Surface interpolation and 3D relatability

Perceptual mechanisms underlying amodal surface integration of 3-D stereoscopic stimuli

The visual system can represent a partially occluded 3-D surface from images of separated surface segments. The underlying amodal surface integration process accomplishes this by amodally extending each surface segment behind the occluder (amodal surface extension) and integrating the extended surfaces to form a whole surface representation. We conducted five experiments to investigate how depth cues, such as binocular disparity, half-occlusion, and monocular depth cues (T-junctions and L-junctions), contribute to amodal surface extension, and how the geometrical relationship and image similarity among the surface segments affect surface integration. This was achieved by having observers adjust the stereoscopic depth and slant of a comparison stimulus to match those of the tested 3-D stimulus. We found that both binocular disparity and half-occlusion cues are used to determine border-ownership assignment of surface segments and for amodal surface extension. We also found that separated surface segments need to have the same luminance contrast-polarity for them to be integrated as a whole surface. Finally, we found that having the same motion direction, minimum misalignment between boundary contours, and proximity among separated segments facilitate their integration. Overall, our findings reveal a set of "perceptual factors" for amodal surface integration, which arguably reflects our visual system's built-in knowledge of the regularities in natural scenes.

Anticipatory scene representation in preschool children's recall and recognition memory

Behavioral and neuroscience research on boundary extension (false memory beyond the edges of a view of a scene) has provided new insights into the constructive nature of scene representation, and motivates questions about development. Early research with children (as young as 6-7 years) was consistent with boundary extension, but relied on an analysis of spatial errors in drawings which are open to alternative explanations (e.g. drawing ability). Experiment 1 replicated and extended prior drawing results with 4-5-year-olds and adults. In Experiment 2, a new, forced-choice immediate recognition memory test was implemented with the same children. On each trial, a card (photograph of a simple scene) was immediately replaced by a test card (identical view and either a closer or more wide-angle view) and participants indicated which one matched the original view. Error patterns supported boundary extension; identical photographs were more frequently rejected when the closer view was the original view, than vice versa. This asymmetry was not attributable to a selection bias (guessing tasks; Experiments 3-5). In Experiment 4, working memory load was increased by presenting more expansive views of more complex scenes. Again, children exhibited boundary extension, but now adults did not, unless stimulus duration was reduced to 5 s (limiting time to implement strategies; Experiment 5). We propose that like adults, children interpret photographs as views of places in the world; they extrapolate the anticipated continuation of the scene beyond the view and misattribute it to having been seen. Developmental differences in source attribution decision processes provide an explanation for the age-related differences observed.

Visual, haptic and bimodal scene perception: evidence for a unitary representation

Participants studied seven meaningful scene-regions bordered by removable boundaries (30s each). In Experiment 1 (N = 80) participants used visual or haptic exploration and then minutes later, reconstructed boundary position using the same or the alternate modality. Participants in all groups shifted boundary placement outward (boundary extension), but visual study yielded the greater error. Critically, this modality-specific difference in boundary extension transferred without cost in the cross-modal conditions, suggesting a functionally unitary scene representation. In Experiment 2 (N = 20), bimodal study led to boundary extension that did not differ from haptic exploration alone, suggesting that bimodal spatial memory was constrained by the more "conservative" haptic modality. In Experiment 3 (N = 20), as in picture studies, boundary memory was tested 30s after viewing each scene-region and as with pictures, boundary extension still occurred. Results suggest that scene representation is organized around an amodal spatial core that organizes bottom-up information from multiple modalities in combination with top-down expectations about the surrounding world.

"Connectability" matters too: completion theories need to be complete

Kogo and Wagemans provide an intriguing way of assigning a polarity value to closed edges in fragmented images (solving the border ownership problem), but their model lacks generality and disregards connectability as a relevant aspect of visual completion. The lack of generality depends on considering concave disk sectors (pacmen) as the main inducers of illusory contours. Connectability is crucial for defining the occurrence, the salience and the shape of completed contours. A complete theory of completion should integrate border ownership and connectability, rather than emphasizing one aspect over the other.

Perceived surface slant is systematically biased in the actively-generated optic flow

Humans make systematic errors in the 3D interpretation of the optic flow in both passive and active vision. These systematic distortions can be predicted by a biologically-inspired model which disregards self-motion information resulting from head movements (Caudek, Fantoni, & Domini 2011). Here, we tested two predictions of this model: (1) A plane that is stationary in an earth-fixed reference frame will be perceived as changing its slant if the movement of the observer's head causes a variation of the optic flow; (2) a surface that rotates in an earth-fixed reference frame will be perceived to be stationary, if the surface rotation is appropriately yoked to the head movement so as to generate a variation of the surface slant but not of the optic flow. Both predictions were corroborated by two experiments in which observers judged the perceived slant of a random-dot planar surface during egomotion. We found qualitatively similar biases for monocular and binocular viewing of the simulated surfaces, although, in principle, the simultaneous presence of disparity and motion cues allows for a veridical recovery of surface slant.

Volume completion in 4.5-month-old infants

In this study, we examined 4.5-month-old infants' visual completion of self-occluding three-dimensional objects. A previous study on this topic reported that 6-month-old, but not 4-month-old infants extrapolate a convex, symmetric prism from a limited view of its surfaces (Soska & Johnson, 2008). As of yet, studies on the development of amodal completion of three-dimensional, self-occluding objects are scarce. Given 4-month-old infants' abilities to derive three-dimensional shape from a variety of visual cues, three-dimensional amodal completion may well depend on the perceptual strength of three-dimensionality in the stimulus displays. The first experiments (1A and 1B) tested this hypothesis by means of a habituation paradigm and showed that 4.5-month-old infants are indeed able to amodally complete the back of a self-occluding object when sufficient three-dimensional cues are available. Further support for volume completion in 4.5-month-old infants was found in a second experiment, again using a habituation paradigm, that measured perceived connectedness between two visually separated, self-occluding, three-dimensional objects.

Rethinking visual scene perception

A classic puzzle in understanding visual scene perception is how to reconcile the physiological constraints of vision with the phenomenology of seeing. Vision captures information via discrete eye fixations, interrupted by saccadic suppression, and limited by retinal inhomogeneity. Yet scenes are effortlessly perceived as coherent, continuous, and meaningful. Two conceptualizations of scene representation will be contrasted. The traditional visual-cognitive model casts visual scene representation as an imperfect reflection of the visual sensory input alone. By contrast, a new multisource model casts visual scene representation in terms of an egocentric spatial framework that is 'filled-in' by visual sensory input, but also by amodal perception, and by expectations and by constraints derived from rapid-scene classification and object-to-context associations. Together, these nonvisual sources serve to 'simulate' a likely surrounding scene that the visual input only partially reveals. Pros and cons of these alternative views will be discussed. WIREs Cogn Sci 2012, 3:117-127. doi: 10.1002/wcs.149 For further resources related to this article, please visit the WIREs website.