Rotating dual-layered checkerboard illusion

It has been suggested that goal-directed actions performed under full vision are immune to certain visual illusions, while movements relying on perception-based visual information are deceived by them (Milner & Goodale, 1995). Consequently, pointing movements should be deceived by visual illusions when a delay is introduced (memory demands) or when antipointing (spatial imagery) is required. In 2 experiments, participants performed either propointing or antipointing movements to different versions of the Müller-Lyer illusion in 2 vision conditions (open-loop vs. delay). Apart from open-loop propointing, all conditions should rely on perceptual processing and should therefore yield similarly illusion effects. While we observed illusion effects in all conditions, their magnitude varied in unexpected ways. Most surprisingly, introducing a delay seemed to reduce illusion effects in antipointing. We show that this decrease can be explained by the fact that pointing after delay is less responsive to physical size changes. After correcting for this, illusion effects in antipointing were similar in both vision conditions but still twice as large as in the delayed propointing task. Our findings highlight the necessity of employing a correction procedure when comparing illusion effects across tasks and do not conform well to the predictions derived from the perception-action model.

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The notion that apparent sizes are perceived relative to the size of one’s body is supported through the discovery of a new visual illusion. When graspable objects are magnified by magnifying goggles, they appear to shrink back to near-normal size when one’s hand (also magnified) is placed next to them. When objects are “minified” by minifying goggles, the opposite occurs. The rescaling effect also occurred when participants who were trained in tool use viewed the tool next to the objects. However, this change in apparent size does not occur when familiar objects or someone else’s hand is placed next to the magnified or minified object. Presumably, objects’ apparent sizes shift closer to their actual sizes when one’s hand is viewed because objects’ sizes relative to the hand are the same with or without the goggles. These findings highlight the role of body scaling in size perception.

Milner and Goodale (1995) have proposed that visuomotor and perceptual processes are mediated by discrete visual systems that reflect the functional independence of action and perception. The visuomotor system is proposed to be insensitive to pictorial illusions of object size, whereas the perceptual system is reliably "tricked" by such figures. Brenner and Smeets (1996) and Jackson and Shaw (2000) demonstrated that grasp preshaping, but not grasping force, is immune to the Ponzo visual illusion, suggesting that not all visuomotor processes operate independently of the perceptual system. The present study investigated the effect of illusory object size on prehension kinematics and grasping dynamics (i.e., grip force and load force) as well as perceptual judgements of object size. Unlike previous investigations, object mass was held constant independent of changes in size. The Ponzo figure reliably affected perceptual estimates of object size, but this effect was restricted to one form of the illusion. Some aspects of the prehension movement were sensitive to veridical but not illusory object size (peak grip aperture, peak grip force, peak vertical wrist acceleration), whereas other movement parameters demonstrated illusory size effects (movement time, peak wrist velocity). Still other movement parameters were not sensitive to veridical or illusory object size (peak load force). Together the data suggest that certain prehension components are immune to pictorial illusions of object size, whereas others are not. Complex interactions between the perceptual and visuomotor systems appear to underlie the anticipatory scaling of grasping forces in prehension.

This paper explores the visual phenomena of a seeming change of the target-object's size (as a focus of concrete visual perception) in the function of an observer's motion so that it 'seems' contrary to the law of linear perspective (in the sense of an expected increase of the target volume/monumentality - by getting closer or a decrease - by getting farther away). This phenomenon is described in a geometrical and perceptual aspect; the result of this comprehensive approach led to identify parameters that determine it phenomenologically. It was established that the explored visual phenomenon is a specific 'size illusion', i.e. an 'angular size illusion' that occurs when influenced by factors of the perceptual kind - activated by a specific dynamic relationship (on a visual plan) between the target object and its surrounding competitive objects, as an observer moves. By understanding the character of this phenomenon (both in a geometrical and perceptual sense), it is possible to apply the acquired knowledge in practice - in programming the visual effects to be obtained (such as to visually optimize or minimize the monumentality of targeted objects) in all architectural and urban fields (planning, designing and reconstruction).

The present study was designed to measure quantitatively the change of size of colored after-image with the passing of time and also, to confirm the relationship between the change of size and the positive-negative phase alternation of after-image.The results obtained were as follows:1) When, in a dark room a red rectangle patch placed vertically (A-form patch) was thrown on a dark screen for thirty seconds and then it was removed, the same color after-image-positive after-image- of enlarged size appeared in about two seconds, and afterwards it got by degrees smaller to agree strictly with the stimulus size in about six seconds. The shrinking of the after-image continued to reach a maximum point in about thirteen seconds, then after returning to neutral state- the same size as the stimulus-, the after-image shifted to expansion (enlargement) phase. Afterwards it kept on enlarging for a while, until the image disappeared. Thus the oscillation of waxing and waning in size of after-image was quantitatively confirmed. (Exp. 1).2) In the inspection of red B-form patches (two rectangles fixated vertically) under the same condition as in Exp. 1 the result showed a similar one as in Exp. 1, with the exception that the amount of shrinking was less. (Exp. 2).3) The effect of the distance between the two stimulus-rectangles. When red B-form stimuli with the distance between the two rectangles of 1, 3, 6, 9, and 12mm were Presenteb darkroom, it was found that the curves of oscillation for each distance displayed a similar feature. In regard to the effect of the distance between the two rectangles, the following was confirmed: the larger the distance was, the larger were the amplitude and the period of oscillation in the curve of after-image (Exp. 3).4) The effect of the stimulus color. When the stimulus-colors of four kinds, red, yellow, green, and blue, were used, almost the same results were obtained excepting that the period of first appearance of after-images for the green and the red stimuli were a little earlier than the rest, and at that time the amount of expansion of after-image for the green and the yellow stimuli was slightly greater than the others. (Exp. 4).5) Concerning the relationship between the size oscillation of after-image and its positive-negative alternation, it was indicated that the positive phase of each after-image corresponds to the period of the enlargement and the negative phase to the shrinking one. This leads us to conclude the existence of close relationship between the size dimension of after-image and its sensory property. (Exp. 4).6) The adequate theory of the optical illusion as well as the figural after-effect requires that the above mentioned facts are explained together with them.

In 1955, English psychiatrist John Todd defined the Alice-in-Wonderland syndrome (AIWS) as self-experienced paroxysmal body-image illusions involving distortions of the size, mass, or shape of the patient's own body or its position in space, often accompanied by depersonalization and/or derealization. AIWS had been described by American Neurologist Caro Lippman in 1952, but Todd's report was the most influential. Todd named the syndrome for the perceptual disorder of altered body image experienced by the protagonist in Alice's Adventures in Wonderland (1865) by Lewis Carroll (Charles Lutwidge Dodgson). In Carroll's original story, Alice experienced several dramatic changes in body size and shape (e.g., shrinking to 10 inches high, growing unnaturally tall but not any wider, and growing unnaturally large). Todd reported 6 cases of AIWS, all of whom had episodic body-image distortions like those experienced by Lewis Carroll's Alice character; some also had visual perceptual disturbances, but none had visual perceptual disorders without body-image distortions. Therefore, AIWS may be accompanied by visual perceptual disorders (e.g., micropsia, macropsia, telopsia, pelopsia), but basing the diagnosis of AIWS on isolated visual perceptual disorders, as has subsequently been done by a number of authors, is inaccurate and misleading. Cases of isolated visual illusions without self-perceived distortions of body size, shape, or form, do not meet Todd's original criteria, nor are they commensurate with the experiences of the protagonist in Alice's Adventures in Wonderland. Furthermore, such cases differ by age and etiology from those that involve somesthetic perceptual disorders. Therefore, the use of the term AIWS for isolated visual illusions is problematic and should be discouraged. Although Todd's and Lippman's cases were adolescents or adults, AIWS is most commonly reported in children. Reported causes include infection (especially with Epstein Barr virus), migraine, epilepsy, depression, and toxic and febrile delirium.

Franz and Gegenfurtner (2008) argue that the evidence for a division of labour within the visual system for action and perception is flawed because perception is often measured by manual estimation, which responds in general with a larger slope to a change of physical size than does adjusting. Therefore results obtained under manual estimation have to be corrected for this difference in slope: In a reanalysis of six studies grasping and perception were equally influenced by the illusion after this correction. However, closer inspection of methods reveals that visual feedback was confounded with conditions (suppressed vision while grasping vs. full vision while adjusting). We argue that studies can produce relevant and decisive data only when they (a) do not confound conditions with visual feedback, (b) do not allow online corrections of the action due to a direct comparison of the hand with the target, and (c) do not provide any risk of grasping being memory driven when the target is removed.

Immediately after focal retinal lesions, receptive fields (RFs) in primary visual cortex expand considerably, even when the retinal damage is limited to the photoreceptor layer. The time course of these changes suggests that mere lack of stimulation in the vicinity of the RF accompanied by stimulation in the surrounding region causes the RF expansion. While recording from single cells in cat area 17, we simulated this pattern of stimulation with a pattern of moving lines in the visual field, masking out an area covering the RF of the recorded cell, thereby producing an "artificial scotoma." Over approximately 10 min this masking resulted in a 5-fold average expansion in RF area. Stimulating the RF center caused the field to collapse in size, returning to near its original extent; reconditioning with the masked stimulus led to RF reexpansion. Stimulation in the surrounding region was required for the RF expansion to occur--little expansion was seen during exposure to a blank screen. We propose that the expansion may account for visual illusions, such as perceptual fill-in of stabilized images and illusory contours and may constitute the prodrome of altered cortical topography after retinal lesions. These findings support the idea that even in adult animals RFs are dynamic, capable of being altered by the sensory context.

There exists a well-known visual illusion with respect to color propagation. That is, a human subject confuses a color in the subject's peripheral field of view (FOV) as another color in the central FOV (with a shape of circular disk) spreads into the peripheral FOV or as a color in the peripheral FOV erodes another color in the central FOV (also with a shape of circular disk) when he/she keeps gazing at a specific color visual stimulus in his/her central FOV for more than several seconds. In this paper, the authors experiment this illusion using multiple naive subjects in conditions of the visual stimuli as the central or peripheral colors and the disk size change. This paper has proposed a rate of propagation as a criterion and has analyzed and discussed the illusion using it.