Spatial Interactions in Interocular and Monocular "Blur Suppression".

Significance: The suppression of blurred images in one eye by clear images in the other eye is thought to contribute to the success of monovision correction. We show that interocular suppression occurs also for low-contrast targets that are not blurred and, to a lesser extent, when clear and low-contrast targets are presented to the same eye.

Purpose: A blurred target presented to one eye may be suppressed when a clear target is presented to the other eye.

Stereothresholds during Voluntary Head Movement and Disconjugate Image Motion.

Significance: Stereothresholds increase in the presence of disconjugate image motion, whether this motion results from vergence errors that occur during active head movements or is imposed externally.

Purpose: During rapid voluntary oscillations of the head, vergence eye position has been reported to vary with a peak-to-peak amplitude of about 0.5°-a considerably greater amplitude than when the head is still.

Characteristics of saccades during the near point of convergence test.

The near point of convergence test is widely used to evaluate binocular vision. It assesses the ability of the eyes to converge at short distances. Although the test consists of a pure symmetrical vergence task, small involuntary saccades occur concurrently.

High- and Low-contrast Letter Acuity during Image Motion in Normal Observers and Observers with Infantile Nystagmus Syndrome.

Significance: High-contrast acuity in individuals with infantile nystagmus syndrome (INS) is poorer than expected from their ongoing retinal image motion, indicating a sensory loss. Conversely, acuity for larger low-contrast letters in these observers may be limited by image motion alone.

Purpose: The aim of this study was to assess visual acuity for letters of different contrast in normal observers and individuals with idiopathic INS under conditions of comparable retinal image motion.

A Comparison of Foveal and Peripheral Contour Interaction and Crowding.

Significance: Performance on clinical tests of visual acuity can be influenced by the presence of nearby targets. This study compared the influence of neighboring flanking bars and letters on foveal and peripheral letter identification.

Purpose: Contour interaction and crowding refer to an impairment of visual resolution or discrimination produced by different types of flanking stimuli.

Number of flankers influences foveal crowding and contour interaction differently.

Nearby flanking objects degrade visual resolution. If the flankers are similar to the acuity target, this influence is called crowding (CW), whereas if the flanking stimuli are simple bars then the phenomenon is known as contour interaction (CI). The aim of this study was to compare the influence of the number and position of flankers on foveal CW and CI to investigate possible differences in mechanism of these two effects.

Technical Report: The Mechanism of Contour Interaction Differs in the Fovea and Periphery.

Significance: Both foveal and peripheral contour interactions are based on, as yet, unexplained neural mechanisms. Our results show that, unlike foveal contour interaction, peripheral contour interaction cannot be explained on the basis of the antagonistic structure of neural receptive fields.

Purpose: Foveal contour interaction is markedly reduced for mesopic compared with photopic targets.

Upturn of the contour-interaction function at small flanking bar-to-target separations.

Nearby flanking bars degrade letter identification and resolution, a phenomenon known as contour interaction. However, many previous studies found that the relationship between foveal letter identification and flanker separation is non-monotonic, with an upturn in performance at very small target-to-flanker separations. Here, we replicate this observation and show that a similar upturn occurs also for targets presented at 5 deg in the inferior field, if the target-to-flanker separation is sufficiently small.

Contrast Energy and Contour Interaction.

Significance: Contour interaction describes an impairment of visual acuity produced by nearby flanking features, which exerts a significant impact in many clinical tests of visual acuity. Our results indicate that the magnitude of interaction depends either on the flanker contrast energy (i.e.

Reading speed of patients with infantile nystagmus for text in different orientations.

Two case studies in the literature report on patients with infantile nystagmus (IN) who preferred to read text that is oriented vertically rather than horizontally. The current study systematically evaluated the effect of text orientation (-60 to +90 deg with respect to horizontal) on reading speed in nine individuals with IN associated with albinism at Hadassah Academic College (HAC), seven individuals with IN at the University of Houston (UH), and a total of 17 normal control observers. Observers at HAC read 40-character passages of Hebrew text from standardized 2nd grade level reading material and observers at UH read MNRead acuity chart sentences.

Contour interaction under photopic and scotopic conditions.

In the present study, we asked whether contour interaction undergoes significant changes for different luminance levels in the central and peripheral visual field. This study included nine normal observers at two laboratories (five at Palacky University Olomouc, Czech Republic and four at the University of Houston, USA). Observers viewed a randomly selected Sloan letter surrounded by four equally spaced bars for several separations measured edge-to-edge in min arc.

Impact of simulated micro-scotomas on reading performance in central and peripheral retina.

Observers with central field loss typically fixate within a non-foveal region called the preferred retinal locus, which can include localized sensitivity losses, or micro-scotomas (Krishnan and Bedell, 2018). In this study, we simulated micro-scotomas at the fovea and in the peripheral retina to assess their impact on reading speed. Ten younger (<36 years old) and 8 older (>50 years old) naïve observers with normal vision monocularly read high and/or low contrast sentences, presented at or above the critical print size for young observers at the fovea and at 5 and 10 deg in the inferior visual field.

The Associations among Metamorphopsia, Orientation Discrimination Threshold, and Retinal Layer Thickness in Patients with Idiopathic Epiretinal Membrane.

Purpose: To explore the association among the metamorphopsia identified by Amsler grid test, orientation discrimination threshold (ODT), and retinal layer thickness in patients with idiopathic epiretinal membrane (ERM).

Methods: A total of 48 ERM patients were divided into a fovea-spared (FS) group (n = 12) and a fovea-involved (FI) group (n = 36). A total of 23 visually normal people served as controls.

The influence of endogenous attention on contrast perception, contrast discrimination, and saccadic reaction time.

Visual spatial attention has been shown to influence both contrast detection and suprathreshold contrast perception, as well as manual and saccadic reaction times (SRTs). Because SRTs are influenced also by stimulus contrast, we investigated if the enhancement of perceived contrast that accompanies attention could account for the shorter SRTs observed for attended targets locations. We conducted two dual-task experiments to assess psychophysical and oculomotor responses to non-foveal targets of various contrast for different spatial-attention-cueing conditions.

Functional changes at the preferred retinal locus in subjects with bilateral central vision loss.

Purpose: Subjects with bilateral central vision loss (CVL) use a retinal region called the preferred retinal locus (PRL) for performing various visual tasks. We probed the fixation PRL in individuals with bilateral macular disease, including age-related macular degeneration (AMD) and Stargardt disease (STGD), for localized sensitivity deficits.

Methods: Three letter words at the critical print size were presented in the NIDEK MP-1 microperimeter to determine the fixation PRL and its radial retinal eccentricity from the residual fovea in 29 subjects with bilateral CVL.

Relationships of orientation discrimination threshold and visual acuity with macular lesions in age-related macular degeneration.

Purpose: To measure visual acuity and metamorphopsia in patients with age-related macular degeneration (AMD) and to explore their relationship with macular lesions.

Methods: In this cross-sectional study, a total of 32 normal subjects (32 eyes) and 35 AMD patients (35 eyes) were recruited. They were categorized into 4 groups: normal, dry AMD, non-active wet AMD, and active wet AMD.

The reference frame for encoding and retention of motion depends on stimulus set size.

The goal of this study was to investigate the reference frames used in perceptual encoding and storage of visual motion information. In our experiments, observers viewed multiple moving objects and reported the direction of motion of a randomly selected item. Using a vector-decomposition technique, we computed performance during smooth pursuit with respect to a spatiotopic (nonretinotopic) and to a retinotopic component and compared them with performance during fixation, which served as the baseline.

Scotoma Visibility and Reading Rate with Bilateral Central Scotomas.

Purpose: In this experiment, we tested whether perceptually delineating the scotoma location and border with a gaze contingent polygon overlay improves reading speed and reading eye movements in patients with bilateral central scotomas.

Methods: Eight patients with age-related macular degeneration and bilateral central scotomas read aloud MNRead style sentences with their preferred eye. Eye movement signals from an EyeLink II eyetracker were used to create a gaze contingent display in which a polygon overlay delineating the area of the patient's scotoma was superimposed on the text during 18 of the 42 trials.

Monocular microsaccades are visual-task related.

During visual fixation, we constantly move our eyes. These microscopic eye movements are composed of tremor, drift, and microsaccades. Early studies concluded that microsaccades, like larger saccades, are binocular and conjugate, as expected from Hering's law of equal innervation.

Stream specificity and asymmetries in feature binding and content-addressable access in visual encoding and memory.

Human memory is content addressable-i.e., contents of the memory can be accessed using partial information about the bound features of a stored item.

Evidence for an eye-movement contribution to normal foveal crowding.

Purpose: Along with contour interaction, inaccurate and imprecise eye movements and attention have been suggested to contribute to poorer acuity for "crowded" versus uncrowded targets. To investigate the role of eye movements in foveal crowding, we compared percent correct letter identification for short and long lines of near-threshold letters with different separations.

Methods: Five normal observers read short (4 to 6 letters) and long (10 to 12 letters) lines of near-threshold, Sloan letters with edge-to-edge letter separations of 0.

Repeatability of Nidek MP-1 Fixation Measurements in Patients With Bilateral Central Field Loss.

Purpose: Visual performance in patients with bilateral central field loss is related to fixation stability. This study evaluated the repeatability of visual-fixation parameters in patients with bilateral central field loss, measured with the MP-1 microperimeter for fixation durations on the order of 15 to 30 seconds.

Methods: Bivariate contour ellipse area (BCEA), and the eccentricity and meridian of the preferred retinal locus (PRL) were determined in 56 eyes of 56 patients, sampled at two investigational sites.

Large crowding zones in peripheral vision for briefly presented stimuli.

When a target is flanked by distractors, it becomes more difficult to identify. In the periphery, this crowding effect extends over a wide range of target-flanker separations, called the spatial extent of interaction (EoI). A recent study showed that the EoI dramatically increases in size for short presentation durations (Chung & Mansfield, 2009).

Visual-function tests for self-monitoring of age-related macular degeneration.

Age-related macular degeneration (AMD) is one of the leading causes of severe visual impairment in the United States. Changes in lifestyle can slow the progression of AMD, and new therapies that arrest choroidal neovascularization can preserve vision in patients who progress to the neovascular form of advanced AMD. Appropriate timing is required for these interventions to be optimally effective, which, in turn, depends critically on early diagnosis.

Fixation locus in patients with bilateral central scotomas for targets that perceptually fill in.

Purpose: In this experiment, we investigated whether target type affects the retinal fixation location and stability in patients with bilateral central scotomas and, specifically, whether targets expected to perceptually fill in are imaged at or near the vestigial fovea.

Methods: The retinal location and stability of fixation were measured using the Nidek MP-1 microperimeter in 12 patients with bilateral central scotomas for six types of fixation target, three expected to fill in and three that included letters. The approximate position of the vestigial fovea was delineated in 10 of the patients either by using residual retinal landmarks or by locating the residual foveal pit in a dense macular scan obtained with a Spectralis optical coherence tomographer.