Monocular reconstruction of shapes of natural objects from orthographic and perspective images.

Human subjects were tested in perception of shapes of 3D objects. The subjects reconstructed 3D shapes by viewing orthographic and perspective images. Perception of natural shapes was very close to veridical and was clearly better than perception of random symmetrical polyhedra.

Combining contour and region for closed boundary extraction of a shape.

This study explored human ability to extract closed boundary of a target shape in the presence of noise using spatially global operations. Specifically, we investigated the contributions of contour-based processing using line edges and region-based processing using color, as well as their interaction. Performance of the subjects was reliable when the fixation was inside the shape, and it was much less reliable when the fixation was outside.

Testing a formal theory of perception is not easy: Comments on Yu, Todd & Petrov (2021) and Yu, Petrov & Todd (2021).

Yu, Todd, and Petrov (2021, Journal of Vision) and their follow-up study (Yu, Petrov, & Todd, 2021, i-Perception) aimed at evaluating the role of three-dimensional (3D) symmetry in binocular shape perception by comparing their experimental data to predictions they derived from our computational models. We point out in this note that their predictions were incorrect, so their studies can neither reject nor support our models of 3D shape perception. We explain (1) the role of the data and the constraints in solving ill-posed inverse problems, (2) the role of binocular depth-order, as opposed to binocular depth-intervals in shape perception, (3) the nature and the effect of 3D compactness as an a priori constraint, and (4) the implications of the separation of binocular disparity and stereoacuity in the two functional streams in the visual cortex.

The Concept of Symmetry and the Theory of Perception.

Perceptual constancy refers to the fact that the perceived geometrical and physical characteristics of objects remain constant despite transformations of the objects such as rigid motion. Perceptual constancy is essential in everything we do, like recognition of familiar objects and scenes, planning and executing visual navigation, visuomotor coordination, and many more. Perceptual constancy would not exist without the geometrical and physical permanence of objects: their shape, size, and weight.

When is Psychology Research Useful in Artificial Intelligence? A Case for Reducing Computational Complexity in Problem Solving.

A problem is a situation in which an agent seeks to attain a given goal without knowing how to achieve it. Human problem solving is typically studied as a search in a problem space composed of states (information about the environment) and operators (to move between states). A problem such as playing a game of chess has possible states, and a traveling salesperson problem with as little as 82 cities already has more than different tours (similar to chess).

Gestalt-like constraints produce veridical (Euclidean) percepts of 3D indoor scenes.

This study, which was influenced a lot by Gestalt ideas, extends our prior work on the role of a priori constraints in the veridical perception of 3D shapes to the perception of 3D scenes. Our experiments tested how human subjects perceive the layout of a naturally-illuminated indoor scene that contains common symmetrical 3D objects standing on a horizontal floor. In one task, the subject was asked to draw a top view of a scene that was viewed either monocularly or binocularly.

Philosophizing cannot substitute for experimentation: comment on Hoffman, Singh & Prakash (2014).

The perception of a 3D shape must be excluded from Hoffman et al.'s "interface theory" primarily because shape is characterized by its symmetries. When these symmetries are used as a priori constraints, 3D shapes are always recovered from 2D retinal images veridically.

Spatially-global integration of closed, fragmented contours by finding the shortest-path in a log-polar representation.

Finding the occluding contours of objects in real 2D retinal images of natural 3D scenes is done by determining, which contour fragments are relevant, and the order in which they should be connected. We developed a model that finds the closed contour represented in the image by solving a shortest path problem that uses a log-polar representation of the image; the kind of representation known to exist in area V1 of the primate cortex. The shortest path in a log-polar representation favors the smooth, convex and closed contours in the retinal image that have the smallest number of gaps.

An especial skill in elite wheelchair basketball players.

We aimed to investigate whether an especial skill is present in elite wheelchair basketball players when taking twenty shots with a regular basketball from five different distances (11 ft, 13 ft, 17 ft, & 19 ft) from the basket including the free throw line (15 ft). Twelve elite male basketball players participated. The results showed that as distance increased shot accuracy decreased in line with force by variability predictions for the 11 ft, 13 ft, 17 ft, & 19 ft distances.

Especial skill effect across age and performance level: the nature and degree of generalization.

It has been claimed that an especial skill emerges after massive amounts of basketball practice. Despite this no direct evidence is available to support this claim. The authors aimed to shed light on this question.

Depth cues versus the simplicity principle in 3D shape perception.

Two experiments were performed to explore the mechanisms of human 3D shape perception. In Experiment 1, the subjects' performance in a shape constancy task in the presence of several cues (edges, binocular disparity, shading and texture) was tested. The results show that edges and binocular disparity, but not shading or texture, are important in 3D shape perception.

A Bayesian model of binocular perception of 3D mirror symmetrical polyhedra.

In our previous studies, we showed that monocular perception of 3D shapes is based on a priori constraints, such as 3D symmetry and 3D compactness. The present study addresses the nature of perceptual mechanisms underlying binocular perception of 3D shapes. First, we demonstrate that binocular performance is systematically better than monocular performance, and it is close to perfect in the case of three out of four subjects.

Human motor transfer is determined by the scaling of size and accuracy of movement.

A transfer of training design was used to examine the role of the Index of Difficulty (ID) on transfer of learning in a sequential Fitts's law task. Specifically, the role of the ratio between the accuracy and size of movement (ID) in transfer was examined. Transfer of skilled movement is better when both the size and accuracy of movement are changed by the same factor (ID is constant) than when only size or accuracy is changed.

New approach to the perception of 3D shape based on veridicality, complexity, symmetry and volume.

This paper reviews recent progress towards understanding 3D shape perception made possible by appreciating the significant role that veridicality and complexity play in the natural visual environment. The ability to see objects as they really are "out there" is derived from the complexity inherent in the 3D object's shape. The importance of both veridicality and complexity was ignored in most prior research.

Binocular disparity only comes into play when everything else fails; a finding with broader implications than one might suppose.

This paper calls attention to research showing that binocular disparity, which is an effective cue to depth, plays a secondary role, at best, in the perception of 3D shape. This claim has implications both for how shape should be studied and how this unique perceptual property should be modeled. These issues are discussed from a historical perspective, which shows how the failure to appreciate the importance of the Gestalt grouping principle called 'Figure-Ground Organization' led to many unfruitful efforts.

Camouflage and visual perception.

How does an animal conceal itself from visual detection by other animals? This review paper seeks to identify general principles that may apply in this broad area. It considers mechanisms of visual encoding, of grouping and object encoding, and of search. In most cases, the evidence base comes from studies of humans or species whose vision approximates to that of humans.

Detection of skewed symmetry.

This study examined the ability of human observers to discriminate between symmetric and asymmetric planar figures from perspective and orthographic images. The first experiment showed that the discrimination is reliable in the case of polygons, but not dotted patterns. The second experiment showed that the discrimination is facilitated when the projected symmetry axis or projected symmetry lines are known to the subject.

A computational model that recovers the 3D shape of an object from a single 2D retinal representation.

Human beings perceive 3D shapes veridically, but the underlying mechanisms remain unknown. The problem of producing veridical shape percepts is computationally difficult because the 3D shapes have to be recovered from 2D retinal images. This paper describes a new model, based on a regularization approach, that does this very well.

Manual Detection of Spatial and Temporal Torque Variation through a Rotary Switch.

We report three experiments on manual detection of torque variations experienced through a rotary switch. The experiments were designed to investigate whether torque perception was determined by the spatial or by the temporal characteristics of the rotary switch. In Exp.

Does contour classification precede contour grouping in perception of partially visible figures?

When a figure is only partially visible and its contours represent a small fraction of total image contours (as when there is much background clutter), a fast contour classification mechanism may filter non-figure contours in order to restrict the size of the input to subsequent contour grouping mechanisms. The results of two psychophysical experiments suggest that the human visual system can classify figure from non-figure contours on the basis of a difference in some contour property (e.g.

Binocular shape constancy from novel views: the role of a priori constraints.

We tested shape constancy from novel views in the case of binocular viewing, using a variety of stimuli, including polyhedra, polygonal lines, and points in 3-D. The results of the psychophysical experiments show that constraints such as planarity of surface contours and symmetry are critical for reliable shape constancy. These results are consistent with the results obtained in our previous psychophysical experiments on shape constancy from novel views in the presence of a kinetic depth effect (Pizlo & Stevenson, 1999).

Solving combinatorial problems: the 15-puzzle.

We present a series of experiments in which human subjects were tested with a well-known combinatorial problem called the 15-puzzle and in different-sized variants of this puzzle. Subjects can solve these puzzles reliably by systematically building a solution path, without performing much search and without using distances among the states of the problem. The computational complexity of the underlying mental mechanisms is very low.