Presaccadic Attention Depends on Eye Movement Direction and Is Related to V1 Cortical Magnification.

With every saccadic eye movement, humans bring new information into their fovea to be processed with high visual acuity. Notably, perception is enhanced already before a relevant item is foveated: During saccade preparation, presaccadic attention shifts to the upcoming fixation location, which can be measured via behavioral correlates such as enhanced visual performance or modulations of sensory feature tuning. The coupling between saccadic eye movements and attention is assumed to be robust and mandatory and considered a mechanism facilitating the integration of pre- and postsaccadic information. However, until recently it had not been investigated as a function of saccade direction. Here, we measured contrast response functions during fixation and saccade preparation in male and female observers and found that the pronounced response gain benefit typically elicited by presaccadic attention is selectively lacking before upward saccades at the group level-some observers even showed a cost. Individual observer's sensitivity before upward saccades was negatively related to their amount of surface area in primary visual cortex representing the saccade target, suggesting a potential compensatory mechanism that optimizes the use of the limited neural resources processing the upper vertical meridian. Our results raise the question of how perceptual continuity is achieved and how upward saccades can be accurately targeted despite the lack of-theoretically required-presaccadic attention.

Saccadic re-referencing training with gaze-contingent FRL-'fixation': Effects of scotoma type and size adaptation.

Foveal vision loss makes the fovea as saccadic reference point maladaptive. Training programs have been proposed that shift the saccadic reference point from the fovea to an extrafoveal location, just outside the area of vision loss. We used a visual search task to train normal-sighted participants to fixate target items with a predetermined 'forced retinal location' (FRL) adjacent to a simulated central scotoma. We found that training was comparatively successful for scotomata that had either a sharp or blurry demarcation from the background. Completing the task with sharp-edged scotoma resulted in overall higher training gains. Training with blurry-edged scotoma, however, yielded overall better results when scotoma size was increased after training and participants needed to adapt to a more eccentric FRL, as may be necessary in patients with progressive degenerative eye diseases.

The Effect of Stimulus Contrast and Spatial Position on Saccadic Eye Movement Parameters.

(1) Background: Saccadic eye movements are rapid eye movements aimed to position the object image on the central retina, ensuring high-resolution data sampling across the visual field. Although saccadic eye movements are studied extensively, different experimental settings applied across different studies have left an open question of whether and how stimulus parameters can affect the saccadic performance. The current study aims to explore the effect of stimulus contrast and spatial position on saccadic eye movement latency, peak velocity and accuracy measurements. (2) Methods: Saccadic eye movement targets of different contrast levels were presented at four different spatial positions. The eye movements were recorded with a Tobii Pro Fusion video-oculograph (250 Hz). (3) Results: The results demonstrate a significant effect of stimulus spatial position on the latency and peak velocity measurements at a medium grey background, 30 cd/m2 (negative and positive stimulus polarity), light grey background, 90 cd/m2 (negative polarity), and black background, 3 cd/m2 (positive polarity). A significant effect of the stimulus spatial position was observed on the accuracy measurements when the saccadic eye movement stimuli were presented on a medium grey background (negative polarity) and on a black background. No significant effect of stimulus contrast was observed on the peak velocity measurements under all conditions. A significant stimulus contrast effect on latency and accuracy was observed only on a light grey background. (4) Conclusions: The best saccadic eye movement performance (lowest latency, highest peak velocity and accuracy measurements) can be observed when the saccades are oriented to the right and left from the central fixation point. Furthermore, when presenting the stimulus on a light grey background, a very low contrast stimuli should be considered carefully.

Opposing functions of glutamatergic inputs between the globus pallidus external segment and substantia nigra pars reticulata.

The indirect pathway of the basal ganglia, including the subthalamic nucleus (STN) and globus pallidus external segment (GPe), is believed to play a crucial role in suppressing involuntary movements. However, recent evidence suggests the STN and GPe also facilitate voluntary movements. This study hypothesized that excitatory inputs from the STN to the GPe contribute to this facilitation, and that excitatory projections to the substantia nigra pars reticulata (SNr) are involved in the inhibition. To disrupt the STN-GPe or STN-SNr projections in monkeys during choice and fixation tasks, glutamate receptor inhibitors were injected into the GPe or SNr, which induced delayed saccade latencies toward good choices in the choice task (GPe) and caused frequent reflexive saccades to objects in the fixation task (SNr). Our findings suggest excitatory inputs to the GPe and SNr work in opposing manners, providing new insights that redefine our understanding of the functions of basal ganglia pathways.

Gait control by the frontal lobe.

The frontal lobe is crucial and contributes to controlling truncal motion, postural responses, and maintaining equilibrium and locomotion. The rich repertoire of frontal gait disorders gives some indication of this complexity. For human walking, it is necessary to simultaneously achieve at least two tasks, such as maintaining a bipedal upright posture and locomotion. Particularly, postural control plays an extremely significant role in enabling the subject to maintain stable gait behaviors to adapt to the environment. To achieve these requirements, the frontal cortex (1) uses cognitive information from the parietal, temporal, and occipital cortices, (2) creates plans and programs of gait behaviors, and (3) acts on the brainstem and spinal cord, where the core posture-gait mechanisms exist. Moreover, the frontal cortex enables one to achieve a variety of gait patterns in response to environmental changes by switching gait patterns from automatic routine to intentionally controlled and learning the new paradigms of gait strategy via networks with the basal ganglia, cerebellum, and limbic structures. This chapter discusses the role of each area of the frontal cortex in behavioral control and attempts to explain how frontal lobe controls walking with special reference to postural control.

Velocity tracking control best explains the modulation of saccade kinematics during eye-hand coordination.

Fast movements like saccadic eye movements that occur in the absence of sensory feedback are thought to be controlled by internal feedback. Such internal feedback provides an instantaneous estimate of the output, which serves as a proxy for sensory feedback, that can be used by the controller to correct deviations from the desired plan. In the predominant view, the desired plan/input is encoded in the form of a static displacement signal (endpoint model), believed to be encoded in the spatial map of the superior colliculus (SC). However, recent evidence has shown that SC neurons have a dynamic signal that correlates with saccade velocity, suggesting that information for velocity-based control is available for generating saccades. Motivated by this observation, we used a novel optimal control framework to test whether saccadic execution could be achieved by tracking a dynamic velocity signal at the input. We validated this velocity tracking model in a task where the peak saccade velocity was modulated by the speed of a concurrent hand movement independent of the saccade endpoint. A comparison showed that in this task, the velocity tracking model performed significantly better than the endpoint model. These results suggest that the saccadic system may have additional flexibility to incorporate a velocity-based internal feedback control when imposed by task goals or context.

Uncorrected errors and correct saccades in the antisaccade task distinguish between early-stage Alzheimer's disease dementia, amnestic mild cognitive impairment, and normal aging.

Alzheimer's disease (AD) dementia is a degenerative illness that is characterized by a gradual decline in cognitive abilities. Amnestic mild cognitive impairment (aMCI) is seen as a precursor to AD. The changes in antisaccade performance that can be seen in MCI may provide important clues in the early detection of AD. Therefore, the antisaccade deficits in AD and aMCI remain a research question. This study aimed to examine antisaccade responses and the relationship between antisaccade and cognitive function in AD, aMCI, and healthy controls (HC). This study included 30 patients with early-stage AD, 34 with aMCI, and 32 HC. Patients with AD showed higher rates of uncorrected error, anticipatory saccades and corrected errors, as well as decreased correct saccade rates, and shortened saccade latency compared to aMCI and HC in this study. Patients with aMCI exhibited increased rates of express saccades relative to HC. The antisaccade task and cognitive domains were found to be significantly related. Our study showed that the rate of correct saccades has the capacity to distinguish AD from HC with 87% sensitivity and 86% specificity (AUC = 0.93, p < 0.001). In addition, the rate of uncorrected errors was found to be capable of distinguishing AD from HC with 84% sensitivity and 83% specificity (AUC = 0.91, p < 0.001). This study presented promising findings that these parameters can be used clinically to differentiate AD and aMCI from healthy older individuals.

Neurologically Healthy Humans' Ability to Make Saccades Toward Unseen Targets.

Some patients with a visual field loss due to a lesion in the primary visual cortex (V1) can shift their gaze to stimuli presented in their blind visual field. The extent to which a similar "blindsight" capacity is present in neurologically healthy individuals remains unknown. Using retinotopically navigated transcranial magnetic stimulation (TMS) of V1 (Experiment 1) and metacontrast masking (Experiment 2) to suppress conscious vision, we examined neurologically healthy humans' ability to make saccadic eye movements toward visual targets that they reported not seeing. In the TMS experiment, the participants were more likely to initiate a saccade when a stimulus was presented, and they reported not seeing it, than in trials which no stimulus was presented. However, this happened only in a very small proportion (∼8%) of unseen trials, suggesting that saccadic reactions were largely based on conscious perception. In both experiments, saccade landing location was influenced by unconscious information: When the participants denied seeing the target but made a saccade, the saccade was made toward the correct location (TMS: 68%, metacontrast: 63%) more often than predicted by chance. Signal detection theoretic measures suggested that in the TMS experiment, saccades toward unseen targets may have been based on weak conscious experiences. In both experiments, reduced visibility of the target stimulus was associated with slower and less precise gaze shifts. These results suggest that saccades made by neurologically healthy humans may be influenced by unconscious information, although the initiation of saccades is largely based on conscious vision.

The spectrum of neurological manifestations and genotype-phenotype correlation in Indian children with Gaucher disease.

Gaucher disease (GD), one of the most frequent autosomal recessive lysosomal storage disorders, occurs due to bi-allelic pathogenic variants in the GBA1. Worldwide, the c.1448T>C (L483P) homozygous pathogenic variant is reported to be associated with neurological GD phenotype. Clinical distinction between GD1 and GD3 may be challenging due to subtle neurological features. Objective methods to evaluate neurological signs and saccades may help in early diagnosis. This study was conducted to assess the neurological phenotype, and its severity using a modified severity scoring tool (mSST), and the genotype-phenotype correlation. A total of 45 children aged 2 years 6 months to 15 years with a confirmed enzymatic and molecular diagnosis of GD with or without therapy were recruited. mSST tool was used to assess the severity of the neurological phenotype. A digital eye movement tracker (View Point Tracker) was used to assess eye movements. Clinical and genetic findings were analyzed. Out of 45 patients, 39 (86.7%) had at least one neurological phenotype detected using the mSST tool, with impairment of cognitive function (68.8%, 31/45) being the commonest feature. Thirty-two of 45 (71%) were assessed for saccadic eye movements using the eye tracker. Of these, 62.5% (20/32) had absent saccades. Four children (8.9%, 4/32) without clinical oculomotor apraxia had absent saccades on the viewpoint eye tracker. Overall, 77.7% (35/45), had homozygosity for c.1448T>C in GBA1 of which 91.4% (32/35) had neurological manifestations. Other alleles associated with neurological phenotype included c.1603C>T(p.R535C), c.1184C>T (p.S395F), c.115+1G>A (g.4234G>A), c.260G>A (p.R87Q) and c.1352A>G (p.Y451C). To conclude, in India, the c.1448T>C pathogenic variant in GBA1 is the commonest  and is associated with neurological phenotype of GD. Therefore, every patient of GD should be assessed using the mSST scoring tool for an early pick up of neurological features. The routine use of a viewpoint eye tracker in children with GD would be useful for early recognition of saccadic abnormalities.

Foveal vision anticipates defining features of eye movement targets.

High-acuity foveal processing is vital for human vision. Nonetheless, little is known about how the preparation of large-scale rapid eye movements (saccades) affects visual sensitivity in the center of gaze. Based on findings from passive fixation tasks, we hypothesized that during saccade preparation, foveal processing anticipates soon-to-be fixated visual features. Using a dynamic large-field noise paradigm, we indeed demonstrate that defining features of an eye movement target are enhanced in the pre-saccadic center of gaze. Enhancement manifested as higher Hit Rates for foveal probes with target-congruent orientation and a sensitization to incidental, target-like orientation information in foveally presented noise. Enhancement was spatially confined to the center of gaze and its immediate vicinity, even after parafoveal task performance had been raised to a foveal level. Moreover, foveal enhancement during saccade preparation was more pronounced and developed faster than enhancement during passive fixation. Based on these findings, we suggest a crucial contribution of foveal processing to trans-saccadic visual continuity: Foveal processing of saccade targets commences before the movement is executed and thereby enables a seamless transition once the center of gaze reaches the target.

Exogenous capture accounts for fundamental differences between pro- and antisaccade performance.

To generate the next eye movement, oculomotor circuits take into consideration the physical salience of objects in view and current behavioral goals, exogenous and endogenous influences, respectively. However, the interactions between exogenous and endogenous mechanisms and their dynamic contributions to target selection have been difficult to resolve because they evolve extremely rapidly. In a recent study (Salinas et al., 2019), we achieved the necessary temporal precision using an urgent variant of the antisaccade task wherein motor plans are initiated early and choice accuracy depends sharply on when exactly the visual cue information becomes available. Empirical and modeling results indicated that the exogenous signal arrives ∼80 ms after cue onset and rapidly accelerates the (incorrect) plan toward the cue, whereas the informed endogenous signal arrives ∼25 ms later to favor the (correct) plan away from the cue. Here, we scrutinize a key mechanistic hypothesis about this dynamic, that the exogenous and endogenous signals act at different times and independently of each other. We test quantitative model predictions by comparing the performance of human participants instructed to look toward a visual cue or away from it under high urgency. We find that, indeed, the exogenous response is largely impervious to task instructions; it simply flips its sign relative to the correct choice, and this largely explains the drastic differences in psychometric performance between the two tasks. Thus, saccadic choices are strongly dictated by the alignment between salience and behavioral goals.

Shortening of Saccades as a Possible Easy-to-Use Biomarker to Detect Risk of Alzheimer's Disease.

BACKGROUND: Wide-ranging functional defects in eye movements have been reported in Alzheimer's disease (AD) dementia. The detection of abnormal eye movements and reading problems may identify persons at risk of AD when clear clinical symptoms are lacking. OBJECTIVE: To examine whether computer-based eye-tracking (ET) analysis of King-Devick (KD) test results differentiates cognitively healthy persons from persons with minor problems in cognitive testing or diagnosed mild AD. METHODS: We recruited 78 participants (57 non-demented, 21 with mild AD) who underwent neurological examination, the Consortium to Establish a Registry for Alzheimer's Disease neuropsychological test battery (CERAD-NB), and a Clinical Dementia Rating (CDR) interview. The non-demented participants were further divided into control (normal CERAD subtests, mean MMSE = 28) and objective mild cognitive impairment (MCI; decline in at least one CERAD memory score, mean MMSE = 27) groups. The KD reading test was performed using computer-based ET. The total time used for the reading test, errors made, fixation and saccade durations, and saccade amplitudes were analyzed. RESULTS: We found significant differences between the control, objective MCI, and AD groups in regard to the mean saccade amplitude (3.58, 3.33, and 3.21 ms, respectively, p < 0.03) and duration (27.1, 25.3, and 24.8 ms, respectively, p < 0.05). The KD error scores in the AD group differed significantly (p < 0.01) from the other groups. CONCLUSION: Computed ET analysis of the KD test may help detect persons with objective MCI early when clear clinical symptoms are lacking. The portable device for ET is easy to use in primary health care memory clinics.

The effect of spatial structure on presaccadic attention costs and benefits assessed with dynamic 1/f noise.

Already before the onset of a saccadic eye movement, we preferentially process visual information at the upcoming eye fixation. This 'presaccadic shift of attention' is typically assessed via localized test items, which potentially bias the attention measurement. Here we show how presaccadic attention shapes perception from saccade origin to target when no scene-structuring items are presented. Participants made saccades into a 1/f ('pink') noise field, in which we embedded a brief orientation signal at various locations shortly before saccade onset. Local orientation discrimination performance served as a proxy for the allocation of attention. Results demonstrate that (1) the presaccadic attention shift is accompanied by considerable attentional costs at the presaccadic eye fixation; (2) saccades are preceded by shifts of attention to their goal location even if they are directed into an unstructured visual field, but the spread of attention, compared to target-directed saccades, is broad; We conclude that the absence or presence of saccade target objects markedly shapes the distribution of presaccadic attention, and likely the underlying (space-based or object-based) cortical control mechanism. Our findings demonstrate the relevance of an item-free approach for measuring attentional dynamics across the visual field.

Video head impulse test in bilateral vestibulopathy / Teste do impulso efálico com vídeo (vHIT) na vestibulopatia bilateral

Abstract Introduction: Bilateral vestibulopathy is a rare chronic condition with multiple etiologies. Bilateral vestibulopathy is characterized mainly by unsteadiness when walking or standing, which worsens in darkness, as well as oscillopsia. The degree of handicap caused by bilateral vestibulopathy is variable and remains controversial. Objectives: To determine the value of the video Head Impulse Test in quantifying vestibular deficit and to establish its impact on the quality of life. Methods: Twenty patients (mean age, 41.9 years; range 14-80 years) fulfilling the recent Barany criteria of bilateral vestibulopathy, responded to the Situational Vertigo Questionnaire and underwent vestibular examination including fixation, positional tests, oculomotor test battery and video head impulse test. Results: The relation between each of the video head impulse test parameters and the scores from the questionnaire were statistically analyzed. We observed that patients with covert saccades on the video head impulse test were more likely to have a better quality of life than those with both covert and overt saccades, regardless of the vestibulo-ocular reflex gain in each semicircular canal. The presence of covert saccades was found to be associated with an improved quality of life regardless of the severity of vestibule ocular reflex-deficit. Our conclusion was that vestibule ocular reflex gain, measured by video head impulse test, does not quantify the severity of affection of quality of life in patients with bilateral vestibulopathy. Conclusion: Covert saccades are strategies aiming at minimizing the blurring of vision during head movement, that is an adaptive mechanism that improves quality of life. Therefore, we recommend that video head impulse test should be a part of the routine diagnostic workup of bilateral vestibulopathy.

Resumo Introdução: A vestibulopatia bilateral é uma condição crônica rara, com múltiplas etiologias. É caracterizada principalmente por instabilidade ao caminhar ou ficar de pé, que piora na escuridão, e oscilopsia. O grau de deficiência causado pela vestibulopatia bilateral é variável e permanece controverso. Objetivos: Determinar o valor do teste do impulso cefálico na quantificação do déficit vestibular e estabelecer seu impacto na qualidade de vida. Método: Vinte pacientes (média de 41,9 anos; variação de 14 a 80) que atendiam aos critérios recentes da Bárány Society de vestibulopatia bilateral responderam ao Situational Vertigo Questionnaire e foram submetidos a exame vestibular, inclusive fixação, testes posicionais, bateria de testes oculomotores e teste do impulso cefálico com vídeo. Resultados: A relação entre cada um dos parâmetros do teste do impulso cefálico com vídeo e os escores do questionário foram analisados estatisticamente. Observamos que pacientes com sacadas corretivas cobertas do tipo covert no teste de impulso cefálico com vídeo tinham maior probabilidade de ter melhor qualidade de vida do que aqueles com ambas sacadas corretivas cobertas e sacadas corretivas abertas do tipo overt, independentemente do ganho no reflexo vestíbulo-ocular em cada canal semicircular. Verificou-se que a presença de sacadas corretivas do tipo covert está associada a uma melhor qualidade de vida, independentemente da gravidade do déficit no reflexo vestibulo-ocular. Concluímos que o ganho no reflexo vestíbulo-ocular, medido pelo teste do impulso cefálico com vídeo, não quantifica a gravidade do comprometimento da qualidade de vida em pacientes com vestibulopatia bilateral. Conclusão: As sacadas corretivas do tipo covert são estratégias que visam minimizar o embaçamento da visão durante o movimento da cabeça, ou seja, um mecanismo adaptativo que melhora a qualidade de vida. Portanto, recomendamos que o teste do impulso cefálico com vídeo faça parte da rotina de diagnóstico da vestibulopatia bilateral.

Vestibular and oculomotor function in male combat sport athletes.

OBJECTIVES: To investigate for differences in vestibulo-ocular function between active male combat sport athletes and a healthy control group. In addition, to explore the relationship between symptom-based outcome measures with vestibulo-ocular function. DESIGN: Cross-sectional. METHODS: 40 male adult combat sport athletes and 40 active male control participants were recruited from 4 martial arts schools and a University campus in Queensland, Australia. All participants completed a standardised protocol which was used to assess vestibulo-ocular function. The protocol included 3 components: 1) oculomotor function, 2) benign paroxysmal positional vertigo screening, and 3) vestibulo-ocular reflex function. The Post-Concussion Symptom Scale, Vestibular/Ocular Motor Screening tool and Dizziness Handicap Inventory were used as symptom-based outcome measures. RESULTS: More combat sport athletes had oculomotor abnormalities than control group participants. There were no between group differences in benign paroxysmal positional vertigo, vestibulo-ocular reflex function and the video-head impulse test gain (ms). Combat sport athletes had higher symptom-based outcome scores. The Vestibular/Ocular Motor Screening tool and Dizziness Handicap Inventory were found to have moderate positive relationships with the total number of abnormalities detected in the combat sport group. CONCLUSIONS: Vestibulo-ocular function is imperative for combat sport athletes to perform evasive manoeuvres and land their own strikes. The present study findings may aid clinicians in the identification of combat sport athletes with underlying vestibulo-ocular dysfunction, prompting further investigation.

Video head impulse test in bilateral vestibulopathy.

INTRODUCTION: Bilateral vestibulopathy is a rare chronic condition with multiple etiologies. Bilateral vestibulopathy is characterized mainly by unsteadiness when walking or standing, which worsens in darkness, as well as oscillopsia. The degree of handicap caused by bilateral vestibulopathy is variable and remains controversial. OBJECTIVES: To determine the value of the video Head Impulse Test in quantifying vestibular deficit and to establish its impact on the quality of life. METHODS: Twenty patients (mean age, 41.9 years; range 14-80 years) fulfilling the recent Barany criteria of bilateral vestibulopathy, responded to the Situational Vertigo Questionnaire and underwent vestibular examination including fixation, positional tests, oculomotor test battery and video head impulse test. RESULTS: The relation between each of the video head impulse test parameters and the scores from the questionnaire were statistically analyzed. We observed that patients with covert saccades on the video head impulse test were more likely to have a better quality of life than those with both covert and overt saccades, regardless of the vestibulo-ocular reflex gain in each semicircular canal. The presence of covert saccades was found to be associated with an improved quality of life regardless of the severity of vestibule ocular reflex-deficit. Our conclusion was that vestibule ocular reflex gain, measured by video head impulse test, does not quantify the severity of affection of quality of life in patients with bilateral vestibulopathy. CONCLUSION: Covert saccades are strategies aiming at minimizing the blurring of vision during head movement, that is an adaptive mechanism that improves quality of life. Therefore, we recommend that video head impulse test should be a part of the routine diagnostic workup of bilateral vestibulopathy.

Spontaneous modulations of high-frequency cortical activity.

OBJECTIVE: We clarified the clinical and mechanistic significance of physiological modulations of high-frequency broadband cortical activity associated with spontaneous saccadic eye movements during a resting state. METHODS: We studied 30 patients who underwent epilepsy surgery following extraoperative electrocorticography and electrooculography recordings. We determined whether high-gamma activity at 70-110 Hz preceding saccade onset would predict upcoming ocular behaviors. We assessed how accurately the model incorporating saccade-related high-gamma modulations would localize the primary visual cortex defined by electrical stimulation. RESULTS: The dynamic atlas demonstrated transient high-gamma suppression in the striatal cortex before saccade onset and high-gamma augmentation subsequently involving the widespread posterior brain regions. More intense striatal high-gamma suppression predicted the upcoming saccade directed to the ipsilateral side and lasting longer in duration. The bagged-tree-ensemble model demonstrated that intense saccade-related high-gamma modulations localized the visual cortex with an accuracy of 95%. CONCLUSIONS: We successfully animated the neural dynamics supporting saccadic suppression, a principal mechanism minimizing the perception of blurred vision during rapid eye movements. The primary visual cortex per se may prepare actively in advance for massive image motion expected during upcoming prolonged saccades. SIGNIFICANCE: Measuring saccade-related electrocorticographic signals may help localize the visual cortex and avoid misperceiving physiological high-frequency activity as epileptogenic.

Saccadic Eye Movements in Young-Onset Parkinson's Disease - A BOLD fMRI Study.

The objective of the present study was to understand control of saccadic eye movements in patients with young onset Parkinson's disease (YOPD) where onset of disease symptoms appears early in life (<40 years of age). Functional magnetic resonance imaging (fMRI) was performed in patients with YOPD and control subjects while they performed saccadic tasks, which consisted of a reflexive task and another task that required inhibitory control of eye movements (Go-NoGo task). Functional imaging related to saccadic eye movements in this group of patients has not been widely reported. A 1.5T MR scanner was used for structural and functional imaging. Analysis of blood-oxygen-level-dependent (BOLD) fMRI was performed using Statistical Parametric Mapping (SPM) software and compared in patients and controls. In patients with YOPD greater activation was seen significantly in the middle frontal gyrus, medial frontal gyrus, angular gyrus, cingulate gyrus, precuneus and cerebellum, when compared with the control group, during the saccadic tasks. Gap and overlap protocols revealed differential activation patterns. The abnormal activation during reflexive saccades was observed in the overlap condition, while during Go-NoGo saccades in the gap condition. The results suggest that impaired circuitry in patients with YOPD results in recruitment of more cortical areas. This increased frontal and parietal cortical activity possibly reflects compensatory mechanisms for impaired cognitive and saccadic circuitry.

Wearing a head-mounted eye tracker may reduce body sway.

This study investigated the effects of wearing a head-mounted eye tracker on upright balance during different visual tasks. Twenty five young adults stood upright on a force plate while performing the visual tasks of fixation, horizontal saccades, and eyes closed, during eighteen trials wearing or not a head-mounted eye tracker. While wearing the eye tracker, participants showed a reduction in mean sway amplitude and velocity of the CoP in the AP and ML directions and more regular CoP fluctuations, in the ML axis in all conditions. Higher mean sway amplitude and velocity of CoP were observed during eyes closed than fixation and saccades. Moreover, horizontal saccades reduced mean sway velocity of CoP compared to fixation. Therefore, wearing the eye tracker minimized the body sway of young adults; however, visual task-related effects on postural stability remained unchanged.

Visual processing speed in hemianopia patients secondary to acquired brain injury: a new assessment methodology.

BACKGROUND: There is a clinical need to identify diagnostic parameters that objectively quantify and monitor the effective visual ability of patients with homonymous visual field defects (HVFDs). Visual processing speed (VPS) is an objective measure of visual ability. It is the reaction time (RT) needed to correctly search and/or reach for a visual stimulus. VPS depends on six main brain processing systems: auditory-cognitive, attentional, working memory, visuocognitive, visuomotor, and executive. We designed a new assessment methodology capable of activating these six systems and measuring RTs to determine the VPS of patients with HVFDs. METHODS: New software was designed for assessing subject visual stimulus search and reach times (S-RT and R-RT respectively), measured in seconds. Thirty-two different everyday visual stimuli were divided in four complexity groups that were presented along 8 radial visual field positions at three different eccentricities (10o, 20o, and 30o). Thus, for each HVFD and control subject, 96 S- and R-RT measures related to VPS were registered. Three additional variables were measured to gather objective data on the validity of the test: eye-hand coordination mistakes (ehcM), eye-hand coordination accuracy (ehcA), and degrees of head movement (dHM, measured by a head-tracker system). HVFD patients and healthy controls (30 each) matched by age and gender were included. Each subject was assessed in a single visit. VPS measurements for HFVD patients and control subjects were compared for the complete test, for each stimulus complexity group, and for each eccentricity. RESULTS: VPS was significantly slower (p < 0.0001) in the HVFD group for the complete test, each stimulus complexity group, and each eccentricity. For the complete test, the VPS of the HVFD patients was 73.0% slower than controls. They also had 335.6% more ehcMs, 41.3% worse ehcA, and 189.0% more dHMs than the controls. CONCLUSIONS: Measurement of VPS by this new assessment methodology could be an effective tool for objectively quantifying the visual ability of HVFD patients. Future research should evaluate the effectiveness of this novel method for measuring the impact that any specific neurovisual rehabilitation program has for these patients.