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Results for “OPTICAL ILLUSIONS”

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At least 19 recordsLinked to original sources
PubMed2006

[Influence of "optical illusion" on detectability in diagnosis for head CT images: participation of optical illusion of light perception in medical image reading and diagnosis].

Even if the visual impression of the photographic density of the brain in head CT images is shown as physically the same, it is known that optical illusions of lightness perception (assimilation, contrast, picture frame effect, etc.) occur and that practical density can be observed psychologically differently, according to differences in the color of the skull and background, and differences in cases (differences in picture pattern). Therefore, in this study, in order to clarify the influence of optical illusion on detectability in diagnosis, the author attempted to compare detectability in four sample cases, consisting of acute cerebral infarction (1), acute epidural hematoma (1), and chronic subdural hematoma (2), using visual subjective evaluation. In the case of acute cerebral infarction, there was no significant difference in detectability between the original image and the virtual images. Further, it clarified that the original head CT image (acute epidural hematoma) with the high-density hematoma recognized at the marginal limited part of the brain was inferior to virtual images in detectability, while it clarified that the original head CT image (chronic subdural hematoma) with the low-density hematoma was superior to virtual images in detectability, because of visual psychological emphasis on the difference of the film contrast between the hematoma and white skull.

Brain↗
PubMed1998

Increase of optical illusion in demented patients.

Assuming a particular psychological function of optical gestalt perception, its impairment would lead to a decreasing extent of gestalt related optical illusion. An increase of optical illusion would be expected in the case of a loss of adaptability and cognitive compensation, usually revising the phenomenon of optical illusion. 16 demented out-patients were compared to 16 hospitalized schizophrenics by a 'Computerized Assessment of Change in Optical Illusion' (CACOI), measuring the extent of optical illusion by patient's assessment of 12 variations of the figure of Mueller-Lyer, differing in baseline length. The results showed a significant increase of optical illusion in demented patients compared to the schizophrenic controls (p = 0.019). Taking into account that the extent of optical illusion by the figure of Mueller-Lyer usually is decreasing with age and was found to be increased in schizophrenics, our results support the hypothesis of an early loss of adaptability and cognitive compensation in dementia.

Aged↗
PubMed1977

Feature analysers, optical illusions, and figural aftereffects.

Simple displacement models cannot explain some aspects of optical illusions and figural aftereffects. The orientation-detector interaction model proposed by Blakemore and others is more suitable to explain many aspects of the Zöllner illusion, positive and negative illusions, the effect of gap between the inducing and test lines, and the anisotropy of illusions. If we hypothesize size detectors whose tuning width and distribution steps are proportional to logarithmic size, interactions between them explain well the fact that the Delboeuf illusion and figural aftereffects of circles are determined by the size of the inducing to test circle, not by the absolute distance between the contours of these circles.

Figural Aftereffect↗
PubMed2004

Uncertainty in visual processes predicts geometrical optical illusions.

It is proposed in this paper that many geometrical optical illusions, as well as illusory patterns due to motion signals in line drawings, are due to the statistics of visual computations. The interpretation of image patterns is preceded by a step where image features such as lines, intersections of lines, or local image movement must be derived. However, there are many sources of noise or uncertainty in the formation and processing of images, and they cause problems in the estimation of these features; in particular, they cause bias. As a result, the locations of features are perceived erroneously and the appearance of the patterns is altered. The bias occurs with any visual processing of line features; under average conditions it is not large enough to be noticeable, but illusory patterns are such that the bias is highly pronounced. Thus, the broader message of this paper is that there is a general uncertainty principle which governs the workings of vision systems, and optical illusions are an artifact of this principle.

Humans↗
PubMed2002

[Visual impression of photographic density of the brain in head CT images: verification of optical illusion by visual subjective evaluation of medical images].

The purpose of this study was to clarify the psychological influence of optical illusion on the photographic density of the brain in head CT images. In this study, I attempted to compare the visual impression of photographic density of the brain using visual subjective evaluation according to observers and cases. The results showed that the visual impression of photographic density of the brain at cerebellar CT depended upon the mode of appearance of the optical illusion (assimilation, contrast, picture frame effect, etc.). In addition, that impression varied according to differences in cases (difference of picture pattern) and observers. Further, it was clarified that the optical illusion had been observed according to individual differences among observers. Moreover, cases could be divided into two main classes. Some cases were recognized as a kind of outline figure (the white skull was recognized as an induction color, and the brain as a non-induction color) with assimilation, and consequently the brain seemed whitish. In other cases (the white skull was not recognized as an induction color) in which there was no assimilation, the brain did not seem whitish. This was considered to have occurred because the degree of influence of the skull on the visual impression of the photographic density of the brain had changed according to differences in cases.

Brain↗
PubMed1997

A combination of focusing and defocusing through yoga reduces optical illusion more than focusing alone.

The degree of optical illusion was assessed using standard Muller-Lyer lines in two groups (yoga and control) of thirty subjects each. All subjects were between eighteen and forty two years of age. The difference between the reading at which the lines were actually equal and the reading at which the subject felt them to be equal, was noted as the degree of illusion ("di"). Each subject was assessed at the beginning and end of a month. During the month the yoga group received training in yoga, while the control group carried on with their usual routine. At the end of the month the yoga group showed a significant (two factor ANOVA, Tukey test, P < .001) decrease in the "di" (86%), whereas the control group showed no change. The improvement following yoga could be attributed to the combination of focusing and defocusing involved in yoga practice, as these factors are known to influence the "di". Previous results which mentioned a 79% decrease in "di" with focusing alone, provided a comparison.

Adolescent↗
PubMed2003

Optical illusions in scanning electron micrographs: the case of the eggshell of Acrosternum (Chinavia) marginatum (Hemiptera: Pentatomidae).

Scanning electron microscopy revealed that-as is common in this family of the Hemiptera-the eggs of the green stink bug Acrosternum (Chinavia) marginatum are roughly barrel-shaped and possess at their apical pole a row of slender extensions, the aero-micropylar processes. The outer surface of the eggshell carries hexagonally arranged pits. The analysis of cross-fractured eggshells showed that the pits have slender basal extensions with transverse diaphragms. When scanning electron micrographs of the egg surface of A. marginatum are viewed upside down, the perception flips and the pits appear as elevations to all observers addressed. Thus, we are dealing with an optical illusion, which is known as the 'shape-from-shading effect'. The perceived dents remain robust to changes in the angle of recording (zero to ca. 60 degrees tilt), the magnification (ca. x100 to x1400), and the number of pits included in the micrograph (one to several hundred). When through appropriate positioning of the specimen under the electron beam, contrast is significantly reduced and the distinct shadows at the slope of the pits are eliminated, the optical illusion does not appear. It is inferred that shades provide the decisive clue that determines whether bumps or dents will be perceived. Owing to the low resolution of their compound eyes, the shape-from-shading effect on the eggshell of the bug is in all likelihood not perceived by insects.

Animals↗
PubMed1994

The KoWa model: metric relations in geometric optical illusions.

The KoWa model described here gives a parametric account of the geometric conditions for 6 optical illusions from which prediction of illusory qualities of the figures in perceptual judgements may be accomplished using selected stimulus dimensions. The model is designed to allow integration of visual information.

Attention↗