Perception Of Illusory Contours Research Articles

Perception of illusory contours in children and adults: An eye-tracking study.

The eye-tracking study investigated the perception of subjective Kanizsa and Ehrenstein figures in adults and in children aged 3-4, 5-6, 7-8, and 9-11 years of age. More specifically, the distribution of looking at the inner stimulus part versus the inducing elements was measured for illusory figures, figures with real contours, and control displays. It was hypothesized that longer looking at the inner area of the illusory figures indicates global contour interpolation, whereas longer looking at the inducing elements indicates a local processing mode. According to the results, participants of all ages looked longer at the illusory Kanizsa and Ehrenstein contours than at the figures' inducing elements. However, performance was lowest in the children aged 3-4 years and increased during the preschool period. Moreover, the illusory contour displays elicited comparable visual responses as did the real contour displays. The use of the control displays that contained no contour information ensured that the participants' looking behavior was not driven by a spontaneous tendency to attend to the inner stimulus parts. The study confirms the view that sensitivity to illusory contours emerges very early in life.

Challenging deep learning models with image distortion based on the abutting grating illusion

Even state-of-the-art deep learning models lack fundamental abilities compared with humans. While many image distortions have been proposed to compare deep learning with humans, they depend on mathematical transformations instead of human cognitive functions. Here, we propose an image distortion based on the abutting grating illusion, which is a phenomenon discovered in humans and animals. The distortion generates illusory contour perception using line gratings abutting each other. We applied the method to MNIST, high-resolution MNIST, and "16-class-ImageNet" silhouettes. Many models, including models trained from scratch and 109 models pretrained with ImageNet or various data augmentation techniques, were tested. Our results show that abutting grating distortion is challenging even for state-of-the-art deep learning models. We discovered that DeepAugment models outperformed other pretrained models. Visualization of early layers indicates that better-performing models exhibit the endstopping property, which is consistent with neuroscience discoveries. Twenty-four human subjects classified distorted samples to validate the distortion.

EEG Signal-Assisted Algebraic Topological Feature-Enhanced Deep Neural Networks for Gestalt Illusory Contour Perception

EEG Signal-Assisted Algebraic Topological Feature-Enhanced Deep Neural Networks for Gestalt Illusory Contour Perception

Predictive coding feedback results in perceived illusory contours in a recurrent neural network

Modern feedforward convolutional neural networks (CNNs) can now solve some computer vision tasks at super-human levels. However, these networks only roughly mimic human visual perception. One difference from human vision is that they do not appear to perceive illusory contours (e.g. Kanizsa squares) in the same way humans do. Physiological evidence from visual cortex suggests that the perception of illusory contours could involve feedback connections. Would recurrent feedback neural networks perceive illusory contours like humans? In this work we equip a deep feedforward convolutional network with brain-inspired recurrent dynamics. The network was first pretrained with an unsupervised reconstruction objective on a natural image dataset, to expose it to natural object contour statistics. Then, a classification decision head was added and the model was finetuned on a form discrimination task: squares vs. randomly oriented inducer shapes (no illusory contour). Finally, the model was tested with the unfamiliar “illusory contour” configuration: inducer shapes oriented to form an illusory square. Compared with feedforward baselines, the iterative “predictive coding” feedback resulted in more illusory contours being classified as physical squares. The perception of the illusory contour was measurable in the luminance profile of the image reconstructions produced by the model, demonstrating that the model really “sees” the illusion. Ablation studies revealed that natural image pretraining and feedback error correction are both critical to the perception of the illusion. Finally we validated our conclusions in a deeper network (VGG): adding the same predictive coding feedback dynamics again leads to the perception of illusory contours.

Interference of Illusory Contour Perception by a Distractor.

The visual system is capable of recognizing objects when object information is widely separated in space, as revealed by the Kanizsa-type illusory contours (ICs). Attentional involvement in perception of ICs is an important topic, and the present study examined whether and how the processing of ICs is interfered with by a distractor. Discrimination between thin and short deformations of an illusory circle was investigated in the absence or presence of a central dynamic patch, with difficulty of discrimination varied in three levels (easy, medium, and hard). Reaction time (RT) was significantly shorter in the absence compared to the presence of the distractor in the easy and medium conditions. Correct rate (CR) was significantly higher in the absence compared to the presence of the distractor in the easy condition, and the magnitude of the difference between CRs of distracted and non-distracted responses significantly reduced as task difficulty increased. These results suggested that perception of ICs is more likely to be vulnerable to distraction when more attentional resources remain available. The present finding supports that attention is engaged in perception of ICs and that distraction of IC processing is associated with perceptual load.

Impaired perception of illusory contours and cortical hypometabolism in patients with Parkinson’s disease

Neuroimaging evidence suggests that areas of the higher-order visual cortex, including the lateral occipital complex (LOC), are engaged in the perception of illusory contours; however, these findings remain unsubstantiated by human lesion data. Therefore, we assessed the presentation time necessary to perceive two types of illusory contours formed by Kanizsa figures or aligned line ends in patients with Parkinson's disease (PD). Additionally, we used 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) to measure regional cerebral glucose metabolism in PD patients. Although there were no significant differences in the stimulus durations required for perception of illusory contours formed by aligned line ends between PD patients and controls, PD patients required significantly longer stimulus durations for the perception of Kanizsa illusory figures. Difficulty in perceiving Kanizsa illusory figures was correlated with hypometabolism in the higher-order visual cortical areas, including the posterior inferior temporal gyrus. These findings indicate an association between dysfunction in the posterior inferior temporal gyrus, a region corresponding to a portion of the LOC, and impaired perception of Kanizsa illusory figures in PD patients.

Auditory Enhancement of Illusory Contour Perception.

Illusory contours (ICs) are borders that are perceived in the absence of contrast gradients. Until recently, IC processes were considered exclusively visual in nature and presumed to be unaffected by information from other senses. Electrophysiological data in humans indicates that sounds can enhance IC processes. Despite cross-modal enhancement being observed at the neurophysiological level, to date there is no evidence of direct amplification of behavioural performance in IC processing by sounds. We addressed this knowledge gap. Healthy adults ( n = 15) discriminated instances when inducers were arranged to form an IC from instances when no IC was formed (NC). Inducers were low-constrast and masked, and there was continuous background acoustic noise throughout a block of trials. On half of the trials, i.e., independently of IC vs NC, a 1000-Hz tone was presented synchronously with the inducer stimuli. Sound presence improved the accuracy of indicating when an IC was presented, but had no impact on performance with NC stimuli (significant IC presence/absence× Sound presence/absence interaction). There was no evidence that this was due to general alerting or to a speed-accuracy trade-off (no main effect of sound presence on accuracy rates and no comparable significant interaction on reaction times). Moreover, sound presence increased sensitivity and reduced bias on the IC vs NC discrimination task. These results demonstrate that multisensory processes augment mid-level visual functions, exemplified by IC processes. Aside from the impact on neurobiological and computational models of vision, our findings may prove clinically beneficial for low-vision or sight-restored patients.

Top-Down Feedback Controls the Cortical Representation of Illusory Contours in Mouse Primary Visual Cortex.

Visual systems have evolved to recognize and extract features from complex scenes using limited sensory information. Contour perception is essential to this process and can occur despite breaks in the continuity of neighboring features. Such robustness of the animal visual system to degraded or occluded shapes may also give rise to an interesting phenomenon of optical illusions. These illusions provide a great opportunity to decipher neural computations underlying contour integration and object detection. Kanizsa illusory contours have been shown to evoke responses in the early visual cortex despite the lack of direct receptive field activation. Recurrent processing between visual areas has been proposed to be involved in this process. However, it is unclear whether higher visual areas directly contribute to the generation of illusory responses in the early visual cortex. Using behavior, in vivo electrophysiology, and optogenetics, we first show that the primary visual cortex (V1) of male mice responds to Kanizsa illusory contours. Responses to Kanizsa illusions emerge later than the responses to the contrast-defined real contours in V1. Second, we demonstrate that illusory responses are orientation-selective. Finally, we show that top-down feedback controls the neural correlates of illusory contour perception in V1. Our results suggest that higher-order visual areas may fill in the missing information in the early visual cortex necessary for illusory contour perception.SIGNIFICANCE STATEMENT Perception of the Kanizsa illusory contours is impaired in neurodevelopmental disorders such as schizophrenia, autism, and Williams syndrome. However, the mechanism of the illusory contour perception is poorly understood. Here we describe the behavioral and neural correlates of Kanizsa illusory contours perception in mice, a genetically tractable model system. We show that top-down feedback controls the neural responses to Kanizsa illusion in V1. To our knowledge, this is the first description of the neural correlates of the Kanizsa illusion in mice and the first causal demonstration of their regulation by top-down feedback.

Illusory contour perception in domestic dogs

One way to better understand how animals visually perceive their environment is to assess the way in which visual information is interpreted and adapted based on preconceptions. Domestic dogs represent a unique species in which to evaluate visual perception as recent findings suggest they may differ from humans and other animal species in terms of their susceptibility to geometric visual illusions. Dogs have demonstrated human-like, reversed, and null susceptibility depending on the type of illusion. To further evaluate how dogs perceive their environment, it is necessary to perform additional assessments of visual perception. One such assessment is the perceptual filling-in of figures, which may be invoked when presented with illusory contours. Six dogs were assessed on their perception of the Ehrenstein illusory contour illusion in a two-choice size-discrimination task. Dogs, as a group, demonstrated equivocal perception of illusory contours. Some individual dogs, however, demonstrated human-like perception of the subjective contours, providing preliminary evidence that this species is capable of perceiving illusory contour illusions, thereby improving the current understanding of canine visual perception capabilities. Additional assessments using alternative illusory contour illusions are needed to clarify these results and identify features that underpin the individual differences observed.

Preference for illusory contours: Beyond object symmetry, familiarity, and nameability.

It has previously been reported that individuals prefer figures from which they can extract shapes via illusory contours (Kanisza figures) over figures in which this is not possible. However, based on the past research in this area, it is not possible to distinguish the influence of illusory contour perception from other factors such as the symmetry, familiarity, prototypicality, and nameability of the perceived shape. Here, we investigate the influence of illusory contours in the absence of these confounding variables by measuring participants' aesthetic/liking ratings for symmetric Kanisza figures and for unfamiliar and asymmetric Kanisza figures. Results show that illusory contours do indeed influence preference above and beyond any effects of these other factors. (PsycINFO Database Record

Affect from mere perception: Illusory contour perception feels good.

Can affect be evoked by mere perception? Earlier work on processing fluency, which manipulated the dynamics of a running perceptual process, has shown that efficient processing can indeed trigger positive affect. The present work introduces a novel route by not manipulating the dynamics of an ongoing perceptual process, but by blocking or allowing the whole process in the first place. We used illusory contour perception as one very basic such process. In 5 experiments (total N = 422), participants briefly (≤100 ms) viewed stimuli that either allowed illusory contour perception, so-called Kanizsa shapes, or proximally identical control shapes that did not allow for this process to occur. Self-reported preference ratings (Experiments 1, 2, and 4) and facial muscle activity (Experiment 3) showed that participants consistently preferred Kanizsa over these control shapes. Moreover, even within Kanizsa shapes, those that most likely instigated illusory contour perception (i.e., those with the highest support ratio) were liked the most (Experiment 5). At the same time, Kanizsa stimuli with high support ratios were objectively and subjectively the most complex, rendering a processing fluency explanation of this preference unlikely. These findings inform theorizing in perception about affective properties of early perceptual processes that are independent from perceptual fluency and research on affect about the importance of basic perception as a source of affectivity. (PsycINFO Database Record

Perceptual overloading reveals illusory contour perception without awareness of the inducers

Unconscious perception is frequently examined by restricting visual input (e.g., using short stimulus durations followed by masking) to prevent that information from entering visual awareness. Failures to demonstrate perception without awareness may thus be a consequence of this restricted input rather than of limitations in unconscious perception. Here, we demonstrate a novel method that circumvents these significant drawbacks inherent in other methods. Using this new perceptual overloading technique (POT), in which stimuli are repeatedly presented in alternation with a stream of variable masks, we demonstrate illusory contour perception and modal completion even when subjects are completely unaware of the inducing elements. In addition to demonstrating a powerful new method to study consciousness by effectively gating robust visual input from visual awareness, we show that more complex contextual effects, previously considered to be a privilege only of conscious vision, can occur without awareness.

Independence of the completion effect from the noncompletion effect in illusory contour perception.

Spatially separated object information can be effortlessly completed in the visual system, as demonstrated by the well-known Kanizsa-type illusory contours. The perception of illusory contours is closely associated with the spatial configuration of contour fragments, leading to the long-lasting difficulty in distinguishing the effect of the completion process that interpolates the contour fragments from the effect of the noncompletion process that analyzes the contour fragments. However, a close relationship does not necessarily imply nonindependence, e.g., two people may show similar behaviors in one situation but may not in another situation. Inspired by this simple common sense, we conducted a contour discrimination task (i.e., discriminating between the interpolated contours) and a fragment discrimination task (i.e., discriminating between the physically-specified contour fragments) for Kanizsa squares and Kanizsa circles. The performance difference between the contour and fragment discrimination tasks was much larger for Kanizsa circles than for Kanizsa squares. This independence of the completion effect--as indicated by the performance in the contour task--from the noncompletion effect--as indicated by the performance in the fragment task--provides new insights into the understanding of the mechanism of visual completion.

From local to global processing: The development of illusory contour perception

Global visual processing is important for segmenting scenes, extracting form from background, and recognizing objects. Local processing involves attention to the local elements, contrast, and boundaries of an image at the expense of extracting a global percept. Previous work is inconclusive regarding the relative development of local and global processing. Some studies suggest that global perception is already present by 8months of age, whereas others suggest that the ability arises during childhood and continues to develop during adolescence. We used a novel method to assess the development of global processing in 3- to 10-year-old children and an adult comparison group. We used Kanizsa illusory contours as an assay of global perception and measured responses on a touch-sensitive screen while monitoring eye position with a head-mounted eye tracker. Participants were tested using a similarity match-to-sample paradigm. Using converging measures, we found a clear developmental progression with age such that the youngest children performed near chance on the illusory contour discrimination, whereas 7- and 8-year-olds performed nearly perfectly, as did adults. There was clear evidence of a gradual shift from a local processing strategy to a global one; young children looked predominantly at and touched the “pacman” inducers of the illusory form, whereas older children and adults looked predominantly at and touched the middle of the form. These data show a prolonged developmental trajectory in appreciation of global form, with a transition from local to global visual processing between 4 and 7years of age.

Border-ownership computation reflecting consistency of surface properties

Convexity preference is one of the factors that influence figure-ground organization. However, in certain conditions, the convexity preference can be suppressed and non-convex regions might be perceived as figural. It has been suggested that consistency of surface properties plays a key role for this reversal. For example, if a convex region is in the middle of another surface and has the same color/texture as the background, it is often perceived as a hole. The preference of convex regions in repetitive columnar configurations is also reduced if the concave regions have inconsistent colors (Peterson & Salvagio, 2008, Journal of Vision, 8(16), 4.1–13). Importantly, Zhou et al. (2000, Journal of Neuroscience, 20(17), 6594–6611) showed that many border-ownership (BOWN) sensitive neurons in V2/V4 were also sensitive to contrast polarity. Accordingly, Zhaoping (2005, Neuron, 47(1), 143–153) developed a model in which BOWN signals are enhanced when they are consistent in both the ownership and the contrast polarity. Inspired by her model, we first developed a simplified algorithm to compute BOWN that exhibit the convexity preference. It successfully reproduced illusory contour perception (DISC model, Kogo et al, 2010, Psychological Review., 117(2), 406–439). We, then, tested the performance of the model which also reflects the consistency of the surface colors at the location of the signals as in Zhaoping's model. We report that this approach gives extremely robust responses to various images with complexities both in shapes and in depth orders such as the examples mentioned above, suggesting the importance of this approach for BOWN computation. We further investigated, 1: the role of contrast insensitive BOWN signals, 2: the role of concavity preference algorithm, and 3: the effect of inhibitory connections. We will report how these factors affect the model's responses to reproduce figure-ground perception of complex figures. Meeting abstract presented at VSS 2014

Differential neural responses to naturally occurring envelopes in the electrosensory system

Natural sensory stimuli frequently consist of a fine structure whose amplitude (i.e. envelope) varies more slowly. Previous studies have demonstrated that envelope signals are found across sensory systems and are necessary for perception. For example, envelope signals in the auditory system carry information pertaining to the perception of pitch fluctuations in communication vocalizations [1], while envelopes in the visual system are responsible for object grouping and the perception of illusory contours [2,3]. However, the neural mechanisms underlying the encoding of these envelope signals are poorly understood in general. Gymnotiform wave-type weakly electric fish constitute an attractive model system for studying envelope processing in the brain because of its well-characterized anatomy and physiology [4]. These fish generate around themselves a weak quasi-sinusoidal electric field through the electric organ discharge (EOD) [5]. Recent studies have shown that the beat amplitude (i.e. the envelope) can vary in time during different behavioral contexts and display differential frequency content: while envelopes caused by movement primarily contain low ( 1 Hz) temporal frequencies [7]. While it is known that electrosensory neurons can respond to envelopes [7], whether these neurons respond differentially to envelopes arising from movement and social interaction is unknown in part because their tuning to envelope frequencies has not been characterized. Here we used well established techniques [8] to record from electrosensory pyramidal neurons across different maps of the body surface within the electrosensory lateral line lobe (ELL) in response to envelope stimuli with different frequency content spanning the behaviorally relevant range (0.05-10 Hz). Using standard measures of linear systems identification techniques as well as more quantitative methods of information theory, we found that pyramidal neurons in different maps displayed differential responses to envelopes arising from different behavioral contexts. Our results suggest that information about envelopes arising from different behavioral contexts begins to be segregated at the level of the ELL and provide new insights as to how these behaviorally relevant stimuli are encoded in early sensory pathways.

Development of Kanizsa Illusory Contour perception in Autism Spectrum Disorder

Development of Kanizsa Illusory Contour perception in Autism Spectrum Disorder

Perception of illusory contours forms intermodulation responses of steady state visual evoked potentials as a neural signature of spatial integration

Perception of illusory contours was shown to be a consequence of neural activity related to spatial integration in early visual areas. Candidates for such filling-in phenomena are long-range horizontal connections of neurons in V1/V2, and feedback from higher order visual areas. To get a direct measure of spatial integration in early visual cortex, we presented two differently flickering inducers, which evoked steady-state visual evoked potentials (SSVEPs) while manipulating the formation of an illusory rectangle. As a neural marker of integration we tested differences in amplitudes of intermodulation frequencies i.e. linear combinations of the driving frequencies. These were significantly increased when an illusory rectangle was perceived. Increases were neither due to changes of any of the two driving frequencies nor in the frequency that tagged the processing of the compound object, indicating that results are not a consequence of paying more attention to inducers when the illusory rectangle was visible.

Exploratory MEG Study of the Illusory Contour Perception: Positive and Inverted Effects

The illusory contour is one of the most often used models in studies of Gestalt perception. In our MEG study we observed the so-called illusory contour effect (IC-effect): the activity of nonprimary visual and associative cortical areas was increased during the 150-250 ms time window after a stimulus onset in response to illusory stimulus, compared with the control stimulus. In addition to the positive IC-effect, the inverted IC-effect was revealed for the first time in adults. In our study it was manifested during the 60-120 ms window after the onset of stimulus. The inverted IC-effect is an early decrease in the activity of the visual cortex in response to the illusory contour compared with the control stimulus. The mechanism of the inverted IC-effect is yet unclear. The “bottom-up” and “top-down” hypotheses of the origin of the inverted IC-effect are discussed.

The “side” matters: How configurality is reflected in completion

The perception of figure-ground organization is a highly context-sensitive phenomenon. Accumulating evidence suggests that the so-called completion phenomenon is tightly linked to this figure-ground organization. While many computational models have applied borderline completion algorithms based on the detection of boundary alignments, we point out the problems of this approach. We hypothesize that completion is a result of computing the figure-ground organization. Specifically, the global interactions in the neural network activate the “border-ownership” sensitive neurons at the location where no luminance contrast is given and this activation corresponds to the perception of illusory contours. The implications of this result to the general property of emerging Gestalt percepts are discussed.