Method to Quickly Map Multifocal Pupillary Response Fields (mPRF) Using Frequency Tagging.

We present a method for mapping multifocal Pupillary Response Fields in a short amount of time using a visual stimulus covering 40° of the visual angle divided into nine contiguous sectors simultaneously modulated in luminance at specific, incommensurate, temporal frequencies. We test this multifocal Pupillary Frequency Tagging (mPFT) approach with young healthy participants (N = 36) and show that the spectral power of the sustained pupillary response elicited by 45 s of fixation of this multipartite stimulus reflects the relative contribution of each sector/frequency to the overall pupillary response. We further analyze the phase lag for each temporal frequency as well as several global features related to pupil state. Test/retest performed on a subset of participants indicates good repeatability. We also investigate the existence of structural (RNFL)/functional (mPFT) relationships. We then summarize the results of clinical studies conducted with mPFT on patients with neuropathies and retinopathies and show that the features derived from pupillary signal analyses, the distribution of spectral power in particular, are homologous to disease characteristics and allow for sorting patients from healthy participants with excellent sensitivity and specificity. This method thus appears as a convenient, objective, and fast tool for assessing the integrity of retino-pupillary circuits as well as idiosyncrasies and permits to objectively assess and follow-up retinopathies or neuropathies in a short amount of time.

Spatial attention and central crowding in primary open angle glaucoma.

CLINICAL RELEVANCE: Measuring the impact of spatial attention on signal detection in damaged parts of the visual field can be a useful tool for eye care practitioners. BACKGROUND: Studies on letter perception have shown that glaucoma exacerbates difficulties to detect a target within flankers (crowding) in parafoveal vision. A target can be missed because it is not seen or because attention was not focused at that location. This prospective study evaluates the contribution of spatial pre-cueing on target detection. METHOD: Fifteen patients and 15 age-matched controls were presented with letters displayed for 200 ms. Participants were asked to identify the orientation of the target letter T in two conditions: an isolated letter (uncrowded condition) and a letter with two flankers (crowded condition). The spacing between target and flankers was manipulated. The stimuli were randomly displayed at the fovea and at the parafovea at 5° left or right of fixation. A spatial cue preceded the stimuli in 50% of the trials. When present, the cue always signalled the correct location of the target. RESULTS: Pre-cueing the spatial location of the target significantly improved performance for both foveal and parafoveal presentations in patients but not in controls who were at ceiling level. Unlike controls, patients exhibited an effect of crowding at the fovea with a higher accuracy for the isolated target than for the target flanked by two letters with no spacing between the elements. CONCLUSION: Higher susceptibility to central crowding supports data showing abnormal foveal vision in glaucoma. Exogenous orienting of attention facilitates perception in parts of the visual field with reduced sensitivity.

Impact of glaucoma on the spatial frequency processing of scenes in central vision.

Glaucoma is an eye disease characterized by a progressive vision loss usually starting in peripheral vision. However, a deficit for scene categorization is observed even in the preserved central vision of patients with glaucoma. We assessed the processing and integration of spatial frequencies in the central vision of patients with glaucoma during scene categorization, considering the severity of the disease, in comparison to age-matched controls. In the first session, participants had to categorize scenes filtered in low-spatial frequencies (LSFs) and high-spatial frequencies (HSFs) as a natural or an artificial scene. Results showed that the processing of spatial frequencies was impaired only for patients with severe glaucoma, in particular for HFS scenes. In the light of proactive models of visual perception, we investigated how LSF could guide the processing of HSF in a second session. We presented hybrid scenes (combining LSF and HSF from two scenes belonging to the same or different semantic category). Participants had to categorize the scene filtered in HSF while ignoring the scene filtered in LSF. Surprisingly, results showed that the semantic influence of LSF on HSF was greater for patients with early glaucoma than controls, and then disappeared for the severe cases. This study shows that a progressive destruction of retinal ganglion cells affects the spatial frequency processing in central vision. This deficit may, however, be compensated by increased reliance on predictive mechanisms at early stages of the disease which would however decline in more severe cases.

Higher susceptibility to central crowding in glaucoma.

CLINICAL RELEVANCE: Crowding limits many daily life activities, such as reading and the visual search for objects in cluttered environments. Excessive sensitivity to crowding, especially in central vision, may amplify the difficulties of patients with ocular pathologies. It is thus important to investigate what limits visual activities and how to improve it. BACKGROUND: Numerous studies have reported reduced contrast sensitivity in central vision in patients with glaucoma. However, deficits have also been observed for letter recognition at high contrast, suggesting that contrast alone cannot completely account for impaired central perception. METHOD: Seventeen patients and fifteen age-matched controls were randomly presented with letters in central or parafoveal vision at 5° eccentricity for 200 ms. They were asked to decide whether the central T was upright or inverted. The T was either presented in isolation (uncrowded) or flanked by two Hs (crowded) at various spacings. Contrast was manipulated: 60% and 5%. RESULTS: Compared to controls, patients exhibited a significant effect of crowding in central vision, with higher accuracy for the isolated T than for HTH only at low contrast. In parafoveal vision, an effect of crowding was also observed only in patients. The spacing to escape crowding varied as a function of contrast. Larger spacing was required at low contrast than at high contrast. Susceptibility to crowding was related to central visual field defect for central presentations and to contrast sensitivity for parafoveal presentations, only at low contrast. Controls were at ceiling level both for central and parafoveal presentations. CONCLUSION: Crowding limits visual perception, impeding reading and object recognition in cluttered environments. Visual field defects and lower contrast sensitivity in glaucoma can increase susceptibility to central and parafoveal crowding, the deleterious effect of which can be improved by manipulating contrast and spacing between elements.

Impact of neovascular age-related macular degeneration on eye-movement control during scene viewing: Viewing biases and guidance by visual salience.

Human vision requires us to analyze the visual periphery to decide where to fixate next. In the present study, we investigated this process in people with age-related macular degeneration (AMD). In particular, we examined viewing biases and the extent to which visual salience guides fixation selection during free-viewing of naturalistic scenes. We used an approach combining generalized linear mixed modeling (GLMM) with a-priori scene parcellation. This method allows one to investigate group differences in terms of scene coverage and observers' well-known tendency to look at the center of scene images. Moreover, it allows for testing whether image salience influences fixation probability above and beyond what can be accounted for by the central bias. Compared with age-matched normally sighted control subjects (and young subjects), AMD patients' viewing behavior was less exploratory, with a stronger central fixation bias. All three subject groups showed a salience effect on fixation selection-higher-salience scene patches were more likely to be fixated. Importantly, the salience effect for the AMD group was of similar size as the salience effect for the control group, suggesting that guidance by visual salience was still intact. The variances for by-subject random effects in the GLMM indicated substantial individual differences. A separate model exclusively considered the AMD data and included fixation stability as a covariate, with the results suggesting that reduced fixation stability was associated with a reduced impact of visual salience on fixation selection.

Reduced peripheral vision in glaucoma and boundary extension.

CLINICAL RELEVANCE: Peripheral vision is known to be critical for spatial navigation. However, visual cognition, which impacts peripheral vision, has not been studied extensively in glaucoma. BACKGROUND: Spatial memory was assessed with a known to induce a robust memory distortion called "boundary extension" in which participants erroneously remember seeing more of a scene than was present in the sensory input. METHODS: Fifteen patients with glaucoma and 15 age-matched normally sighted controls participated in the experiment. Participants were shown 10 photographs of natural scenes randomly displayed for 0.5 s or 10 s. Following each scene, the participant was asked to draw it from memory. RESULTS: On average, boundary extension was larger, by 12%, for patients than for controls, but the difference was significant for 4 photographs. Patients tended to add more space between the object and the edges than there was between the objects and the border of the photograph. A control experiment in which participants were asked to draw isolated objects without scene context resulted in a significant reduction of the memory distortion in both groups, but patients still drew the objects smaller than controls. CONCLUSION: The reduced field of view in glaucoma has an impact on spatial memory for scenes and on perception of size.

Semantic and Physical Properties of Peripheral Vision Are Used for Scene Categorization in Central Vision.

Theories of visual recognition postulate that our ability to understand our visual environment at a glance is based on the extraction of the gist of the visual scene, a first global and rudimentary visual representation. Gist perception would be based on the rapid analysis of low spatial frequencies in the visual signal and would allow a coarse categorization of the scene. We aimed to study whether the low spatial resolution information available in peripheral vision could modulate the processing of visual information presented in central vision. We combined behavioral measures (Experiments 1 and 2) and fMRI measures (Experiment 2). Participants categorized a scene presented in central vision (artificial vs. natural categories) while ignoring another scene, either semantically congruent or incongruent, presented in peripheral vision. The two scenes could either share the same physical properties (similar amplitude spectrum and spatial configuration) or not. Categorization of the central scene was impaired by a semantically incongruent peripheral scene, in particular when the two scenes were physically similar. This semantic interference effect was associated with increased activation of the inferior frontal gyrus. When the two scenes were semantically congruent, the dissimilarity of their physical properties impaired the categorization of the central scene. This effect was associated with increased activation in occipito-temporal areas. In line with the hypothesis of predictive mechanisms involved in visual recognition, results suggest that semantic and physical properties of the information coming from peripheral vision would be automatically used to generate predictions that guide the processing of signal in central vision.

Sensitivity to Central Crowding for Faces in Patients With Glaucoma.

PRECIS: Some patients with glaucoma report difficulties to recognize faces when they are far away. We show that this deficit could result from a higher sensitivity to crowding in central vision. PURPOSE: The aim of the study is to investigate whether face recognition difficulties reported by some patients with glaucoma result from a greater sensitivity to inner crowding in central vision. METHODS: Seventeen patients with glaucoma and 17 age-matched normally sighted controls participated in the study. An isolated mouth (uncrowded condition) or a mouth within a face (crowded condition) was randomly displayed centrally for 200 ms. For each condition, participants were asked to decide whether the mouth was closed or open. The stimuli were presented at 3 angular sizes (0.6×0.4, 1×0.72, and 1.5×1.08 degrees). Accuracy was measured. RESULTS: Crowding affected performance differentially for patients and controls. Consistent with previous studies controls exhibited a "face superiority effect," with a better accuracy when the mouth was located within the face than when it was isolated. Sensitivity to crowding, reflected in a better accuracy with the isolated mouth, was observed in 10 of 17 patients only for small images. Crowding disappeared for larger faces, as the facial features were spaced out. Five patients were not sensitive to crowding. Importantly, no difference was found between the 2 subgroups of patients (sensitive vs. nonsensitive) in terms of mean deviation, contrast sensitivity, acuity, thickness of the retinal nerve fiber layer, or macular ganglion cell-inner plexiform layer. CONCLUSIONS: An excessive sensitivity to central crowding might explain the difficulties in face perception and reading reported by some patients with glaucoma. The sensory or cognitive processes underlying this excessive sensitivity must be elucidated to improve central perception in glaucoma.

A Saccadic Choice Task for Target Face Detection at Large Visual Eccentricities in Patients with Glaucoma.

SIGNIFICANCE: Little is known about the perception of glaucomatous patients at large visual eccentricities. We show that the patients' performance drops beyond 40° eccentricity even for large images of scenes, suggesting that clinical tests should assess the patients' vision at larger eccentricities than 24 or 30°. PURPOSE: Daily activities such as visual search, spatial navigation, and hazard detection require rapid scene recognition on a wide field of view. We examined whether participants with visual field loss at standard automated perimetry 30-2 were able to detect target faces at large visual eccentricities. METHODS: Twelve patients with glaucoma and 14 control subjects were asked to detect a face in a two-alternative saccadic forced choice task. Pairs of scenes, one containing a face, were randomly displayed at 10, 20, 40, 60, or 80° eccentricity on a panoramic screen covering 180° horizontally. Participants were asked to detect and to saccade toward the scene containing a face. RESULTS: Saccade latencies were significantly slower in patients (264 milliseconds; confidence interval [CI], 222 to 306 milliseconds) than in control subjects (207 milliseconds; CI, 190 to 226 milliseconds), and accuracy was significantly lower in patients (70% CI, 65 to 85%) than in control subjects (75.7% CI, 71.5 to 79.5%). Although still significantly above chance at 60°, the patients' performance dropped beyond 40° eccentricity. The control subjects' performance was still above chance at 80° eccentricity. CONCLUSIONS: In patients with various degrees of peripheral visual field defect, performance dropped beyond 40° eccentricity for large images at a high contrast. This result could reflect reduced spread of exploration in glaucoma.

What is the Nature of the Reach-and-Grasp Deficit in Glaucoma?

PRéCIS:: In a reach-and-grasp task, patients with glaucoma exhibited a motor disorder, even when they had time to explore their environment. The motor performance of glaucoma patients should be taken into account in rehabilitation. PURPOSE: Vision plays an important role in planning and executing manual prehension (reaching and grasping). We assess the impact of glaucoma on motor production, as a function of the visual exploration time available to the patients. METHODS: We compared performance in 2 reach-and-grasp tasks determined by whether or not the participants (16 glaucoma patients, 14 age-matched and 18 young controls) had time to explore the objects before reaching and grasping a target object defined by its color. RESULTS: Differences were observed between glaucoma patients and age-matched controls on movement duration and peak velocity (reaching phase) only when participants were not provided time to look at the objects before the movement (immediate condition). CONCLUSIONS: Glaucoma patients exhibited a motor disorder (grasping phase) only when they had no time to explore their environment before performing the reach-and-grasp task. The motor abnormalities in reaching phase observed in glaucoma patients in previous studies seem to result from difficulties in target identification rather than from visuomotor deficits. From a clinical point of view, motor performances of glaucoma patients could be modulated by task, especially by temporal constraints of task.

Perception of Gaze Direction in Glaucoma: A Study on Social Cognition.

SIGNIFICANCE: Discriminating quickly where another person's gaze is directed is a key component of social interaction, as gaze direction conveys information about others' intentions (approach or avoidance) and shift in gaze is used in group conversation. This study shows that patients with glaucoma are delayed in their discrimination of gaze direction. PURPOSE: The purpose of this study was to investigate whether glaucoma affects the perception of gaze direction. METHODS: Twenty-four patients with open-angle glaucoma, 24 age-matched controls, and 20 young normally sighted controls were presented with faces displayed centrally for 200 milliseconds. The gaze could either be direct or averted, and the head could be a frontal view or a rotated view. Half of the participants in each group were asked to press a key only for faces with a direct gaze. The other half responded for a face with an averted gaze. The orientation of the head had to be ignored. RESULTS: Accuracy was greater than 90% correct for all three groups. We found no difference in performance between young and older controls, except for shorter response times for the frontal view than for the rotated face in young participants. Patients with glaucoma needed on average 140 milliseconds longer to decide if the gaze was averted than for the direct gaze, and they were less accurate than controls in perceiving the gaze as direct when the head was rotated. CONCLUSIONS: Patients with glaucoma often experience impaired vision due to a reduced sensitivity in central vision. Although lower central sensitivity had little effect on their ability to discriminate gaze orientation, they required on average 140 milliseconds longer than age-matched controls to perceive an averted gaze.

Rapid scene categorization: From coarse peripheral vision to fine central vision.

Studies on scene perception have shown that the rapid extraction of low spatial frequencies (LSF) allows a coarse parsing of the scene, prior to the analysis of high spatial frequencies (HSF) containing details. Many studies suggest that scene gist recognition can be achieved with only the low resolution of peripheral vision. Our study investigated the advantage of peripheral vision on central vision during a scene categorization task (indoor vs. outdoor). In Experiment 1, we used large scene photographs from which we built one central disk and four circular rings of different eccentricities. The central disk either contained or not an object semantically related to the scene category. Results showed better categorization performances for the peripheral rings, despite the presence of an object in central vision that was semantically related to the scene category that significantly improved categorization performances. In Experiment 2, the central disk and rings were assembled from Central to Peripheral vision (CtP sequence) or from Peripheral to Central vision (PtC sequence). Results revealed better performances for PtC than CtP sequences, except when no central object was present under rapid categorization constraints. As Experiment 3 suggested that the PtC advantage was not explained by a reduction of the visibility of the object in the central disk by the surrounding peripheral rings (CtP sequence), results are interpreted in the context of a predominant coarse-to-fine processing during scene categorization, with greater efficiency and utility of coarse peripheral vision relative to fine central vision during rapid scene categorization.

Object search in neovascular age-related macular degeneration: the crowding effect.

BACKGROUND: Visual search, an activity that relies on central vision, is frequent in daily life. This study investigates the effect of spacing between items in an object search task in participants with central vision loss. METHODS: Patients with neovascular age-related macular degeneration (AMD), age-matched controls, and young controls were included. The stimuli were displays of four, six and nine objects randomly presented in a 'crowded' (spacing 1.5°) or 'uncrowded' (spacing 6°) condition. For each of 96 trials, participants were asked to search for a predefined target that remained on the screen until the response was recorded. Accuracy, search time, and eye movements (number of fixations and scan path ratio) were recorded. RESULTS: Compared to older controls, accuracy decreased by 31 per cent and search time increased by 61 per cent in AMD participants. Ageing also affected performance with a lower accuracy by 13.5 per cent and longer search times by 46 per cent in older compared to younger controls. Increasing the spacing between elements increased accuracy by 21 per cent in AMD participants but it had no effect in older and younger controls. Performance was not related to visual acuity or to duration of neovascular AMD, but search time was correlated to the lesion size in the 'crowded' condition. CONCLUSIONS: Object search is ubiquitous in daily life activities. When visual acuity is irrevocably reduced, increasing the spacing between elements can reliably improve object search performance in patients.

The contributions of central and peripheral vision to scene-gist recognition with a 180° visual field.

We investigated the relative contributions of central versus peripheral vision in scene-gist recognition with panoramic 180° scenes. Experiment 1 used the window/scotoma paradigm of Larson and Loschky (2009). We replicated their findings that peripheral vision was more important for rapid scene categorization, while central vision was more efficient, but those effects were greatly magnified. For example, in comparing our critical radius (which produced equivalent performance with mutually exclusive central and peripheral image regions) to that of Larson and Loschky, our critical radius of 10° had a ratio of central to peripheral image area that was 10 times smaller. Importantly, we found different functional relationships between the radius of centrally versus peripherally presented imagery (or the proportion of centrally versus peripherally presented image area) and scene-categorization sensitivity. For central vision, stimulus discriminability was an inverse function of image radius, while for peripheral vision the relationship was essentially linear. In Experiment 2, we tested the photographic-bias hypothesis that the greater efficiency of central vision for rapid scene categorization was due to more diagnostic information in the center of photographs. We factorially compared the effects of the eccentricity from which imagery was sampled versus the eccentricity at which imagery was presented. The presentation eccentricity effect was roughly 3 times greater than the sampling eccentricity effect, showing that the central-vision efficiency advantage was primarily due to the greater sensitivity of central vision. We discuss our results in terms of the eccentricity-dependent neurophysiology of vision and discuss implications for computationally modeling rapid scene categorization.

Glaucoma Affects Viewing Distance for Recognition of Sex and Facial Expression.

Purpose: To measure the distance for sex and facial expression recognition in patients with glaucoma. Methods: Sixteen patients with open-angle glaucoma, 16 age-matched controls, and 12 young controls participated. During each trial, a face covering 0.36° × 0.5°, simulating the angular size of a face viewed at 20 m, was presented centrally. The angular size increased automatically by steps of 5 cm, simulating the face moving progressively closer. The participants were asked to stop the progression with a keypress, first, when they were able to recognize the sex, and second, when they were able to recognize the facial expression (angry, happy, neutral). We measured the threshold equivalent viewing distance to recognize the sex and the facial expression. Results: Participants with glaucoma, both those with and without reduced central acuity, required a shorter viewing distance (i.e., a larger face) than did controls to recognize both the sex (by 2.59 m, F1,30 = 8.7, P < 0.006) and the facial expression (by 3.64 m, F1,30 = 14, P < 0.001). No significant difference was found between younger and older controls. Conclusions: Face perception is a skill that is reliant on central vision. Our behavioral results are consistent with the hypothesis of reduced central sensitivity in glaucoma. We suggest that the necessity to view larger faces in patients might result from a higher sensitivity to crowding that increases the difficulty to perceive the relevant features for recognition of both sex and facial expressions, akin to normal peripheral vision.

Attentional capture by incongruent object/background scenes in patients with Alzheimer disease.

AIM: Object/background association is critical to understand the context of visual scenes but also in daily life tasks like object search. Patients with Alzheimer disease (AD) exhibit impairment in scene processing at different levels: perception, recognition, memory and spatial navigation. We explored whether patients with AD make use of contextual information in congruent and incongruent target/background conditions in three different saccadic choice tasks. EXPERIMENT: We recruited 36 participants (12 young, 12 patients with AD at a moderate stage and 12 age-matched controls). Pairs of scenes (one congruent and one incongruent object/background) were displayed. In a free viewing task we recorded whether the participants spontaneously direct their gaze (eye tracker recordings) toward the congruent or the incongruent scene. In a task referred as "implicit", the participants had to saccade toward a pre-defined target (animal or piece of furniture) in a scene (congruent or not with the target). In a task, called "explicit", participants had to saccade towards the congruent scene. RESULTS: In contrast with both young and older controls patients with AD showed difficulties to refrain a first saccade toward incongruent scenes in the free viewing and the implicit tasks. They were at chance level in the explicit task. When given time to explore the two scenes, in a manual response condition, they were able to accomplish the implicit and explicit tasks with good accuracy. CONCLUSION: In contrast to healthy controls patients with AD exhibited a strong, significant, bias towards incongruent object/background scenes, even in the free viewing task, suggesting that unfamiliar or deviant stimuli attract their attention spontaneously. This result is in line with studies showing impairments in filtering out irrelevant distractors in visual search tasks and with studies suggesting inefficient top-down control to select relevant information at early stage of the disease.

Scene and human face recognition in the central vision of patients with glaucoma.

Primary open-angle glaucoma (POAG) firstly mainly affects peripheral vision. Current behavioral studies support the idea that visual defects of patients with POAG extend into parts of the central visual field classified as normal by static automated perimetry analysis. This is particularly true for visual tasks involving processes of a higher level than mere detection. The purpose of this study was to assess visual abilities of POAG patients in central vision. Patients were assigned to two groups following a visual field examination (Humphrey 24-2 SITA-Standard test). Patients with both peripheral and central defects and patients with peripheral but no central defect, as well as age-matched controls, participated in the experiment. All participants had to perform two visual tasks where low-contrast stimuli were presented in the central 6° of the visual field. A categorization task of scene images and human face images assessed high-level visual recognition abilities. In contrast, a detection task using the same stimuli assessed low-level visual function. The difference in performance between detection and categorization revealed the cost of high-level visual processing. Compared to controls, patients with a central visual defect showed a deficit in both detection and categorization of all low-contrast images. This is consistent with the abnormal retinal sensitivity as assessed by perimetry. However, the deficit was greater for categorization than detection. Patients without a central defect showed similar performances to the controls concerning the detection and categorization of faces. However, while the detection of scene images was well-maintained, these patients showed a deficit in their categorization. This suggests that the simple loss of peripheral vision could be detrimental to scene recognition, even when the information is displayed in central vision. This study revealed subtle defects in the central visual field of POAG patients that cannot be predicted by static automated perimetry assessment using Humphrey 24-2 SITA-Standard test.

What Is the Nature of the Reach and Grasp Deficit in Wet Age-related Macular Degeneration?

SIGNIFICANCE: Vision is paramount for motor actions directed toward objects. Vision allows not only the identification of objects and their shape and spatial location, but also the adaptation of our movement when it arrives on the object. These findings show that vision deficits, as in age-related macular degeneration (AMD), can lead to reaching and grasping deficits. PURPOSE: Few studies have investigated reaching and grasping in patients with AMD. They showed a deficit in the execution of motor actions in people with AMD, even though these people do not mention difficulties in their daily lives. The purpose of this study was to understand the nature of impairments in motor actions in patients. METHODS: We compared performance in two reach-and-grasp tasks determined by whether the participants (16 people with wet AMD and 17 age-matched control subjects) had time to look at the object before reaching and grasping it. RESULTS: The results show that the kinematic parameters of reach-and-grasp movements do not differ between groups when participants are provided time to look at the object before the movement. In contrast, performance in terms of movement duration, acceleration time, time to reach the maximum grip aperture, and the maximum velocity differ between patients and control subjects when the object is displayed immediately before the movement. CONCLUSIONS: The motor perturbations observed in people with AMD in previous studies seem to result from difficulties in target identification rather than from visuomotor deficits.

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

BACKGROUND: 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). METHOD: Twenty-one participants with AMD, 16 age-matched controls and 16 young observers were included. Realistic indoor scenes were presented on a panoramic five metre diameter screen. Twelve different objects were used as targets. The participants were asked to search for a target object, shown on paper before each trial, within a room composed of various objects. A joystick was used for navigation within the scene views. A target object was present in 24 trials and absent in 24 trials. The percentage of correct detection of the target, the percentage of false alarms (that is, the detection of the target when it was absent), the number of scene views explored and the search time were measured. RESULTS: The search time was slower for participants with AMD than for the age-matched controls, who in turn were slower than the young participants. The participants with AMD were able to accomplish the task with a performance of 75 per cent correct detections. This was slightly lower than older controls (79.2 per cent) while young controls were at ceiling (91.7 per cent). Errors were mainly due to false alarms resulting from confusion between the target object and another object present in the scene in the target-absent trials. CONCLUSION: The outcomes of the present study indicate that, under realistic conditions, although slower than age-matched, normally sighted controls, participants with AMD were able to accomplish visual searches of objects with high accuracy.

Do low spatial frequencies explain the extremely fast saccades towards human faces?

The visual perception of human faces by man is fast and efficient compared to that of other categories of objects. Using a saccadic choice task, recent studies showed that participants were able to initiate fast reliable saccades in just 100-110ms toward an image of a human face, when this was presented alongside another image without a face. This extremely fast saccadic reaction time is barely predicted using classical models of visual perception. Thus, the present research investigates whether this result might be explained by the low spatial frequency content of images. Using the same paradigm, with two images simultaneously presented to the left or right visual fields, participants were asked to make a saccade towards a target image. The target was defined as an image belonging to one category: human face, animal or vehicle. The other image corresponded to the distractor and belongs to the other categories. We compared performance to saccade toward one category of target. The two images were displayed either in color, gray-level, low-pass filtered or high-pass filtered. As previous studies, we found that the shortest SRT was observed for saccades towards faces rather than towards animals or vehicles. Analysis of saccadic reaction time distributions showed that, in 130-140ms, participants were able to make more correct than incorrect saccades towards faces for unfiltered (color and gray-level) and low-pass filtered images whereas they needed more time for high-pass filtered images. In contrast, the minimum time participants needed to correctly saccade towards animals and vehicles was longer for low-pass and high-pass filtered than for unfiltered images. The analysis of the image statistics in the Fourier domain revealed that the amplitude spectrum of faces was mainly contained in the low spatial frequencies. Consistent with a coarse-to-fine processing of visual information, our results suggest that extremely fast saccades towards faces could be initiated by low spatial frequencies.