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At least 1,153 records · Page 64Linked to original sources
PubMed2004

Negative priming effects in children engaged in nonspatial tasks: evidence for early development of an intact inhibitory mechanism.

Three experiments are reported that examined conceptual negative priming effects in children 5 to 12 years of age. Experiment 1 used a negative priming variant of a flanker task requiring the naming of a central color blob flanked by irrelevant distractors. Experiment 2 used a negative priming variant of the Stroop color-word task. Experiment 3 used a same-different matching task with novel 3-D shapes. Results revealed significant and equivalent magnitudes of negative priming across the tested age groups for all 3 tasks. It is concluded that the inhibitory mechanism underlying conceptual (i.e., identity or semantic) negative priming in visual selective attention tasks is intact in young children. Because the findings and conclusions diverge from the developmental literature on negative priming, the authors attempt to reconcile the contradictions by pinning down the reasons for the discrepancies.

Association Learning↗
PubMed2003

Color brings relief to human vision.

In natural scenes, chromatic variations, and the luminance variations that are aligned with them, mainly arise from surfaces such as flowers or painted objects. Pure or near-pure luminance variations, on the other hand, mainly arise from inhomogeneous illumination such as shadows or shading. Here, I provide evidence that knowledge of these color-luminance relationships is built into the machinery of the human visual system. When a pure-luminance grating is added to a differently oriented chromatic grating, the resulting 'plaid' appears to spring into three-dimensional relief, an example of 'shape-from-shading'. By psychophysical measurements, I found that the perception of shape-from-shading in the plaid was triggered when the chromatic and luminance gratings were not aligned, and suppressed when the gratings were aligned. This finding establishes a new role for color vision in determining the three-dimensional structure of an image: one that exploits the natural relationships that exist between color and luminance in the visual world.

Brain↗
PubMed1992

Vision with equiluminant colour contrast: 2. A large-scale technique and observations.

A simple technique is described for producing large-scale, tritanopic displays. The technique reproduces the various phenomena of vision with equiluminous-colour contrast that have previously been reported with red/green stimuli. It is, however, much less demanding technically, robust against artifacts, and can be used on large-scale scenes. One advantage of the technique is that a piece of blue filter can be used individually by each observer to compare quickly tritanopic and luminance conditions.

Attention↗
PubMed1997

Ambiguities in colour constancy and shape from shading.

A new visual phenomenon--called the AMBEGUJAS phenomenon--is presented, together with some descriptive data from two initial exploratory experiments. The phenomenon is basically one of shape from shading, but ambiguous as to both shape and colour. There are two spontaneously alternating and mutually exclusive perceived 3-D shapes, and--as the most surprising observation--the colour impressions of these two shapes are markedly different. The stimulus situation is very simple with two differently coloured illuminations (with sharp edges) adjacently cast onto a flat, grey striped surface. In one 3-D shape almost the whole chromatic content disappears, and the surface goes towards its veridically grey colour. In the other the perceived object assumes the two illumination colours as clear surface colours. The decolorised percept is interpreted as a striking example of colour constancy: a perceptual solution with the classical 'discounting of the illuminant'. Experiments show that the phenomenon is robust and appears in varying display layouts and different combinations of chromatic illuminations.

Color Perception↗
PubMed2004

A biologically inspired algorithm for the recovery of shading and reflectance images.

We present an algorithm for separating the shading and reflectance images of photographed natural scenes. The algorithm exploits the constraint that in natural scenes chromatic and luminance variations that are co-aligned mainly arise from changes in surface reflectance, whereas near-pure luminance variations mainly arise from shading and shadows. The novel aspect of the algorithm is the initial separation of the image into luminance and chromatic image planes that correspond to the luminance, red-green, and blue-yellow channels of the primate visual system. The red-green and blue-yellow image planes are analysed to provide a map of the changes in surface reflectance, which is then used to separate the reflectance from shading changes in both the luminance and chromatic image planes. The final reflectance image is obtained by reconstructing the chromatic and luminance-reflectance-change maps, while the shading image is obtained by subtracting the reconstructed luminance-reflectance image from the original luminance image. A number of image examples are included to illustrate the successes and limitations of the algorithm.

Algorithms↗
PubMed1989

Physical characteristics and perceptual effects of "blue-blocking" lenses.

The transmission-optical properties of a "blue-blocking" lens and its influence on several aspects of human visual performance were assessed. Results showed that the lens was effective in absorbing ultraviolet and blue wavelengths and that its effects on contrast sensitivity and visual evoked potentials (VEP's) were similar to those produced by an equivalent neutral density (ND) filter. Although the lens did not alter stereopsis, it did produce severe color discrimination losses for normal and dichromatic subjects.

Adult↗
PubMed1993

New procedures for evaluating vision functions of special populations.

Research over the last few decades has demonstrated the rapid development of vision function that occurs in infancy with near-adult levels reached before the age of 1 year. This period of rapid development coincides with the period of maximum sensitivity to insult. These facts emphasize the importance of effective screening techniques for visual disorders. Off-axis photorefraction is described as a new and effective screening technique for detection of refractive errors, media opacities, and strabismus. Separate from screening, a significant need exists for optometric vision evaluations in special populations. Normal infants, developmentally delayed or multi-handicapped children and adults, and cognitively impaired adults are examples of special populations who are difficult to examine with standard optometric techniques. New procedures for measuring visual acuity, contrast sensitivity, color vision, and stereopsis using behavioral or electrophysiological measures are described. Advantages and disadvantages of the different techniques are discussed.

Color Perception↗
PubMed1993

Redefining the optometric examination: addressing the vision needs of older adults.

The aging of America's population will result in an increased number of older adult patients in optometric practices. Although older patients frequently report declines in their vision, the results of high contrast testing procedures often do not correlate with the symptoms. Age-related functional vision decrements can impact upon an individual's ability to perform the activities of daily living. I explored the relation between reported visual complaints and the results of objective tests for older adults (N = 50) as compared with middle-aged adults (N = 20). Decrements in visual acuity, contrast sensitivity, glare sensitivity, color vision, and stereopsis were apparent in the older group and all were significant at alpha = 0.05. Open-ended questions elicited more visual complaints from older adults than from middle-aged adults. However, only the reported complaint of decreased vision was related to visual decrements as determined by clinical testing (chi 2; p = 0.0596). These results indicate that task-specific case history questions may provide greater insight into older adults' visual performance in their normal environment. Additional testing in the areas of contrast sensitivity, glare sensitivity, stereopsis, and color vision should also be included in the optometric examination when warranted.

Adult↗
PubMed1992

Stereopsis at isoluminance in the absence of chromatic aberrations.

Stereo (front-back) discrimination thresholds were measured in a two-interval forced-choice paradigm for chromatic (red-green) random-dot stereograms that had all detectable longitudinal and transverse aberrations removed by low-pass filtering. The thresholds were measured as a function of the luminance ratio of the red and the green stereo elements. Although individual differences were apparent, three subjects were able to fuse all the stimuli, including those at isoluminance. A quantitative, ideal-observer analysis was used to determine the neural efficiency with which color and luminance information was used in this stereo task. For two subjects, efficiency was constant as a function of the red-to-green ratio; for the third subject, efficiency was less near isoluminance.

Color Perception↗
PubMed1990

Effect of alcohol on sensory and sensorimotor visual functions.

The literature on the effect of alcohol on sensory and sensorimotor visual functions is extensive. The findings are often contradictory and early studies did not correlate the effects with blood alcohol levels. This study was designed to test the effects of alcohol on various visual functions using equipment that is freely available to the clinician. A significant loss of visual field, accommodation and convergence that correlated with increasing blood alcohol levels was found. Visual acuity, color vision and stereoacuity were not significantly altered by alcohol.

Accommodation, Ocular↗
PubMedDate not supplied

Scotopic vision, color vision, and stereopsis in infants.

Infants as young as 1 month postnatal have scotopic spectral sensitivity closely resembling the CIE standard curve and thus appear to have a functional, rhodopsin-based rod system. Neutrally adapted photopic spectral sensitivities are broad and roughly equal to those of adults tested under similar conditions, although infants may show an elevated sensitivity in the short-wavelength region of the spectrum. Spectral sensitivity has been shown to change with changes in chromatic adaptation. Some wavelength discriminations are possible under conditions in which brightness artifacts can be ruled out. All of these factors support the conclusion that young infants are at least dichromats. However, 2-month-olds to date have shown some unpredicted failures of chromatic discrimination (for example, yellow-greens from white), and the percentage of infants who demonstrate discriminations (for example, among wavelengths greater than or equal to 550 nm) improves with age in early infancy. Thus the status of young infants as trichromats is not yet clearly established. Stereopsis develops rapidly during months 3 to 7, and stereoacuities as good as 1' have been reported by 5 months postnatal. In summary, a variety of visual capabilities can now be measured in infants. Infants' visual capacities are rather surprisingly well established shortly after birth and undergo clear improvements during the first few postnatal months. The interpretation of developmental data and their bearing on visual theory are discussed.

Adult↗
PubMed2006

Location matters: why target location impacts performance in orientation tasks.

This research explores human performance in a spatial orientation task. In three experiments, participants saw a target highlighted in a visual scene and were asked to locate it on a map of the space. Across all of the experiments, the target's location in the visual scene influenced the participants' response times. Generally, response times increased when the target was located farther away from the viewer, when the target was farther to one side or the other, and when more distractors were nearby. However, there were important exceptions to these findings, suggesting that participants encode the location of a target hierarchically, using different features of the space depending on the target's particular location. We conclude that participants perform such tasks by extracting a description from the egocentric view and then transforming that description to allow them to find the target on the map.

Adult↗
PubMed1992

Size-distance invariance: kinetic invariance is different from static invariance.

The static form of the size-distance invariance hypothesis asserts that a given proximal stimulus size (visual angle) determines a unique and constant ratio of perceived object size to perceived object distance. A proposed kinetic invariance hypothesis asserts that a changing proximal stimulus size (an expanding or contracting solid visual angle) produces a constant perceived size and a changing perceived distance such that the instantaneous ratio of perceived size to perceived distance is determined by the instantaneous value of visual angle. The kinetic invariance hypothesis requires a new concept, an operating constraint, to mediate between the proximal expansion or contraction pattern and the perception of rigid object motion in depth. As a consequence of the operating constraint, expansion and contraction patterns are automatically represented in consciousness as rigid objects. In certain static situations, the operation of this constraint produces the anomalous perceived-size-perceived-distance relations called the size-distance paradox.

Depth Perception↗
PubMed1993

Distinctness of perceived three-dimensional form induced by modulated illumination: effects of certain display and modulation conditions.

The present study concerns the distinctness of the 3-D shape induced on flat displays by space-modulated illumination ("shape from shading"). The displays that we used varied in structure, hue contrast, lightness contrast, and in the number of reflectance edges present. The modulations of the illumination were a square-wave grating, a gradual modulation (a blurred grating), and an "O'Brien modulation," which combines an edge and a gradient. The displays were compared, using the paired comparison method, as to the distinctness of the perceived 3-D form. The results showed that the structure and chromatic color of the display were important factors facilitating the distinctness of the induced 3-D shape under all the modulation conditions. The results are discussed in relation to the "vector model" for color constancy, proposed in earlier papers.

Adult↗