Free Visual Exploration Research Articles

Fast feature- and category-related parafoveal previewing support free visual exploration.

While humans typically saccade every ∼250 ms in natural settings, studies on vision tend to prevent or restrict eye movements. As it takes ∼50 ms to initiate and execute a saccade, this leaves only ∼200 ms to identify the fixated object and select the next saccade goal. How much detail can be derived about parafoveal objects in this short time interval, during which foveal processing and saccade planning both occur? Here, we had male and female human participants freely explore a set of natural images while we recorded magnetoencephalography and eye movements. Using multivariate pattern analysis, we demonstrate that future parafoveal images could be decoded at the feature and category level with peak decoding at ∼110 ms and ∼165 ms respectively, while the decoding of fixated objects at the feature and category level peaked at ∼100 ms and ∼145 ms. The decoding of features and categories was contingent on the objects being saccade goals. In sum, we provide insight on the neuronal mechanism of pre-saccadic attention by demonstrating that feature and category specific information of foveal and parafoveal objects can be extracted in succession within a ∼200 ms intersaccadic interval. These findings rule out strict serial or parallel processing accounts but are consistent with a pipeline mechanism in which foveal and parafoveal objects are processed in parallel but at different levels in the visual hierarchy.Significance Statement We provide neural evidence that future parafoveal saccade goals are processed surprisingly quickly at the feature and the category level before we saccade to them. Specifically, using multivariate pattern analysis applied to magnetoencephalography and eye-tracking data, we found that information about the colour and the category of parafoveal objects emerged at ∼110 ms and ∼165 ms respectively, with the same information about foveal objects emerging ∼100 ms and ∼145 ms. Our findings provide novel insight into the neuronal dynamics of parafoveal previewing during free visual exploration. The dynamics rule out strict serial or parallel processing, but are consistent with a pipelining mechanism in which foveal and parafoveal objects are processed in parallel but at different levels in the visual hierarchy.

Why did Rubens add a parrot to Titian's The Fall of Man? A pictorial manipulation of joint attention.

Almost 400 years ago, Rubens copied Titian's The Fall of Man, albeit with important changes. Rubens altered Titian's original composition in numerous ways, including by changing the gaze directions of the depicted characters and adding a striking red parrot to the painting. Here, we quantify the impact of Rubens's choices on the viewer's gaze behavior. We displayed digital copies of Rubens's and Titian's artworks-as well as a version of Rubens's painting with the parrot digitally removed-on a computer screen while recording the eye movements produced by observers during free visual exploration of each image. To assess the effects of Rubens's changes to Titian's composition, we directly compared multiple gaze parameters across the different images. We found that participants gazed at Eve's face more frequently in Rubens's painting than in Titian's. In addition, gaze positions were more tightly focused for the former than for the latter, consistent with different allocations of viewer interest. We also investigated how gaze fixation on Eve's face affected the perceptual visibility of the parrot in Rubens's composition and how the parrot's presence versus its absence impacted gaze dynamics. Taken together, our results demonstrate that Rubens's critical deviations from Titian's painting have powerful effects on viewers' oculomotor behavior.

A case study of left visual neglect after right pontine lesion: pathophysiological evidence for the infratentorial involvement in human visual attention.

Hemispatial neglect, the inability to attend to the contralesional side of space, is the most common disturbance of visuospatial attention. Both hemispatial neglect and visuospatial attention are typically associated with extended cortical networks. Nevertheless, recent accounts challenge this so-called corticocentric view and postulate the participation of structures well beyond the telencephalic cortex, in particular advocating the role of the brainstem. However, to the best of our knowledge, hemispatial neglect after a brainstem lesion has not yet been described. We describe, for the first time in a human, the occurrence and remission of contralesional visual hemispatial neglect after a focal lesion in the right pons. Hemispatial neglect was assessed by means of video-oculography during free visual exploration, a very sensitive and established method, and its remission was followed up until 3 wk after stroke. Moreover, by means of a lesion-deficit approach complemented by imaging, we identify a pathophysiological mechanism involving the disconnection of cortico-ponto-cerebellar and/or tecto-cerebellar-tectal pathways passing through the pons. Our findings offer, for the first time in a human, causal, lesion-based support for recent seminal accounts postulating the role of infratentorial structures participating in the activity of cerebral cortical attentional networks mediating attentional processes.NEW & NOTEWORTHY Visuospatial attention and its most common disturbance, hemispatial neglect, are typically associated with extended cortical networks. However, recent accounts challenge this corticocentric view and advocate the role of infratentorial structures. We describe, for the first time in a human, the occurrence of contralesional visual hemispatial neglect after a focal lesion in the right pons. We provide causal, lesion-based evidence for a pathophysiological mechanism involving the disconnection of cortico-ponto-cerebellar and/or tecto-cerebellar-tectal pathways passing through the pons.

SaFiDe: Detection of saccade and fixation periods based on eye-movement attributes from video-oculography, scleral coil or electrooculography data

In this work we present SaFiDe, a deterministic method to detect eye movements (saccades and fixations) from eye-trace data. We developed this method for human and nonhuman primate data from video- and coil-recorded eye traces and further applied the algorithm to eye traces computed from electrooculograms. All the data analyzed were from free-exploration paradigms, where the main challenge was to detect periods of saccades and fixations that were uncued by the task. The method uses velocity and acceleration thresholds, calculated from the eye trace, to detect saccade and fixation periods. We show that our fully deterministic method detects saccades and fixations from eye traces during free visual exploration. The algorithm was implemented in MATLAB, and the code is publicly available on a GitHub repository.•The algorithm presented is entirely deterministic, simplifying the comparison between subjects and tasks.•Thus far, the algorithm presented can operate over video-based eye tracker data, human electrooculogram records, or monkey scleral eye coil data.

Increased scene complexity during free visual exploration reveals residual unilateral neglect in recovered stroke patients

Unilateral neglect is a common cognitive syndrome after stroke, which is defined as a spatially specific unawareness of the contralesional space. The syndrome is caused by disruptions of attentional networks in the brain, which impair the patients’ ability to direct attention towards the contralesional space. During recovery, patients often learn to compensate by voluntarily directing their attention to the neglected side at the expense of cognitive resources. In this study, we examined the impact of the complexity of visual input on free visual exploration behavior of unilateral neglect and apparently recovered patients. We asked whether increasing scene complexity would allow the detection of residual unilateral neglect in recovered patients by increasing the amount of cognitive resources needed for visual processing and limiting capacities for compensation. Using virtual reality, we analyzed the spatial distribution of gaze of unilateral neglect patients, patients who had, according to conventional diagnostics, recovered from the syndrome, stroke patients with no history of unilateral neglect, and age-matched healthy controls. We manipulated the complexity of an immersive virtual scene presented on head mounted displays. We identified the orientation bias towards the ipsilesional side as a sensitive and specific marker of unilateral neglect, which was present in unilateral neglect and recovered patients but absent in stroke patients with no history of unilateral neglect and controls. Increasing scene complexity exacerbated the orientation shift in unilateral neglect patients and revealed that three out of nine (33%) recovered patients had a high probability of suffering from residual unilateral neglect as estimated by a generalized linear model using the median horizontal gaze position as a predictor.

Stable Working Memory and Perceptual Representations in Macaque Lateral Prefrontal Cortex during Naturalistic Vision.

Primates use perceptual and mnemonic visuospatial representations to perform everyday functions. Neurons in the lateral prefrontal cortex (LPFC) have been shown to encode both of these representations during tasks where eye movements are strictly controlled and visual stimuli are reduced in complexity. This raises the question of whether perceptual and mnemonic representations encoded by LPFC neurons remain robust during naturalistic vision-in the presence of a rich visual scenery and during eye movements. Here we investigate this issue by training macaque monkeys to perform working memory and perception tasks in a visually complex virtual environment that requires navigation using a joystick and allows for free visual exploration of the scene. We recorded the activity of 3950 neurons in the LPFC (areas 8a and 9/46) of two male rhesus macaques using multielectrode arrays, and measured eye movements using video tracking. We found that navigation trajectories to target locations and eye movement behavior differed between the perception and working memory tasks, suggesting that animals used different behavioral strategies. Single neurons were tuned to target location during cue encoding and working memory delay, and neural ensemble activity was predictive of the behavior of the animals. Neural decoding of the target location was stable throughout the working memory delay epoch. However, neural representations of similar target locations differed between the working memory and perception tasks. These findings indicate that during naturalistic vision, LPFC neurons maintain robust and distinct neural codes for mnemonic and perceptual visuospatial representations.SIGNIFICANCE STATEMENT We show that lateral prefrontal cortex neurons encode working memory and perceptual representations during a naturalistic task set in a virtual environment. We show that despite eye movement and complex visual input, neurons maintain robust working memory representations of space, which are distinct from neuronal representations for perception. We further provide novel insight into the use of virtual environments to construct behavioral tasks for electrophysiological experiments.

Auditory spatial cueing reduces neglect after right-hemispheric stroke: A proof of concept study

Spatial neglect after right-hemispheric stroke, characterized by the failure to attend or respond to the contralesional space, is a strong negative outcome predictor. Neglect is a supramodal syndrome affecting not only the visual but also the auditory modality. Preliminary studies used this audio-visual cross-modal effect to show short-lasting effects on attention towards the neglected space. The aim of the present study was to introduce a new technique of auditory stimulation combining the unspecific effect of music (i.e., patients choose their preferred music) with the effects of auditory spatial cueing (i.e., the music is presented dynamically as moving from right to left). The effect of this new auditory stimulation technique was investigated in two proof-of-concept experiments using repeated-measures, cross-over designs including 21 patients with visual neglect after a first right-hemispheric stroke. In Experiment I (n = 9), neglect patients showed a significantly larger improvement in Letter Cancellation after listening to preferred music with than without auditory spatial cueing. After granting the feasibility of this new auditory stimulation technique, we investigated the long-term aftereffects in Experiment II (n = 12). Herefore, we used video-oculography during Free Visual Exploration, a sensitive and reliable tool to assess spatial attention over time. Listening to music with auditory spatialcueing – as compared to music without auditory spatialcueing – significantly improved neglect severity in terms of visual exploration behaviour for up to 3h. A voxel-based-lesion-symptom mapping analysis over all patients revealed that the response variability in listening to music with auditory spatial cueing is determined by the integrity of the right inferior parietal lobule, the second branch of the superior longitudinal fascicle, and parieto-parietal callosal fibres. Our study shows that listening to music with auditory spatial cueing significantly reduces neglect severity and has the potential to be used as an add-on in the neurorehabilitation of neglect.

Conventional and HD-tDCS May (or May Not) Modulate Overt Attentional Orienting: An Integrated Spatio-Temporal Approach and Methodological Reflections.

Transcranial Direct Current Stimulation (tDCS) has been employed to modulate visuo-spatial attentional asymmetries, however, further investigation is needed to characterize tDCS-associated variability in more ecological settings. In the present research, we tested the effects of offline, anodal conventional tDCS (Experiment 1) and HD-tDCS (Experiment 2) delivered over the posterior parietal cortex (PPC) and Frontal Eye Field (FEF) of the right hemisphere in healthy participants. Attentional asymmetries were measured by means of an eye tracking-based, ecological paradigm, that is, a Free Visual Exploration task of naturalistic pictures. Data were analyzed from a spatiotemporal perspective. In Experiment 1, a pre-post linear mixed model (LMM) indicated a leftward attentional shift after PPC tDCS; this effect was not confirmed when the individual baseline performance was considered. In Experiment 2, FEF HD-tDCS was shown to induce a significant leftward shift of gaze position, which emerged after 6 s of picture exploration and lasted for 200 ms. The present results do not allow us to conclude on a clear efficacy of offline conventional tDCS and HD-tDCS in modulating overt visuospatial attention in an ecological setting. Nonetheless, our findings highlight a complex relationship among stimulated area, focality of stimulation, spatiotemporal aspects of deployment of attention, and the role of individual baseline performance in shaping the effects of tDCS.

Visual attention reveals affordances during Lower Palaeolithic stone tool exploration

Tools, which have a cognitive background rooted in our phylogenetic history, are essential for humans to interact with their environment. One of the characteristics of human beings is the coordination between the eyes and hands, which is associated with a skilled visuospatial system. Vision is the first input of an action that influences interaction with tools, and tools have affordances, known as behavioural possibilities, which indicate their possible uses and potentialities. The aim of the present study is to investigate body–tool interaction from a cognitive perspective, focusing on visual affordances during interaction with the early stone tools. We analyse visual attention, applying eye tracking technology, during a free visual exploration and during haptic manipulation of the Lower Palaeolithic stone tools. The central area of the tool is the most observed region, followed by the top and the base, while knapped areas trigger more attention than the cortex. There are differences between stone tool types, but visual exploration does not differ when aided by haptic exploration. The results suggest that visual behaviour is associated with the perception of affordances, possibly from the beginning of the brain–body–tool interaction, associated with the Lower Palaeolithic culture.

Spatial asymmetries (\u201cpseudoneglect\u201d) in free visual exploration\u2014modulation of age and relationship to line bisection

When humans visually explore an image, they typically tend to start exploring its left side. This phenomenon, so-called pseudoneglect, is well known, but its time-course has only sparsely been studied. Furthermore, it is unclear whether age influences pseudoneglect, and the relationship between visuo-spatial attentional asymmetries in a free visual exploration task and a classical line bisection task has not been established. To address these questions, 60 healthy participants, aged between 22 and 86, were assessed by means of a free visual exploration task with a series of naturalistic, colour photographs of everyday scenes, while their gaze was recorded by means of a contact-free eye-tracking system. Furthermore, a classical line bisection task was administered, and information concerning handedness and subjective alertness during the experiment was obtained. The results revealed a time-sensitive window during visual exploration, between 260 and 960 ms, in which age was a significant predictor of the leftward bias in gaze position, i.e., of pseudoneglect. Moreover, pseudoneglect as assessed by the line bisection task correlated with the average gaze position throughout a time-window of 300–1490 ms during the visual exploration task. These results suggest that age influences visual exploration and pseudoneglect in a time-sensitive fashion, and that the degree of pseudoneglect in the line bisection task correlates with the average gaze position during visual exploration in a time-sensitive manner.

Video-Oculography During Free Visual Exploration to Detect Right Spatial Neglect in Left-Hemispheric Stroke Patients With Aphasia: A Feasibility Study.

Spatial neglect has been shown to occur in 17–65% of patients after acute left-hemispheric stroke. One reason for this varying incidence values might be that left-hemispheric stroke is often accompanied by aphasia, which raises difficulties in assessing attention deficits with conventional neuropsychological tests entailing verbal instructions. Video-oculography during free visual exploration (FVE) requires only little understanding of simple non-verbal instruction and has been shown to be a sensitive and reliable tool to detect spatial neglect in patients with right-hemispheric stroke. In the present study, we aimed to investigate the feasibility of FVE to detect neglect in 10 left-hemispheric stroke patients with mild to severe aphasia as assessed by means of the Token Test, Boston Naming Test and Aachener Aphasie Test. The patient’s individual deviation between eye movement calibration and validation was recorded and compared to 20 age-matched healthy controls. Furthermore, typical FVE parameters such as the landing point of the first fixation, the mean gaze position (in ° of visual angle), the number and duration of visual fixations and the mean visual exploration area were compared between groups. In addition, to evaluate for neglect, the Bells cancellation test was performed and neglect severity in daily living was measured by means of the Catherine Bergego Scale (CBS). Our results showed that the deviation between calibration and validation did not differ between aphasia patients and healthy controls highlighting its feasibility. Furthermore, FVE revealed the typical neglect pattern with a significant leftward shift in visual exploration bahaviour, which highly correlated with neglect severity as assessed with CBS. The present study provides evidence that FVE has the potential to be used as a neglect screening tool in left-hemispheric stroke patients with aphasia in which compliance with verbal test instructions may be compromised by language deficits.

Test-Retest-Reliability of Video-Oculography During Free Visual Exploration in Right-Hemispheric Stroke Patients With Neglect.

The Mean gaze position during free visual exploration (FVE) is a sensitive tool to detect neglect in patients after a right-hemispheric stroke. Here we investigated the test-retest-reliability of mean gaze position during FVE in 23 patients with left-sided neglect after a first-ever sub-acute right-hemispheric stroke. We analyzed the reliability between different test sets administered within 11 days (test sets A and B, each including different images and their mirrored versions), and between repeated measures using the same test set administered three times within 2 days (test set C, including the same images and their mirrored versions). The intra-class correlation coefficient (ICC) showed good reliability between the two different test sets (test sets A and B; ICC = 0.819), and excellent reliability for the repeated measures with the same test set C (ICC = 0.964). FVE can therefore be recommended for the longitudinal assessments of patients’ neglect severity during neurorehabilitation as well as in treatment trials.

Eyetracking during free visual exploration detects neglect more reliably than paper-pencil tests

Neglect after stroke is most accurately diagnosed by a systematic, ecological observation during everyday behaviour using the Catherine Bergego Scale (CBS). However, the CBS is time-consuming and often omitted in clinical settings, especially stroke units. In this study, we aimed to explore if video-oculography during free visual exploration (FVE), which can be performed in few minutes, is sensitive in mirroring neglect in everyday behaviour and whether it is more sensitive than conventional neuropsychological paper-pencil tests. In this retrospective, observational, multicentre study, we identified 78 patients in our database with subacute right-hemispheric stroke, with and without neglect in everyday behaviour, diagnosed by the CBS, who also performed FVE. 40 age-matched healthy participants served as controls. The sensitivity to detect neglect was compared between FVE (i.e., mean gaze position on the horizontal axis) and conventional neuropsychological paper-pencil tests, i.e., Random Shape Cancellation, Line Bisection, Two-Part Picture, Bells, Star Cancellation, Letter Cancellation, Sensitive Neglect, and Five-Point. FVE correctly identified neglect in 85%of patients, with an AUC-value of .922 in ROC-analysis. Conventional neuropsychological paper-pencil tests, considered alone or in combination, showed heterogeneous results, and identified neglect significantly less often (21.74%–68.75%). Moreover, there was a significant correlation between mean gaze position and CBS scores, providing evidence for the relationship between FVE and neglect in everyday behaviour. Furthermore, VLSM analyses suggested that the absence of a pathological rightward bias in FVE might depend on the integrity of the second branch of the right Superior Longitudinal Fascicle (SLF II), a white-matter tract connecting cortical areas critical for visual attention. Video-oculography during FVE has a high sensitivity and specificity to diagnose neglect after stroke and it is more sensitive than conventional neuropsychological paper-pencil tests. It can be performed in short time and has the potential to be used as a fast and accurate screening tool that allows the initiation of comprehensive neuropsychological diagnostics and therapy from early on.

Eye tracking as an objective measure of hyperphagia in children with Prader-Willi syndrome.

This study examined sensitivity of eye tracking measures to hyperphagia severity in Prader-Willi syndrome (PWS). Gaze data were collected in 57 children with PWS, age 3-11 years, and 47 typically developing peers at two study sites during free visual exploration of complex stimulus arrays that included images of food, animals, and household objects. Analysis of the number and duration of fixations as well as gaze perseverations revealed that food items are not exceptionally salient for children with PWS. Instead, increased attention to food in the context of other high-interest items (e.g., animals) was associated with caregiver reports of more severe hyperphagia and more advanced nutritional phase. The study also provided preliminary evidence of possible genetic subtype and sex differences as well as demonstrated that multiple investigators in a wide range of settings can effectively implement the eye tracking protocol. The results indicate that gaze characteristics derived from eye tracking may be a promising objective marker of hyperphagia in PWS for use in research and clinical trials.

Visual Exploration Area in Neglect: A New Analysis Method for Video-Oculography Data Based on Foveal Vision.

Video-oculography during free visual exploration (FVE) is a valuable tool to evaluate visual attention spatial allocation in neglect patients after right-hemispheric stroke. In conventional FVE analyses, the position of a visual fixation is conceived as a single point in space. Here, we describe a new complementary method to analyze FVE data based on foveal vision, leading to an accurate estimate of the portion of the picture that was effectively explored. In 15 neglect patients and 20 healthy controls, visual exploration areas (i.e., considering 1° visual angle around every single fixation) were computed. Furthermore, the proportion of single and overlapping fixations was analyzed. Overlapping fixations were further categorized into capture fixations (successive overlapping fixation, putatively reflecting problem of disengagement) and re-capture fixations (temporally distant overlapping fixations, putatively reflecting spatial working memory deficits). The results of this new analysis approach were compared to the ones of conventional approaches. Conventional analyses showed the typical visual attention deficits in neglect patients versus healthy controls: significantly less fixations and time spent within the left and significantly more fixations and time spent within the right screen half. According to the results of our new approach, patients showed a significantly smaller visual exploration area within the left screen half. However, the right visual exploration area did not differ between groups. Furthermore, in neglect patients, the proportion of overlapping fixations within the right screen half was significantly higher than within the left screen half, as well as significantly higher than in healthy controls within either screen halves. Whereas neglect patients showed significantly more capture fixations than healthy controls, the number of re-capture fixations did not differ between groups. These results suggest that, in neglect patients, the efficiency of visual exploration is also reduced within the right screen half and that impaired disengagement might be an important mechanism leading to overlapping fixations. Our new analysis of the visual exploration area, based on foveal vision, may be a promising additional approach in visual attention research. It allows to accurately measure the portion of the picture that was effectively explored, disentangle single from overlapping fixations, and distinguish between capture and re-capture fixations.

Re-fixation and perseveration patterns in neglect patients during free visual exploration.

The literature suggests that neglect patients not only show impairments in directing attention toward the left, contralesional space, but also present with perseverative behavior. Moreover, previous studies described re-fixations during visual search tasks, and interpreted this finding as an impairment of spatial working memory. The aim of the present study was to study re-fixations and perseverations (i.e., recurrent re-fixations to same locations) during free visual exploration, a task with high ecological validity. We hypothesized that: (1) neglect patient would perform re-fixations more frequently than healthy controls within the right hemispace; and, (2) the re-fixation behavior of neglect patients would be characterized by perseverative fixations. To test these hypotheses, we assessed 22 neglect patients and 23 healthy controls, measuring their eye movements during free exploration of naturalistic pictures. The results showed that neglect patients tend to re-fixate locations within the ipsilesional hemispace when they freely explore naturalistic pictures. Importantly, the saliency of discrete locations within the pictures has a stronger influence on fixation behavior within the contralesional than within the ipsilesional hemispace in neglect patients. Finally, the results indicated that, for re-fixations, saliency plays a more important role within the contralesional than the ipsilesional hemispace. Moreover, we found evidence that re-fixation behavior of neglect patients is characterized by frequent recurrent re-fixations back to the same spatial locations which may be interpreted as perseverations. Hence, with the present study, we could better elucidate the mechanism leading to re-fixations and perseverative behavior during free visual exploration in neglect patients.

Further to the right: Viewing distance modulates attentional asymmetries (‘pseudoneglect’) during visual exploration

Previous studies showed that the small leftward bias found in healthy humans’ spatial judgments of lines (“pseudoneglect”) shifts to the right with increasing distance between stimuli and observer. In this study, we investigated whether such a modulation of attentional asymmetry can also be observed in free visual exploration. Participants freely explored photographs of naturalistic scenes for 7 s in near (60 cm) and far (140 cm) space. After an initial leftward bias, followed by a compensatory rightward bias, gaze positions were significantly more leftward in near compared to far space (around 4 s from scene onset). Our results show that the modulation of attentional asymmetries by viewing distance previously reported for spatial judgments generalizes to free visual exploration, and we revealed the temporal dynamics of these asymmetries by fine-grained eye movement analysis. In contrast, an effect of viewing distance was reduced or absent when eye movements are under strong top-down control, as in systematic serial visual search (Sensitive Negelct Test). Finally, there was no effect of viewing distance in the landmark task (as also reported in a minority of other studies), suggesting that this effect may depend on specific, yet unidentified task characteristics.

Eye-Tracking Provides a Sensitive Measure of Exploration Deficits After Acute Right MCA Stroke.

The eye-tracking study aimed at assessing spatial biases in visual exploration in patients after acute right MCA (middle cerebral artery) stroke. Patients affected by unilateral neglect show less functional recovery and experience severe difficulties in everyday life. Thus, accurate diagnosis is essential, and specific treatment is required. Early assessment is of high importance as rehabilitative interventions are more effective when applied soon after stroke. Previous research has shown that deficits may be overlooked when classical paper-and-pencil tasks are used for diagnosis. Conversely, eye-tracking allows direct monitoring of visual exploration patterns. We hypothesized that the analysis of eye-tracking provides more sensitive measures for spatial exploration deficits after right middle cerebral artery stroke. Twenty-two patients with right MCA stroke (median 5 days after stroke) and 28 healthy controls were included. Lesions were confirmed by MRI/CCT. Groups performed comparably in the Mini–Mental State Examination (patients and controls median 29) and in a screening of executive functions. Eleven patients scored at ceiling in neglect screening tasks, 11 showed minimal to severe signs of unilateral visual neglect. An overlap plot based on MRI and CCT imaging showed lesions in the temporo–parieto–frontal cortex, basal ganglia, and adjacent white matter tracts. Visual exploration was evaluated in two eye-tracking tasks, one assessing free visual exploration of photographs, the other visual search using symbols and letters. An index of fixation asymmetries proved to be a sensitive measure of spatial exploration deficits. Both patient groups showed a marked exploration bias to the right when looking at complex photographs. A single case analysis confirmed that also most of those patients who showed no neglect in screening tasks performed outside the range of controls in free exploration. The analysis of patients’ scoring at ceiling in neglect screening tasks is of special interest, as possible deficits may be overlooked and thus remain untreated. Our findings are in line with other studies suggesting considerable limitations of laboratory screening procedures to fully appreciate the occurrence of neglect symptoms. Future investigations are needed to explore the predictive value of the eye-tracking index and its validity in everyday situations.

Eye Tracking as a Marker of Hyperphagia in Prader-Willi Syndrome

ABSTRACTThis study examined the feasibility of eye tracking measures as markers of hyperphagia in 42 children and adults with Prader-Willi syndrome (PWS). Gaze data collected during free visual exploration of complex displays revealed that food images may not have an overall superior salience in PWS. However, increased attention to food in the context of other high-interest items was associated with higher scores on caregiver reports of hyperphagia. The study also provided preliminary evidence of test-retest reliability of eye tracking measures, suggesting that gaze characteristics may be a promising objective marker of food-related interests in PWS.

Free visual exploration of natural movies in schizophrenia.

Eye tracking dysfunction (ETD) observed with standard pursuit stimuli represents a well-established biomarker for schizophrenia. How ETD may manifest during free visual exploration of real-life movies is unclear. Eye movements were recorded (EyeLink®1000) while 26 schizophrenia patients and 25 healthy age-matched controls freely explored nine uncut movies and nine pictures of real-life situations for 20s each. Subsequently, participants were shown still shots of these scenes to decide whether they had explored them as movies or pictures. Participants were additionally assessed on standard eye-tracking tasks. Patients made smaller saccades (movies (p = 0.003), pictures (p = 0.002)) and had a stronger central bias (movies and pictures (p < 0.001)) than controls. In movies, patients' exploration behavior was less driven by image-defined, bottom-up stimulus saliency than controls (p < 0.05). Proportions of pursuit tracking on movies differed between groups depending on the individual movie (group*movie p = 0.011, movie p < 0.001). Eye velocity on standard pursuit stimuli wasreduced in patients (p = 0.029) but did not correlate with pursuit behavior on movies. Additionally, patients obtained lower rates of correctly identified still shots as movies or pictures (p = 0.046). Our results suggest a restricted centrally focused visual exploration behavior in patients not only on pictures, but also on movies of real-life scenes. While ETD observed in the laboratory cannot be directly transferred to natural viewing conditions, these alterations support a model of impairments in motion information processing in patients resulting in a reduced ability to perceive moving objects and less saliency driven exploration behavior presumably contributing to alterations in the perception of the natural environment.