Ponzo Illusion Research Articles

A review on various explanations of Ponzo-like illusions.

This article reviews theoretical and empirical arguments for and against various theories that explain the classic Ponzo illusion and its variants from two different viewpoints concerning the role of perceived depth in size distortions. The first viewpoint argues that all Ponzo-like illusions are driven by perceived depth. The second viewpoint argues that the classic Ponzo illusion is unrelated to depth perception. This review will give special focus to the first viewpoint and consists of three sections. In the first section, the role of the number of pictorial depth cues and previous experience in the strength of all Ponzo-like illusions are discussed. In the second section, we contrast the first viewpoint against the theories that explain the classic Ponzo illusion with mechanisms that are unrelated to depth perception. In the last section, we propose a Bayesian-motivated reconceptualization of Richard Gregory's misapplied size constancy theory that explains Ponzo-variant illusions in terms of prior information and prediction errors. The new account explains why some studies have provided inconsistent evidence for misapplied size constancy theory.

Number is not just an illusion: Discrete numerosity is encoded independently from perceived size

While seminal theories suggest that nonsymbolic visual numerosity is mainly extracted from segmented items, more recent views advocate that numerosity cannot be processed independently of nonnumeric continuous features confounded with the numerical set (i.e., such as the density, the convex hull, etc.). To disentangle these accounts, here we employed two different visual illusions presented in isolation or in a merged condition (e.g., combining the effects of the two illusions). In particular, in a number comparison task, we concurrently manipulated both the perceived object segmentation by connecting items with Kanizsa-like illusory lines, and the perceived convex-hull/density of the set by embedding the stimuli in a Ponzo illusion context, keeping constant other low-level features. In Experiment 1, the two illusions were manipulated in a compatible direction (i.e., both triggering numerical underestimation), whereas in Experiment 2 they were manipulated in an incompatible direction (i.e., with the Ponzo illusion triggering numerical overestimation and the Kanizsa illusion numerical underestimation). Results from psychometric functions showed that, in the merged condition, the biases of each illusion summated (i.e., largest underestimation as compared with the conditions in which illusions were presented in isolation) in Experiment 1, while they averaged and competed against each other in Experiment 2. These findings suggest that discrete nonsymbolic numerosity can be extracted independently from continuous magnitudes. They also point to the need of more comprehensive theoretical views accounting for the operations by which both discrete elements and continuous variables are computed and integrated by the visual system.

On the Search for Brain Bifurcation Parameters: Lessons From FMRI Studies on Visual Illusions

Data from three functional magnetic resonance imaging (fMRI) studies that involved in total about 100 participants and showed that the strength of several visual illusions such as the Ebbinghaus, Ponzo, and Muller-Lyer illusions depends on neuroanatomical subject measures such as visual cortex surface area and parahippocampal cortex gray matter volume were evaluated using a dynamical systems perspective to determine brain bifurcation parameters. Bifurcation parameters that involved power laws and captured relational dependencies were fitted separately to the three fMRI studies. The bifurcation parameter hypothesis that states that such parameters show unique quantities and are no longer correlated to structural systems properties was tested. The power law exponents and mean bifurcation parameter values were determined. For all three studies and three illusion types, the bifurcation parameter hypothesis was supported. Accordingly, the constructed parameters characterized the reactions of the participants under the Ebbinghaus, Ponzo, and Muller-Lyer illusions in terms of unique threshold values that no longer depended on neuroanatomical subject measures. Power law exponents in the range from 1 to 7 were found. The fMRI data describing gray matter volume of certain active regions in the parahippocampal cortex showed some interesting relationship between the mean bifurcation parameter values.

Anodal Occipital Transcranial Direct Current Stimulation Enhances Perceived Visual Size Illusions.

Human early visual cortex has long been suggested to play a crucial role in context-dependent visual size perception through either lateral interaction or feedback projections from higher to lower visual areas. We investigated the causal contribution of early visual cortex to context-dependent visual size perception using the technique of transcranial direct current stimulation and two well-known size illusions (i.e., the Ebbinghaus and Ponzo illusions) and further elucidated the underlying mechanism that mediates the effect of transcranial direct current stimulation over early visual cortex. The results showed that the magnitudes of both size illusions were significantly increased by anodal stimulation relative to sham stimulation but left unaltered by cathodal stimulation. Moreover, the anodal effect persisted even when the central target and surrounding inducers of the Ebbinghaus configuration were presented to different eyes, with the effect lasting no more than 15 min. These findings provide compelling evidence that anodal occipital stimulation enhances the perceived visual size illusions, which is possibly mediated by weakening the suppressive function of the feedback connections from higher to lower visual areas. Moreover, the current study provides further support for the causal role of early visual cortex in the neural processing of context-dependent visual size perception.

Interocular transfer effects of linear perspective cues and texture gradients in the perceptual rescaling of size

Our objective was to determine whether the influence of linear perspective cues and texture gradients in the perceptual rescaling of stimulus size transfers from one eye to the other. In experiment 1, we systematically added linear perspective cues and texture gradients in a background image of the corridor illusion. To determine whether perceptual size rescaling takes place at earlier or later stages, we tested how the perceived size of top and bottom rings changed under binocular (rings and background presented to both eyes), monocular (rings and background presented to the dominant eye only), and dichoptic (rings and background presented separately to the dominant and nondominant eyes, respectively) viewing conditions. We found differences between viewing conditions in the perceived size of the rings when linear perspective cues, but not texture gradients, were presented. Specifically, linear perspective cues produced a stronger illusion under the monocular compared to the dichoptic viewing condition. Hence, there was partial interocular transfer from the linear perspective cues, suggesting a dominant role of monocular neural populations in mediating the corridor illusion. In experiment 2, we repeated similar procedures with a more traditional Ponzo illusion background. Contrary to findings from experiment 1, there was a full interocular transfer with the presence of the converging lines, suggesting a dominant role of binocular neural populations. We conclude that higher order visual areas, which contain binocular neural populations, are more involved in the perceptual rescaling of size evoked by linear perspective cues in the Ponzo compared to the corridor illusion.

Double dissociation between perception and action in children

Previous research has demonstrated a functional dissociation between vision for perception and vision for action. However, the developmental trajectory of this functional dissociation is not well understood. We directly compared the sensitivity of grasping and perceptual estimations within the same experimental design to the real and illusory sizes of objects positioned in the Ponzo illusion display. Two different-sized objects were placed such that the differences between their real sizes and their perceived sizes were pitted against each other. Children aged 5–8 years and adults made perceptual size discriminations and then grasped (action) or estimated (perception) one of the objects based on its perceived size. Consistent with previous results, for the action task, grasping apertures of adults were scaled with the physical differences in the objects’ sizes, even in trials where their overt perceptual decisions were deceived by the illusion. In contrast, perceptual estimations were robustly modulated by the illusion. Interestingly, children outperformed adults in their perceptual discriminations but exhibited adult-like behavior in grasping and in perceptual estimations of the objects, demonstrating a dissociation between perception and action. These results suggest that although the two visual functions are not operating at fully mature levels during childhood, some key mechanisms that support a dissociation between these functions are already in place.

Consciously monitored grasping is vulnerable to perceptual intrusions.

The idea of functional differentiation between vision-for-action and vision-for-perception has been supported by evidence from different domains. According to this account, perception is based on consciously accessible, relative representations, whereas vision-for-action is performed in an analytic, automatic manner. Support for this idea comes from studies that showed that unlike perception, grasping movements are refractory to illusions and to Weber's law. Yet, interactions between the systems may occur when an action is performed in a less automated fashion. To test this idea, we asked participants to monitor their fingers apertures in flight and to halt their movement for a short duration when they felt that their aperture reached a maximum amount. The results showed that movements in the monitored condition were biased by the Ponzo illusion and showed atypical adherence to Weber's law. These results show that action and perception are more likely to interact when movements are performed in a controlled manner.

A double dissociation between action and perception in bimanual grasping: evidence from the Ponzo and the Wundt\u2013Jastrow illusions

Research on visuomotor control suggests that visually guided actions toward objects rely on functionally distinct computations with respect to perception. For example, a double dissociation between grasping and between perceptual estimates was reported in previous experiments that pit real against illusory object size differences in the context of the Ponzo illusion. While most previous research on the relation between action and perception focused on one-handed grasping, everyday visuomotor interactions also entail the simultaneous use of both hands to grasp objects that are larger in size. Here, we examined whether this double dissociation extends to bimanual movement control. In Experiment 1, participants were presented with different-sized objects embedded in the Ponzo Illusion. In Experiment 2, we tested whether the dissociation between perception and action extends to a different illusion, the Wundt–Jastrow illusion, which has not been previously used in grasping experiments. In both experiments, bimanual grasping trajectories reflected the differences in physical size between the objects; At the same time, perceptual estimates reflected the differences in illusory size between the objects. These results suggest that the double dissociation between action and perception generalizes to bimanual movement control. Unlike conscious perception, bimanual grasping movements are tuned to real-world metrics, and can potentially resist irrelevant information on relative size and depth.

When illusions merge.

We recently found only weak correlations between the susceptibility to various visual illusions. However, we observed strong correlations among different variants of an illusion, suggesting that the visual space of illusions includes several illusion-specific factors. Here, we specifically examined how factors for the vertical–horizontal, Müller–Lyer, and Ponzo illusions relate to each other. We measured the susceptibility to each illusion separately and to combinations of two illusions, which we refer to as a merged illusion; for example, we tested the Müller–Lyer illusion and the vertical–horizontal illusion, as well as a merged version of both illusions. We used an adjustment procedure in two experiments with 306 and 98 participants, respectively. Using path analyses, correlations, and exploratory factor analyses, we found that the susceptibility to a merged illusion is well predicted from the susceptibilities to the individual illusions. We suggest that there are illusion-specific factors that, by independent combinations, represent the whole visual structure underlying illusions.

Individual differences in the Müller-Lyer and Ponzo illusions are stable across different contexts.

Vision scientists have attempted to classify visual illusions according to certain aspects, such as brightness or spatial features. For example, Piaget proposed that visual illusion magnitudes either decrease or increase with age. Subsequently, it was suggested that illusions are segregated according to their context: real-world contexts enhance and abstract contexts inhibit illusion magnitudes with age. We tested the effects of context on the Müller-Lyer and Ponzo illusions with a standard condition (no additional context), a line-drawing perspective condition, and a real-world perspective condition. A mixed-effects model analysis, based on data from 76 observers with ages ranging from 6 to 66 years, did not reveal any significant interaction between context and age. Although we found strong intra-illusion correlations for both illusions, we found only weak inter-illusion correlations, suggesting that the structure underlying these two spatial illusions includes several specific factors.

Neural Correlates of Perceptual Grouping Under Conditions of Inattention and Divided Attention.

Grouping local elements of the visual environment together is crucial for meaningful perception. While our attentional system facilitates perception, it is limited in that we are unaware of some aspects of our environment that can still influence how we experience it. In this study, the neural mechanisms underlying the Ponzo illusion were examined under inattention and divided-attention conditions using functional magnetic resonance imaging to investigate the brain regions responsible for accessing visual stimuli. A line discrimination task was performed in which two horizontal lines were superimposed on a background of black and white dots that, on occasion, induced the Ponzo illusion if perceptually grouped together. Our findings revealed activation for perceptual grouping in the frontal, parietal, and occipital regions of the brain and activation in the bilateral frontal, temporal, and cingulate gyrus in response to divided attention compared with inattention trials. A direct comparison between grouping and attention showed involvement of the right supramarginal gyrus in grouping specifically under conditions of inattention, suggesting that even during implicit grouping complex visual processing occurs. Given that much of the visual world is not represented in conscious perception, these findings provide crucial information about how we make sense of visual scenes in the world.

The estimation of the Müller-lyer and Ponzo illusions under the influence of physical fatigue induced by Harvard step test

Abstract We had studied the influence of physical fatigue induced by 5 min Harvard step test onto the strength of well-known visual illusions - Muller-Lyer and Ponzo. The responses of the volunteers were registered either in visual or in sensorimotor domain. The results did not show any significant changes in illusion’s strength and speed of hand movements on the stimuli shafts between control and experimental group. Thus we propose that the dependence of the illusion’s strength on the physical load or stress reported in some works is due to experimental design but not to the physical load by itself.

Influences of orientation on the Ponzo, contrast, and Craik-O\u2019Brien-Cornsweet illusions

Explanations of the Ponzo size illusion, the simultaneous contrast illusion, and the Craik-O’Brien-Cornsweet brightness illusions involve either stimulus-driven processes (assimilation, enhanced contrast, and anchoring) or prior experiences. Real-world up-down asymmetries for typical direction of illumination and ground planes in our physical environment should influence these illusions if they are experience based, but not if they are stimulus driven. Results presented here demonstrate differences in illusion strengths between upright and inverted versions of all three illusions. A left-right asymmetry of the Cornsweet illusion was produced by manipulating the direction of illumination, providing further support for the involvement of an experience-based explanation. When the inducers were incompatible with the targets being located at the different distances, the Ponzo illusion persisted and so did the influence from orientation, providing evidence for involvement of processes other than size constancy. As defined here, upright for the brightness illusions is consistent with an interpretation of a shaded bulging surface and a 3D object resulting from a light-from-above assumption triggering compensation for varying illumination. Upright for the Ponzo illusion is consistent with the inducers in the form of converging lines being interpreted as railway tracks receding on the ground triggering size constancy effects. The implications of these results, and other results providing evidence against experience-based accounts of the illusions, are discussed.

The contribution of linear perspective cues and texture gradients in the perceptual rescaling of stimuli inside a Ponzo illusion corridor.

We examined the influence of linear perspective cues and texture gradients in the perceptual rescaling of stimuli over a highly-salient Ponzo illusion of a corridor. We performed two experiments using the Method of Constant Stimuli where participants judged the size of one of two rings. In experiment 1, one ring was presented in the upper visual-field at the end of the corridor and the other in the lower visual-field at the front of the corridor. The perceived size of the top and bottom rings changed as a function of the availability of linear perspective and textures. In experiment 2, only one ring was presented either at the top or the bottom of the image. The perceived size of the top but not the bottom ring changed as a function of the availability of linear perspective and textures. In both experiments, the effects of the cues were additive. Perceptual rescaling was also stronger for the top compared to the bottom ring. Additional eye-tracking revealed that participants tended to gaze more in the upper than the lower visual-field. These findings indicate that top-down mechanisms provide an important contribution to the Ponzo illusion. Nonetheless, additional maximum likelihood estimation analyses revealed that linear perspective fulfilled a greater contribution in experiment 2, which is suggestive of a bottom-up mechanism. We conclude that both top-down and bottom-up mechanisms play important roles. However, the former seems to fulfil a more prominent role when both stimuli are presented in the image.

Scenes Modulate Object Processing Before Interacting With Memory Templates

When searching for relevant objects in our environment (say, an apple), we create a memory template (a red sphere), which causes our visual system to favor template-matching visual input (applelike objects) at the expense of template-mismatching visual input (e.g., leaves). Although this principle seems straightforward in a lab setting, it poses a problem in naturalistic viewing: Two objects that have the same size on the retina will differ in real-world size if one is nearby and the other is far away. Using the Ponzo illusion to manipulate perceived size while keeping retinal size constant, we demonstrated across 71 participants that visual objects attract attention when their perceived size matches a memory template, compared with mismatching objects that have the same size on the retina. This shows that memory templates affect visual selection after object representations are modulated by scene context, thus providing a working mechanism for template-based search in naturalistic vision.

Effects of Five-Day “Dry” Immersion on the Strength of the Ponzo and the Müller-Lyer Illusions

The parameters of the verbal and sensorimotor responses to the Muller-Lyer and Ponzo illusions were determined in two groups spending five days in support unloading produced by “dry” immersion. Subjects in the “immersion” (IM) group were not exposed to any treatment other than immersion. Subjects of the “immersion + weight loading” (IM + L) group underwent weight loading using a Penguin axial loading costume for 4 h each day. Differences in the verbal and sensorimotor responses were seen in the two groups, along with differences in assessments of the two illusions. Verbal reports indicated that the strength of the Ponzo and Muller-Lyer illusions decreased linearly as the experiment progressed; sensorimotor responses indicated that being in the Penguin suit led to increases in illusion strength; the strength of the Muller-Lyer illusion increased after immersion fi nished. It is suggested that the main factor affecting illusion strength is gravitational unloading, which decreases the level of activation of the left hemisphere, leading to use of a metric representation system mainly associated with activity in the right hemisphere.

Contrast sensitivity indicates processing level of visual illusions.

A nearly linear contrast response function (CRF) is found in the lower level striate cortex whereas a steep, nonlinear increase at lower contrasts that gradually increases toward response saturation for higher contrasts is found in the higher level extrastriate cortex. This change of CRFs along the ventral cortical pathway indicates a shift from stimulus- and energy-dependent coding at lower levels to percept- and information-dependent coding at higher levels. The increase of nonlinearity at higher levels optimizes the extraction of perceptual information by amplifying responses to the ubiquitous low-contrast inputs in the environment. We used this difference of CRFs between lower and higher levels, particularly at lower contrasts (.0 to .30), as a tool to investigate examples of 2 lower level (simultaneous brightness and simultaneous tilt) and 2 higher level (Poggendorff and Ponzo) illusions. As predicted, the Poggendorff and Ponzo illusions yielded strong nonlinear increases in their CRFs compared to the more linear functions found for the simultaneous-brightness and simultaneous-tilt illusions. We conclude that the Poggendorff-Ponzo illusions rely more heavily on high-level, percept-dependent cortical processing than do the simultaneous-brightness-simultaneous-tilt illusions and, more generally, that differences between contrast-dependent changes may be a useful tool in determining the relative level of cortical processing of many other visual effects. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

Subconscious processing reveals dissociable contextual modulations of visual size perception

Visual size perception is highly context-dependent. In a series of experiments reported here, we demonstrated that the contextual modulation of visual size processing could occur independent of conscious awareness. Specifically, the Ebbinghaus illusion, which is mediated by lateral connections within the early visual processing stream, persisted even when the surrounding inducers were rendered invisible. Moreover, when the central target was initially interocularly suppressed, the identical target emerged from suppression faster when surrounded by small relative to large inducers, with the suppression time difference well predicted by the strength of the illusion. By contrast, there were no such subconscious contextual modulation effects associated with the Ponzo illusion, which largely relies on feedback projections to the early visual cortices. These results indicate that contextual information can modulate visual size perception without conscious awareness, and the dissociated modulation effects further suggest that subconscious contextual modulation takes place in the early visual processing stream and is largely independent of high-level feedback influences.

Do Dogs Demonstrate Susceptibility to a Vertically Presented Ponzo Illusion?

Do Dogs Demonstrate Susceptibility to a Vertically Presented Ponzo Illusion?

Developmental trends in susceptibility to perceptual illusions: Not all illusions are created equal.

This study examined the development of the utilization of contextual information in visuospatial integration during childhood. We examined four contextual size illusions in children and adults asking whether young children's sensitivity to context is reduced or varies with the perceptual mechanisms or the levels of integration involved. We tested susceptibility to contextual illusions in four-year-olds, seven-year-olds, and adults, employing two psychophysical paradigms, perceptual estimation and a 2AFC discrimination task. We tested susceptibility to Ebbinghaus and Ponzo illusions to estimate the effect of the interaction of object size with its contextual background on the rescaling of its perceived size; we also tested susceptibility to the rectangle and 3D-cube illusions to estimate the effect of the interaction of two dimensions of the target object on the rescaling of its perceived size. While four-year-olds were affected by the Ebbinghaus and Ponzo illusions, they showed no susceptibility to the rectangle or 3D-cube illusion. The results show that, overall, sensitivity to context is not reduced in early childhood; rather, it varies with the perceptual mechanisms or the levels of integration involved. In particular, development is protracted for size illusions in which contextual effects entail the extraction of the relations of dimensions within an object.