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At least 883 records · Page 49Linked to original sources
PubMed2001

Visual search for dimensionally redundant pop-out targets: evidence for parallel-coactive processing of dimensions.

In two visual search experiments, the detection of singleton feature targets redundantly defined on multiple dimensions was investigated. Targets differed from the distractors in orientation, color, or both (redundant targets). In Experiment 1, the various target types were presented either in separate blocks or in random order within blocks. Reaction times to redundant targets significantly violated the race model inequality (Miller, 1982), but only when there was constancy of the target-defining dimension(s) within trial blocks. In Experiment 2, there was dimensional variability within blocks. Consistent with Experiment 1, constancy of the target-defining dimension(s), but this time across successive trials (rather than within blocks), was critical for observing violations of the race model inequality. These results provide evidence for parallel-coactive processing of multiple dimensions, consistent with the dimension-weighting account of Müller, Heller, and Ziegler (1995).

Adolescent↗
PubMed2001

Sequential priming of 3-D perceptual organization.

In four experiments, the effects of sequential priming on the perceptual organization of complex three-dimensional (3-D) displays were examined. Observers were asked to view stereoscopic arrays and to search an embedded subset of items for an odd-colored target while 3-D orientation of the stimuli was varied randomly between trials. Search times decreased reliably when 3-D stimulus orientation was unchanged on consecutive trials, indicating substantial sequential priming by 3-D stimulus layout. The priming was nonsensory and was independent of priming by additional stimulus characteristics. Finally, priming by 3-D layout was unaffected by observers' foreknowledge of display orientation. Results indicate that perceptual organization of 3-D stimuli is guided by a short-term trace of 3-D spatial relationships between stimuli.

Adult↗
PubMed2002

The duration of 3-d form analysis in transformational apparent motion.

Transformational apparent motion (TAM) occurs when a figure changes discretely from one configuration to another overlapping configuration. Rather than an abrupt shape change, the initial shape is perceived to transform smoothly into the final shape as if animated by a series of intermediate shapes. We find that TAM follows an analysis of form that takes 80-140 msec. Form analysis can function both at and away from equiluminance and can occur over contours defined by uniform regions as well as outlines. Moreover, the forms analyzed can be 3-D, resulting in motion paths that appear to smoothly project out from or into the stimulus plane. The perceived transformation is generally the one that involves the least change in the shape or location of the initial figure in a 3-D sense. We conclude that perception of TAM follows an analysis of 3-D form that takes approximately 100 msec. This stage of form analysis may be common to both TAM and second-order motion.

Color Perception↗
PubMed1993

Neural dynamics of motion perception: direction fields, apertures, and resonant grouping.

A neural network model of global motion segmentation by visual cortex is described. Called the motion boundary contour system (BCS), the model clarifies how ambiguous local movements on a complex moving shape are actively reorganized into a coherent global motion signal. Unlike many previous researchers, we analyze how a coherent motion signal is imparted to all regions of a moving figure, not only to regions at which unambiguous motion signals exist. The model hereby suggests a solution to the global aperture problem. The motion BCS describes how preprocessing of motion signals by a motion oriented contrast (MOC) filter is joined to long-range cooperative grouping mechanisms in a motion cooperative-competitive (MOCC) loop to control phenomena such as motion capture. The motion BCS is computed in parallel with the static BCS of Grossberg and Mingolla (1985a, 1985b, 1987). Homologous properties of the motion BCS and the static BCS, specialized to process motion directions and static orientations, respectively, support a unified explanation of many data about static form perception and motion form perception that have heretofore been unexplained or treated separately. Predictions about microscopic computational differences of the parallel cortical streams V1-->MT and V1-->V2-->MT are made--notably, the magnocellular thick stripe and parvocellular interstripe streams. It is shown how the motion BCS can compute motion directions that may be synthesized from multiple orientations with opposite directions of contrast. Interactions of model simple cells, complex cells, hyper-complex cells, and bipole cells are described, with special emphasis given to new functional roles in direction disambiguation for endstopping at multiple processing stages and to the dynamic interplay of spatially short-range and long-range interactions.

Animals↗
PubMed1994

Parallel processing of part-whole information in visual search tasks.

Combination of information from the parallel processing of different basic features (color, size, etc.) can be used to guide attention to targets defined by conjunctions of those features. Wolfe et al. (1990) argued that, although it was possible to guide attention to the conjunction of, for instance, color and orientation, it was not possible to guide attention to targets defined by conjunctions of two colors or two orientations. The present experiments demonstrate an exception to this rule. Although it is true that attention cannot be guided to a target that has red and green parts, attention can be guided to an item that can be described as a whole red target with a green part. In Experiments 1 and 2, we illustrate this point. In Experiments 3 and 4, we rule out some simple size-based accounts of this finding. In Experiments 5 and 6, we begin to explore the nature of these first steps toward dividing the visual scene into parts and wholes.

Adolescent↗
PubMed1999

Stimulus-determined discrimination mechanisms for color search.

Visual attention can be goal driven, stimulus driven, or a combination of the two. Here we report evidence for an unexpectedly stimulus-driven component of visual search for a target defined by color. Observers demonstrated a surprisingly cost-free ability to incorporate multiple classifiers in search for a target of one color from among distractors of other colors. A target color was presented among distractors that could change from trial to trial (intermixed presentation) or that remained constant across all trials in a block (blocked presentation). For blocked presentation, a single search classifier (a mechanism that segregates the target from distractors in color space) could be adopted, whereas for intermixed presentation different classifiers had to be used when the distractor colors changed. The benefit of blocked presentation was very small, suggesting that the appropriate classifier was determined very quickly in trials for which the classifier changed. The results suggest that the stimulus-driven activation of an appropriate stimulus classifier can be very efficient.

Adult↗
PubMed1992

The role of attention in different visual-search tasks.

Observers viewed displays containing a variable number of distractors of one color and a target of another color. In some experiments, the target and distractors maintained their color from trial to trial; in others, they reversed unpredictably. Observers made a speeded two-choice judgment concerning either the presence, the color, or the shape of the odd-colored target. With only one exception, all of these conditions produced the same pattern of results: reaction times remained constant as the number of distractors increased. The exceptional result occurred when observers judged the shape of the odd-colored target and the color of the target and distractors reversed unpredictably. In this case, reaction times decreased as the number of distractors increased. These results are interpreted in terms of the attentional requirements of the different judgments and the mechanisms that guide attention.

Adult↗
PubMed1999

Perception of artificial stereoscopic stimuli from an incorrect viewing point.

The present study investigates the distortions in the perception of artificial stereoscopic displays seen from an inappropriate distance and/or orientation. Stereoscopic displays represent 3-D information correctly, provided they are seen from the correct station point. The viewing point may differ from the correct station point in its distance or in its orientation to the screen. These differences lead to distortions that can be predicted mathematically. However, the perceptual function may be different from the predictions, since people may possibly compensate for the distortions. To test the degree of this compensation, participants saw anaglyphic stereoscopic stimuli that showed angles in the horizontal plane, and their perception of the configuration was tested for various orientations and distances. The estimates were compared with the values predicted from the mathematical functions, and participants' virtual positions were reconstructed via nonlinear regressions. The analyses revealed a moderate compensation for viewing orientations and a systematically overestimation of the viewing distances. These results indicate that people compensate partially for distortions in stereopsis, given that the relevant information is available.

Adult↗
PubMed1977

Strabismus in childhood.

We have discussed what constitutes a normal visual and ocular system in children and the inherent mechanisms that help each person develop and maintain normal visual function. This ideal status should include good visual acuity in each eye, straight eyes, and the development of fusion. Strabismus represents an obstacle to obtaining these goals and may be caused by poor vision, refractive errors, or anatomic, structural, or innervational abnormalities. Each of these conditions is treatable and correctable when discovered early. With early identification, proper treatment can be instituted and the patient can have the opportunity to develop optimal vision with fusion and depth perception -- a lifetime benefit. Several other types of strabismus respond poorly to the use of glasses, prisms, exercises, or medications and can be effectively treated only by surgical methods. Most divergent and vertical deviations fall into this group, as do ocular deviations associated with paretic or structurally abnormal muscles.

Amblyopia↗
PubMedDate not supplied

The polarized three-dot test.

A new binocular sensory test was designed using polarizing filters. The polarized three-dot test (P3D) subtends the same visual angle as the Worth four-dot test (W4D). Sensory testing was performed at distance and near in 100 patients using the W4D and P3D tests. Every patient reliably completing the W4D test also completed the P3D test. Twelve patients failed to complete both tests. Fifteen patients could not reliably complete the W4D test but were able to perform the P3D, thus increasing the interpretable response rate from 73% for the W4D test to 88% for the P3D (chi square, p less than .0001). In every case but one, fusion by W4D testing was also found by the P3D test. In addition, the P3D identified 19 cases of fusion not found by W4D testing. The results suggest that the P3D test is superior to the W4D test in the clinical assessment of central and peripheral fusion.

Adolescent↗
PubMed1986

[Visual information processing from the retina to the prefrontal cortex].

Studies on the neural bases of visual information processing were reviewed by tracing connections from the retina to the prefrontal cortex in the monkey; i.e., retina--lateral geniculate body (LGB)--striate cortex--prestriate cortex--inferotemporal (IT) cortex or posterior parietal (PP) cortex--prefrontal cortex. The retinotopy exists up to the level of prestriate cortex, but it is lost in the IT or PP cortex. A general tendency is observed that the later is the stage of information processing, the longer is the latency of cell activity changes, the larger is the size of receptive field, and more complex become trigger features. Small spot stimuli activate retinal ganglion cells or LGB cells while bars or edges with proper orientation are trigger stimuli for striate and some prestriate cells. In restricted prestriate areas, cells which are selective to color or movement are observed. IT cells are activated by complex pattern stimuli, while PP cells are selective to spatial aspects of the stimulus. Some prefrontal cells encode the meaning of the stimulus independent of its physical properties.

Animals↗
PubMed1993

Duodenal and gastric ulcer prevention with misoprostol in arthritis patients taking NSAIDs. Misoprostol Study Group.

OBJECTIVES: To determine the efficacy of misoprostol for the prevention of nonsteroidal anti-inflammatory drug (NSAID)-induced duodenal and gastric ulcers in arthritis patients receiving NSAID therapy. DESIGN: A randomized, double-blind, multicenter, placebo-controlled trial. SETTING: Six hundred thirty-eight private, Veterans Affairs, health maintenance, and academic practices. PATIENTS: Six hundred thirty-eight patients with chronic inflammatory or noninflammatory arthritis who were taking an NSAID but who did not have a gastric or duodenal ulcer on screening endoscopy received treatment with ibuprofen, piroxicam, naproxen, sulindac, tolmetin, indomethacin, or diclofenac daily for 3 months. Four hundred fifty-five (71%) patients completed the trial. INTERVENTIONS: Patients meeting the entry criteria were randomized to receive either misoprostol, 200 micrograms, or placebo, four times a day for 12 weeks. MAIN OUTCOME MEASURES: The endoscopy was repeated at 4, 8, and 12 weeks. The development of a duodenal or gastric ulcer (defined as a circumscribed mucosal defect > or = 0.5 cm in diameter and with perceptible depth) was regarded as prophylactic failure. RESULTS: By 12 weeks, a duodenal ulcer developed in 2 of 320 (0.6%; 95% CI, 0.2% to 3.9%) patients randomized to receive misoprostol, compared with 15 of 323 (4.6%; CI, 2.8% to 8%) patients receiving placebo (P = 0.002). A gastric ulcer developed in 6 of 320 (1.9%; (CI, 0.8% to 4.4%) patients, compared with in 25 of 323 (7.7%; CI, 5.1% to 11.4%), respectively. CONCLUSION: Misoprostol significantly lowers the frequency of both duodenal and gastric ulcer development in patients who require long-term therapy with NSAIDS.

Adult↗
PubMed1996

[Characteristics and limitations of three-dimensional spiral CT--experimental evaluation].

We evaluated the image quality of three-dimensional (3D) spiral CT using a Somatom Plus CT scanner (Siemens, Germany). A T-shaped acrylate plastic model was made and scanning was performed with a table speed of 5 mm/sec for 24 seconds. The thickness of the X-ray beam was 5mm with one second per rotation. The various images of the model were created based on the shaded surface display (SSD) method and the effect of threshold and rotation (spin and tilt) on the quality of the 3D images was studied. The increase of threshold caused a rapid decrease in the diameter of the stick observed on the film, and this phenomenon was particularly remarkable on the transverse stick and the junctional portion of the longitudinal stick. The change of spin or tilt did not affect the diameter of the stick on the film. It was found that the depth perception of the stick could be achieved with the gray scale technique. We concluded that the interpretation of the 3D spiral CT image obtained with SSD needs caution and the diagnosis should not be made only on this image.

Humans↗
PubMed2002

Spatiotemporal features of early neuronogenesis differ in wild-type and albino mouse retina.

In albino mammals, lack of pigment in the retinal pigment epithelium is associated with retinal defects, including poor visual acuity from a photoreceptor deficit in the central retina and poor depth perception from a decrease in ipsilaterally projecting retinal fibers. Possible contributors to these abnormalities are reported delays in neuronogenesis (Ilia and Jeffery, 1996) and retinal maturation (Webster and Rowe, 1991). To further determine possible perturbations in neuronogenesis and/or differentiation, we used cell-specific markers and refined birth dating methods to examine these events during retinal ganglion cell (RGC) genesis in albino and pigmented mice from embryonic day 11 (E11) to E18. Our data indicate that relative to pigmented mice, more ganglion cells are born in the early stages of neuronogenesis in the albino retina, although the initiation of RGC genesis in the albino is unchanged. The cellular organization of the albino retina is perturbed as early as E12. In addition, cell cycle kinetics and output along the nasotemporal axis differ in retinas of albino and pigmented mice, both absolutely, with the temporal aspect of the retina expanded in albino, and relative to the position of the optic nerve head. Finally, blocking melanin synthesis in pigmented eyecups in culture leads to an increase in RGC differentiation, consistent with a role for melanin formation in regulating RGC neuronogenesis. These results point to spatiotemporal defects in neuronal production in the albino retina, which could perturb expression of genes that specify cell fate, number, and/or projection phenotype.

Albinism↗
PubMed1976

Marathon running and vision.

Sixteen optometric tests were administered to 29 athletes prior to and following their running the 1974 26-mile B.A.A. Boston Marathon. The tests included amplitude of accommodation, near point of convergence, stereopsis, depth perception, near phorias, ACA, near ductions, peripheral fields, and suppression. It appears that the systemic fatigue did not significantly affect the test values and it is reasonable to assume similar findings for other forms of athletics. While few optometrists' or ophthalmologists' patients are marathon runners, this study's findings may be extrapolatable to more common conditions.

Adult↗
PubMed1999

Vitamins and brain development.

Effects of deficiency of vitamins on early development of brain have been reviewed. Unusual developmental problems in neurogenesis specific for the brain and impairment of its functional capacities due to vitamin deficiency have been discussed. The species-specific "critical periods" in development of various systems have been mentioned. Indices such as reflex activity, locomotion, special senses, cognition and adaptive behavior were used for assessing brain maturation in experimental models and humans. Significant examples include brain anomalies in humans and other mammals caused by retinoid excess or deficit; increase in calbindin D28K, a vitamin D dependent calcium-binding protein during postnatal period in rat; hydrocephalus and exencephaly in prenatal rats and subarachnoidal or intracerebral hemorrhage in infants caused by vitamin E deficiency. Peripheral neuropathic lesions leading to infantile beriberi is caused by thiamine deficiency. Impaired growth in retinal layers leading to delay in maturation of electroretinogram and depth-perception in postnatal rats occur due to pyridoxine deficiency. Infants of severely vitamin B12 deficient mothers show abnormalities in behavior involving basal ganglia and pyramidal tract. Folic acid deficiency results in delayed maturation of the basic electroencepalographic patterns. In addition, vitamin-interactions leading to developmental errors have been pointed out. Vitamin B6 deficiency impairs vitamin B12 absorption and biotin deficiency may be aggravated by pantothenic acid deficiency. Vitamin C deficiency resulting in impaired metabolism may produce symptoms of deficiency of folic acid. Another characteristic examples is that iron absorption from dietary sources is dependent on ascorbic acid.

Animals↗