Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “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 19 recordsLinked to original sources
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↗
PubMed1990

Illusion decrement and transfer of illusion decrement in obtuse- and acute-angle variants of the Poggendorff illusion.

Illusion-decrement and transfer-of-illusion-decrement procedures were used to examine the contribution of the obtuse- and acute-angle components of the Poggendorff pattern to the standard Poggendorff illusion. In the first four experiments, subjects were required to scan between the oblique lines of the Poggendorff pattern during the inspection phase of the decrement procedure. However, because of a possible confound associated with this procedure, a different decrement technique was used in Experiment 5. The results of Experiment 5 confirm and extend MacKay and Newbigging's (1977) finding that similar amounts of transfer to the standard pattern are obtained from the obtuse- and acute-angle patterns as from the standard pattern itself: In showing that the acute- and obtuse-angle components both contribute to the illusion, these findings question the plausibility of those theories of the Poggendorff illusion which do not assign any significant role to the acute-angle component. Furthermore, the potential confound associated with the decrement procedure of Experiments 1-4 suggests that the results of other studies obtained with similar procedures need to be reevaluated.

Attention↗
PubMed1991

Effects of tryptophan depletion on Poggendorff illusion, corner Poggendorff illusion, and attention.

The effects of a tryptophan-free amino acid mixture on Poggendorff illusion, corner Poggendorff illusion, and attention were investigated with 12 male subjects who ingested either a balanced amino acid mixture or a tryptophan-free mixture, the latter known to cause a marked depletion of brain tryptophan and serotonin. No significant difference between the two mixtures on the perceptual illusions was found.

Adult↗
PubMed1992

Anisotropic perception of visual angle: implications for the horizontal-vertical illusion, overconstancy of size, and the moon illusion.

Three experiments investigated anisotropic perception of visual angle outdoors. In Experiment 1, scales for vertical and horizontal visual angles ranging from 20 degrees to 80 degrees were constructed with the method of angle production (in which the subject reproduced a visual angle with a protractor) and the method of distance production (in which the subject produced a visual angle by adjusting viewing distance). In Experiment 2, scales for vertical and horizontal visual angles of 5 degrees-30 degrees were constructed with the method of angle production and were compared with scales for orientation in the frontal plane. In Experiment 3, vertical and horizontal visual angles of 3 degrees-80 degrees were judged with the method of verbal estimation. The main results of the experiments were as follows: (1) The obtained angles for visual angle are described by a quadratic equation, theta' = a + b theta + c theta 2 (where theta is the visual angle; theta', the obtained angle; a, b, and c, constants). (2) The linear coefficient b is larger than unity and is steeper for vertical direction than for horizontal direction. (3) The quadratic coefficient c is generally smaller than zero and is negatively larger for vertical direction than for horizontal direction. And (4) the obtained angle for visual angle is larger than that for orientation. From these results, it was possible to predict the horizontal-vertical illusion, over-constancy of size, and the moon illusion.

Adult↗
PubMed1992

[An examination of Metzger's theory on geometrical illusions by using the illusion of major and minor axes in ellipse].

An experiment with ellipses was conducted to evaluate the validity of Metzger's theory on geometrical illusions (the law of good Gestalt) by examining whether its major axis is underestimated and its minor axis overestimated. If the horizontal or vertical dimension of a circle with a fixed diameter is reduced, " smaller" ellipses with major axes equal to the circle's diameter will be constructed. On the other hand, if the dimension is enlarged, "larger" ellipses with minor axes equal to the circle's diameter will be produced. Ten university students estimated the apparent lengths of such axes. It was found that the major axes were underestimated, while the minor axes were overestimated, irrespective of the relative sizes of the ellipses. The same result was obtained when the orientation of the axis was rotated 90 degrees. These results may be interpreted in line with Metzger's theory to the illusion of major and minor axes in ellipse.

Adult↗
PubMed1977

Component analysis of orientation illusions.

Orientation illusions occur when the inducing figure is a line or grating (the tilt illusion) or a square outline frame (the rod-and-frame illusion). In the range of inducing figure tilts between vertical and horizontal, the tilt illusion describes one cycle of positive (direct) and negative (indirect) effects but the rod-and-frame illusion describes two such cycles. In two experiments, angular functions of illusions were measured with the six possible inducing figures which result when two of the four sides of a square inducing frame are deleted. As expected, the parallel-side frame amputations induced angular functions similar to the tilt illusion and these functions differed from those induced by the orthogonal-sided amputations. In agreement with previous findings on the nonadditivity of tilt illusions, the sum of angular functions induced by frame amputations, which together form a complete frame, were not always equivalent to the angular function induced by a complete frame, and there were asymmetries in the data fro which neither of two simple hypotheses could adequately account. The discussion focuses upon properties of inducing figures which psychophysical hypotheses might need to consider in order to account for the shapes of angular functions of orientation illusions and, in particular,a distinction is drawn between the global orientation of the inducing figure and the orientations of it (local) component features. It is suggested that it might be fruitful if the tilt illusion and the rod-and-frame illusion were conceived of as illusions resulting from inducing figures composed of all or part of n gratings of spatial frequency fn intersecting at angles of 180 degrees/n.

Female↗
PubMed1991

The Fraser illusion: complex figures.

The cause of the Fraser illusion, which occurs when a line made up of tilted segments itself appears tilted, is examined further. In this series of experiments, we used figures that resembled the original Fraser illusion; they were more complex than those reported on in our previous paper (Stuart & Day, 1988). The figures were used to explore two theories of the Fraser illusion further: that it is the result of interactions between orientation selective units, and that it is a consequence of the local, distributed processing of orientation. The presence of background elements like those used in the original illusion led to an increase in the strength of the illusion, but the shape of these elements had no differential effect on illusion strength. There was a differential effect of the background on the assimilative and contrast illusions, owing respectively to small and large tilts of the inducing elements. The illusion was markedly reduced at small visual angles when the background was absent, but it was only slightly affected when the background was present. All these findings are difficult to explain in terms of interactions between single units, either at the same or at different scales in the image. The effects of luminance contrast and isoluminance on the illusion were not consistent with either theory, but they indicated that researchers need to consider the role of figure-ground organization in this illusion.

Adolescent↗
PubMed1990

Illusion reversal rate as a function of subjective depth.

Undergraduate students (N = 48) served as subjects in a test of Gregory's theory of illusions. Twenty-four students made judgments about the subjective depth of three reversible illusions--Necker cube, Book, and Pyramid--under the conditions of complete versus incomplete illusions and illusions without depth cues versus with depth cues. An additional 24 subjects recorded the three illusion reversal rates under slightly altered conditions. Differences were found among the various illusions with respect to complete versus incomplete illusions, reversal rate, subjective judgments of depth, and certain correlation values. Support for Gregory's theory of illusion as displaced or misleading depth perception is offered by these results.

Adolescent↗
PubMed1992

The effect of unilateral brain lesions on perception of visual illusions.

The study tested the effect of the left and right hemisphere lesions on the susceptibility to visual illusions. Twenty-five patients with left hemisphere damage, 22 patients with right hemisphere damage and 23 control subjects inspected series of figures producing four different illusions: Ponzo, Ehrenstein-Orbison, Poggendorff and Zoellner. Series of stimuli configurations were constructed so that different degrees of distortion opposite to the illusory effect were introduced in each pattern. The amount of distortion was increased in steps so that at a certain point of the series the patterns produced percepts opposite to the illusory ones. That point indicated the strength of the illusion. Stimuli of a given series were presented to each subject 5 times in random order and subject's judgements of illusions were collected. The illusion strength was established using the Spearman distribution method for determining psychophysical thresholds. The results showed that the left and right hemisphere lesions either did not affect the subject's susceptibility to illusions (in Ponzo and Poggendorff) or their effects were similar, i.e. they reduced the strength of the perceived illusions (in Ehrenstein-Orbison and Zoellner). Our data contradict the hypothesis of hemisphere differences in the perception of visual illusions and support the view that those phenomena are multiple-caused.

Attention↗
PubMed1991

Three-dimensional Müller-Lyer illusion.

Three-dimensional (3-D) variants of the Müller-Lyer pattern were created to address the question of where along the path of information flow in the visual system the illusion might occur. These variants, which yielded a robust illusion, included dihedral angles in place of the arrowheads of the classical pattern. The enormous difference in the shape of the resulting retinal image, compared with that of the classical pattern, makes it difficult to explain the present illusion by resorting to image-processing theories such as selective filtering (Ginsburg, 1984, 1986) or depth processing (Gregory, 1963, 1966, 1968). It was also shown that this 3-D illusion is homologous with the classical illusion, and that the two may thus share a common causal mechanism. A new type of 3-D figure, which yielded the same retinal image as did the classical pattern, was then employed. However, since the figure was 3-D, its shape in spatial coordinates was very different compared to that of the classical pattern. The magnitude of the illusion obtained with this figure was half that of the classical pattern. This finding suggests that the illusion might be caused by processes that occur after the computation of depth. All three experiments indicated that the illusion may be produced later in the processing stream than has previously been suggested.

Depth Perception↗
PubMed1979

Changes in apparent body orientation and sensory localization induced by vibration of postural muscles: vibratory myesthetic illusions.

Illusions of continuous body tilt and rotation can be elicited by vibrating postural muscles of subjects standing in the dark. During such illusory motion, the apparent pivot point of the body can be influenced systematically by touch and pressure cues. Strong apparent movement is sometimes accompained by nystagmus of compensatory sign. If a small target light is visible during vibration, visual motion of like direction and velocity will accompany the illusory body motion. We have designated this pattern of apparent body and visual motion the "propriogyral illusion". Full room illumination abolishes both components of the propiogyral illusion. When the propriogyral illusion is being experienced, there is a dissociation between apparent displacement and apparent velocity; the extent of displacement is always less than would be expected on the basis of apparent velocity. The illusions of continuous body motion and the propriogyral illusion represent elements of a general set of vibratory myesthetic illusions that influence apparent posture, sensory, localization, and position sense of the body. These illusions demonstrate an important contribution of muscle afferent and touch-pressure information to the central mechanisms that determine apparent spatial orientation and visual localization. They also provide evidence that somatosensory information about orientation can influence oculomotor control.

Aerospace Medicine↗
PubMed1976

[The unmasking of consciousness by means of criticism of illusion and ideology].

The author contends that the constitution of Psychology as a Science requires the elucidation of the conceptual instruments to be used in the approach of its specific theoretical object. In order to meet that requirement, three main methodological subjects are considered: I. The image, conceived as embodiment of the illusory and the deceptive, vs. the image as "the imaginary". Images are defined as representations determined a priori as the sole possibility of understanding reality. The distinction is made between two modes of this gnoseological process: the one, apparent, the other real. The first one, image as a representation having no correspondence whatsoever with reality, conveys only deceptive features: illusion at the individual level, and ideology at the broader scale of the socioeconomical class. Illusion and ideology are subject to parallel in that both mask reality, uncovering a part of it in order to hide the whole; and they imply each other in that to each illusion of individual consciousness corresponds a single socio-economical ideology. The unmasking must be performed both at the individual (illusion) and the collective (ideology) levels, through a conceptual work under a clear conception of knowledge and its methods, leading to an actually objectivating neutral act-Husserl. II. The imaginary as a project of irreality. Accepting that the image has a double function: a) an essential (gnoseological) one, and b) an unesential, supplementary one, as the support of illusion and ideology, there is yet a double manner for the concealment: a) subjective or belonging to the psychological level, and b) objective-intersubjective level, or actual social level. The image provides the object for the "belief", being thus the basis for the creation of a super-reality, an invention over another invention, with the goal of fulfilling desire. This goal implies failure in itself, as desire is always beyond the reality that seeks its fulfillment. The process of illusion can be explained by the triple link: desire-imagination-illusion, leading to belief. In desire there is a double work: a) a positive one, or trend towards the appropriation of the object; and b) a negative one, or the all-present frustration leading, precisely, to illusion. III. Desire and discourse: dialectics of possibility. Reality provides a limit-border to desire: it sets the frontiers of impossibility. Only the discourse provides a program, a planification of the being-desire. But desire exceeds the limits of possibility, and sets the underlying framework on which the impossibility of desire is expressed. Two different answers have been attempted from a logical-gnoseological-methodological stand point, consisting of reductionisms or pseudo-answers. Firstly, intellectualism, professing to reduce everything to rational cathegories and their logico-formal methods; and secondly, naturalism, professing to reduce everything to a factic-empirical scheme and to its experimental method...

Consciousness↗
PubMed1976

Effects of unilateral hemispheric lesions on two types of optico-geometric illusions.

Two optico-geometrical illusions--the Müller-Lyer (ML) and the Ponzo (P) illusion--have been studied in normal subjects and in patients with unilateral cortical lesions. Patients with left-sided lesions have stronger illusions than normal subjects, the increase being significant only for the ML illusion. In the case of right-sided lesions, the P illusion is weakened while the ML illusion is equivalent to that of control subjects. The findings are discussed in relation to the mode of apprehension of information.

Adult↗
PubMed1977

Necker cube and autokinetic illusions after awakening from REM and NONREM sleep: lack of effect.

Earlier studies demonstrated differential perceptions of the visual illusions, beta movements and spiral aftereffect, following awakening from REM and NONREM sleep. The present study tested the effects of awakening from the two phases of sleep on two additional visual illusions, the Necker cube and autokinetic illusions. 12 young adults were wakened from REM and NONREM sleep and tested on both illusions for three 1-min. trials, within 1 to 2 min. of the awakening. Comparison of the post-REM and post-NONREM illusions indicated a nonsignificant difference between the two waking conditions in the passive spontaneous reversal rates of the Necker cube. Data for the autokinetic illusion were not reported as they were unreliable.

Adolescent↗
PubMed1977

The case for misapplied constancy scaling: depth associations elicited by illusion configurations.

It has been suggested that many visual-geometric illusions arise from inappropriate evocation of size-constancy by depth cues implicit in illusion configurations. Observers gave free association responses while viewing illusion figures. Analysis of these responses provides weak but consistent evidence for the elicitation of depth in the Sander parallelogram, Mueller-Lyer, Zoellner, and Ehrenfels variant of the Ponzo illusion. No evidence for depth is found in the normal form of the Ponzo, Poggendorff, and horizontal-vertical illusions, and the evidence is ambiguous in the Orbison configurations. These results indicate that depth processing may be evoked by some, but not all, classical illusion forms.

Cues↗
PubMed1992

Structural alterations of an ambiguous musical figure: the scale illusion revisited.

The scale illusion (Deutsch, 1975) shows the importance of frequency range in the perceptual organization of a sequence of notes. This paper includes three experiments on the scale illusion. Experiments 1 and 2 demonstrated that if the structure of the pattern of notes used in the original scale illusion study is altered slightly, by adding or subtracting a pair of notes from the ends of the sequence, there is a significant decrease in the rate of frequency-based responses, suggesting a weaker illusion. Experiment 3 investigated two features of the note patterns that may have led to this change. Specifically, it asked whether the decrease in the strength of the illusion is due to (1) the nature of the notes at the extremes of the frequency range and/or (2) the nature of the notes at the crossing point of the two scales. While both sources were found to affect the strength of the scale illusion, the former had a greater influence.

Adult↗