Infants’ ability to extract three-dimensional shape from coherent motion

Our capacity to perceive three-dimensional (3D) object structure from two-dimensional (2D) retinal input is fundamental to object perception. The present research examined infants’ ability to extract 3D form from structure-from-motion (SFM) displays using a familiarization/visual-paired-comparison paradigm. In SFM displays dots are projected onto the surfaces of a shape that rotates around a 3D axis and it is the coherent structure of the dots’ motion that gives rise to the percept of shape. Infants mean age 4.5 and 9 months were familiarized to a SFM display (e.g., cylinder); in test they were presented the familiar SFM display paired with a novel SFM display (e.g., cube). Infants in both age groups displayed a significant preference for the novel SFM test display. These results are consistent with those obtained previously using habituation paradigms and provide converging evidence for infants’ early emerging capacity to use coherent motion – in the absence of figural information – as a cue to depth structure. In addition, these results demonstrate that infants’ ability to extract 3D shape from coherent motion can be successfully assessed with a neuroimaging-friendly protocol, which was one of the goals of this study.     

Sounds exaggerate visual shape

While perceiving speech, people see mouth shapes that are systematically associated with sounds. In particular, a vertically stretched mouth produces a /woo/ sound, whereas a horizontally stretched mouth produces a /wee/ sound. We demonstrate that hearing these speech sounds alters how we see aspect ratio, a basic visual feature that contributes to perception of 3D space, objects and faces. Hearing a /woo/ sound increases the apparent vertical elongation of a shape, whereas hearing a /wee/ sound increases the apparent horizontal elongation. We further demonstrate that these sounds influence aspect ratio coding. Viewing and adapting to a tall (or flat) shape makes a subsequently presented symmetric shape appear flat (or tall). These aspect ratio aftereffects are enhanced when associated speech sounds are presented during the adaptation period, suggesting that the sounds influence visual population coding of aspect ratio. Taken together, these results extend previous demonstrations that visual information constrains auditory perception by showing the converse - speech sounds influence visual perception of a basic geometric feature.     

Surface perception and the generic view principle

The hypothesis that perceptual experience can be understood in terms of rule-based processing has strongly influenced recent theories of visual surface perception. However, many of the rules that these theories propose apply only in relatively restricted situations. I suggest that more general and robust principles for reducing perceptual ambiguity are available, such as the generic view principle (GVP) described here. According to the GVP, vision assumes that qualitative (e.g. topological) image structure is stable with respect to small changes of viewpoint. Some consequences of the GVP for visual surfaces, including illusory surfaces, are described. I also demonstrate the decisive role of real and illusory background surfaces in specifying the 3-D shape and layout of visual objects and scenes.     

The perception of shape and curvedness from binocular stereopsis and structure from motion

The integration of binocular stereopsis and kinetic depth was measured for two distinct aspects of 3-Dstructure: (1)shape index, which is a measure of scale-independent structure, and (2)curvedness, which is a measure of scale-dependent structure. We found that motion contributes significantly more to judged shape index than it does to judged curvedness, and stereo contributes significantly more to judged curvedness than it does to judged shape index. This suggests that the differences in the relative contribution of motion and stereo reported here occurred because these two sources do not equally specify the scale-dependent and scale-independent aspects of surface structure. Furthermore, these results seem to be inconsistent with integration models in which the different visual cues all initially contribute to the same single representation of 3-Dstructure.     

Perceiving the shape and material properties of 3D surfaces

Our visual experience of the world relies on the interaction of light with the different substances, surfaces, and objects in our environment. These optical interactions generate images that contain a conflated mixture of different scene variables, which our visual system must somehow disentangle to extract information about the shape and material properties of the world. Such problems have historically been considered to be ill-posed, but recent work suggests that there are complex patterns of covariation in light that co-specify the 3D shape and material properties of surfaces. This work provides new insights into how the visual system acquired the ability to solve problems that have historically been considered intractable.     

Automatic priming for translation- and scale-invariant representations of object shape

A series of visual search experiments explored whether early visual processes are sensitive to the overall shape of objects. Previous work (Wolfe & Bennett, 1997) has suggested that information concerning overall shape is not coded in early vision. However, in Experiment 1, we demonstrate that these previous findings are explicable in terms of non-target heterogeneity rather than an absence of shape information in early vision. In Experiments 2 and 3, we demonstrate that shape similarity, rather than individual contour similarity, can determine search efficiency. In Experiments 4 and 5, we show that manipulating the contrast polarity of contours and defining shape using texture significantly impeded search for an odd-one-out shape. The implications of these results for shape processing in early vision are discussed.     

The role of perspective effects and accelerations in perceived three-dimensional structure-from-motion

It has been suggested that perceived three-dimensional (3D) structure-from-motion can be accounted for by a 2-frame orthographic approximation of the flow field. This study investigated the extent to which higher order cues (perspective and acceleration) are used in addition to first-order flow. Participants matched the 3D dihedral angle of a hinged plane (probe) defined by multiple-depth cues to one defined by motion only, for stimulus sizes of 8 and 33 degrees, using perspective and orthographic projection. The results show that perspective effects can be important even for relatively small stimuli (8 degrees) and that accelerations contribute to perceived shape. In all conditions, large biases were found. These are well accounted for by a model in which all relevant flow measurements (first-order, perspective, and acceleration) are used together with estimates of the noise in each. The model has no built-in bias toward particular 3D shapes. Instead, the visual system may act as an optimal estimator of 3D structure-from-motion.     

Encoding multielement scenes: statistical learning of visual feature hierarchies

The authors investigated how human adults encode and remember parts of multielement scenes composed of recursively embedded visual shape combinations. The authors found that shape combinations that are parts of larger configurations are less well remembered than shape combinations of the same kind that are not embedded. Combined with basic mechanisms of statistical learning, this embeddedness constraint enables the development of complex new features for acquiring internal representations efficiently without being computationally intractable. The resulting representations also encode parts and wholes by chunking the visual input into components according to the statistical coherence of their constituents. These results suggest that a bootstrapping approach of constrained statistical learning offers a unified framework for investigating the formation of different internal representations in pattern and scene perception.     

Widgets: A new set of parametrically defined 3D objects for use in haptic and visual categorization tasks

IntroductionMost research to date on human categorization ability has concentrated on the visual and auditory domains. However, a limited – but non-negligible – range of studies has also examined the categorization of familiar or unfamiliar (i.e., novel) objects in the haptic (i.e., tactile-kinesthetic) modality.ObjectiveIn this paper, we describe how we developed a new set of parametrically defined objects, called widgets, that can be used as 3D (or 2D) materials for haptic (or visual) categorization purposes.MethodWidgets are unfamiliar complex 3D shapes with an ovoid body and four types of elements attached to it (eyes, tail, crest, and legs). The stimulus set comprises 24 objects divided into four categories of six exemplars each (the files used for 3D printing are provided as Supplementary Material).ResultsWe also assessed and demonstrated the validity of our stimulus set by conducting two separate studies of haptic and visual categorization, involving participants of different ages: young adults (Study 1), and children and adolescents (Study 2). Results showed that humans can categorize our 3D complex shapes on the basis of both haptically and visually perceived similarities in shape attributes.ConclusionWidgets are very useful new experimental stimuli for categorization studies using 3D printing technology.     

Curvature and the visual perception of shape: theory on information along object boundaries and the minima rule revisited

Previous empirical studies have shown that information along visual contours is known to be concentrated in regions of high magnitude of curvature, and, for closed contours, segments of negative curvature (i.e., concave segments) carry greater perceptual relevance than corresponding regions of positive curvature (i.e., convex segments). Lately, Feldman and Singh (2005, Psychological Review, 112, 243-252) proposed a mathematical derivation to yield information content as a function of curvature along a contour. Here, we highlight several fundamental errors in their derivation and in its associated implementation, which are problematic in both mathematical and psychological senses. Instead, we propose an alternative mathematical formulation for information measure of contour curvature that addresses these issues. Additionally, unlike in previous work, we extend this approach to 3-dimensional (3D) shape by providing a formal measure of information content for surface curvature and outline a modified version of the minima rule relating to part segmentation using curvature in 3D shape.     

Functional theory of illusory conjunctions and neon colors

Illusory conjunctions are the incorrect perceptual combination of briefly presented colors and shapes. In the neon colors illusion, achromatic figures take on the color of an overlaid grid of colored lines. Both illusions are explained by a theory that assumes (a) poor location information or poor spatial resolution for some aspects of visual information and (b) that the spatial location of features is constrained by perceptual organization. Computer simulations demonstrate that the mechanisms suggested by the theory are useful in veridical perception and they are sufficient to produce illusory conjunctions. The theory suggests mechanisms that economically encode visual information in a way that filters noise and fills in missing data. Issues related to neural implementation are discussed. Four experiments illustrate the theory. Illusory conjunctions are shown to be affected by objective stimulus organization, by subjective organization, and by the linguistic structure of ambiguous Hebrew words. Neon colors are constrained by linguistic structure in the same way as illusory conjunctions.     

The structure of three-dimensional object representations in human vision: evidence from whole-part matching

This article examines how the human visual system represents the shapes of 3-dimensional (3D) objects. One long-standing hypothesis is that object shapes are represented in terms of volumetric component parts and their spatial configuration. This hypothesis is examined in 3 experiments using a whole-part matching paradigm in which participants match object parts to whole novel 3D object shapes. Experiments 1 and 2, consistent with volumetric image segmentation, show that whole-part matching is faster for volumetric component parts than for either open or closed nonvolumetric regions of edge contour. However, the results of Experiment 3 show that an equivalent advantage is found for bounded regions of edge contour that correspond to object surfaces. The results are interpreted in terms of a surface-based model of 3D shape representation, which proposes edge-bounded 2-dimensional polygons as basic primitives of surface shape.     

Shape from shadows

The colors, textures, and shapes of shadows are physically constrained in several ways in natural scenes. The visual system appears to ignore these constraints, however, and to accept many patterns as shadows even though they could not occur naturally. In the stimuli that we have studied, the only requirements for the perception of depth due to shadows were that shadow regions be darker than the surrounding, nonshadow regions and that there be consistent contrast polarity along the shadow border. Three-dimensional shape due to shadows was perceived when shadow areas were filled with colors or textures that could not occur in natural scenes, when shadow and nonshadow regions had textures that moved in different directions, or when they were presented on different depth planes. The results suggest that the interpretation of shadows begins with the identification of acceptable shadow borders by a cooperative process that requires consistent contrast polarity across a range of scales at each point along the border. Finally, we discuss how the identification of a shadow region can help the visual system to patch together areas that are separated by shadow boundaries, to identify directions of surface curvature, and to select a preferred three-dimensional interpretation while rejecting others.     

Acts of perceptual inquiry: problems for any stimulus-based simplicity theory

Stimulus-specified simplicity is simply insufficient to predict the appearance of objects' 3D forms and figural shapes, etc., as originally intended. Which information a viewer chooses to attend can determine both what 3D structure is perceived and its attendant perceptual consequences; moreover, a shape's meaningfulness or denotivity [M.A. Peterson, Current Directions in Psychological Science 3 (1994) 105] can overcome simplicity-based figure-ground segregation. In both cases, perceptual consequences, such as subsequent perceived movements, are constrained or primed in ways that can help us corroborate and define what the viewer has perceived; that may help us in studying the underlying events in brain processing; and that should help in designing such perceptual applications as still and animated displays. Demonstrations, theoretical framework, and potential research tools are offered.     

Perceptual causality and animacy

Certain simple visual displays consisting of moving 2-D geometric shapes can give rise to percepts with high-level properties such as causality and animacy. This article reviews recent research on such phenomena, which began with the classic work of Michotte and of Heider and Simmel. The importance of such phenomena stems in part from the fact that these interpretations seem to be largely perceptual in nature - to be fairly fast, automatic, irresistible and highly stimulus driven - despite the fact that they involve impressions typically associated with higher-level cognitive processing. This research suggests that just as the visual system works to recover the physical structure of the world by inferring properties such as 3-D shape, so too does it work to recover the causal and social structure of the world by inferring properties such as causality and animacy.     

Perception of three-dimensional shape from specular highlights, deformations of shading, and other types of visual information

There have been numerous computational models developed in an effort to explain how the human visual system analyzes three-dimensional (3D) surface shape from patterns of image shading, but they all share some important limitations. Models that are applicable to individual static images cannot correctly interpret regions that contain specular highlights, and those that are applicable to moving images have difficulties when a surface moves relative to its sources of illumination. Here we describe a psychophysical experiment that measured the sensitivity of human observers to small differences of 3D shape over a wide variety of conditions. The results provide clear evidence that the presence of specular highlights or the motions of a surface relative to its light source do not pose an impediment to perception, but rather, provide powerful sources of information for the perceptual analysis of 3D shape.     

Resolving competition when naming an object in a multiple-object display

Naming an object in the context of other objects requires the selection and processing of the target object at different levels, while the processing of competing representations activated by context objects has to be constrained. At what stage are these competing representations attenuated? To address this question, we presented pairs of target and context objects that were either similar in visual shape (e.g., umbrella–palm tree) or dissimilar in visual shape (e.g., umbrella–ladder), so that the context object would attract various amounts of attention. The activation of the context object at different levels of processing was assessed by means of auditory distractors (semantically related, or phonologically related, or unrelated to the context object). Semantic and phonological distractor effects were observed for shape-related object pairs, but not for unrelated object pairs. This finding suggests that context objects do not activate their associated lexical representations to any substantial amount, unless they capture attention. In that case, they undergo full lexical processing up to a phonological level. Implications for models of word production are discussed.     

Seeing structure: Shape skeletons modulate perceived similarity

An intrinsic part of seeing objects is seeing how similar or different they are relative to one another. This experience requires that objects be mentally represented in a common format over which such comparisons can be carried out. What is that representational format? Objects could be compared in terms of their superficial features (e.g., degree of pixel-by-pixel overlap), but a more intriguing possibility is that they are compared on the basis of a deeper structure. One especially promising candidate that has enjoyed success in the computer vision literature is the shape skeleton—a geometric transformation that represents objects according to their inferred underlying organization. Despite several hints that shape skeletons are computed in human vision, it remains unclear how much they actually matter for subsequent performance. Here, we explore the possibility that shape skeletons help mediate the ability to extract visual similarity. Observers completed a same/different task in which two shapes could vary either in their skeletal structure (without changing superficial features such as size, orientation, and internal angular separation) or in large surface-level ways (without changing overall skeletal organization). Discrimination was better for skeletally dissimilar shapes: observers had difficulty appreciating even surprisingly large differences when those differences did not reorganize the underlying skeletons. This pattern also generalized beyond line drawings to 3-D volumes whose skeletons were less readily inferable from the shapes’ visible contours. These results show how shape skeletons may influence the perception of similarity—and more generally, how they have important consequences for downstream visual processing.