Senescent changes in photopic spatial summation.

Previous studies have demonstrated an inverse relation between the size of the complete spatial summation area and ganglion cell density. We hypothesized that if this relation is dynamic, the spatial summation area at 6° nasal would expand to compensate for age-related losses of retinal ganglion cells but not in the fovea where age-related loss in ganglion cell density is not significant. This hypothesis was tested by measuring contrast thresholds with a series of Gabor patches varying in size.

The influence of perceptual training on working memory in older adults.

Normal aging is associated with a degradation of perceptual abilities and a decline in higher-level cognitive functions, notably working memory. To remediate age-related deficits, cognitive training programs are increasingly being developed. However, it is not yet definitively established if, and by what mechanisms, training ameliorates effects of cognitive aging.

Cognitive speed of processing training delays driving cessation.

Background: As our population ages, interventions that can prolong safe driving for older adults will be increasingly important.

Methods: Data from two studies were combined in order to investigate the effectiveness of cognitive training in delaying driving cessation. Stratified Cox hazard regressions were used to examine risk of driving cessation as a function of training participation, baseline driving, and visual acuity.

The effect of senescence on orientation discrimination and mechanism tuning.

Accurately processing orientation information is a fundamental component of visual performance. Single-unit recordings have shown that the orientation tuning of individual neurons in macaque cortical areas V1 and V2 is reduced dramatically with age (M. T.

Perceptual image quality: Effects of tone characteristics.

Tone mapping refers to the conversion of luminance values recorded by a digital camera or other acquisition device, to the luminance levels available from an output device, such as a monitor or a printer. Tone mapping can improve the appearance of rendered images. Although there are a variety of algorithms available, there is little information about the image tone characteristics that produce pleasing images.

Bayesian model of human color constancy.

Vision is difficult because images are ambiguous about the structure of the world. For object color, the ambiguity arises because the same object reflects a different spectrum to the eye under different illuminations. Human vision typically does a good job of resolving this ambiguity-an ability known as color constancy.

Illusory spreading of watercolor.

The watercolor effect (WCE) is a phenomenon of long-range color assimilation occurring when a dark chromatic contour delineating a figure is flanked on the inside by a brighter chromatic contour; the brighter color spreads into the entire enclosed area. Here, we determined the optimal chromatic parameters and the cone signals supporting the WCE. To that end, we quantified the effect of color assimilation using hue cancellation as a function of hue, colorimetric purity, and cone modulation of inducing contours.

Spatial dependence of color assimilation by the watercolor effect.

Color assimilation with bichromatic contours was quantified for spatial extents ranging from von Bezold-type color assimilation to the watercolor effect. The magnitude and direction of assimilative hue change was measured as a function of the width of a rectangular stimulus. Assimilation was quantified by hue cancellation.

Cone-mediated multifocal electroretinogram in age-related macular degeneration: progression over a long-term follow-up.

Objective: To evaluate the progression of change in the cone-driven multifocal electroretinogram (mfERG) responses in patients previously identified as having high-risk, soft drusen 63 mum or greater.

Methods: Seventeen eyes of 14 patients were reevaluated after 28 to 41 months. Fundus changes were graded depending on drusen size and extent.

The watercolor effect: quantitative evidence for luminance-dependent mechanisms of long-range color assimilation.

When a dark chromatic contour delineating a figure is flanked on the inside by a brighter chromatic contour, the brighter color will spread into the entire enclosed area. This is known as the watercolor effect (WCE). Here we quantified the effect of color spreading using both color-matching and hue-cancellation tasks.

Senescence of spatial chromatic contrast sensitivity. II. Matching under natural viewing conditions.

Age-related changes in the spatial chromatic contrast sensitivity function of detection, measured along S and L - M cone axes, were demonstrated in a companion paper [Hardy et al., J. Opt.

Senescence of spatial chromatic contrast sensitivity. I. Detection under conditions controlling for optical factors.

Chromatic contrast thresholds for spatially varying patterns of various spatial frequencies (0.5, 1, 2, and 4 cycles per degree) were measured for ten older (65-77 yr of age) and ten younger (18-30 yr of age) observers. The stimuli were Gabor patches modulated along S-varying or (L - M)-varying chromatic axes.

Long-term renormalization of chromatic mechanisms following cataract surgery.

The optical density of the human crystalline lens progressively increases with age, the greatest increase in the visible spectrum being at short wavelengths. This produces a gradual shift in the spectral distribution of the light reaching the retina, yet color appearance remains relatively stable across the life span, implying that the visual system adapts to compensate for changes in spectral sensitivity. We explored properties of this adaptive renormalization by measuring changes in color appearance following cataract surgery.

Color constancy under changes in reflected illumination.

Distinct physical processes can change the spectrum of the illumination that impinges on a surface. Here we consider two such changes. The first is a change in the spectrum of the light source that provides the scene illumination (light source change).

Chromatic-Spatial Vision of the Aging Eye.

The human visual system undergoes continuous anatomical, physiological and functional changes throughout the life span. There is also continuous change in the spectral distribution and intensity of light reaching the retina from infancy through senescence, primarily due to changes in the absorption of short-wave light by the lens. Despite these changes in the retinal stimulus and the signals leaving the retina for perceptual analysis, color appearance is relatively stable during aging as measured by broadband reflective or self-luminous samples, the wavelengths of unique blue and yellow, and the achromatic locus.

Does human color constancy incorporate the statistical regularity of natural daylight?

The chromaticities of natural daylights cluster around the blackbody locus. We investigated whether the mechanisms that mediate human color constancy embody this statistical regularity of the natural environment, so that constancy is best when the illuminant change is one likely to occur. Observers viewed scenes displayed on a CRT-based stereoscope and adjusted a test patch embedded in the scene until it appeared achromatic.

Assessment of multifocal electroretinogram abnormalities and their relation to morphologic characteristics in patients with large drusen.

Objectives: To determine the extent of functional changes in the first-order kernel multifocal electroretinogram (mfERG) responses in patients with large drusen by means of a localized analysis and to determine correlations between mfERG responses and morphologic changes.

Methods: Thirty-one eyes from 20 patients ages 58 to 84 years with large drusen (> or =5 drusen > or =63 microm diameter) were studied. The mfERGs were recorded with a stimulus of 103 hexagons and a flash intensity of 2.

Topography of the chromatic pattern-onset VEP.

The chromatic pattern-onset VEP has been used successfully as a sensitive and objective technique to determine congenital and acquired color vision deficiency. It also has been applied to characterize development, maturation and aging of the chromatic visual pathways. Here we determine the topographic components of the full-field VEP using the multifocal technique.