Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Optical Illusions”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 73 records · Page 4Linked to original sources
PubMedDate not supplied

Optical illusions.

Explore the source record for details and available documents.

Astronomical Phenomena↗
PubMed1978

Another optical-geometrical illusion.

A new optical-geometrical illusion is described. The parallelism of short rows of dots is affected by some unknown factor, so that the rows appear as pivoting on their middle point. Some explanations of the illusion are considered, but with no success.

Humans↗
PubMed1995

Measurements of geometric illusions, illusory contours and stereo-depth at luminance and colour contrast.

We investigated four geometric optical illusions (Zöllner, Müller-Lyer, Ponzo and Delboeuf), plus illusory contour/border induction (Kanizsa) and depth in random-dot stereograms (Julesz). Two different display conditions were compared: equiluminance with chromaticity contrast and heteroluminance without chromaticity contrast. The main results are as follows. (1) The strength of the four geometric optical illusions is the same under both display conditions. The Zöllner illusion reaches its maximum and levels off at a luminance contrast of about 80%; it disappears at luminance contrasts of less than 15%. (2) No illusory contours are perceived in equiluminant Kanizsa figures. The minimum luminance contrast for illusory contour induction in the Kanizsa square is on average 1.8%, for illusory border induction in the abutting grating illusion it is 5.3%. (3) Random-dot stereograms were found to induce depth equally well in both display modes. The disparity threshold for perceiving depth in isochromatic random-dot stereograms levels off at a luminance contrast of 30%. With larger disparities, depth is perceived down to about 10% contrast. The findings suggest that geometric optical illusions of parallelness (orientation), length and size are mediated by the parvocellular system; furthermore, that stereoscopic depth is mediated both by the magnocellular and the parvocellular systems; and that illusory contours are mediated by the magnocellular system.

Color Perception↗
PubMed1992

Orbital prosthesis following temporal muscle or forehead flap reconstruction: use of optics and illusions.

Temporalis myocutaneous flap reconstruction of orbital defects may cause difficulty with fabrication of esthetic orbital prostheses because of limited space. Two patient treatments are presented to show the wide variation in defect size that may be encountered after surgical reconstruction. Methods for using optics and illusions to enhance the esthetic result are also presented.

Adult↗
PubMed1993

The optical-geometrical illusion "corner Poggendorff" re-examined.

In 1988 Greene noted, if a straight pair of obliques are drawn outside of two orthogonal lines, the segments appears to be angled slightly one relative to the other. This illusion, designated as "corner Poggendorff" is different from the Poggendorff effect (the two obliques seem to lie on a parallel path). The results of the present experiments (N = 76 students) suggest that the general conditions for the corner Poggendorff are similar to those for the Judd illusion.

Adult↗
PubMed1999

Optic flow illusion and single neuron behaviour reconciled by a population model.

Radial patterns of optic flow contain a centre of expansion that indicates the observer's direction of self-movement. When the radial pattern is viewed with transparently overlapping unidirectional motion, the centre of expansion appears to shift in the direction of the unidirectional motion [Duffy, C.J. & Wurtz, R.H. (1993) Vision Res., 33, 1481-1490]. Neurons in the medial superior temporal (MST) area of monkey cerebral cortex are thought to mediate optic flow analysis, but they do not shift their responses to parallel the illusion created by transparent overlap. The population-based model of optic flow analysis proposed by Lappe and Rauschecker replicates the illusory shift observed in perceptual studies [Lappe, M. & Rauschecker, J.P. (1995) Vision Res., 35, 1619-1631]. We analysed the behaviour of constituent neurons in the model, to gain insight into neuronal mechanisms underlying the illusion. Single model neurons did not show the illusory shift but rather graded variations of their response specificity. The shift required the aggregate response of the population. We compared the model's predictions about the behaviour of single neurons with the responses recorded from area MST. The predicted distribution of overlap effects agreed with that observed in area MST. The success of the population-based model in predicting the illusion and the neuronal behaviour suggests that area MST uses the graded responses of single neurons to create a population response that supports optic flow perception.

Animals↗
PubMed1998

Global induced motion and visual stability in an optic flow illusion.

When an expansion flow field of moving dots is overlapped by planar motion, observers perceive an illusory displacement of the focus of expansion (FOE) in the direction of the planar motion (Duffy and Wurtz, Vision Research, 1993;33:1481-1490). The illusion may be a consequence of induced motion, wherein an induced component of motion relative to planar dots is added to the motions of expansion dots to produce the FOE shift. While such a process could be mediated by local 'center-surround' receptive fields, the effect could also be due to a higher level process which detects and subtracts large-field planar motion from the flow field. We probed the mechanisms underlying this illusion by adding varying amounts of rotation to the expansion stimulus, and by varying the speed and size of the planar motion field. The introduction of rotation into the stimulus produces an illusory shift in a direction perpendicular to the planar motion. Larger FOE shifts were perceived for greater speeds and sizes of planar motion fields, although the speed effect saturated at high speeds. While the illusion appears to share a common mechanism with center-surround induced motion, our results also point to involvement of a more global mechanism that subtracts coherent planar motion from the flow field. Such a process might help to maintain visual stability during eye movements.

Cues↗
PubMed1992

Geometrical haptic illusions revisited: haptic illusions compared with visual illusions.

Révész (1934) reported that haptic illusions were observed in almost all of the geometrical optical illusion figures. The present study reexamined seven geometrical illusions in both haptic and visual modes. In the Müller-Lyer, Ponzo, and vertical-horizontal figures, haptic illusions equivalent to the visual illusions were observed. In the Oppel-Kundt figure, a haptic illusion similar to the visual one was obtained. In the haptic Delboeuf stimuli, the size illusion of the outer circle occurred, whereas that of the inner circle did not. No haptic illusion was obtained in the Poggendorff figure. In the Zöllner figure, a haptic illusion directionally opposite to the visual one was obtained. These results show that haptic illusions do not occur in all of the geometrical illusion figures. They also suggest that haptic illusions are not necessarily mediated by visualization and that haptic processing of the figures often occurs in a manner different from vision.

Adult↗
PubMed1963

Cultural differences in the perception of geometric illusions.

Data from 15 societies are presented showing substantial intersocietal differences of two types in susceptibility to geometric optical illusions. The pattern of response differences suggests the existence of different habits of perceptual inference which relate to cultural and ecological factors in the visual environment.

Culture↗
PubMed1996

[Cartilaginous grafts in primary rhinoplasty].

In staging and performing secondary iatrogenous or post-traumatic rhinoplasty, it has clearly been shown that the use of grafts plays a key role in reconstructing the defective or missing anatomical parts. On the other hand, in primary rhinoplasty, in general the one prevailing concept is removal of the osteo-cartilage to shape the nose. However, in order to achieve a good balance between aesthetics of the various parts of the nasal pyramid and their coherence with the face as a whole, it is often necessary to add at one or more points so that you can remove less elsewhere. In effect, a naturally short nasal tip, unless suitably increased, would require marked removal of the gibbus which could, in turn, throw the nasal pyramid out of proportion with the rest of the face. On the other hand, if the back of the nose is naturally too short, it creates the optical illusion of a tip which is longer than it really is. This also holds true for a tight nose-lip angle or when the portion of the face anterior to the upper jaw is set back, creating the optical illusion of a downward or elongated tip. Integrating the back of the nose, the anterior nasal spine or the canine fossae with a graft makes it possible to achieve more natural results in harmony with the rest of the face. The material of choice for the grafts used by the authors is the quadrangular cartilage of the nasal septum, both autologous and homologous. This material is preserved in a aqueous solution of 10% mertiolate. An alternative can be provided by the cartilage of the auricular concha.

Humans↗
PubMed1977

Pseudofracture of the dens: Mach bands.

Mach bands are an optical phenomenon in which dark and light lines appear at the borders of structures of different radiodensity on radiographs. In most instances they do not cause a diagnostic dilemma. However, in a patient who has sustained trauma to the cervical spine, the commonly occuring negative Mach band across the base of the dens may be mistaken for a fracture. Failure to recognize this optical illusion may result in unnecessary treatment by skeletal traction. The production of Mach bands, methods of proving their illusory nature, and several illustrative cases are presented.

Adult↗
PubMed2002

Modal completion in the Poggendorff illusion: support for the depth-processing theory.

The Poggendorff illusion is one of the most prominent geometrical-optical illusions and has attracted enduring interest for more than a hundred years. Most modern theories explain the illusion by postulating various kinds of distortion of the "test" component of the figure by the context or the inducing component. They make no reference to the importance of processes involved in three-dimensional scene perception for understanding the illusion. We measured the strength of the Poggendorff illusion in configurations containing solid inducing surfaces as opposed to the usual parallel lines. The surface, oblique-line, and background luminances were manipulated separately to create configurations consistent with modal completion of the obliques in front of the surface. The marked decrease in the size of the illusion in conditions favoring modal completion is consistent with claims that perceived spatial layout is a major determinant of the Poggendorff illusion.

Cues↗