Quadrant Of Visual Field Research Articles

Comparing a Head-Mounted Smartphone Visual Field Analyzer to Standard Automated Perimetry in Glaucoma: A Prospective Study.

Wang et al compare an FDA-registered head-mounted smartphone device (PalmScan VF2000) with standard automated perimetry (SAP) in glaucoma patients and find that the head-mounted device may not fully recapitulate SAP testing. This study prospectively compared visual field testing using the PalmScan VF2000 Visual Field Analyzer, a head-mounted smartphone device, with standard automated perimetry (SAP). Patients with glaucoma undergoing Humphrey Field Analyzer SAP testing were asked to complete in-office PalmScan testing using a Samsung S5 smartphone in a virtual reality-style headset. Glaucoma severity was defined as SAP mean deviation (MD) >-6 dB for mild, between -6 and -12 dB for moderate, and <-12 dB for severe. Global parameters MD and pattern SD from PalmScan and SAP were compared using t -tests and Bland-Altman analyses. Bland-Altmann analyses of PalmScan and SAP MD were conducted for the superonasal, superotemporal, inferonasal, and inferotemporal visual field quadrants. The repeatability of PalmScan was assessed using Spearman's correlations and intraclass correlation coefficients (ICCs). Fifty-one patients (51 eyes) completed both SAP and PalmScan testing and met the criteria for analysis. Compared with SAP, global MD and pattern SD measurements from PalmScan differed by an average of +0.62±0.26 dB (range: -3.25 to +4.60 dB) and -1.00±0.24 dB (range: -6.03 to +2.77 dB), respectively, while MD scores from individual visual field quadrants differed by as much as -6.58 to +11.43 dB. The agreement between PalmScan and SAP in classifying glaucoma severity was 86.3% across all eyes. PalmScan and SAP identified the same quadrant as having the worst visual field defect in 66.7% of eyes. Despite advantages in cost and accessibility, the PalmScan head-mounted perimetry device may not be able to fully recapitulate SAP testing.

Diffusion spectrum imaging based semi-automatic optic radiation tractography for vision preservation in SEEG-guided radiofrequency thermocoagulation

ObjectiveTo assess the efficacy and safety of stereoelectroencephalography (SEEG)-guided radiofrequency thermocoagulation (RFTC), using diffusion spectrum imaging (DSI) tractography to preoperatively delineate the optic radiation (OR) and reduce the risk of visual field defects (VFDs) where the epileptogenic zones (EZs) are located in or close to the eloquent visual areas. MethodsWe prospectively followed up twenty-four consecutive patients (12 males and 12 females) who underwent SEEG-guided RFTC in or near the OR pathway. A distance of ≥ 3.5 mm away from the OR on the targeted electrodes contacts that exhibited relevant ictal onset patterns, IEDs and EES during SEEG recordings, was required as our selection criterion prior to performing RFTC, enough to theoretically prevent VFDs. Using default tracking parameters, the optic radiation was tracked semi-automatically in DSI-studio. ResultsThere were 12 male and 12 female patients ranging in age from 6 to 57 years, with follow-up period ranging from 6 to 37 months. Nineteen patients responded to RFTC (R+, 79.16 %), and 5 patients did not benefit from RFTC (R-, 20.83 %). The preoperative application of DSI semi-automatic based OR tractography was successful in the protection of the OR in all 24 patients. Three patients experienced a neurologic deficit following RFTC, and five patients had a partial quadrant visual field deficit prior to surgery that did not worsen, and none of the remaining nineteen patients had a quadrant visual field deficit. ConclusionOur study validates the safety and efficacy of SEEG-RFTC as a viable therapeutic approach for epileptic foci situated in or adjacent to the visual eloquent regions. We demonstrate that DSI-based tractography offers superior precision in delineating the OR compared to DTI. We establish that implementing a criterion of a minimum distance of ≥ 3.5 mm in radius from the OR on the targeted electrode contacts prior to conducting RFTC can effectively mitigate the risk of VFDs.

Fast Optical Signals for Real-Time Retinotopy and Brain Computer Interface.

A brain-computer interface (BCI) allows users to control external devices through brain activity. Portable neuroimaging techniques, such as near-infrared (NIR) imaging, are suitable for this goal. NIR imaging has been used to measure rapid changes in brain optical properties associated with neuronal activation, namely fast optical signals (FOS) with good spatiotemporal resolution. However, FOS have a low signal-to-noise ratio, limiting their BCI application. Here FOS were acquired with a frequency-domain optical system from the visual cortex during visual stimulation consisting of a rotating checkerboard wedge, flickering at 5 Hz. We used measures of photon count (Direct Current, DC light intensity) and time of flight (phase) at two NIR wavelengths (690 nm and 830 nm) combined with a machine learning approach for fast estimation of visual-field quadrant stimulation. The input features of a cross-validated support vector machine classifier were computed as the average modulus of the wavelet coherence between each channel and the average response among all channels in 512 ms time windows. An above chance performance was obtained when differentiating visual stimulation quadrants (left vs. right or top vs. bottom) with the best classification accuracy of ~63% (information transfer rate of ~6 bits/min) when classifying the superior and inferior stimulation quadrants using DC at 830 nm. The method is the first attempt to provide generalizable retinotopy classification relying on FOS, paving the way for the use of FOS in real-time BCI.

Comparison of Visual Field Measurements in Glaucomatous Eyes using Oculus and Metrovision Perimeters.

To investigate the agreement between the Oculus and Metrovision perimeters in the visual field evaluation of glaucoma patients. In this cross-sectional study, 41 consecutive glaucoma patients were enrolled. After detailed clinical examinations, visual field testing was performed for all patients using the Oculus and Metrovision perimeters. The interval time between the two visual field examinations was 30 min. A total of 22 participants were male (53.7%) and the mean ± standard deviation (SD) age was 58.6 ± 9.1 years. The absolute average of the mean deviation (MD) in the oculus perimeter (8.24 ± 4.92 dB) was higher compared to the Metrovision perimeter (4.02 ± 4.62; P < 0.001). This difference was also evident in the Bland-Altman graph. The loss variance (pattern SD) values of Oculus perimeter (28.58 ± 16.40) and Metrovision perimeter (28.10 ± 28.45) were not significantly different; although based on the Bland-Altman plots in the lower MDs, the agreement is better and the data dispersion is lower, and in the higher MDs, the agreement is lower. The parameters of four visual field quadrants were also compared and showed poor correlations (P < 0.001). The Oculus and Metrovision perimeter devices have good agreement in lower MDs; however, they cannot be used interchangeably.

Hyperbaric oxygen treatment for paracentral acute middle maculopathy: a case study

A 47-year-old active-duty Navy diver with a complicated past medical history which resulted in his designation as not physically qualified (NPQ) for diving duty in 2016 presented on 07 May 2021 complaining of left-sided blurred vision. On exam by the attending undersea medical officer he was found to have a left upper inner and upper outer quadrant visual field defect along with a central scotoma. Urgent referral to ophthalmology ruled out retinal detachment but resulted in an initial diagnosis of a left branch retinal artery occlusion without embolus. Considering this a variant of central retinal artery occlusion, hyperbaric oxygen (HBO2) therapy was initiated approximately 12 hours after symptom onset, resulting in complete, though temporary, resolution of the visual field defect. He reported that after completion of his first HBO2 treatment, his visual field deficit began to return, but the deficit again resolved after initiating surface oxygen therapy between HBO2 treatments. After two days of continuous surface oxygen and daily HBO2 treatments, which kept his visual field defect minimized, his deficits changed to a persistent left lateral peripheral defect and a recurrent central nasal defect. At this time, his periodic ophthalmology evaluation revised his diagnosis to cilioretinal artery occlusion (CrAO). Further evaluation by ophthalmology revealed retinal changes consistent with a secondary diagnosis of paracentral acute middle maculopathy (PAMM), an ophthalmologic condition only recently defined in the literature (2013) [10] secondary to advances in retinal imaging technology. This case is presented to share the findings of this complicated case and to postulate a benefit from the use of HBO2 for cilioretinal artery occlusion with PAMM.

Abstract P19: Developing an Innovative Visual Fields Rapid Assessment Device (VRAD) for Acute Telestroke Use

Background: Acute telestroke evaluations rely on the ability to rapidly and accurately calculate the NIH Stroke Scale. Remote visual field deficit (VFD) testing is often challenging, requiring trained bedside assistance particularly in rural hospital settings. These deficits account for up to 3 points on the NIHSS, which is enough to affect treatment decisions and impact outcomes. Objective: To create a simple, rapid, and robust screening telemedicine peripheral device to standardize visual field testing during acute telestroke consults and to reduce reliance on bedside assistants for this task. Methods: A one-size-fits-all device was designed such that an LED stimulus is located in each quadrant of the peripheral visual field. Bioengineers, neuro-ophthalmologists, and vascular neurologists collaborated in the development of the prototype. A randomized investigator-blinded pilot clinical trial is in progress. Stroke patients with fully-mapped visual fields were selected. The device, in the form of glasses, is easily placed on the patient’s face, and LED lights are flashed in the standard 8 fields, via a repeatable algorithm, during a simulated acute telestroke encounter. Lights are visible to the remote teleprovider for interpretation of the responses. Patients and examiners will be surveyed for feedback on ease of use of the device (primary outcome). Results from device will be compared to in-person confrontational testing and to previously recorded Humphrey mapped deficits in this same patient population (secondary). Validation is set at a sensitivity of 90% compared to confrontational or to the Humphrey static visual field test results. Results/Conclusion: Remote testing of VFDs in acute telestroke patients is difficult, especially in smaller community rural hospitals. We developed a simple and rapidly applied facial device that can assist the teleprovider in VFD evaluations, potentially affecting treatment options of thrombectomy, thrombolytics, or transfer. An on-going pilot study will test the sensitivity of the device against confrontational and static VF assessments. Innovative telestroke peripherals represent the future of the next generation of diagnostic tools specifically engineered fo remote acute stroke patient evaluations.

An electrophysiological biomarker for the classification of cataract-reversal patients: A case-control study.

BackgroundUntreated congenital blindness through cataracts leads to lasting visual brain system changes, including substantial alterations of extrastriate visual areas. Consequently, late-treated individuals (> 5 months of age) with dense congenital bilateral cataracts (CC) exhibit poorer visual function recovery compared to individuals with bilateral developmental cataracts (DC). Reliable methods to differentiate between patients with congenital and developmental cataracts are often lacking, impeding efficient rehabilitation management and introducing confounds in clinical and basic research on recovery prognosis and optimal timing of surgery. A persistent reduction of the P1 wave of visual event-related potentials (VERPs), associated with extrastriate visual cortical activity, has been reported in CC but not in DC individuals. Using two experiments, this study developed and validated P1-based biomarkers for diagnosing a history of congenital blindness in cataract-reversal individuals.MethodsCongenital and developmental cataract-reversal individuals as well as typically sighted matched controls took part in a first experiment used for exploring an electrophysiological biomarker (NCC = 13, NDC = 13, NControl = 26). Circular stimuli containing gratings were presented in one of the visual field quadrants while visual event-related potentials (VERPs) were recorded. Two biomarkers were derived from the P1 wave of the VERP: (1) The mean of the normalized P1 amplitude at posterior electrodes, and (2) a classifier obtained from a linear support vector machine (SVM). A second experiment with partially new CC/DC individuals and their matched controls (NCC = 14, NDC = 15, NControl = 29) was consecutively used to validate the classification based on both biomarkers. Performance of the classifiers were evaluated using receiver operating characteristic (ROC) curve analyses. All cataract-reversal individuals were tested after at least one year of vision recovery.FindingsThe normalized P1 amplitude over posterior electrodes allowed a successful classification of the CC from the DC individuals and typically sighted controls (area under ROC curve, AUC = 0.803 and 0.929 for the normalized P1 amplitude and the SVM-based biomarker, respectively). The validation for both biomarkers in experiment 2 again resulted in a high classification success (AUC = 0.800 and 0.883, respectively for the normalized P1 amplitude and the SVM-based biomarker). In the most conservative scenario involving classification of CC from DC individuals in a group of only cataract-reversal individuals, excluding typically sighted controls, the SVM-based biomarker was found to be superior to the mean P1 amplitude based biomarker (AUC = 0.852 compared to 0.757 for the mean P1 based biomarker in validation). Minimum specificity obtained was 80% across all biomarkers.InterpretationA persistent reduction of the P1 wave provides a highly specific method for classifying cataract patients post-surgically as having suffered from bilateral congenital vs. bilateral developmental cataracts. We suggest that using the P1 based non-invasive electrophysiological biomarker will augment existing clinical classification criteria for individuals with a history of bilateral congenital cataracts, aiding clinical and basic research, recovery prognosis, and rehabilitation efforts.FundingGerman Research Foundation (DFG) and the European Research Council (ERC).

The anterior hippocampus is associated with spatial memory encoding

There are many hypotheses regarding specialization of the anterior versus posterior hippocampus including memory encoding versus retrieval and other cognitive processes versus spatial memory. In the present functional magnetic resonance imaging study, we distinguished between the hypothesis linking encoding to the anterior hippocampus and the hypothesis linking spatial memory to the posterior hippocampus by evaluating whether spatial memory encoding involved the anterior hippocampus or the posterior hippocampus. During encoding, participants viewed abstract shapes in each of four visual field quadrants while instructed to maintain central fixation. During retrieval, old shapes were presented at fixation and participants identified the previous quadrant of each shape. A general linear model analysis did not reveal encoding activations in the anterior or posterior hippocampus. These results motivated a multi-voxel pattern analysis to assess whether there were distinct patterns of activity associated with encoding shapes in each quadrant within the anterior or posterior hippocampus. For each participant, patterns of activity associated with each quadrant were split by run (i.e., odd runs versus even runs) and the patterns in half the data were used to classify patterns in the other half of the data. Classification accuracy for items at encoding, collapsed over subsequent accuracy, was significantly above chance in the anterior but not posterior hippocampus. The present findings indicate that spatial memory encoding is associated with patterns of activity in the anterior hippocampus.

Left-Right and Upper-Lower Light Sensitivity Asymmetry in Visual Field Defects Caused by Pituitary Adenoma: A Retrospective Observational Study.

PurposeThe purpose of this study was to quantitatively investigate light sensitivity asymmetry both between left and right eyes and between upper and lower quadrant in the 30-degree visual field of patients with visual field defects caused by pituitary adenoma.Patients and MethodsPreoperative Humphrey 30–2 perimetry results were reviewed retrospectively using the charts of 28 pituitary adenoma patients who underwent surgery. Inter-eye light sensitivity comparisons of the temporal and nasal hemifields between the left and right eyes were conducted in each patient to study left-right asymmetry. Upper-lower asymmetry was investigated by comparing the frequency of severe scotoma (light sensitivity 5 dB or less) in the upper and lower visual field quadrants in the temporal and nasal hemifields.ResultsLeft-right asymmetry was demonstrated in 61% of cases in the temporal hemifield and in 57% of cases in the nasal hemifield. Severe scotoma test points were investigated in the worse eye of each patient and were more frequent in the superotemporal quadrant of the visual field compared with the inferotemporal quadrant (P = 0.00029) and in the inferonasal quadrant compared to the superonasal quadrant (P = 0.00268).ConclusionAsymmetric visual field defects between left and right eyes are common in patients with pituitary adenoma. Severe scotoma is more frequent in the upper quadrant of the temporal hemifield and in the lower quadrant of the nasal hemifield.

Ocular syphilis in an immunocompetent man.

A healthy 47-year-old immunocompetent man from Northern Canada presented for ophthalmologic assessment after experiencing one month of right-sided photopsias, floaters, and a right lower nasal quadrant visual field defect. Optic disc swelling, vitritis, chorioretinitis, peripheral retinal infiltrates and hemorrhages were noted in the right eye. A broad right inferior arcuate and nasal visual field defect were also present. Fluorescein angiography of the right retina showed dilated disc vessels and staining of the optic disc.Treponemal antibody testing, using chemiluminescent microparticle immunoassay, was highly positive; this was followed by a Venereal Disease Research Laboratory (VDRL) test with a titre of 1:32 and confirmed by Treponema pallidum particle agglutination (TP-PA) test. Testing did not demonstrate any co-infections.Cerebrospinal fluid (CSF) analysis revealed strong reactivity (4+) to the Treponemal antibody by immunofluorescence antibody absorbed (FTA-ABS) test and non-reactivity by CSF VDRL test. Syphilis PCR of CSF was negative. A diagnosis of neurosyphilis was made. He was treated with ceftriaxone 2 grams IV q24h for 14 days. The vitritis gradually improved.Familiarity with syphilis diagnostics is becoming increasingly important, especially given its recent resurgence amongst several at risk groups. This patient’s case highlights that non-reactive CSF VDRL is not a reliable test in the context of positive serum results and a compatible clinical picture. CSF Treponemal tests such as TP-PA and FTA-ABS offer higher sensitivity than non-treponemal tests such as VDRL in the context of CNS involvement and ocular syphilis.

Object-based attention is modulated by shift direction and visual field quadrant

Object-based attention is modulated by shift direction and visual field quadrant

Radial asymmetries in population receptive field size and cortical magnification factor in early visual cortex

Human visual cortex does not represent the whole visual field with the same detail. Changes in receptive field size, population receptive field (pRF) size and cortical magnification factor (CMF) with eccentricity are well established, and associated with changes in visual acuity with eccentricity. Visual acuity also changes across polar angle. However, it remains unclear how RF size, pRF size and CMF change across polar angle. Here, we examine differences in pRF size and CMF across polar angle in V1, V2 and V3 using pRF modeling of human fMRI data. In these visual field maps, we find smaller pRFs and larger CMFs in horizontal (left and right) than vertical (upper and lower) visual field quadrants. Differences increase with eccentricity, approximately in proportion to average pRF size and CMF. Similarly, we find larger CMFs in the lower than upper quadrant, and again differences increase with eccentricity. However, pRF size differences between lower and upper quadrants change direction with eccentricity. Finally, we find slightly smaller pRFs in the left than right quadrants of V2 and V3, though this difference is very small, and we find no differences in V1 and no differences in CMF. Moreover, differences in pRF size and CMF vary gradually with polar angle and are not limited to the meridians or visual field map discontinuities. PRF size and CMF differences do not consistently follow patterns of cortical curvature, despite the link between cortical curvature and polar angle in V1. Thus, the early human visual cortex has a radially asymmetric representation of the visual field. These asymmetries may underlie consistent reports of asymmetries in perceptual abilities.

Diffusion tensor imaging and magnetic resonance spectroscopy in a patient with adult onset tuberous sclerosis complex

Tuberous sclerosis complex (TSC) 1 or TSC2 is mutated in most TSC patients. TSC2 mutations are more frequently associated with worse outcomes, earlier age at seizure onset, more severe intellectual disability, and higher tuber load than TSC1. The degree of white matter involvement is thought to be associated with the severity of neurological impairment. At present, genotype–phenotype correlations and relationship between tuber burden and neurological disability in TSC are debatable. We presented a 43-year-old patient with TSC2 mutation, whose symptom was only incomplete quadrantic visual field deficit in spite of multiple brain tubers. The visual field deficit was thought to be due to a small lesion in the upper medial part of the optic radiation revealed by diffusion tensor imaging. Her brain tubers showed normal findings in magnetic resonance spectroscopy. Our case suggested that neurological and neuropsychiatric manifestations of TSC are affected by the quality rather than number of the lesions. In addition, MRS may be useful to identify the correlation between brain tubers and neurological disability in TSC patients.

Visually evoked responses from the blind field of hemianopic patients

Hemianopia is a visual field defect characterized by decreased vision or blindness in the contralesional visual field of both eyes. The presence of well documented above-chance unconscious behavioural responses to visual stimuli presented to the blind hemifield (blindsight) has stimulated a great deal of research on the neural basis of this important phenomenon. The present study is concerned with electrophysiological responses from the blind field. Since previous studies found that transient Visual Evoked Potentials (VEPs) are not entirely suitable for this purpose here we propose to use Steady-State VEPs (SSVEPs). A positive result would have important implications for the understanding of the neural bases of conscious vision. We carried out a passive SSVEP stimulation with healthy participants and hemianopic patients. Stimuli consisted of four black-and-white sinusoidal Gabor gratings presented one in each visual field quadrant and flickering one at a time at a 12Hz rate. To assess response reliability a Signal-to-Noise Ratio analysis was conducted together with further analyses in time and frequency domains to make comparisons between groups (healthy participants and patients), side of brain lesion (left and right) and visual fields (sighted and blind).The important overall result was that stimulus presentation to the blind hemifield yielded highly reliable responses with time and frequency features broadly similar to those found for cortical extrastriate areas in healthy controls. Moreover, in the intact hemifield of hemianopics and in healthy controls there was evidence of a role of prefrontal structures in perceptual awareness. Finally, the presence of different patterns of brain reorganization depended upon the side of lesion.

Do areas of retinal ganglion cell degeneration coincide with areas of decreased representation in V1 following stroke?

Stroke in the territory of the posterior cerebral artery leads to cortical blindness in a hemifield or quadrant of the contralesional visual field. While about 50% of patients experience some degree of visual recovery within the first 6 months post-stroke, only 12.5% experience complete recovery (Tiel K., Kolmel, 1990). One limiting factor that may prevent further visual recovery is trans-synaptic retrograde degeneration of retinal ganglion cells, which has been observed in stroke patients starting as early as 3 months after stroke (Jindahra, Petrie, & Plant, 2009, 2012; Park, Park, Cho, & Park, 2013; Tanito & Ohira, 2013; Yamahachi, Marik, McManus, Denk, & Gilbert, 2009). Retinal ganglion cell thickness is easily measured in the clinic with optical coherence tomography, a technique that generates a 3-D image of the retina from which the thickness of the retinal ganglion cell complex can be measured. The visual cortex is organized in a retinotopic manner that can be measured with fMRI by presenting visual stimuli in various locations in the participant's visual field and then determining the stimulus location for which each voxel maximally responds (Sereno et al., 1995). Here we test the hypothesis that chronic stroke patients exhibit a homonymous decrease in retinal ganglion cell thickness specifically for visual locations with poor representation in V1. This research has implications for timely rehabilitative treatment because once the retina degenerates, visual recovery in that retinotopic location is impossible. Furthermore, this research may highlight the need for novel treatment strategies that prevent retinal ganglion cell degeneration in order to prolong the window of effective rehabilitation.

Retinotopic fMRI Reveals Visual Dysfunction and Functional Reorganization in the Visual Cortex of Mild to Moderate Glaucoma Patients.

To investigate retinotopic functional representation in the visual cortex of mild to moderate primary open-angle glaucoma (POAG) participants and age-matched normal volunteers using high-resolution retinotopic blood oxygenation level dependent (BOLD) functional magnetic resonance imaging (fMRI). fMRI was performed on 9 POAG participants (61±11 y old) and 9 age-matched controls (58±5 y old) were studied. A wide-view visual presentation (±55 degrees) was used to evaluate central and peripheral vision. Cortical magnification factors and BOLD% changes as a function of eccentricity. Correlation analysis between BOLD% changes and visual field scores, and between BOLD% changes and retinal nerve fiber layer thicknesses was performed. Comparison of BOLD% changes for individual visual field quadrants between POAG subgroups and normal group was performed. BOLD% changes of POAG participants in peripheral visual regions were reduced compared to normals but similar in central visual regions, consistent with the notion of peripheral vision being affected first and more compared to central vision. fMRI retinotopic mapping revealed enlarged representation of the parafovea in the visual cortex of POAG participants compared to normals. Cortical magnification of the central, but not peripheral, visual representation in the visual cortex was larger in POAG participants, suggesting functional remapping. BOLD% changes of individual visual field quadrants were significantly correlated with visual field scores and with retinal nerve fiber layer thickness in the corresponding quadrants. These results support the hypothesis that there are functional alteration and remapping in the topographic representation of the visual cortex in POAG participants, and these changes are correlated with disease severity.

Long-term Repeatability and Reproducibility of Phosphene Characteristics in Chronically Implanted Argus II Retinal Prosthesis Subjects

Previously published literatures of acute studies on few subjects have shown contradictory evidence on the reproducibility and characteristics of the elicited phosphenes, despite using the same stimulating parameters with epiretinal electrode arrays. In this study, we set out to investigate the long-term repeatilibity and reproducibility of phosphenes in subjects chronically implanted with the Argus II retinal prosthesis (Second Sight Medical Products, Inc., Sylmar, CA, USA). Retrospective interventional case series and reliability study. Six Argus II subjects of >5 years implantation from a single site participated. The 4-electrode cluster ("quad") closest to fovea was stimulated in each subject with a fixed biphasic current. Perceived phosphenes were depicted relative to subjective visual field center. The stimulus was applied at reducing time intervals from 20minutes to 1 second. Two sets of stimulations were performed on the same day and 2 further sets repeated on a separate visit >1week apart. Each subject depicted phosphenes of consistent shapes and sizes, and reported seeing the same colors with the fixed stimulating parameters, irrespective of the interstimuli intervals. However, there is a wide intersubject variation in the phosphene characteristics. Four subjects drew phosphenes in the same visual field quadrant, as predicted by the quad-fovea location. Two subjects depicted phosphenes in the same hemifield as the expected locations. Phosphenes for each subject were consistently reproducible in all our chronically implanted subjects. This has important implications in the development of long-term pixelated prosthetic vision for future devices.

On the Differentiation of Foveal and Peripheral Early Visual Evoked Potentials.

The C1 is one of the earliest visual evoked potentials observed following the onset of a patterned stimulus. The polarity of its peak is dependent on whether stimuli are presented in the upper or lower regions of the peripheral visual field, but has been argued to be negative for stimuli presented to the fovea. However, there has yet to be a systematic investigation into the extent to which the peripheral C1 (pC1) and foveal C1 (fC1) can be differentiated on the basis of response characteristics to different stimuli. The current study employed checkerboard patterns (Exp 1) and sinusoidal gratings of different spatial frequency (Exp 2) presented to the fovea or within one of the four quadrants of the peripheral visual field. The checkerboard stimuli yielded a sizable difference in peak component latency, with the fC1 peaking~32ms after the pC1. Further, the pC1 showed a band-pass response magnitude profile that peaked at 4 cycles per degree (cpd), whereas the fC1 was high-pass for spatial frequency, with a cut-off around 4cpd. Finally, the scalp topographies of the pC1 and fC1 in both experiments differed greatly, with the fC1 being more posterior than the pC1. The results reported here call into question recent attempts to characterize general C1 processes without regard to whether stimuli are placed in the fovea or in the periphery.

Hemifield-specific resources for controlling apparent motion

The visual hemifields contain processing resources that are substantially independent across a handful of tasks, such as object tracking and extraction of visual statistics. We add a new task to this category - the ability to control ambiguous apparent motion. Participants viewed two simultaneous and identical dot quartet animations (300ms/frame) where each could be perceived as undergoing either vertical or horizontal motion. The default percept of such dual animations is to see both quartets move in the same manner, and careful mental control is needed to perceive them as moving differently. Each trial began with a cue for mental control: see this quartet moving vertically, and that quartet moving horizontally. The dependent measure was the amount of proximity-based 'help' (making dots closer either vertically or horizontally) that a participant needed to add using the method of adjustment, before they were confident that they could robustly perceive the cued motion pattern differently across the two quartets. This threshold level of needed help was lower when the quartets straddled the hemifield boundary in the lower visual field (mean aspect ratio of 1:1.2), compared to when the quartets were contained entirely within the left or right quadrant of the lower visual field (mean aspect ratio of 1:1.3), p< 0.05 with eccentricity controlled between conditions. We speculate that the separate resources that underlie this benefit for apparent motion share roots with the resources that bring hemifield benefits for object tracking tasks - more efficient deployment of multiple attentional 'spotlights' across the hemifield boundary. Meeting abstract presented at VSS 2015

Spatial integration of optic flow information in direction of heading judgments.

While we know that humans are extremely sensitive to optic flow information about direction of heading, we do not know how they integrate information across the visual field. We adapted the standard cue perturbation paradigm to investigate how young adult observers integrate optic flow information from different regions of the visual field to judge direction of heading. First, subjects judged direction of heading when viewing a three-dimensional field of random dots simulating linear translation through the world. We independently perturbed the flow in one visual field quadrant to indicate a different direction of heading relative to the other three quadrants. We then used subjects' judgments of direction of heading to estimate the relative influence of flow information in each quadrant on perception. Human subjects behaved similarly to the ideal observer in terms of integrating motion information across the visual field with one exception: Subjects overweighted information in the upper half of the visual field. The upper-field bias was robust under several different stimulus conditions, suggesting that it may represent a physiological adaptation to the uneven distribution of task-relevant motion information in our visual world.