A review on various explanations of Ponzo-like illusions

Visual perceptual learning is effective in the illusory far but not in the near space

Visual shape discrimination is faster for objects close to the body, in the peripersonal space (PPS), compared with objects far from the body. Visual processing enhancement in PPS occurs also when perceived depth is based on 2D pictorial cues. This advantage has been observed from relatively low-level (detection, size, orientation) to high-level visual features (face processing). While multisensory association also displays proximal advantages, whether PPS influences visual perceptual learning remains unclear. Here, we investigated whether perceptual learning effects vary according to the distance of visual stimuli (near or far) from the observer, illusorily induced by leveraging the Ponzo illusion. Participants performed a visual search task in which they reported whether a specific target object orientation (e.g., triangle pointing downward) was present among distractors. Performance was assessed before and after practicing the visual search task (30 minutes/day for 5 days) at either the close (near group) or far (far group) distance. Results showed that participants that performed the training in the near space did not improve. By contrast, participants that performed the training in the far space showed an improvement in the visual search task in both the far and near spaces. We suggest that such improvement following the far training is due to a greater deployment of attention in the far space, which could make the learning more effective and generalize across spaces.

An attentional approach to geometrical illusions

It is known for a long time that some drawings composed of points, lines, and areas are systematically misperceived. The origin of these geometrical illusions is still unknown. Here we outline how a recent progress in attentional research contributes to a better understanding of such perceptual distortions. The basic idea behind this approach is that crucial elements of a drawing are differently attended. These changes in the allocation of spatial attention go along with systematic changes in low-level spatial coding. As a result, changes in the perception of spatial extent, angles, positions, and shapes can arise. How this approach can be applied to individual illusions is discussed.

Overlapping yet dissociable contributions of superiority illusion features to Ponzo illusion strength and metacognitive performance

Humans are typically inept at evaluating their abilities and predispositions. People dismiss such a lack of metacognitive insight into their capacities while even enhancing (albeit illusorily) self-evaluation such that they should have more desirable traits than an average peer. This superiority illusion helps maintain a healthy mental state. However, the scope and range of its influence on broader human behavior, especially perceptual tasks, remain elusive. As belief shapes the way people perceive and recognize, the illusory self-superiority belief potentially regulates our perceptual and metacognitive performance. In this study, we used hierarchical Bayesian estimation and machine learning of signal detection theoretic measures to understand how the superiority illusion influences visual perception and metacognition for the Ponzo illusion. Our results demonstrated that the superiority illusion correlated with the Ponzo illusion magnitude and metacognitive performance. Next, we combined principal component analysis and cross-validated regularized regression (relaxed elastic net) to identify which superiority components contributed to the correlations. We revealed that the "extraversion" superiority dimension tapped into the Ponzo illusion magnitude and metacognitive ability. In contrast, the "honesty-humility" and "neuroticism" dimensions only predicted Ponzo illusion magnitude and metacognitive ability, respectively. These results suggest common and distinct influences of superiority features on perceptual sensitivity and metacognition. Our findings contribute to the accumulating body of evidence indicating that the leverage of superiority illusion is far-reaching, even to visual perception.

A novel model of divergent predictive perception

Predictive processing theories state that our subjective experience of reality is shaped by a balance of expectations based on previous knowledge about the world (i.e. priors) and confidence in sensory input from the environment. Divergent experiences (e.g. hallucinations and synaesthesia) are likely to occur when there is an imbalance between one's reliance on priors and sensory input. In a novel theoretical model, inspired by both predictive processing and psychological principles, we propose that predictable divergent experiences are associated with natural or environmentally induced prior/sensory imbalances: inappropriately strong or inflexible (i.e. maladaptive) high-level priors (beliefs) combined with low sensory confidence can result in reality discrimination issues, a characteristic of psychosis; maladaptive low-level priors (sensory expectations) combined with high sensory confidence can result in atypical sensory sensitivities and persistent divergent percepts, a characteristic of synaesthesia. Crucially, we propose that whether different divergent experiences manifest with dominantly sensory (e.g. hallucinations) or nonsensory characteristics (e.g. delusions) depends on mental imagery ability, which is a spectrum from aphantasia (absent or weak imagery) to hyperphantasia (extremely vivid imagery). We theorize that imagery is critically involved in shaping the sensory richness of divergent perceptual experience. In sum, to predict a range of divergent perceptual experiences in both clinical and general populations, three factors must be accounted for: a maladaptive use of priors, individual level of confidence in sensory input, and mental imagery ability. These ideas can be expressed formally using nonparametric regression modeling. We provide evidence for our theory from previous work and deliver predictions for future research.

Internal representations of the canonical real-world distance of objects

In the real world, every object has its canonical distance from observers. For example, airplanes are usually far away from us, whereas eyeglasses are close to us. Do we have an internal representation of the canonical real-world distance of objects in our cognitive system? If we do, does the canonical distance influence the perceived size of an object? Here, we conducted two experiments to address these questions. In Experiment 1, we first asked participants to rate the canonical distance of objects. Participants gave consistent ratings to each object. Then, pairs of object images were presented one by one in a trial, and participants were asked to rate the distance of the second object (i.e., a priming paradigm). We found that the rating of the perceived distance of the target object was modulated by the canonical real-world distance of the prime. In Experiment 2, participants were asked to judge the perceived size of canonically near or far objects that were presented at the converging end (i.e., far location) or the opening end (i.e., near location) of a background image with converging lines. We found that regardless of the presentation location, participants perceived the canonically near object as smaller than the canonically far object even though their retinal and real-world sizes were matched. In all, our results suggest that we have an internal representation of the canonical real-world distance of objects, which affects the perceived distance of subsequent objects and the perceived size of the objects themselves.

Linear perspective cues have a greater effect on the perceptual rescaling of distant stimuli than textures in the virtual environment

The presence of pictorial depth cues in virtual environments is important for minimising distortions driven by unnatural viewing conditions (e.g., vergence-accommodation conflict). Our aim was to determine how different pictorial depth cues affect size constancy in virtual environments under binocular and monocular viewing conditions. We systematically removed linear perspective cues and textures of a hallway in a virtual environment. The experiment was performed using the method of constant stimuli. The task required participants to compare the size of 'far' (10 m) and 'near' (5 m) circles displayed inside a virtual environment with one or both or none of the pictorial depth cues. Participants performed the experiment under binocular and monocular viewing conditions while wearing a virtual reality headset. ANOVA revealed that size constancy was greater for both the far and the near circles in the virtual environment with pictorial depth cues compared to the one without cues. However, the effect of linear perspective cues was stronger than textures, especially for the far circle. We found no difference between the binocular and monocular viewing conditions across the different virtual environments. We conclude that linear perspective cues exert a stronger effect than textures on the perceptual rescaling of far stimuli placed in the virtual environment, and that this effect does not vary between binocular and monocular viewing conditions.

Phenomenology, Quantity, and Numerosity

There are many situations in which we interact with collections of objects, from a crowd of people to a bowl of blackberries. There is an experience of the quantity of these items, although not a precise number, and we have this impression quickly and effortlessly. It can be described as an expressive property of the whole. In the literature, the study of this sense of numerosity has a long history, which is reviewed here with examples. I argue that numerosity is a direct perceptual experience, and that all experiences of numerosity, not only estimations, are affected by perceptual organisation.

Effects of normalized summation in the visual illusion of extent

In the present study, the features of summation of effects caused by contextual distracting dots in the length-matching task (a variant of the filled-space illusion) were investigated. In the first two series of psychophysical experiments, the illusion magnitude was measured as a function of the displacement of distractors (either single or double sets of dots) orthogonally to the main axis of the stimulus. It was demonstrated that with increasing displacement, the illusion smoothly decreases for a single set of distractors, while for two sets, the illusion first increases to a certain maximum value, and then gradually decreases. In the third and fourth series of experiments, magnitude of the illusion was measured as a function of the luminance of one set of distracting dots, while the luminance of the other set was fixed. It has been shown that increasing the luminance until the same value is reached for both sets leads to a monotonous growth in the illusion magnitude; after that, the illusion asymptotically decreases to an almost constant level. The theoretical interpretation of the established functional dependencies was performed using a quantitative model based on the assumption that the illusion may arise due to the weighted summation of the distractor-induced normalized neural activity, which leads to the perceptual mislocalization of terminators of stimulus spatial intervals.

The long and short of it? A novel geometric illusion

Here we present what we believe to be a novel geometric illusion where identical lines are perceived as being of differing lengths. Participants were asked to report which of the two parallel rows of horizontal lines contained the longer individual lines (two lines on one row and 15 on the other). Using an adaptive staircase we adjusted the length of the lines on the row containing two to estimate the point of subjective equality (PSE). At the PSE, the two lines were consistently shorter than the row containing the fixed length of 15 lines demonstrating a disparity in perceived length such that lines of identical length are perceived as longer in a row of two than in a row of 15. The illusion magnitude was unaffected by which row was presented above the other. Additionally, the effect persisted when using one as opposed to two test lines, and when the line stimuli on both rows were presented with alternating luminance polarity the illusion magnitude decreased, but was not abolished. The data indicate a robust geometric illusion that may be modulated by perceptual grouping processes.

Deconfounded and mixed-symmetry versions of the Ponzo illusion figure

One of the original Ponzo illusion figures, which consists of two converging lines between which two parallel lines of similar length have been inserted orthogonal to the figure's axis of mirror symmetry, was itself mirror-reflected so that the overall shape of the figure became "< >" or "> <", and one line at a time was inserted into each half. The usual illusion - the overestimation of the length of a line that is nearer to a vertex than a farther-away comparison line - occurred. Experiments 1 and 2 used different distances of target and comparison lines to the vertices, but identical distances of these lines from the converging lines, and so, as a tandem, deconfounded the two variables. Experiments 3 and 4 changed the symmetries of the modified Ponzo figure by reducing opposing half-angles of the converging lines or by tilting target and comparison lines concordantly or discordantly. The first measure, which created unequal distances of the endpoints of the target and comparison lines from the converging lines, hardly affected the amount of illusion. The second measure often attenuated the illusion - equally so for concordant and discordant tilts - suggesting that global and local symmetries of the stimuli, and their accordance, were less important than the vertical versus oblique orientation of target and comparison lines. Descriptively, the main cause of the Ponzo illusion seems to be the size of the gap between target and converging lines. The neural substrate of the effect may be interactions between orientation-sensitive and end-inhibited neurons.

Intrinsic excitability of human right parietal cortex shapes the experienced visual size illusions

Converging evidence has found that the perceived visual size illusions are heritable, raising the possibility that visual size illusions might be predicted by intrinsic brain activity without external stimuli. Here we measured resting-state brain activity and 2 classic visual size illusions (i.e. the Ebbinghaus and the Ponzo illusions) in succession, and conducted spectral dynamic causal modeling analysis among relevant cortical regions. Results revealed that forward connection from right V1 to superior parietal lobule (SPL) was predictive of the Ebbinghaus illusion, and self-connection in the right SPL predicted the Ponzo illusion. Moreover, disruption of intrinsic activity in the right SPL by repetitive transcranial magnetic stimulation (TMS) temporally increased the Ebbinghaus rather than the Ponzo illusion. These findings provide a better mechanistic understanding of visual size illusions by showing the causal and distinct contributions of right parietal cortex to them, and suggest that spontaneous fluctuations in intrinsic brain activity are relevant to individual difference in behavior.

The combination of target motion and dynamic changes in context greatly enhance visual size illusions

Perceived size is a function of viewing distance, retinal images size, and various contextual cues such as linear perspective and the size and location of neighboring objects. Recently, we demonstrated that illusion magnitudes of classic visual size illusions may be greatly enhanced or reduced by adding dynamic elements. Specifically, a dynamic version of the Ebbinghaus illusion (classically considered a “size contrast” illusion) led to a greatly enhanced illusory effect, whereas a dynamic version of the Corridor illusion (a “size constancy” illusion) led to a greatly diminished illusory effect. Although these differences may arise from the different processes underlying these illusions (size contrast vs. size constancy), the dynamic variants we tested in our previous work also differed in the nature of the dynamic elements; specifically, whereas the Dynamic Ebbinghaus included a moving target and inducers that changed size and position, the Dynamic Corridor only included a moving target on a static background. Here, we explore further dynamic versions of the Ebbinghaus illusion and the Corridor and Ponzo illusions by separately manipulating three types of dynamic elements: target motion, context translation, and dynamic changes in context. Across five experiments examining 21 dynamic illusory configurations, adding target motion or a dynamically changing context separately resulted in little-to-no illusory effect. In contrast, the combination of target motion and a dynamically changing context led to a robust size illusion, consistent with an interactive effect. However, illusory effects that exceeded the matched classic, static illusory configuration were only observed for the dynamic versions of the Ebbinghaus illusion and the Revealed Ponzo illusions, in which the contextual elements changed size. We conclude that the combination of target motion and a dynamically changing context are necessary to produce dynamic size illusions, but that enhancement above and beyond static illusions may be largely specific to size contrast effects. Our results have important implications for the integration of motion signals, a ubiquitous environmental stimulus, in the perception of object size.

The Effects of Adding Pictorial Depth Cues to the Poggendorff Illusion

We tested if the misapplication of perceptual constancy mechanisms might explain the perceived misalignment of the oblique lines in the Poggendorff illusion. Specifically, whether these mechanisms might treat the rectangle in the middle portion of the Poggendorff stimulus as an occluder in front of one long line appearing on either side, causing an apparent decrease in the rectangle’s width and an apparent increase in the misalignment of the oblique lines. The study aimed to examine these possibilities by examining the effects of adding pictorial depth cues. In experiments 1 and 2, we presented a central rectangle composed of either large or small bricks to determine if this manipulation would change the perceived alignment of the oblique lines and the perceived width of the central rectangle, respectively. The experiments demonstrated no changes that would support a misapplication of perceptual constancy in driving the illusion, despite some evidence of perceptual size rescaling of the central rectangle. In experiment 3, we presented Poggendorff stimuli in front and at the back of a corridor background rich in texture and linear perspective depth cues to determine if adding these cues would affect the Poggendorff illusion. The central rectangle was physically large and small when presented in front and at the back of the corridor, respectively. The strength of the Poggendorff illusion varied as a function of the physical size of the central rectangle, and, contrary to our predictions, the addition of pictorial depth cues in both the central rectangle and the background decreased rather than increased the strength of the illusion. The implications of these results with regards to different theories are discussed. It could be the case that the illusion depends on both low-level and cognitive mechanisms and that deleterious effects occur on the former when the latter ascribes more certainty to the oblique lines being the same line receding into the distance.

Information Exchange between Cortical Areas: The Visual System as a Model

As nearly all brain functions, perception, motion, and higher-order cognitive functions require coordinated neural information processing within distributed cortical networks. Over the past decades, new theories and techniques emerged that advanced our understanding of how information is transferred between cortical areas. This review surveys critical aspects of interareal information exchange. We begin by examining the brain’s structural connectivity, which provides the basic framework for interareal communication. We then illustrate information exchange between cortical areas using the visual system as an example. Next, well-studied and newly proposed theories that may underlie principles of neural communication are reviewed, highlighting recent work that offers new perspectives on interareal information exchange. We finally discuss open questions in the study of the neural mechanisms underlying interareal information exchange.