 to 34 years) participants with normal visual acuity had to match a target with a congruent scene by moving their index finger on a 22-in touch screen. Results Patients were as accurate (98.7% correct responses) as the age-matched control (98.9% correct responses) and young participants (99.3% correct responses) at performing the task. The duration of exploration was significantly longer for the AMD patients (mean, 4.13 seconds) compared with the age-matched group (mean, 2.96 seconds). The young participants were also significantly faster than the old group (mean, 0.93 seconds). The movement parameters of the older participants (patients and old control subjects) were affected compared with the young; the peak speed decreased (−8 cm/s) and the movement duration increased (+0.9 seconds) with age compared with the young group. Conclusions People with AMD are able to perform a contextual association task on a touch screen with high accuracy. The AMD patients were specifically affected in the “exploration” phase; their accuracy and movement parameters did not differ from the old control group. Our study suggests that the decline associated with AMD is more focused on the duration of exploration than on movement parameters in touch screen use.