Pupil dilation reveals the intensity of touch.

Touch is important for many aspects of our daily activities. One of the most important tactile characteristics is its perceived intensity. However, quantifying the intensity of perceived tactile stimulation is not always possible using overt responses. Here, we show that pupil responses can objectively index the intensity of tactile stimulation in the absence of overt participant responses. In Experiment 1 (n = 32), we stimulated three reportedly differentially sensitive body locations (finger, forearm, and calf) with a single tap of a tactor while tracking pupil responses. Tactile stimulation resulted in greater pupil dilation than a baseline without stimulation. Furthermore, pupils dilated more for the more sensitive location (finger) than for the less sensitive location (forearm and calf). In Experiment 2 (n = 20) we extended these findings by manipulating the intensity of the stimulation with three different intensities, here a short vibration, always at the little finger. Again, pupils dilated more when being stimulated at higher intensities as compared to lower intensities. In summary, pupils dilated more for more sensitive parts of the body at constant stimulation intensity and for more intense stimulation at constant location. Taken together, the results show that the intensity of perceived tactile stimulation can be objectively measured with pupil responses - and that such responses are a versatile marker for touch research. Our findings may pave the way for previously impossible objective tests of tactile sensitivity, for example in minimally conscious state patients.

Zooming in on abnormal local and global processing biases after stroke: Frequency, lateralization, and associations with cognitive functions.

OBJECTIVES: The 'attentional spotlight' can be adjusted depending on the task requirements, resulting in processing information at either the local or global level. Stroke can lead to local or global processing biases, or the inability to simultaneously attend both levels. In this study, we assessed the (1) prevalence of abnormal local and global biases following stroke, (2) differences between left- and right-sided brain damaged patients, and (3) relations between local and global interference, the ability to attend local and global levels simultaneously, and lateralized attention, search organization, search speed, visuo-construction, executive functioning, and verbal (working) memory. METHODS: Stroke patients admitted for inpatient rehabilitation completed directed (N = 192 total; N = 46 left-sided/N = 48 right-sided lesion) and divided (N = 258 total; N = 67 left-sided/N = 66 right-sided lesion) local-global processing tasks, as well as a conventional neuropsychological assessment. Processing biases and interference effects were separately computed for directed and divided tasks. RESULTS: On the local-global tasks, 7.8-10.9% of patients showed an abnormal local bias and 6.3-8.3% an abnormal global bias for directed attention, and 5.4-10.1% an abnormal local bias and 6.6-15.9% an abnormal global bias for divided attention. There was no significant difference between patients with left- and right-sided brain damage. There was a moderate positive relation between local interference and search speed, and a small positive relation between global interference and neglect. CONCLUSIONS: Abnormal local and global biases can occur after stroke and might relate to a range of cognitive functions. A specific bias might require a different approach in assessment, psycho-education, and treatment.

Gaze data of 4243 participants shows link between leftward and superior attention biases and age.

Healthy individuals typically show more attention to the left than to the right (known as pseudoneglect), and to the upper than to the lower visual field (known as altitudinal pseudoneglect). These biases are thought to reflect asymmetries in neural processes. Attention biases have been used to investigate how these neural asymmetries change with age. However, inconsistent results have been reported regarding the presence and direction of age-related effects on horizontal and vertical attention biases. The observed inconsistencies may be due to insensitive measures and small sample sizes, that usually only feature extreme age groups. We investigated whether spatial attention biases, as indexed by gaze position during free viewing of a single image, are influenced by age. We analysed free-viewing data from 4,243 participants aged 5-65 years and found that attention biases shifted to the right and superior directions with increasing age. These findings are consistent with the idea of developing cerebral asymmetries with age and support the hypothesis of the origin of the leftward bias. Age modulations were found only for the first seven fixations, corresponding to the time window in which an absolute leftward bias in free viewing was previously observed. We interpret this as evidence that the horizontal and vertical attention biases are primarily present when orienting attention to a novel stimulus - and that age modulations of attention orienting are not global modulations of spatial attention. Taken together, our results suggest that attention orienting may be modulated by age and that cortical asymmetries may change with age.

Visuospatial perception is not affected by self-related information.

Previous research suggests that attention is drawn by self-related information. Three online experiments were conducted to investigate whether self-related stimuli alter visuospatial perceptual judgments. In a matching task, associations were learned between labels ('Yourself'/friend/stranger's name) paired with cues. Cues were coloured outlines (Experiment 1, N = 135), geometric shapes (Experiment 2, N = 102), or coloured gradients (Experiment 3, N = 110). Visuospatial perception bias was measured with a greyscales task. Cues were presented prior to, and/or alongside greyscales. We hypothesized there would be a bias towards the self-related cue. In all experiments, we found a self-related bias in the matching task. Furthermore, there was an overall leftward visuospatial perceptual bias (pseudoneglect). However, we found anecdotal to moderate evidence for the absence of an effect of self-related cues on visuospatial perception judgments. Although self-related stimuli influence how our attention is oriented to stimuli, attention mechanisms that influence perceptual judgements are seemingly not affected by a self-bias.

Visual Sensitivity in Complex Regional Pain Syndrome and Fibromyalgia: An Online Study.

Perceptual anomalies can provide insights into underlying pathologies even when they are not the main symptom of many clinical conditions. Complex regional pain syndrome (CRPS) and fibromyalgia are chronic pain conditions associated with changes in the central nervous system, possibly leading to enhanced visual sensitivity. It is unclear whether this occurs more than for people with other types of pain. We examined visual sensitivity elicited by different stimuli and in daily life, through an online study of people with CRPS (n = 57), fibromyalgia (n = 74), other pain (n = 50), and no pain (n = 89). Respondents rated changes in pain, discomfort, or distress from viewing patterns with different spatial frequencies (lower-order visual processing), and reversible figures (bistable images; higher-order visual processing). We assessed visual sensitivity in daily life using the Leiden Visual Sensitivity Scale and Visual Discomfort Scale. Respondents with CRPS or fibromyalgia reported more visual discomfort than pain-related and pain-free controls while viewing striped patterns and a circle, with no effect of spatial frequency. They reported more pain while viewing a nonreversible square, but not reversible figures (Necker Cube, Duck/Rabbit). Finally, they reported more daily visual sensitivity than pain-related and pain-free controls. Suppressing visual cortical activity might benefit people with CRPS or fibromyalgia.

Predictors of Self-Reported Neglect-like Symptoms and Involuntary Movements in Complex Regional Pain Syndrome Compared to Other Chronic Limb Pain Conditions.

OBJECTIVE: In addition to pain, people with complex regional pain syndrome (CRPS) often report inattention to and disengagement from their affected limb (i.e., "neglect-like symptoms"). Understanding how these symptoms relate to other characteristics of CRPS, and chronic pain generally, could provide insights for preventing and treating CRPS. METHODS: We administered an online survey to people who received a diagnosis of CRPS (n = 335) and other chronic limb pain (n = 407). Neglect-like symptoms were assessed using the Neurobehavioral questionnaire. RESULTS: A principal component analysis identified two components: motor and cognitive neglect-like symptoms, and involuntary movements. Internal consistency of the components was acceptable. We conducted regression analyses with these as outcomes. Having CRPS, a painful lower limb, higher pain intensity, and somatic symptoms were associated with more motor and cognitive neglect-like symptoms. Having CRPS, higher pain intensity, depression, and somatic symptoms were associated with more involuntary movements. Age, gender, anxiety, disease duration, hours of pain per day, affected side, whether the limb was the most painful body part, and number of pain-related medical diagnoses were no predictors. Finally, motor and cognitive neglect-like symptoms were related to tremor; and involuntary movements to changes in skin color, swelling, sweating, toenails, weakness, and tremor. CONCLUSIONS: This study confirms the specificity of inattention to and disengagement from the affected limb in CRPS, independent of other factors. Furthermore, two components of the Neurobehavioral questionnaire were disentangled: motor and cognitive neglect-like symptoms, and involuntary movements. Results could potentially help clinicians to better assess neglect-like symptoms in chronic pain .

Validation of the Leiden Visual Sensitivity Scale and Visual Discomfort Scale in Chronic Pain Conditions.

Discomfort provoked by normally innocuous visual stimuli has been reported by people with chronic pain. Visual discomfort may be higher in pain conditions in which central sensitization is implicated, such as Complex Regional Pain Syndrome (CRPS) and fibromyalgia. In an online study, we validated the Leiden Visual Sensitivity Scale (L-VISS) and Visual Discomfort Scale (VDS) in people with CRPS (n = 57), fibromyalgia (n = 75), and general chronic pain (n = 53); investigated whether these groups and pain-free controls (n = 125) differed in visual discomfort; and evaluated the effect of age. The L-VISS and VDS had good internal consistency. Both scales were positively related with experimentally induced visual distortions for mid-spatial frequency striped patterns, suggesting good construct validity. The scales were positively related with each other, and dissociated between the pain and pain-free groups in similar ways, suggesting good construct validity. There was no relationship between age and L-VISS scores and a small negative relationship between age and VDS scores. Visual discomfort was highest in the fibromyalgia group, followed by the CRPS group. This research confirms the utility of the L-VISS and VDS for measuring visual sensitivity in chronic pain and adds to evidence that central sensitization is an important mechanism of visual discomfort.

What Does It Take to Search Organized? The Cognitive Correlates of Search Organization During Cancellation After Stroke.

OBJECTIVES: Stroke could lead to deficits in organization of visual search. Cancellation tests are frequently used in standard neuropsychological assessment and appear suitable to measure search organization. The current aim was to evaluate which cognitive functions are associated with cancellation organization measures after stroke. METHODS: Stroke patients admitted to inpatient rehabilitation were included in this retrospective study. We performed exploratory factor analyses to explore cognitive domains. A digital shape cancellation test (SC) was administered, and measures of search organization (intersections rate and best r) were computed. The following cognitive functions were measured by neuropsychological testing: neglect (SC, line bisection; LB, Catherine Bergego Scale; CBS, and Balloons Test), visuospatial perception and construction (Rey Complex Figure Test, RCFT), psychomotor speed (Trail Making Test; TMT-A), executive functioning/working memory (TMT-B), spatial planning (Tower Test), rule learning (Brixton Test), short-term auditory memory (Digit Span Forward; DSF), and verbal working memory (Digit Span Backward; DSB). RESULTS: In total, 439 stroke patients were included in our analyses. Four clusters were separated: "Executive functioning" (TMT-A, TMT-B, Brixton Test, and Tower Test), "Verbal memory" (DSF and DSB), "Search organization" (intersections rate and best r), and "Neglect" (CBS, RCFT copy, Balloons Test, SC, and LB). CONCLUSIONS: Search organization during cancellation, as measured with intersections rate and best r, seems a distinct cognitive construct compared to existing cognitive domains that are tested during neuropsychological assessment. Administering cancellation tests and analyzing measures of search organization could provide useful additional insights into the visuospatial processes of stroke patients. (JINS, 2018, 24, 424-436).

Pharmacological Treatment of Visuospatial Neglect: A Systematic Review.

OBJECTIVES: The aims of the current review were (1) to give an overview of human studies investigating pharmacotherapy to ameliorate visuospatial neglect and (2) to evaluate the quality of those studies. METHODS: A systematic literature search using PubMed, Scopus, and ResearchGate was conducted in regard to studies that evaluated pharmacological interventions aiming to ameliorate poststroke visuospatial neglect. The search was limited in the following features: species (human), adults (≥18 years of age), language (English), and type of neglect (visuospatial). Two independent authors extracted data on study content and effectiveness and evaluated the quality of studies and methods. RESULTS: A total of 11 studies were identified. Three studies were considered to be of moderate quality, the others of low quality. Seven studies represented dopaminergic treatment; 3 studies represented cholinergic treatment; and 1 study represented noradrenergic treatment. Three dopaminergic studies showed primarily positive effects of dopaminergic stimulation on visuospatial neglect, whereas three others showed adverse effects. All 3 cholinergic studies found positive effects in some outcome measures concerning visuospatial neglect. Noradrenergic stimulation improved maintenance of attention when exploring space. CONCLUSIONS: Currently, cholinergic therapy might be the best option for future research. However, we must emphasize the explorative nature and the limited quality of the reviewed studies.

Study protocol of 'Prism Adaptation in Rehabilitation': a randomized controlled trial in stroke patients with neglect.

BACKGROUND: A frequent disorder after stroke is neglect, resulting in a failure to report or respond to contralesional stimuli. Rehabilitation of neglect is important, given the negative influence on motor recovery, independence in self-care, transfers, and locomotion. Effects of prism adaptation (PA) to alleviate neglect have been reported. However, either small groups or no control group were included and few studies reported outcome measurements on the level of activities of daily living (ADL). The current ongoing RCT investigates the short- and long-term effects of PA in a large population in a realistic clinical setting. Measures range from the level of function to the level of ADL. METHODS/DESIGN: Neglect patients in the sub-acute phase after stroke are randomly assigned to PA (n = 35) or sham adaptation (SA; n = 35). Adaptation is performed for 10 consecutive weekdays. Patients are tested at start of the study, 1 and 2 weeks after starting, and 1, 2, 4 and 12 weeks after ending treatment. Primary objectives are changes in performance on neuropsychological tests and neglect in ADL. Secondary objectives are changes in simulated driving, eye movements, balance, visual scanning and mobility, subjective experience of neglect in ADL and independence during ADL. DISCUSSION: If effective, PA could be implemented as a treatment for neglect. TRIAL REGISTRATION: This trial is registered at the Dutch Trial Register # NTR3278 .

Exploring bias in horizontal and vertical spatial representations using mental number lines and the greyscales task.

People have a leftward bias when making visuospatial judgements about horizontally arranged stimuli ("pseudoneglect"), and a superior bias when making visuospatial judgements about vertically arranged stimuli. The leftward visuospatial bias in physical space seems to extend to the mental representation of space. However, whether any bias exists in mental representation of vertical space is unknown. We investigated whether people show a visuospatial bias in the mental representation of vertical space, and if any bias in mental representations of horizontal and vertical space related to the extent of bias in physical space. Participants (n = 171) were presented with three numbers and asked which interval was smaller/larger (counterbalanced): the interval between the first and middle, or middle and last number. Participants were instructed to either think of the numbers as houses on a street or as floors of a building, or were given no imagery instructions. Participants in the houses on a street condition showed a leftward bias, but there was no superior bias in the floors of a building condition. In contrast, we replicated previous findings of leftward and superior bias on greyscales tasks. Our findings reinforce previous evidence that numbers are represented horizontally and ascending left to right by default.

Investigating Object Affordance in People with Complex Regional Pain Syndrome: No Alterations in the Automatic Activation of Motor Plans.

Complex Regional Pain Syndrome (CRPS) is a condition of chronic pain, predominantly affecting one limb. CRPS is characterised by motor changes including slowed or uncoordinated movements. Cognitive processes that drive movement planning and/or execution might contribute to these changes. We aimed to investigate the potential alterations to such cognitive mechanisms using an 'object affordance' paradigm. Object affordance refers to the observation that viewing an object modulates associated motor responses, presumably due to the automatic activation of a motor plan. We hypothesised that people with CRPS would show reduced object affordance effects for their affected compared to unaffected hand, and compared to pain-free controls. First, we validated an online object affordance task involving button press responses to everyday objects with handles, in pain-free participants (n = 63; Experiment 1). Object affordance was reflected by faster and more accurate responses when the object handle was aligned to the responding hand ("aligned") compared to when the handle was aligned to the other hand ("non-aligned"). These results were similar for the online task as when administered in person. Second, in a case-control study, we administered the online object affordance task to people with CRPS predominantly affecting the upper limb (n = 25), and age-matched pain-free controls (n = 68; Experiment 2). People with CRPS responded faster and more accurately in the aligned versus non-aligned condition (ie, an object affordance effect), both for the affected and unaffected hands. There were no differences to pain-free participants. Therefore, object affordance effects were seen in people with CRPS, providing no evidence for altered motor planning. PERSPECTIVE: This article presents research investigating cognitive processes related to motor planning in Complex Regional Pain Syndrome (CRPS). Using an online object affordance paradigm, validated in pain-free controls, the authors found that people with CRPS showed intact object affordance effects in the affected and unaffected hand, suggesting unaltered motor planning. DATA AVAILABILITY: The experiment materials, data, pre-processing scripts, and analysis scripts can be found via Open Science Framework (https://osf.io/nc825/files/osfstorage).

Reduced Visuospatial Attention in Personal Space is Not Limited to the Affected Limb in Complex Regional Pain Syndrome.

Purpose: Alterations in spatial attention have been reported in people with chronic pain and may be relevant to understanding its cortical mechanisms and developing novel treatments. There is conflicting evidence as to whether people with Complex Regional Pain Syndrome (CRPS) have reduced visuospatial attention to their affected limb and/or its surrounding space, with some evidence that these deficits may be greater in personal (bodily) space. We aimed to test the competing hypotheses of whether the visuospatial attentional bias is specific to the personal space of the affected limb or generalizes to the personal space of other parts of the affected side of the body. Patients and Methods: Using visual Temporal Order Judgement tasks, we measured spatial attention in the personal space of the hands and feet of patients with upper (n=14) or lower (n=14) limb CRPS and pain-free controls (n=17). Participants judged the order of two light flashes presented at different temporal offsets on each of their hands or feet. Slower processing of the flash on one side relative to the other reflects reduced attention to that side of space. Results: Controls prioritized stimuli on the non-dominant (left) relative to dominant side, consistent with the well-documented normal leftward bias of attention (ie "pseudoneglect"). Regardless of the location (upper or lower limb) of the pain or visual stimuli, people with CRPS showed no such asymmetry, representing reduced attention to the affected side (compared to the greater attention of controls to their non-dominant side). More severe CRPS symptoms were associated with a greater tendency to deprioritize stimuli on the affected side. Conclusion: Our findings suggest that relative visuospatial bias in CRPS is generalized to the personal space of the affected side of the body, rather than being specific to the personal space of the CRPS-affected limb.

Uncovering the (un)attended: Pupil light responses index persistent biases of spatial attention in neglect.

Visuospatial neglect is a frequent and disabling disorder, mostly after stroke, that presents in impaired awareness to stimuli on one side of space. Neglect causes disability and functional dependence, even long after the injury. Improving measurements of the core attentional deficit might hold the key for better understanding of the condition and development of treatment. We present a rapid, pupillometry-based method that assesses automatic biases in (covert) attention, without requiring behavioral responses. We exploit the phenomenon that pupil light responses scale with the degree of covert attention to stimuli, and thereby reveal what draws (no) attention. Participants with left-sided neglect after right-sided lesions following stroke (n = 5), participants with hemianopia/quadrantanopia following stroke (n = 11), and controls (n = 22) were presented with two vertical bars, one of which was white and one of which was black, while fixating the center. We varied which brightness was left and right, respectively across trials. In line with the hypotheses, participants with neglect demonstrated biased pupil light responses to the brightness on the right side. Participants with hemianopia showed similar biases to intact parts of the visual field, whilst controls exhibited no bias. Together, this demonstrates that the pupil light response can reveal not only visual, but also attentional deficits. Strikingly, our pupillometry-based bias estimates were not in agreement with neuropsychological paper-and-pencil assessments conducted on the same day, but were with those administered in an earlier phase post-stroke. Potentially, we pick up on persistent biases in the covert attentional system that participants increasingly compensate for in classical neuropsychological tasks and everyday life. The here proposed method may not only find clinical application, but also advance theory and aid the development of successful restoration therapies by introducing a precise, longitudinally valid, and objective measurement that might not be affected by compensation.

No short-term treatment effect of prism adaptation for spatial neglect: An inclusive meta-analysis.

Despite 25 years of research on the topic, there is still no consensus on whether prism adaptation is an effective therapy for visuospatial neglect. We have addressed this question through a meta-analysis of the most well-controlled studies on the topic. Our main meta-analytic model included studies with a placebo/sham/treatment-as-usual control group from which data from right hemisphere stroke patients and left-sided neglect could be aggregated. The short-term treatment effects on the two commonly used standard tests for neglect, the conventional Behavioural Inattention Test (BIT-C) and cancellation test scores were combined into one random effect model justified by the fact that 89% of the BIT-C score is determined by cancellation tasks. With this approach, we were able to obtain a larger and more homogeneous dataset than previous meta-analyses: sixteen studies including 430 patients. No evidence for beneficial effects of prism adaptation was found. The secondary meta-analysis including data from the Catherine Bergego Scale, a functional measure of activities of daily living, also found no evidence for the therapeutic effects of prism adaptation, although half as many studies were available for this analysis. The results were consistent after the removal of influential outliers, after studies with high risk-of-bias were excluded, and when an alternative measure of effect size was considered. These results do not support the routine use of prism adaptation as a therapy for spatial neglect.

A registered re-examination of the effects of leftward prism adaptation on landmark judgements in healthy people.

It has long been known that active adaptation to a shift of the visual field, caused by laterally-displacing prisms, induces short-term sensorimotor aftereffects. More recent evidence suggests that prism adaptation may also stimulate higher-level changes in spatial cognition, which can modify the spatial biases of healthy people. The first reported, and most replicated, higher-level aftereffect is a rightward shift in the point of subjective equality (PSE) for a perceptual bisection task (the landmark task), following adaptation to leftward prisms. A recent meta-analysis suggests that this visuospatial aftereffect should be robustly induced by an extended period of adaptation to strong leftward prisms (15°, ∼26.8 prism dioptres). However, we have been unable to replicate this effect, suggesting that the effect size estimated from prior literature might be over-optimistic. This Registered Report compared visuospatial aftereffects on the landmark task for a 15° leftward prism adaptation group (n = 102) against a sham-adaptation control group (n = 102). The effect size for the comparison was Cohen's d = .27, 95% CI [-.01, .55], which did not pass the criterion set for significance. A Bayesian analysis indicated that the data were more than 4.1 times as likely under the null than under an informed experimental hypothesis. Exploratory analyses showed no evidence for a rightward shift of landmark judgements in the prism group considered alone, and no relationship between sensorimotor and visuospatial aftereffects. We further found no support for previous suggestions that visuospatial aftereffects are modulated by a person's baseline bias (leftward or rightward) for the landmark task. Null findings are also presented for a preliminary group of 62 participants adapted to 15° leftward prisms, and an additional group of 29 participants adapted to 10° leftward prisms. We do not rule out the possibility that leftward prisms might induce higher-level visuospatial aftereffects in healthy people, but we should be more sceptical about this claim.

Eye Movements as Proxy for Visual Working Memory Usage: Increased Reliance on the External World in Korsakoff Syndrome.

In the assessment of visual working memory, estimating the maximum capacity is currently the gold standard. However, traditional tasks disregard that information generally remains available in the external world. Only when to-be-used information is not readily accessible, memory is taxed. Otherwise, people sample information from the environment as a form of cognitive offloading. To investigate how memory deficits impact the trade-off between sampling externally or storing internally, we compared gaze behaviour of individuals with Korsakoff amnesia (n = 24, age range 47-74 years) and healthy controls (n = 27, age range 40-81 years) on a copy task that provoked different strategies by having information freely accessible (facilitating sampling) or introducing a gaze-contingent waiting time (provoking storing). Indeed, patients sampled more often and longer, compared to controls. When sampling became time-consuming, controls reduced sampling and memorised more. Patients also showed reduced and longer sampling in this condition, suggesting an attempt at memorisation. Importantly, however, patients sampled disproportionately more often than controls, whilst accuracy dropped. This finding suggests that amnesia patients sample frequently and do not fully compensate for increased sampling costs by memorising more at once. In other words, Korsakoff amnesia resulted in a heavy reliance on the world as 'external memory'.

The mobility assessment course: A ready-to-use dynamic measure of visuospatial neglect.

The Mobility Assessment Course (MAC) is a tool to measure visuospatial neglect in a dynamic fashion. Although the MAC has been shown to dissociate between patients with and without neglect, it remains unclear whether it is applicable in clinical settings. We evaluated the MAC regarding its (1) feasibility as a diagnostic tool as part of standard care, (2) construct validity, and (3) underlying constructs and potential confounders. A consecutive sample of stroke patients admitted to inpatient rehabilitation completed the MAC, shape cancellation, line bisection, and/or Catherine Bergego Scale (CBS) as part of the standard assessment. To assess feasibility, we computed the percentage of patients who completed the MAC. Construct validity was tested by evaluating MAC performance between patients with and without neglect and controls. Finally, a regression analysis was conducted to assess underlying constructs and potential confounders of MAC performance (i.e., level of mobility and lesion side). The MAC was completed by 82% of patients (N = 182/223; of whom 145 completed all tasks). Patients with neglect performed worse on the MAC (indicating more severe neglect) compared to patients without neglect and controls. The MAC had a lower sensitivity and higher specificity than paper-and-pencil tasks and the CBS. Performance on shape cancellation, line bisection, and CBS were predictors of MAC performance. Level of mobility and lesion side did not predict MAC scores, indicating that these factors do not confound its reliability. To conclude, the MAC is an easy-to-implement tool to evaluate neglect in a dynamic manner, which can be administered in addition to conventional paper-and-pencil tasks.

The orienting response drives pseudoneglect-Evidence from an objective pupillometric method.

Spatial attention is generally slightly biased leftward ("pseudoneglect"), a phenomenon typically assessed with paper-and-pencil tasks, limited by the requirement of explicit responses and the inability to assess on a subsecond timescale. Pseudoneglect is often stable within experiments, but differs vastly between investigations and is sometimes directed to the left, sometimes to the right. To date, no exhaustive explanation to this phenomenon has been provided. Here, we objectively assessed lateralized attention over time, exploiting the phenomenon that changes in the pupil reflect the allocation of attention in space. Pupil sizes of 41 healthy participants fixating the center were influenced stronger by the differential background luminance of the left side compared to the right side of the visual display. These differences were mainly driven by visual information in the periphery. Differences in pupil sizes positively related with greyscales scores. Time-based analyses within trials show strongest effects early on. With increasing trial number (not time), the initial leftward bias shifted central in pupillometry-based and greyscales measures. This suggests that the orienting response determines the degree of attention bias. In our amplification hypothesis we pose that the quality of pseudoneglect (i.e., the direction) is determined by higher order factors such as hemispheric imbalances, whereas the quantity (i.e., the degree) is determined by the orienting network. This account might explain numerous-previously thought opposing-findings. We here show how pupil light responses reveal pseudoneglect, in a next step, this might allow clinical diagnosis of hemispatial neglect.