Impact of blur on clinical and occupational colour vision test results.

Purpose: To evaluate whether colour vision normal (CVN) adults pass two Fletcher-Evans (CAM) lantern tests and to investigate the impact of imposed blur on Ishihara, CAM lantern and computerised colour discrimination test (colour assessment and diagnosis test [CAD] and Cambridge colour test [CCT]) results.

Methods: In a pilot experiment, 20 (16 CVN and 4 colour vision deficient [CVD]) participants with normal VA were tested with the CAM lantern. In the main experiment, the impact of imposed dioptric blur (up to +8.

Coloured filters can simulate colour deficiency in normal vision but cannot compensate for congenital colour vision deficiency.

Red-green colour vision deficiency (CVD) affects ~ 4% of Caucasians. Notch filters exist to simulate CVD when worn by colour vision normal (CVN) observers (simulation tools), or to improve colour discrimination when worn by CVD observers (compensation tools). The current study assesses effects of simulation (Variantor) and compensation (EnChroma) filters on performance in a variety of tasks.

Contrast-modulated stimuli produce more superimposition and predominate perception when competing with comparable luminance-modulated stimuli during interocular grouping.

Interocular grouping (IOG) is a binocular visual function that can arise during multi-stable perception. IOG perception was initiated using split-grating stimuli constructed from luminance (L), luminance-modulated noise (LM) and contrast-modulated noise (CM). In Experiment 1, three different visibility levels were used for L and LM (or first-order) stimuli, and compared to fixed-visibility CM (or second-order) stimuli.

Interocular ND filter suppression: Eccentricity and luminance polarity effects.

The depth and extent of interocular suppression were measured in binocularly normal observers who unilaterally adapted to neutral density (ND) filters (0, 1.5, 2, and 3 ND). Suppression was measured by dichoptically matching sectors of a ring presented to the adapted eye to a fixed contrast contiguous ring presented to the non-adapted eye.

Grouping Effects on Foveal Spatial Interactions in Children.

Purpose: Grouping of flankers from the target can modulate crowding in adults. Visual acuity in children is measured clinically using charts with targets and different flankers to enhance spatial interactions. We investigated grouping effects on interactions using visual acuity letters, flanked by contours and letters, in children.

Levelt's laws do not predict perception when luminance- and contrast-modulated stimuli compete during binocular rivalry.

Incompatible patterns viewed by each of the two eyes can provoke binocular rivalry, a competition of perception. Levelt's first law predicts that a highly visible stimulus will predominate over a less visible stimulus during binocular rivalry. In a behavioural study, we made a counterintuitive observation: high visibility patterns do not always predominate over low visibility patterns.

More superimposition for contrast-modulated than luminance-modulated stimuli during binocular rivalry.

Luminance-modulated noise (LM) and contrast-modulated noise (CM) gratings were presented with interocularly correlated, uncorrelated and anti-correlated binary noise to investigate their contributions to mixed percepts, specifically piecemeal and superimposition, during binocular rivalry. Stimuli were sine-wave gratings of 2 c/deg presented within 2 deg circular apertures. The LM stimulus contrast was 0.

Interocular suppression patterns in binocularly abnormal observers using luminance- and contrast-modulated noise stimuli.

In binocular viewing, images presented to the amblyopic eye are suppressed in the cortex to prevent confusion or diplopia. The present study measures depth and extent of interocular suppression across the central circular 24° visual field in observers with strabismus and microstrabismus. Visual stimuli were concentric rings of alternating polarity, each divided into sectors.

Crowding and visual acuity measured in adults using paediatric test letters, pictures and symbols.

Crowding refers to the degradation of visual acuity for target optotypes with, versus without, surrounding features. Crowding is important clinically, however the effect of target-flanker spacing on acuity for symbols and pictures, compared to letters, has not been investigated. Five adults with corrected-to-normal vision had visual acuity measured for modified single target versions of Kay Pictures, Lea Symbols, HOTV and Cambridge Crowding Cards, tests.

Very few exclusive percepts for contrast-modulated stimuli during binocular rivalry.

Binocular rivalry properties for contrast-modulated (CM) gratings were examined to gain insight into their locus of processing. Two orthogonally orientated gratings were presented, one to each eye. Perceptual change rates, proportions of exclusivity and mixed percepts, and mean durations were calculated.

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.

Investigation of interocular blur suppression using luminance-modulated and contrast-modulated noise stimuli.

Presenting two sufficiently dissimilar images, one to each eye, may result in interocular suppression. The present study measured interocular suppression depth and extent in binocularly normal participants when blurring one eye only with varying dioptric lens powers (+0.5, +1, +2, and +4 D).

The effects of blur and eccentric viewing on adult acuity for pediatric tests: implications for amblyopia detection.

Purpose: The detection of amblyopia in children relies on an accurate assessment of visual acuity. Visual deficits in anisometropic and strabismic amblyopia are different, but the influence of chart design, in particular position, and type of crowding features on visual acuity in the two types of amblyopia, is not clear. Certain aspects of amblyopic spatial vision are mimicked in healthy individuals by imposing increasing levels of blur and retinal eccentricity.

Foveal visual acuity is worse and shows stronger contour interaction effects for contrast-modulated than luminance-modulated Cs.

Contrast-modulated (CM) stimuli are processed by spatial mechanisms that operate at larger spatial scales than those processing luminance-modulated (LM) stimuli and may be more prone to deficits in developing, amblyopic, and aging visual systems. Understanding neural mechanisms of contour interaction or crowding will help in detecting disorders of spatial vision. In this study, contour interaction effects on visual acuity for LM and CM C and bar stimuli are assessed in normal foveal vision.

The psychophysics of detecting binocular discrepancies of luminance.

In the natural world, a binocular discrepancy of luminance can signal a glossy surface. Using a spatial forced choice task, we have measured the ability of subjects to detect binocular luminance disparities. We show that the detection of binocular luminance disparity shares several basic psychophysical features with the detection of surface properties such as lightness and chromaticity: an approximation to Weber's Law, spatial summation, temporal summation, and a deterioration with increasing eccentricity.