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.

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.

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.

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 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.

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.

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.

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.

Effects of Methylphenidate on Default-Mode Network/Task-Positive Network Synchronization in Children With ADHD

OBJECTIVE

A failure of the anti-phase synchronization between default-mode (DMN) and task-positive networks (TPN) may be involved in a main manifestation of ADHD: moment-to-moment variability. The study investigated whereby methylphenidate may improve TPN/DMN synchronization in ADHD.

METHOD

Eleven drug-naive ADHD children and 11 typically developing (TD) children performed a flanker task during functional magnetic resonance imaging. The ADHD group was scanned without and 1 month later with methylphenidate. The signal was analyzed by independent component analysis.

RESULTS

The TD group showed anti-phase DMN/TPN synchronization. The unmedicated ADHD group showed synchronous activity in the posterior DMN only, which was positively correlated with response time variability for the flanker task. Methylphenidate initiated a partial anti-phase TPN/DMN synchronization, reduced variability, and abolished the variability/DMN correlation.

CONCLUSION

Although results should be interpreted cautiously because the sample size is small, they suggest that a failure of the TPN/DMN synchronization could be involved in the moment-to-moment variability in ADHD. Methylphenidate initiated TPN/DMN synchronization, which in turn appeared to reduce variability.

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.

Eye movement during retrieval of emotional autobiographical memories

This study assessed whether specific eye movement patterns are observed during emotional autobiographical retrieval. Participants were asked to retrieve positive, negative and neutral memories while their scan path was recorded by an eye-tracker. Results showed that positive and negative emotional memories triggered more fixations and saccades but shorter fixation duration than neutral memories. No significant differences were observed between emotional and neutral memories for duration and amplitude of saccades. Positive and negative retrieval triggered similar eye movement (i.e., similar number of fixations and saccades, fixation duration, duration of saccades, and amplitude of saccades). Interestingly, the participants reported higher visual imagery for emotional memories than for neutral memories. The findings demonstrate similarities and differences in eye movement during retrieval of neutral and emotional memories. Eye movement during autobiographical retrieval seems to be triggered by the creation of visual mental images as the latter are indexed by autobiographical reconstruction.

Impact of Wet Macular Degeneration on the Execution of Natural Actions

PURPOSE

To use eye movements to investigate how people with a central scotoma might be impaired in the execution of natural actions and whether task familiarity affects performance.

METHODS

Sixteen participants with AMD and 16 age-matched controls performed two natural actions: (1) a familiar sandwich-making task and (2) a less familiar model-building task. In each action, task-relevant and task-irrelevant objects were placed on a table, covering 90°. The participants were asked to execute the actions without a time constraint. Eye movements were recorded.

RESULTS

The people with AMD were significantly slower than the controls, both in the exploration phase (before the first reaching movement) and in the working phase (execution of action), especially in the unfamiliar task. Gaze duration was longer on relevant than irrelevant objects in both groups and tasks, as might be expected. However, for the participants with AMD, gaze durations were longer on all of the objects, whether relevant or irrelevant, except in the more familiar task. This suggests that participants with AMD take longer to extract the information they need but that this can be counteracted when the task items are familiar. The number of saccades/min of the task was significantly greater for the people with AMD than for the controls.

CONCLUSIONS

The present results show that people with AMD can accomplish natural actions efficiently, but need longer gaze durations and more eye movements than normally sighted people. This effect can be reduced when executing a familiar 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.

Donepezil increases contrast sensitivity for the detection of objects in scenes

We assessed the effects of donepezil, a drug that stimulates cholinergic transmission, and scopolamine, an antagonist of cholinergic transmission, on contrast sensitivity. 30 young male participants were tested under three treatment conditions: placebo, donepezil, and scopolamine in a random order. Pairs of photographs varying in contrast were displayed left and right of fixation for 50 ms. Participants were asked to locate the scene containing an animal. Accuracy was better under donepezil than under scopolamine, particularly for signals of high intensity (at higher levels of contrast). A control experiment showed that the lower performance under scopolamine did not result from the mydriasis induced by scopolamine. The results suggest that cholinergic stimulation, through donepezil, facilitates signal detection in agreement with studies on animals showing that the pharmacological activation of cholinergic receptors controls the gain in the relationship between the stimulus contrast (intensity of the visual input) and visual response. As Alzheimer disease is associated to depletion in acetylcholine, and there is evidence of deficits in contrast sensitivity in Alzheimer, it might be interesting to integrate such rapid and sensitive visual tasks in the biomarkers at early stage of drug development.

Misidentifying a tennis racket as keys: object identification in people with age-related macular degeneration

PURPOSE

Previous studies showed that people with age-related macular degeneration (AMD) can categorise a pre-defined target object or scene with high accuracy (above 80%). In these studies participants were asked to detect the target (e.g. an animal) in serial visual presentation. People with AMD must rely on peripheral vision which is more adapted to the low resolution required for detection than for the higher resolution required to identify a specific exemplar. We investigated the ability of people with central vision loss to identify photographs of objects and scenes.

METHODS

Photographs of isolated objects, natural scenes and objects in scenes were centrally displayed for 2 s each. Participants were asked to name the stimuli. We measured accuracy and naming times in 20 patients with AMD, 15 age-matched and 12 young controls.

RESULTS

Accuracy was lower (by about 30%) and naming times were longer (by about 300 ms) in people with AMD than in age-matched controls in the three categories of images. Correct identification occurred in 62-66% of the stimuli for patients. More than 20% of the misidentifications resulted from a structural and/or semantic similarity between the object and the name (e.g. spectacles for dog plates or dolphin for shark). Accuracy and naming times did not differ significantly between young and older normally sighted participants indicating that the deficits resulted from pathology rather than to normal ageing.

CONCLUSIONS

These results show that, in contrast to performance for categorisation of a single pre-defined target, people with central vision loss are impaired at identifying various objects and scenes. The decrease in accuracy and the increase in response times in patients with AMD indicate that peripheral vision might be sufficient for object and scene categorisation but not for precise scene or object identification.

Scene categorization in Alzheimer's disease: a saccadic choice task

AIMS

We investigated the performance in scene categorization of patients with Alzheimer's disease (AD) using a saccadic choice task.

METHOD

24 patients with mild AD, 28 age-matched controls and 26 young people participated in the study. The participants were presented pairs of coloured photographs and were asked to make a saccadic eye movement to the picture corresponding to the target scene (natural vs. urban, indoor vs. outdoor).

RESULTS

The patients' performance did not differ from chance for natural scenes. Differences between young and older controls and patients with AD were found in accuracy but not saccadic latency.

CONCLUSIONS

The results are interpreted in terms of cerebral reorganization in the prefrontal and temporo-occipital cortex of patients with AD, but also in terms of impaired processing of visual global properties of scenes.

Autobiographical recall triggers visual exploration

Autobiographical recall is thought to rely on the ability to generate a visual image of the remembered event. Neuropsychological studies suggest a relationship between deterioration in visual mental imagery and autobiographical distortions, while neuroimaging data similarly implicate visual brain areas in autobiographical recall. However, neither whether autobiographical retrieval is associated with visual exploration, or not. Our paper aimed to provide such evidence one way or the other. Using an eye tracking system, we recorded eye movements of 40 participants during autobiographical recall and during a control condition in which participants had to count aloud. In both conditions, the participants had to look at a blank screen while their gaze location was recorded by the eye-tracker. Autobiographical recall triggered a lower number of fixations and reduced their duration. In contrast, the number, duration, and amplitude of saccades increased compared to the control condition. Our data suggest that autobiographical recall is characterized by visual processing.

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 Alzheimer's 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.

Differential processing of natural scenes in posterior cortical atrophy and in Alzheimer's disease, as measured with a saccade choice task

Atrophy of the medial temporal lobe structures that support scene perception and the binding of an object to its context (i.e., the hippocampus and the parahippocampal cortex) appears early in the course of Alzheimer’s disease (AD). However, few studies have investigated scene perception in people with AD. Here, we assessed the ability to find a target object within a natural scene in people with AD and in people with posterior cortical atrophy (PCA, a variant of AD). Pairs of color photographs were displayed on the left and right of a fixation cross for 1 s. In separate blocks of trials, participants were asked to categorize the target (an animal) by either moving their eyes toward the photograph containing the target (the saccadic choice task) or pressing a key corresponding to the target’s location (the manual choice task). Isolated objects and objects within scenes were studied in both tasks. Participants with PCA were more impaired in detection of a target within a scene than participants with AD. The latter’s performance pattern was more similar to that of age-matched controls in terms of accuracy, saccade latencies and the benefit gained from contextual information. Participants with PCA benefited less from contextual information in both the saccade and the manual choice tasks—suggesting that people with posterior brain lesions have impairments in figure/ground segregation and are more sensitive to object crowding.

The contribution of central and peripheral vision in scene categorization: a study on people with central vision loss

Studies in normally sighted people suggest that scene recognition is based on global physical properties and can be accomplished by the low resolution of peripheral vision. We examine the contribution of peripheral and central vision in scene gist recognition in patients with central vision loss and age-matched controls. Twenty-one patients with neovascular age related macular degeneration (AMD), with a visual acuity lower than 20/50, and 15 age-matched normally sighted controls participated in a natural/urban scene categorization task. The stimuli were colored photographs of natural scenes presented randomly at one of five spatial locations of a computer screen: centre, top left, top right, bottom left and bottom right at 12° eccentricity. Sensitivity (d') and response times were recorded. Normally sighted people exhibited higher sensitivity and shorter response times when the scene was presented centrally than for peripheral pictures. Sensitivity was lower and response times were longer for people with AMD than for controls at all spatial location. In contrast to controls patients were not better for central than for peripheral pictures. The results of normally sighted controls indicate that scene categorization can be accomplished by the low resolution of peripheral vision but central vision remains more efficient than peripheral vision for scene gist recognition. People with central vision loss likely categorized scenes on the basis of low frequency information both in normal peripheral vision and in low acuity central vision.

Incongruent object/context relationships in visual scenes: where are they processed in the brain?

Rapid object visual categorization in briefly flashed natural scenes is influenced by the surrounding context. The neural correlates underlying reduced categorization performance in response to incongruent object/context associations remain unclear and were investigated in the present study using fMRI. Participants were instructed to categorize objects in briefly presented scenes (exposure duration=100ms). Half of the scenes consisted of objects pasted in an expected (congruent) context, whereas for the other half, objects were embedded in incongruent contexts. Object categorization was more accurate and faster in congruent relative to incongruent scenes. Moreover, we found that the two types of scenes elicited different patterns of cerebral activation. In particular, the processing of incongruent scenes induced increased activations in the parahippocampal cortex, as well as in the right frontal cortex. This higher activity may indicate additional neural processing of the novel (non experienced) contextual associations that were inherent to the incongruent scenes. Moreover, our results suggest that the locus of object categorization impairment due to contextual incongruence is in the right anterior parahippocampal cortex. Indeed in this region activity was correlated with the reaction time increase observed with incongruent scenes. Representations for associations between objects and their usual context of appearance might be encoded in the right anterior parahippocampal cortex.

Eye movements during natural actions in patients with schizophrenia

BACKGROUND

Visual scanning and planning of actions are reported to be abnormal in patients with schizophrenia. Most studies that monitored eye movements in these patients were performed under free-viewing conditions and used 2- dimensional images. However, images differ from the natural world in several ways, including task demands and the dimensionality of the display. Our study was designed to assess whether abnormalities in visual exploration in patients with schizophrenia generalize to active-viewing tasks in realistic conditions of viewing and to examine whether disturbances in action sequencing in these patients are reflected in their visual scanning patterns while executing natural tasks.

METHODS

We monitored visual scan paths in patients with schizophrenia and healthy controls. Participants performed several tasks in which they were asked to look at a realistic scene on a table (free-viewing) and perform 2 active-viewing tasks: a familiar task (sandwich-making) and an unfamiliar task (model-building). The scenes contained both task-relevant and task-irrelevant objects.

RESULTS

We included 15 patients and 15 controls in our analysis. Patients exhibited abnormalities in the free-viewing condition. Their patterns of exploration were similar to those of controls in the familiar task, but they showed scanning differences in the unfamiliar task. Patients were also slower than controls to accomplish both tasks.

LIMITATIONS

Patients with schizophrenia were taking antipsychotic medications, so the presence of medication effects cannot be excluded.

CONCLUSION

People with schizophrenia present a basic psychomotor slowing and seem to establish a less efficient planning strategy in the case of more complex and unfamiliar tasks.

Imagined motor action and eye movements in schizophrenia

Visual exploration and planning of actions are reported to be abnormal in schizophrenia. Most of the studies monitoring eye movements in patients with schizophrenia have been performed under free-viewing condition. The present study was designed to assess whether mentally performing an action modulates the visuomotor behavior in patients with schizophrenia and in healthy controls. Visual scan paths were monitored in eighteen patients with schizophrenia and in eighteen healthy controls. Participants performed two tasks in which they were asked either to (1) look at a scene on a computer screen (free viewing), or (2) picture themselves making a sandwich in front of a computer screen (active viewing). The scenes contained both task-relevant and task-irrelevant objects. Temporal and spatial characteristics of scan paths were compared for each group and each task. The results indicate that patients with schizophrenia exhibited longer fixation durations, and fewer fixations, than healthy controls in the free viewing condition. The patients' visual exploration improved in the active viewing condition. However, patients looked less at task-relevant objects and looked more at distractors than controls in the active viewing condition in which they were asked to picture themselves making a sandwich in moving their eyes to task-relevant objects on an image. These results are consistent with the literature on deficits in motor imagery in patients with schizophrenia and it extends the impairment to visual exploration in an action imagery task.

Low Spatial Frequency Bias in Schizophrenia is Not Face Specific: When the Integration of Coarse and Fine Information Fails

Studies have shown that patients with schizophrenia exhibit visual processing impairments, particularly regarding the processing of spatial frequencies. In a previous work, we found that, compared to healthy volunteers, patients were biased toward low spatial frequencies (LSF) to identify facial expression at a glance. Given the ubiquity of faces in visual perception, it remains an open question whether the LSF bias is face specific or also occurs with other visual objects. Here, 15 patients with schizophrenia and 11 healthy control adults performed a categorization task with hybrid stimuli. These stimuli were single images consisting of two different objects, a fruit and an animal, each in a specific spatial frequency range, either low (LSF) or high (HSF). Observers were asked to report if they saw an animal or a fruit. The reported category demonstrated which spatial scale was preferentially perceived in each trial. In a control experiment, participants performed the same task but with images of only a single object, either a LSF or HSF filtered animal or fruit, to verify that participants could perceive both HSF or LSF when presented in isolation. The results on the categorization task showed that patients chose more frequently LSF with hybrid stimuli compared to healthy controls. However, both populations performed equally well with HSF and LSF filtered pictures in the control experiment, demonstrating that the LSF preference found with hybrid stimuli in patients was not due to an inability to perceive HSF. The LSF preference found in schizophrenia confirms our previous study conducted with faces, and shows that this LSF bias generalizes to other categories of objects. When a broad range of spatial frequencies are present in the image, as in normal conditions of viewing, patients preferentially rely on coarse visual information contained in LSF. This result may be interpreted as a dysfunction of the guidance of HSF processing by LSF processing.

Visual exploration and action processing in schizophrenia

INTRODUCTION

Visual scanning is widely reported to be abnormal in schizophrenia. The majority of eye movement studies in schizophrenic patients have used pictures of a face in isolation in free viewings. This study was designed to examine whether attentional control, through instructions, modulates the visuomotor behaviour in schizophrenia with pictures presenting a face accompanied by its body, and to investigate the ability of schizophrenic patients to recognise others' actions.

METHOD

Visual scan paths were monitored in 26 schizophrenic patients and 26 controls. Participants performed three tasks in which they were asked either to look at the picture in any way they liked, to determine the character's gender, or to recognise the action that the character was making with an object.

RESULTS

Patients explored less the pictures than controls in the free viewing. Their scan paths did not differ from that of controls in the active viewings, though patients tended to "avoid" looking at the character's face in the action recognition task.

CONCLUSION

The results show that patients are able to normalise their pattern of exploration as a function of task demands. The results are discussed in relation to attentional control, cognitive flexibility, dopamine, and processing of context information.

Scene categorization at large visual eccentricities

Studies of scene perception have shown that the visual system is particularly sensitive to global properties such as the overall layout of a scene. Such global properties cannot be computed locally, but rather require relational analysis over multiple regions. To what extent is observers' perception of scenes impaired in the far periphery? We examined the perception of global scene properties (Experiment 1) and basic-level categories (Experiment 2) presented in the periphery from 10° to 70°. Pairs of scene photographs were simultaneously presented left and right of fixation for 80ms on a panoramic screen (5m diameter) covering the whole visual field while central fixation was controlled. Observers were instructed to press a key corresponding to the spatial location left/right of a pre-defined target property or category. The results show that classification of global scene properties (e.g., naturalness, openness) as well as basic-level categorization (e.g., forests, highways), while better near the center, were accomplished with a performance highly above chance (around 70% correct) in the far periphery even at 70° eccentricity. The perception of some global properties (e.g., naturalness) was more robust in peripheral vision than others (e.g., indoor/outdoor) that required a more local analysis. The results are consistent with studies suggesting that scene gist recognition can be accomplished by the low resolution of peripheral vision.

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.

Influence of visual deficits on object categorization in normal aging

BACKGROUND/STUDY CONTEXT: The authors assessed whether age-related changes in low-level vision affects higher-level processes involved in object categorization.

METHODS

Thirty young and 30 older observers were asked to categorize gray levels photographs of natural and artifactual objects. The authors manipulated contrast (8% vs. 30%) and eccentricity (central vs. 21° peripheral presentations).

RESULTS

Older people were slower and less accurate than young people but this impairment varied with contrast and eccentricity. The pattern of performance was equivalent for young and for old people when pictures were presented centrally with a 30% contrast. Performance was impaired for older people when pictures were presented peripherally with a low contrast. Moreover, a category-specific deficit was found in the old group, specifically for peripheral presentations.

DISCUSSION

The results are consistent with an age-related deficit in the ability to categorize objects but the deficit was specifically observed under low-contrast condition and peripheral vision, suggesting a reduced response in the magnocellular pathway. The results are interpreted in the framework of age-related deficits in the two main visual streams.

The relationship between visual object exploration and action processing in schizophrenia

INTRODUCTION

Abnormalities in visual exploration and action processing are widely reported in schizophrenia. The aim of this study was to investigate whether object exploration (in order to recognise an action or the object) modulates visuomotor behaviour differently in schizophrenic patients and controls.

METHODS

Visual scan paths were monitored in 36 patients and 36 controls. Participants performed three tasks, in which they were asked to either (1) name the object (the object-naming task), (2) picture themselves interacting with the object and then name the action (the action-naming task), or (3) explore the object (the free-viewing task).

RESULTS

Patients explored objects less than controls did. Controls explored the part needed to identify an object in the object-naming task and the whole object in the action-naming and free-viewing tasks. In contrast, the patients maintained their gaze on the "identity" part of the object in all three tasks.

CONCLUSION

Our results were consistent with the literature findings on impaired action processing in schizophrenia but also extend the known impairment to implicit action processing when the subject is visually exploring an object. We discuss our results in terms of motivation, the effect of dopamine on eye movement, attentional capture, and frontal lobe dysfunction.

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.

Psychomotor slowing in mild cognitive impairment, Alzheimer's disease and lewy body dementia: mechanisms and diagnostic value

BACKGROUND

Although psychomotor slowing is frequent in Alzheimer's disease (AD) and Lewy body dementia (LBD), its mechanism and diagnostic value have not been examined.

OBJECTIVE

To (i) assess psychomotor speed in patients with mild cognitive impairment (MCI), AD and LBD, (ii) determine the underlying mechanisms, and (iii) examine whether psychomotor slowing constitutes a useful diagnostic marker.

METHODS

Psychomotor speed was assessed in MCI (n = 11) and mild dementia due to AD (n = 23) or LBD (n = 18) and controls (n = 52) with visual inspection time (VIT), digital tapping, simple reaction time (SRT) and choice reaction time (CRT) tests.

RESULTS

MCI did not differ from controls. Both dementia groups showed different patterns. In AD, VIT (p = 0.0001), tapping (p = 0.021), SRT (p = 0.0001) and decision time (p = 0.0001) were impaired as compared to controls. In LBD, VIT (p = 0.0001) was very impaired and correlated with visual hallucinations (p = 0.001); SRT lengthening (p = 0.0001) was related to attentional disorders (p = 0.0001).

CONCLUSIONS

Psychomotor slowing of AD is due to slower perceptuomotor and decision processes. In LBD, psychomotor slowing is due to visual and attention disorders, and subtle visual disorders contribute to hallucinations. VIT and CRT are useful diagnostic markers.

Gaze control during face exploration in schizophrenia

Patients with schizophrenia perform worse than controls on various face perception tasks. Studies monitoring eye movements have shown reduced scan paths and a lower number of fixations to relevant facial features (eyes, nose, mouth) than to other parts. We examine whether attentional control, through instructions, modulates visual scanning in schizophrenia. Visual scan paths were monitored in 20 patients with schizophrenia and 20 controls. Participants started with a "free viewing" task followed by tasks in which they were asked to determine the gender, identify the facial expression, estimate the age, or decide whether the face was known or unknown. Temporal and spatial characteristics of scan paths were compared for each group and task. Consistent with the literature, patients with schizophrenia showed reduced attention to salient facial features in the passive viewing. However, their scan paths did not differ from that of controls when asked to determine the facial expression, the gender, the age or the familiarity of the face. The results are interpreted in terms of attentional control and cognitive flexibility.

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.

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.