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Motion silencing is a striking and unexplained visual illusion wherein changes that are otherwise salient become difficult to perceive when the changing elements also move. We develop a new method for quantifying illusion strength (Experiments 1a and 1b), and we demonstrate a privileged role for rotational motion on illusion strength compared with highly controlled stimuli that lack rotation (Experiments 2a to 3b). These contrasts make it difficult to explain the illusion in terms of lower-level detection limits. Instead, we explain the illusion as a failure to attribute changes to locations. Rotation exacerbates the illusion because its perception relies upon structured object representations. This aggravates the difficulty of attributing changes by demanding that locations are referenced relative to both an object-internal frame and an external frame. Two final experiments (4a and 4b) add support to this account by employing a synchronously rotating external frame of reference that diminishes otherwise strong motion silencing. All participants were Johns Hopkins University undergraduates.

Across the natural world as well as the artificial worlds of maps, diagrams, and data visualizations, feature similarity (e.g., color and shape) links spatially separate areas into sets. Despite a century of study, it is yet unclear what mechanism underlies this gestalt similarity grouping. One recent proposal is that similarity grouping-for example, seeing a red, vertical, or square group-is just global selection of those features. Although parsimonious, this account makes the counterintuitive prediction that similarity grouping is strictly serial: A green group cannot be constructed at the same time as a red group. We tested this prediction with a novel measure-a grouping illusion within number-estimation tasks that should work only if participants simultaneously construct groups-and found the strongest evidence yet in favor of serial feature-based attention ( Ns = 14, 12, and 12 for Experiment 1, Experiment 2, and Experiment 3, respectively).

The perception of shape, it has been argued, also often entails the perception of time. A cookie missing a bite, for example, is seen as a whole cookie that was subsequently bitten. It has never been clear, however, whether such observations truly reflect visual processing. To explore this possibility, we tested whether the perception of history in static shapes could actually induce illusory motion perception. Observers watched a square change to a truncated form, with a "piece" of it missing, and they reported whether this change was sudden or gradual. When the contours of the missing piece suggested a type of historical "intrusion" (as when one pokes a finger into a lump of clay), observers actually saw that intrusion occur: The change appeared to be gradual even when it was actually sudden, in a type of transformational apparent motion. This provides striking phenomenological evidence that vision involves reconstructing causal history from static shapes., (© The Author(s) 2016.)

There is debate as to whether or not the Ebbinghaus illusion is driven by high-level cognitive size contrast mechanisms as opposed to low-level biphasic contour interactions. In this study, we examine the variability in effects that are shared between this illusion and a different illusion that cannot be explained logically by a size contrast account. This comparison revealed that nearly one quarter of the variability for one illusion is shared with the other - demonstrating how a size-contrast account cannot be the sole explanation for the Ebbinghaus illusion., (© The Author(s) 2016.)

Current accounts of the Ebbinghaus illusion emphasize either size contrast or contour interaction processes. To assess these alternatives, four variants of the Ebbinghaus figure were constructed using 1, 5, 9, or 13 small circles dispersed along the perimeter of larger contextual circles. 30 observers ranked the perceived size of the central circles and a single control circle. The rankings indicated that increasing the number of small circles reduced the perceived size of the central circle. The results parallel the effects of contextual arcs on the Ebbinghaus illusion and suggest that the mis-estimations of central circle size in Ebbinghaus figures result primarily from contour interactions.

The Ebbinghaus illusion was produced using figures with four small or large contextual discs located either near or far from the central disc. For similar figures, the discs were either all black or all white; for dissimilar figures, black and white contextual and central discs were used in opposition. 48 observers, in equal numbers, were assigned to one of the four crossings of size and separation of the contextual discs and, using the converging method of limits, illusion magnitude scores for each Ebbinghaus configuration were obtained. The central disc appeared larger when bounded by small contextual discs and smaller when the contextual discs were more distant. Contrary to size contrast theory, uniformly colored discs did not generate greater illusions; instead, white central discs appeared larger than black ones regardless of contextual color. Collectively, the results indicated that contour interactions play a prominent role in producing the Ebbinghaus illusion.

One of the oldest visual illusions consists of observers' tendency to estimate vertical lines as longer than equal horizontal lines. This Horizontal-Vertical Illusion has been studied widely; however, most studies may not generalize to natural contexts because they have not addressed the low-level processes that occur rapidly and in response to context-free lines vs the possibility for high-level processes that arise over time in response to context. These issues were investigated via a novel design: rapid time-sequencing embedded within the context of natural images. Participants saw different levels of context and the Horizontal-Vertical Illusion was measured. In traditional Horizontal-Vertical Illusion displays without natural context, there was a robust invariance of the illusion to stimulus duration. Within context, however, there was strong modulation: the magnitude of the illusion decreased by over 50% or increased over 30%, depending upon placement within context. Knowledge of object properties such as size or line length did not account for this effect. It appears that previous domain-general investigations of the Horizontal-Vertical Illusion did not address the specific higher-order processes that produce the illusion in natural contexts.

A striking example of the constructive nature of visual perception is how the human visual system completes contours of occluded objects. To date, it is unclear whether perceptual completion emerges during early stages of visual processing or whether higher-level mechanisms are necessary. To answer this question, we used transcranial magnetic stimulation to disrupt signaling in V1/V2 and in the lateral occipital (LO) area at different moments in time while participants performed a discrimination task involving a Kanizsa-type illusory figure. Results show that both V1/V2 and higher-level visual area LO are critically involved in perceptual completion. However, these areas seem to be involved in an inverse hierarchical fashion, in which the critical time window for V1/V2 follows that for LO. These results are in line with the growing evidence that feedback to V1/V2 contributes to perceptual completion.

A modified version of the Oppel-Kundt illusion (i.e., a filled space is perceived as more expanded than an empty space of the same length) has been previously employed to distort space representation both in patients with neglect (i.e., failure to report/react to stimuli located in the space contralateral to the brain lesion) and in healthy participants. In those experiments, participants had to bisect or extend horizontal segments on backgrounds of exponentially spaced vertical lines. The exclusive use of visuo-motor tasks, however, did not allow excluding that the results were accounted for by a bias occurring at a response level of stimulus processing rather than by a visual illusion. To address this issue, in addition to a traditional line bisection task, a line length estimation task was employed, which allowed separating response and illusion-related factors. The results demonstrated that performance depended on the visual illusion rather than on a response bias. It was concluded that this version of the Oppel-Kundt illusion can be successfully employed to modulate space representation in humans.

One critical question regarding visual cognition concerns how the physical properties of the visual world are represented in early vision and then relayed to high-level vision. Here, we posit a simple theory: Processes that encode object appearance reduce their response to spatial content that is coarser than the size of the attended object. We show that a filtering procedure based on this theory can account for the relative brightness levels of test patches placed in images of natural scenes and for many hard-to-explain brightness illusions. The implication is that the perception of brightness differences in most brightness illusions actually corresponds to physical differences present in the images. Portions of the visual system may encode these physical differences by means of neural processes that adaptively reduce their response to low-spatial-frequency content.

Visible surfaces of three-dimensional objects are reconstructed from two-dimensional retinal images in the early stages of human visual processing. In the computational model of surface reconstruction based on the standard regularization theory, an energy function is minimized. Two types of model have been proposed, called "membrane" and "thin-plate" after their function formulas, in which the first or the second derivative of depth information is used. In this study, the threshold of surface reconstruction from binocular disparity was investigated using a sparse random dot stereogram, and the predictive accuracy of these models was evaluated. It was found that the thin-plate model reconstructed surfaces more accurately than the membrane model and showed good agreement with experimental results. The likelihood that these models imitate human processing of visual information is discussed in terms of the size of receptive fields in the visual pathways of the human cortex.

Variations of the Craik-O'Brien, Müller-Lyer, reversed Müller-Lyer, orthogonal Müller-Lyer, and Ponzo illusions were created using 10 to 12 parallel lines. 20 participants judged which of two physically equal lines in the patterns appeared longer. For 4 of the 5 patterns, the parallel lines created illusions which corresponded to those produced by the template figures. The results suggest that length is encoded by frequency of neural response and that the parallel line illusions, as well as their classical counterparts, emerge from interactions which distort this frequency code.

The Ternus display is an ambiguous, multi-element, apparent-movement animation which can be perceived in two alternative organizations. One of these involves the simultaneous movement of several elements and is called group movement. The other involves the movement of one element only and is called element movement. The present study examined the influence of retinal eccentricity and organizational orientation on the percentage of group-movement reports obtained across a range of interstimulus intervals. Six participants observed 48 variations of the Ternus display over 100 replications and judged the type of movement seen on each trial. Analysis showed that retinal eccentricity had no effect on the appearance of the display. However, compared with horizontally organized elements, obliquely organized and vertically organized elements yielded progressively more group movement across all but the shortest interstimulus intervals. These results represent an orientational anisotropy in the processing of Ternus apparent movement.

Nakamura, et al. recently showed that pigeons experience the standard Müller-Lyer illusion but not the reversed illusion induced by detaching the arrowheads from the target line. This study re-examined pigeons' perception of this reversed figure by using the stimuli known to induce the maximal contrast effect in humans (Fellows, 1967). Pigeons were retrained to classify six lengths of target lines into "long" and "short" categories by pecking two keys on the monitor, ignoring the two brackets so placed that these would not induce an illusion. In the test that followed, two birds responses were not affected by directions of arrowheads, as shown in the previous study. The third pigeon significantly chose "long" for inward-pointing brackets figures (> <) more frequently than for outward-pointing (< >), that is, the direction of illusion was reversed from what is expected in humans. These results suggest that pigeons may not experience illusions induced by contrast with the surrounding stimuli.

Consciousness takes two forms, transitive and intransitive. Transitive consciousness is a matter of being conscious of something or other whereas intransitive consciousness has no object, as being conscious or awake. Of the different forms of transitive consciousness, perceptual, somatic, kinaesthetic and so on, cognitive neuroscience has concentrated on determining the neural concomitants of perceptual consciousness. To be conscious of a percept is to be aware of it and this requires attending to it. This work sets out a hypothesis as to what brain areas are involved in a schizophrenia subject attending and becoming aware of hallucinations. First, the different areas of cortex that support different visual and auditory illusions of percepts are considered. Next it is argued that endogenous activity in these areas of cortex give rise to hallucinations of percepts that are similar to the percepts that these same areas support during illusions. The basis of such endogenous activity, it is suggested, is to be found in the paucity of afferent synapses to these cortical areas. This may occur as a consequence of loss and regression of synapses due to a degenerative disease or because of abnormal synapse formation and regression during childhood and adolescence, as is likely to be the case in schizophrenia. Finally the neural basis of attention and awareness of these hallucinations are considered for subjects suffering from schizophrenia, and a set of important questions posed that await elucidation through future experimental studies.

A peripheral uniform stimulus on a uniform background tends to fade when a ring enclosing the stimulus is flashed briefly, indicating that neural signals external to the stimulus such as those from the ring or those from the background tend to inhibit the onset-response or after-discharge of the stimulus. In this study, a peripheral achromatic line was flashed briefly on an achromatic background while the subject was steadily fixating on a point on the background. It was predicted that the stimulus line would fade due to background inhibition of the onset-response or afterdischarge of the stimulus. On a reference line, subjects indicated two points delimiting the part of the stimulus line which looked uniform in intensity of color. These points converged toward the center of the reference line as the luminance of the stimulus line approached that of the background. Compared to the central uniform part, the nonuniform parts near the endpoints of the stimulus line looked more faded. These results support the idea that the background surrounding a stimulus tends to inhibit the onset-response of after-discharge of the stimulus.

The present work deals with the perception of illusory surfaces assessed by the apparent motion of equal, parallel, and equidistant vertical stripes. Particularly, the influence of a reduction in length of one single stripe was studied. Two alternative perceptions were reported by participants: (a) the stripes seemed to move in a plastic (nonrigid) fashion, or (b) an apparent illusory rectangle was perceived in motion at the top of a complete row of stripes, which appeared to move in a rigid fashion in the opposite direction. In both perceptions, the single shorter stripe lost its identity and was absorbed by the global pattern of stripes in motion. The tendency to maintain identity seems to regard first of all the whole structure. It was found that these perceptions depended on the velocity of presentation of stripes and on the size of the shorter stripe.

Three experiments assessed the influence of the Ebbinghaus illusion on size judgments that preceded verbal, grasp, or touch responses. Prior studies have found reduced effects of the illusion for the grip-scaling component of grasping, and these findings are commonly interpreted as evidence that different visual systems are employed for perceptual judgment and visually guided action. In the current experiments, the magnitude of the illusion was reduced by comparable amounts for grasping and for judgments that preceded grasping (Experiment 1). A similar effect was obtained prior to reaching to touch the targets (Experiment 2). The effect on verbal responses was apparent even when participants were simply instructed that a target touch task would follow the verbal task. After participants had completed a grasping task, the reduction in the magnitude of the illusion remained for a subsequent verbal-response judgment task (Experiment 3). Overall, the studies demonstrate strong connections between action planning and perception.

32 observers judged the size of a letter, either an "A" or an "S," which was surrounded by a circle. Both letters were overestimated, but larger surrounding circles reduced the illusion. Decreasing the lightness contrast of the surrounding circle relative to the central letter diminished the illusion. The results suggest that, like the Delboeuf illusion, these circumscribed letters illusions are produced by interactions among size-coding neurons.

This research on the binocular fusion of phenomenal yellow, given red-filtered flashes of light in one eye and green-filtered flashes of light in the other, directly compared the effects of wider-bandwidth and narrow-bandwidth filtering. 20 male college students with normal stereopsis, Mage = 19.3 yr., SD = 2.2, were tested for the binocular perception of flashing yellow sensations given wider-bandwidth versus narrow-bandwidth filtering of light flashes which, monocularly, were experienced as red sensations in one eye and as green sensations in the other. When 3 wide-bandwidth tests for binocular yellow fusion were alternated with 3 narrow-bandwidth tests, simultaneous flashes of red-filtered light in one eye and green-filtered light in the other were binocularly perceived as yellowish on 25% of the wide-bandwidth tests (SD = 40%)--as yellow on 8% of the tests, orange on 12% of the tests, yellow-green on 5% of the tests-and were binocularly perceived as yellowish on 0% of the narrow-bandwidth tests. When wider-bandwidth and narrow-bandwidth testing were separated spatially and conducted contemporaneously, the red-filtered flashes in one eye and green-filtered flashes in the other were binocularly experienced as yellowish sensations by 80% of all participants under wider-bandwidth conditions--as yellow by 55%, orange by 10%, yellow-green by 15%--and as yellowish sensations by 0% of the participants under narrow-bandwidth conditions.

Response distributions for five cognitive illusions and one visual illusion were examined in two samples, college students (n = 134) and pharmacists (n = 51). These illusions were selected for study on the basis of pharmacists' judgments about associations of illusions to common dispensing errors. Participants were categorized as Illusion-prone or Illusion-resistant, and distributions of such tendencies for the six stimuli used varied within samples. Significant differences between the two samples on illusion-proneness and resistance were observed for the "Moses' Ark" and -Fcount" illusions. Associations of Illusion-prone and Illusion-resistant responses to field-dependence, psychological type, and the cognitive orientations derived from Psychological Type Theory were examined. Field-independence-field-dependence was the only cognitive dimension associated with Illusion-prone and Illusion-resistant responding. Implications of the data for developing measures based upon visual and cognitive illusions to identify people with error-prone tendencies were discussed.

This study examined the effects of background field-of-view and depth plane on the oculogyral illusion. Seven subjects viewed a stationary fixation stimulus during the postrotatory interval following a 45-sec constant-velocity chair rotation. The duration of the illusory movement of the fixation stimulus during the postrotatory interval was measured, along with the duration of the illusion of whole-body rotation (known as the somatogyral illusion) and the duration of the subject's slow-phase vestibular nystagmus. Subjects viewed the fixation stimulus by itself in a No-background condition or when surrounded by six background fields formed by the combination of two fields-of-view (35 degrees and 115 degrees) and three depth-planes (near, coplanar, and far). The different background fields inhibited the oculogyral illusion relative to the No-background condition but did not differ statistically from each other. The somatogyral durations better matched the oculogyral ones than did nystagmus decay, especially when a background field was present. These results suggest that the oculogyral illusion is more related to the experience of whole-body rotation than to oculomotor mechanisms and that the inhibitory effect of a background scene is only modestly affected by its field-of-view and depth plane.

The horizontal-vertical illusion consists of two lines of the same length (one horizontal and the other vertical) at a 90 degree angle from one another forming either an inverted-T or an L-shape. The illusion occurs when the length of a vertical line is perceived as longer than the horizontal line even though they are the same physical length. The illusion has been shown both visually and haptically. The present purpose was to assess differences between the visual or haptic perception of the illusions and also whether differences occur between the inverted-T and the L-shape illusions. The current study showed a greater effect in the haptic perception of the horizontal-vertical illusion than in visual perception. There is also greater illusory susceptibility of the inverted-T than the L-shape.

36 observers judged the size of a central S in variants of the Ebbinghaus figure having contextual Ss, $s, or Hs. When the figures were composed of similarly shaped elements, underestimation of the central S was obtained. Manipulations of lightness indicated that these underestimations were strongest for figures with gray contextual characters and a black central S and weakest for figures with black contextual characters and a gray central S. All black or all gray figures produced intermediate illusions. The data are consistent with Choplin and Medin's 1999 claim that figural properties rather than semantic similarity influences size contrast and further show that the visual processes underlying size contrast include interactions of contours.

The study compared electrical brain activity of 6 subjects in 5 different conditions. Absolute theta and alpha power in the frontal, parietal, and occipital areas were analyzed, with significant differences found only in the frontal area. Results suggested that the perception of movement requires higher order cognitive processing outside the occipital area. Implications for education and cognitive research are discussed.

Visual phantoms are a perceptual completion illusion wherein contours and surfaces are seen where none physically exist. The visibility of moving phantoms was measured with equiluminant and near equiluminant chromatic inducing gratings for observers having a fundus classified as either darkly or lightly pigmented. Phantom visibility was greatest for observers with a lightly compared to a darkly pigmented fundus with the two groups showing differences in visibility as a function of background luminance. The results are discussed relative to equiluminant stationary phantom findings and a proposed relationship between phantom visibility and magnocellular pathway activity.

It has been suggested that lateral neural interactions contribute to some illusions with intersecting or converging line elements but cannot be present in figures that lack these components. Most attempts to ascertain the contribution of neural interactions in visual illusions have involved changes in the actual pattern of illusion. It has now been demonstrated that certain forms of intermittent light stimulation can enhance lateral inhibitory activity. The Wundt-Hering and the Delboeuf illusions were tested under continuous illumination and "shaped" intermittent illumination which augments lateral inhibition. As expected, the Delboeuf illusion was unchanged with increased lateral inhibition while the magnitude of the Wundt-Hering illusion increased.

Two eponyms, the Purkinje phenomenon and the Bezold-Brücke phenomenon, are sometimes confused in discussions of the effect of light intensity upon perceived color. The former refers to a change in apparent brightness; the latter refers to a change in perceived hue.

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.

The effects of a tryptophan-free amino acid mixture on tilt aftereffect, movement aftereffect, and the Mueller-Lyer illusion were studied. 12 male subjects ingested either a balanced amino acid mixture or a tryptophan-free mixture which causes a marked depletion of brain tryptophan and serotonin. The tryptophan-free mixture significantly increased the strength of tilt aftereffect but had no effect on movement aftereffect or the Mueller-Lyer illusion. These results were discussed with reference to the pharmacological activity of serotonin and its influence on the strength of lateral inhibition in mammalian brains.

Prolonged induced movement-in-depth in a static circle was elicited by a spiral stimulus. Afterwards an aftereffect was observed in the circle. The aftereffect was towards the subject after induced movement away from the subject, and away from the subject after induced movement towards the subject. Longer aftereffect was observed with a circle central to the inducing stimulus than with a circle peripheral to the inducing stimulus. In contrast to some other psychophysical effects, no clear-cut directional asymmetry was observed.

A model for the determination of retinal-image size is presented. The size-analysis is based upon the range of orientation detectors activated by a stimulus. The model is applied to size aftereffects and is also used to predict changes in perceived size in configurations which may be expected to affect the range of orientation detectors activated. The relevance of the model to illusions of direction and the perceived length of lines forming angles is also discussed.

The duration of the aftereffect induced by viewing a rotating disc was recorded separately for the four hemiretinae of the left and right eyes using a new method of measurement. The results showed duration of aftereffect to differ between nasal and temporal hemiretinae of the right eye and between left and right cerebral hemispheres.

A theory is proposed which transforms visual neural signals into the psychological information and which explains visual illusions. As an example, Poggendorff's illusion is explained.

Polarized lenses were employed to present the components of four line illusions separately to each eye. The phenomena were perceived even when both images were disparately presented, leading to the conclusion that the effect originates in the central nervous system and does not require the retina.

Polarized lenses were employed to present the images of the colored shadows effect separately to each eye. The phenomenon was perceived only when both images were viewed on the same retina, leading to the conclusion that the effect is entirely retinal in origin and does not involve the central nervous system.

The effects of artificial pupil size and the effects of a power lens upon the relative prominence of illusory contour were evaluated. The perception of illusory contour was facilitated by conditions associated with increased retinal blur and brightness averaging. This was true whether the blur and averaging were achieved using a large artificial pupil or a power lens. The effects of power lens and the effects of artificial pupil size upon the occurrence of brightness contrast and brightness contrast-reversal (or assimilation) were also investigated. Brightness contrast was changed to brightness contrast-reversal by using either a power lens or a large artificial pupil. The occurrence of vivid illusory contour under conditions found conductive to brightness contrast-reversal was interpreted as evidence that contrast-reversal was more crucial in illusory contour formation that brightness contrast.

To compare the influence of the projected retinal size and of the figure size on the perception of the horizontal-vertical illusion, the target size, the viewing distance, and the slant of an illusion figure were varied. In the first experiment the illusion produced by two figures of the same object size but of different retinal size was compared with that of two figures projecting the same retinal size but differing in object size. The illusion diminished when the size of the retinal projection was increased, whereas a change in figure size did not change the illusion. In Exp. II the illusion figure was tilted backwards which reduced the retinal projection of the 'vertical' figure limb. The illusion decreased and became negative as a function of the retinal projection, but this decrease was relatively small compared with the reduction of the retinal image. The results are interpreted as supporting a retinal origin as an explanation of the illusion. Although there is strong evidence for size-constancy scaling in a tilted figure, constancy scaling is considered of minor importance as a determinant of the usual illusion.

18 RDC-diagnosed schizophrenic patients (11 men, 7 women) were compared to 84 normal men with three computerized neuropsychological methods, assumed to reflect lateralized and frontal cortical functions: (1) Bilateral Finger Tapping and Finger Alternation, (2) Bilateral Trail Making, and (3) passively perceived Necker cube reversals. Schizophrenics differed from normals by (1) inferior Tapping/Alternation but only in the right hand, (2) inferior Trail Making, most pronounced for Form B, and (3) lower frequency of Necker cube reversals. Patients with previous neuroleptic medication and prior psychiatric hospitalizations were inferior in Trail Making and had fewer Necker cube reversals. The findings were interpreted in line with recent models of schizophrenia involving a left-hemisphere dysfunction/over-activation and a frontal dysfunction.

Selective adaptation patterns of simple contours and geometrical illusions under monocular stimulation were studied with five subjects. A strict property analyzer model predicted that adaptation patterns would mirror figural contours of both types of forms. The results supported this hypothesis: the geometrical illusions generated adaptation patterns reflecting their physical stimulus properties rather than the illusory percept resulting from contextual juxtaposition. The results are discussed with respect to a model of feature extraction which assumes that property analyzers possess a sensitivity bandwidth.

The results of earlier monocular experiments on the moon illusion have been either negative or confounded. To test the role of vestibular function, 24 subjects made forced-choice distance comparisons between stimuli mounted in translucent tubes. The stimulus tube for standard distance could be positioned in three viewing angles (45 degrees up, horizontal, and 45 degrees down). A comparison tube adjustable for distance was mounted horizontally. There was a greater perception of depth in the downward looking condition. The relatively weak effects are discussed in terms of a two-hypothesis explanation of the real-life moon illusion and the poor cues for depth perception in monocular viewing.