Effect of ecological viewing conditions on the Ames' distorted room illusion

Ecological theory asserts that the Ames' distorted room illusion (DRI) occurs as a result of the artificial restriction of information pickup. According to Gibson (1966, 1979), the illusion is eliminated when binocular vision and/or head movement are allowed. In Experiment 1, to measure the DRI, we used a size-matching technique employing discs placed within an Ames' distorted room. One hundred forty-four subjects viewed the distorted room or a control apparatus under four different viewing conditions (i.e., restricted or unrestricted head movement), using monocular and binocular vision. In Experiment 2, subjects viewed binocularly and were instructed to move freely while making judgments. Overall, the main findings of this study were that the DRI decreased with increases in viewing access and that the DRI persisted under all viewing conditions. The persistence of the illusion was felt to contradict Gibson's position.     

Influence of the Poggendorff illusion on manual pointing

The results of recent studies indicate that certain visuomotor actions, such as grasping and pointing, are unaffected by visual size illusions. The present study investigated whether the Poggendorff illusion of alignment influences pointing to a target's location. 15 subjects pointed with their unseen hands to the apparent location of the extension of the oblique line onto the target line of a version of the Poggendorff illusion. Analysis indicated the pointing action was influenced by the Poggendorff illusion. The implications of this finding for the claim that different cortical streams of visual processing subserve visuomotor actions and conscious visual perception are discussed.     

The influence of optical aberrations on the magnitude of the Poggendorff illusion

The amount of blurring of the retinal image can be reduced by proper selection of an artificial pupil and a chromatic filter. Reduction of the amount of blurring due to optical aberrations by viewing through a 1-mm artificial pupil and an interference filter in the eye, results in a concomitant reduction in the magnitude of the Poggendorff illusion. The magnitude of the reduction is smaller, however, than would be expected if the illusion was predominantly determined by blur due to optical aberration.     

Model for a three-dimensional optical illusion

A homogeneous coordinate system is used to describe the transformation from a real three-dimensional stimulus to an illusory three-dimensional perceptual object. The model comprises a series of transformations of which one acts as an illusion operator. The illusion operator is specified by a single parameter whose value determines whether the real or the illusory object is perceived. An experiment to test one prediction derived from the model was performed. The results confirm the prediction.     

Sine of an illusion

In an informally observed sine-wave figure in which the vertical extent between contours was constant, apparent extent in the crest and trough (the 'turns') appeared greater than in the straight oblique sections of the figure. This observation was confirmed in two experiments in which the vertical extents were matched by two vertically arranged dots. It was found that in a turn the apparent extent was greater than the true extent, but in a straight section both extents were about equal. These outcomes were confirmed when the two sections were each separated from the figure and presented alone. The illusion is explained in terms of a perceptual compromise between the vertical extent and the greater overall dimensions of the section at the turn of the sine-wave figure and is thereby held to be the same in principle as the Müller-Lyer illusion.     

Variations on the Hermann grid: an extinction illusion

When the white disks in a scintillating grid are reduced in size, and outlined in black, they tend to disappear. One sees only a few of them at a time, in clusters which move erratically on the page. Where they are not seen, the grey alleys seem to be continuous, generating grey crossings that are not actually present. Some black sparkling can be seen at those crossings where no disk is seen. The illusion also works in reverse contrast.     

Feedback versus an illusion in time

The accuracy of many perceptual comparisons depends greatly on the order in which the to-be-compared stimuli are presented. With comparisons of durations around 300 ms, these presentation-order effects do not diminish, even with extended practice, when feedback about response accuracy is withheld. Providing such feedback greatly diminishes presentation-order effects and coincidentally produces substantial increases in response accuracy. The feedback acts in part through inducing response biases and in part through changes in sensitivity. The contradiction between studies which report time-order errors in duration comparison and those which do not is attributable to differences in the use of information feedback.     

Influence of a psychological perspective on scene viewing and memory for scenes

In the study, 33 participants viewed photographs from either a potential homebuyer's or a burglar's perspective, or in preparation for a memory test, while their eye movements were recorded. A free recall and a picture recognition task were performed after viewing. The results showed that perspective had rapid effects, in that the second fixation after the scene onset was more likely to land on perspective-relevant than on perspective-irrelevant areas within the scene. Perspective-relevant areas also attracted longer total fixation time, more visits, and longer first-pass dwell times than did perspective-irrelevant areas. As for the effects of visual saliency, the first fixation was more likely to land on a salient than on a nonsalient area; salient areas also attracted more visits and longer total fixation time than did nonsalient areas. Recall and recognition performance reflected the eye fixation results: Both were overall higher for perspective-relevant than for perspective-irrelevant scene objects. The relatively low error rates in the recognition task suggest that participants had gained an accurate memory for scene objects. The findings suggest that the role of bottom-up versus top-down factors varies as a function of viewing task and the time-course of scene processing.     

Influence of a psychological perspective on scene viewing and memory for scenes

In the study, 33 participants viewed photographs from either a potential homebuyer's or a burglar's perspective, or in preparation for a memory test, while their eye movements were recorded. A free recall and a picture recognition task were performed after viewing. The results showed that perspective had rapid effects, in that the second fixation after the scene onset was more likely to land on perspective-relevant than on perspective-irrelevant areas within the scene. Perspective-relevant areas also attracted longer total fixation time, more visits, and longer first-pass dwell times than did perspective-irrelevant areas. As for the effects of visual saliency, the first fixation was more likely to land on a salient than on a nonsalient area; salient areas also attracted more visits and longer total fixation time than did nonsalient areas. Recall and recognition performance reflected the eye fixation results: Both were overall higher for perspective-relevant than for perspective-irrelevant scene objects. The relatively low error rates in the recognition task suggest that participants had gained an accurate memory for scene objects. The findings suggest that the role of bottom-up versus top-down factors varies as a function of viewing task and the time-course of scene processing.     

Pigeons perceive the Ebbinghaus-Titchener circles as an assimilation illusion

A target circle surrounded by larger "inducer" circles looks smaller, and one surrounded by smaller circles looks larger than they really are. This is the Ebbinghaus-Titchener illusion, which remains one of the strongest and most robust of contrast illusions. Although there have been many studies on this illusion in humans, virtually none have addressed how nonhuman animals perceive the same figures. Here the authors show that the Ebbinghaus-Titchener figures also induce a strong illusion in pigeons but, surprisingly, in the other direction; that is, all five successfully trained pigeons judged the target circle surrounded by larger circles to be larger than it really is and vice versa. Further analyses proved that neither the gaps between target and inducer circles nor the cumulative weighted surface of these figural elements could account for the birds' responses. Pigeons are known to show similarities to humans on various cognitive and perceptual tasks including concept formation, short-term memory, and some visual illusions. Our results, taken together with pigeons' previously demonstrated failure at visual completion, provide strong evidence that pigeons may actually experience a visual world too different for us to imagine.     

An illusion of movement complementary to the horizontal-vertical illusion

Blindfolded subjects moved a stylus held in the hand over a standard distance of 4.5 ins. in a given direction. They then attempted to move the same distance in a direction at right angles to the first. Eight combinations of movements were investigated. The results reveal an illusion such that the extent of movements to left or right across the body is underestimated, while the extent of movements towards or away from the body in the mid-line is overestimated. The illusion applies to speed as well as extent of movement. Movement up or down in a vertical plane is equivalent to movement towards or away from the body in a horizontal plane.

The interaction of this illusion with the well-known horizontal-vertical illusion of visual perception explains a failure to find any net illusory effect where lines visually displayed in different orientations were matched for length by unseen movements in similar orientations.

Whether the visual and movement illusions simply co-exist or whether they are functionally related is not yet clear.     

Spatial limits on the nonvisual self-touch illusion and the visual rubber hand illusion: Subjective experience of the illusion and proprioceptive drift

The nonvisual self-touch rubber hand paradigm elicits the compelling illusion that one is touching one’s own hand even though the two hands are not in contact. In four experiments, we investigated spatial limits of distance (15 cm, 30 cm, 45 cm, 60 cm) and alignment (0°, 90° anti-clockwise) on the nonvisual self-touch illusion and the well-known visual rubber hand illusion. Common procedures (synchronous and asynchronous stimulation administered for 60 s with the prosthetic hand at body midline) and common assessment methods were used. Subjective experience of the illusion was assessed by agreement ratings for statements on a questionnaire and time of illusion onset. The nonvisual self-touch illusion was diminished though never abolished by distance and alignment manipulations, whereas the visual rubber hand illusion was more robust against these manipulations. We assessed proprioceptive drift, and implications of a double dissociation between subjective experience of the illusion and proprioceptive drift are discussed.     

New twists for an old turning illusion

A Vernier-offset illusion induced by rotating lines, introduced by Matin et al (1976 Perception & psychophysics 20 138-142) was re-examined using onset, offset, and reverse trajectories inspired by flash-lag illusion research, with both Vernier and alignment-with-vertical judgments being recorded. The pattern of illusions found was generally in agreement with a differential latency of stimulus ends account described by those authors, although certain variants of modern spatial projection theories, and a differential latency of attribute account, could also accommodate much of the data.     

Effects of high-frequency yoga breathing called kapalabhati compared with breath awareness on the degree of optical illusion perceived

Prior research has shown that methods of meditation, breath control, and different kinds of yoga breathing affect attention and visual perception, including decreasing the size of certain optical illusions. Evaluating relationships sheds light on the perceptual and cognitive changes induced by yoga and related methods, and the locus of the effects. In the present study, the degree of optical illusion was assessed using Müller-Lyer stimuli before and immediately after two different kinds of practice, a high frequency yoga breathing called kapalabhati, and breath awareness. A nonyoga, control session tested for practice effects. Thirty participants (with group M age = 26.9 yr., SD = 5.7) practiced the two techniques for 18 min. on two separate days. The control group had 15 nonyoga practitioners assessed before and after 18 min. in which they did not perform any specific activity but were seated and relaxed. After both kapalabhati and breath awareness there was a significant decrease in the degree of optical illusion. The possibility that this was due to a practice or repetition effect was ruled out when 15 nonyoga practitioners showed no change in the degree of illusion when retested after 18 min. The changes were interpreted as due to changes in perception related to the way the stimuli were judged.