Three-dimensional Form Perception Research Articles

Countershading enhances camouflage by reducing prey contrast

A three-dimensional body shape is problematic for camouflage because overhead lighting produces a luminance gradient across the body's surface. Countershading, a form of patterning where animals are darkest on their uppermost surface, is thought to counteract this luminance gradient and enhance concealment, but the mechanisms of protection remain unclear. Surprisingly, no study has examined how countershading alters prey contrast, or investigated how the presence of a dorsoventral luminance gradient affects detection under controlled viewing conditions. It has also been suggested that the direction of the dorsoventral luminance gradient (darkest or lightest on top) may interfere with predators' abilities to resolve prey's three-dimensional shape, yet this intriguing idea has never been tested. We used live fish predators (western rainbowfish, Melanotaenia australis) and computer-generated prey images to compare the detectability of uniformly pigmented (i.e. non-countershaded) prey with that of optimally countershaded prey of varying contrasts against the background. Optimally countershaded prey were difficult for predators to detect, and the probability and speed of detection depended on prey luminance contrast with the background. In comparison, non-countershaded prey were always highly detectable, even though their average luminance closely matched the luminance of the background. Our findings suggest that uniformly pigmented three-dimensional prey are highly conspicuous to predators because overhead lighting increases luminance contrast between different body parts or between the body and the background. We found no evidence for the notion that countershading interferes with predator perception of three-dimensional form.

Perceptual reversal of bi-stable figures in microgravity and hypergravity during parabolic flight

This experiment investigated whether the perception of depth-reversible figures is altered when the observer is in microgravity or hypergravity. A set of five bi-stable ambiguous figures was presented to ten participants in 1 g, 0 g, and 1.8 g during parabolic flight. The figures included static images such as the Necker cube; kinetic depth displays such as a moving plaid and a sphere cluster of moving dots appearing to rotate in one of two directions; and a silhouette photograph. For each stimulus figure, subjects reported which of the two possible perceptual configurations they saw first and then continuously indicated when perceptual reversals occurred for durations ranging from 20 to 30 s. The same first percept was reported in 1 g, 0 g, and 1.8 g. The time delay for the first reversal between the two possible image interpretations was longer and the number of reversals was fewer in 0 g as compared to 1 g for four of the five figures. The opposite effects were seen when going from 0 g to 1.8 g. These findings confirm that, consistent with a multisensory approach to three-dimensional form perception, gravity has a clear effect on the interpretation of depth-based stimuli and this gravity-based component interferes with visual perception stability.

A neural model of 3D shape-from-texture: Multiple-scale filtering, boundary grouping, and surface filling-in

A neural model is presented of how cortical areas V1, V2, and V4 interact to convert a textured 2D image into a representation of curved 3D shape. Two basic problems are solved to achieve this: (1) Patterns of spatially discrete 2D texture elements are transformed into a spatially smooth surface representation of 3D shape. (2) Changes in the statistical properties of texture elements across space induce the perceived 3D shape of this surface representation. This is achieved in the model through multiple-scale filtering of a 2D image, followed by a cooperative-competitive grouping network that coherently binds texture elements into boundary webs at the appropriate depths using a scale-to-depth map and a subsequent depth competition stage. These boundary webs then gate filling-in of surface lightness signals in order to form a smooth 3D surface percept. The model quantitatively simulates challenging psychophysical data about perception of prolate ellipsoids [Todd, J., & Akerstrom, R. (1987). Perception of three-dimensional form from patterns of optical texture. Journal of Experimental Psychology: Human Perception and Performance, 13(2), 242–255]. In particular, the model represents a high degree of 3D curvature for a certain class of images, all of whose texture elements have the same degree of optical compression, in accordance with percepts of human observers. Simulations of 3D percepts of an elliptical cylinder, a slanted plane, and a photo of a golf ball are also presented.

The evolutionary neuroscience of tool making

The appearance of the first intentionally modified stone tools over 2.5 million years ago marked a watershed in human evolutionary history, expanding the human adaptive niche and initiating a trend of technological elaboration that continues to the present day. However, the cognitive foundations of this behavioral revolution remain controversial, as do its implications for the nature and evolution of modern human technological abilities. Here we shed new light on the neural and evolutionary foundations of human tool making skill by presenting functional brain imaging data from six inexperienced subjects learning to make stone tools of the kind found in the earliest archaeological record. Functional imaging of this complex, naturalistic task was accomplished through positron emission tomography with the slowly decaying radiological tracer 18flouro-2-deoxyglucose. Results show that simple stone tool making is supported by a mosaic of primitive and derived parietofrontal perceptual-motor systems, including recently identified human specializations for representation of the central visual field and perception of three-dimensional form from motion. In the naïve tool makers reported here, no activation was observed in prefrontal executive cortices associated with strategic action planning or in inferior parietal cortex thought to play a role in the representation of everyday tool use skills. We conclude that uniquely human capacities for sensorimotor adaptation and affordance perception, rather than abstract conceptualization and planning, were central factors in the initial stages of human technological evolution.

Perceptual exploration and intersensory merging in a visual–haptic Necker cube

Perceiving the three-dimensional structure of an object often involves merging vision and haptics over extended periods of exploration. An interesting feature of this process is that as exploration progresses, new information may require changing how the two sensory signals are treated. We tested whether (1) bimodal interactions during extended observation can adjust to changes in the quality of unimodal sensory signals; and (2) there are specific temporal constraints on these adjustments. When viewing a three-dimensional Necker cube with one eye, participants experience illusory reversals even while they feel the cube with their hands. This surprising property makes the visual–haptic Necker cube an excellent model to investigate bimodal processes when previously consistent bimodal signals change in quality over time or begin to conflict. Our participants reported reversals while they viewed the cube and, at the same time, they either held it with two-finger grips, felt it with while their hands remained stationary, or actively explored it by moving one hand. Consistent with a multisensory approach to three-dimensional form perception, touch had a clear effect on both the number and the duration of illusory percepts. Additionally, when observers alternated between stationary and moving periods during exploration, transitions from stationary to moving-hand haptics played a crucial role in inhibiting illusory reversals. A temporal analysis of the probability of first reversals occurring after different types of motor transition revealed a “vetoing window” initiating approximately 2 s after the transition and lasting at least another 1–2 s. These results suggest that intersensory merging is sensitive to changes in the quality of unimodal signals during exploration, and that adjustments caused by these changes are characterized by specific temporal dynamics.

A visual–haptic Necker cube reveals temporal constraints on intersensory merging during perceptual exploration

When viewing a three-dimensional Necker cube with one eye, participants can experience illusory reversals even while they feel the cube with their hands. This surprising property of the visual–haptic Necker cube affords a unique opportunity to investigate temporal constraints on interactions between vision and touch during extended observation of a three-dimensional object. Our observers reported reversals while they viewed the cube and, at the same time, they either held it with two-finger grips, felt it with while their hands remained stationary, or actively explored it by moving one hand. Consistent with a multisensory approach to three-dimensional form perception, touch had a clear effect on both the number and the duration of illusory percepts. Additionally, when observers alternated between stationary and moving periods during exploration, transitions from stationary to moving-hand haptics played a crucial role in inhibiting illusory reversals. A temporal analysis of the probability of first reversals occurring after different types of motor transition revealed a “vetoing window” initiating approximately 2 s after the transition and lasting at least another 1–2 s. Implications for multisensory processes during exploration are discussed.

Role of learning in three-dimensional form perception.

One of the most remarkable characteristics of the human visual system is its ability to perceive specific three-dimensional forms in single two-dimensional contour images. This has often been attributed to a few general purpose and possibly innately specified shape biases, such as those favouring symmetry and other structural regularities (Fig. 1). An alternative approach proposed by the early empiricists and since tested suggests that this ability may also be acquired from visual experience, with the three-dimensional percept being the manifestation of a learned association between specific two-dimensional projections and the correlated three-dimensional structures. These studies of shape learning have been considered inconclusive, however, because their results can potentially be accounted for as cognitive decisions that might have little to do with shape perception per se. Here we present an experimental system that enables objective verification of the role of learning in shape perception by rendering the learning to be perceptually manifest. We show that the human visual system can learn associations between arbitrarily paired two-dimensional pictures and (projectionally consistent) three-dimensional structures. These results implicate high-level recognition processes in the task of shape perception.

Perception of three-dimensional form from patterns of optical texture.

The research described in the present article was designed to investigate how patterns of optical texture provide information about the three-dimensional structure of objects in space. Four experiments were performed in which observers were asked to judge the perceived depth of simulated ellipsoid surfaces under a variety of experimental conditions. The results revealed that judged depth increases linearly with simulated depth although the slope of this relation varies significantly among different types of texture patterns. Random variations in the sizes and shapes of individual surface elements have no detectable effect on observers' judgments. The perception of three-dimensional form is quite strong for surfaces displayed under parallel projection, but the amount of apparent depth is slightly less than for identical surfaces displayed under polar projection. Finally, the perceived depth of a surface is eliminated if the optical elements in a display are not sufficiently elongated or if they are not approximately aligned with one another. A theoretical explanation of these findings is proposed based on the neural network analysis of Grossberg and Mingolla.

Perception of three-dimensional form from patterns of optical texture.

Perception of three-dimensional form from patterns of optical texture.

Development of three-dimensional form perception.

In three experiments with infants and one with adults we explored the generality, limitations, and informational bases of early form perception. In the infant studies we used a habituation-of-looking-time procedure and the method of Kellman (1984), in which responses to three-dimensional (3-D) form were isolated by habituating 16-week-old subjects to a single object in two different axes of rotation in depth, and testing afterward for dishabituation to the same object and to a different object in a novel axis of rotation. In Experiment 1, continuous optical transformations given by moving 16-week-old observers around a stationary 3-D object specified 3-D form to infants. In Experiment 2 we found no evidence of 3-D form perception from multiple, stationary, binocular views of objects by 16- and 24-week-olds. Experiment 3A indicated that perspective transformations of the bounding contours of an object, apart from surface information, can specify form at 16 weeks. Experiment 3B provided a methodological check, showing that adult subjects could neither perceive 3-D forms from the static views of the objects in Experiment 3A nor match views of either object across different rotations by proximal stimulus similarities. The results identify continuous perspective transformations, given by object or observer movement, as the informational bases of early 3-D form perception. Detecting form in stationary views appears to be a later developmental acquisition.

Development of three-dimensional form perception.

Development of three-dimensional form perception.

Infants' identification of three-dimensional form from transformations of linear perspective.

The ability of infants to perceive three-dimensional structure from transformations of linear perspective was investigated in two studies. Infants were habituated to the pattern of linear perspective transformations corresponding to a particular three-dimensional object, and their relative preference for that object as compared with a different three-dimensional object was assessed both before and after habituation. The habituation displays showed the distorting shadow cast by a rotating object and therefore provided only transformations of linear perspective as information specifying three-dimensional form. The pre- and posttest displays involved the actual three-dimensional objects and provided binocular, shading, and texture information specifying three-dimensional form, but did not provide informative transformations of linear perspective. In Study 1, 6-month-olds showed changes in preference from pre- to posttest that were related to the identity of the object whose shadow they had seen during habituation; 4-month-olds, however, did not show preference changes related to the habituation object. In Study 2, rhythm information that may have served as a basis for responding in Study 1 was eliminated from the test displays. Six-month-olds again showed changes in preference that were dependent on their habituation experience. It is concluded that, by 6 months of age, infants are able to perceive object structure from the isolated cue of transformations of linear perspective. The findings are discussed with reference to infants’ three-dimensional form perception based on other cues and also with reference to the emergence of certain spatially related moter activities.

The more things change the more they stay the same: Infant perception of three-dimensional form from information given by observer movement

The more things change the more they stay the same: Infant perception of three-dimensional form from information given by observer movement

Measurement and prediction of diagnostic performance during radiology training.

Faculty evaluations of residents' diagnostic performance in radiology subspecialty rotations were examined in two studies in order to ascertain whether the relative capabilities of residents change during training and to predict residents' diagnostic performance using a three-dimensional form perception test. In the first study, numeric ratings by faculty members were averaged to provide interpretive/diagnostic scores for each of 16 residents in each of 5 consecutive half-years. Sixty-seven percent of the relative differences among residents' diagnostic proficiencies persisted during training. The magnitude of these unchanging differences between individuals in diagnostic performance strongly favors resident selection based upon diagnostic potential. An additional 22% of the relative differences correlated with an abrupt change in the rank order of residents in diagnostic performance at the beginning of the second year of residency. This rearrangement of ranks may have resulted from an abrupt change in the tasks and expectations assigned to residents. In the second study, correlations between scores on a recently described Form Test and monthly faculty ratings of diagnostic performance were computed. An average diagnostic performance score for each resident was generated for all rotations combined, each of eleven subspecialties, and all rotations completed within a given half-year. Scores on the Form Test correlated well with these combined diagnostic scores, further substantiating results reported previously. Form Test scores were highly correlated with subspecialty diagnostic performance scores in subspecialties using cross-sectional imaging methods, such as neuroradiology. Although Form Test scores were poorly correlated with half-year diagnostic performance during the first year, they were highly correlated with performance beginning in the second year.

Perception of three-dimensional form by human infants.

Human adults can perceive the three-dimensional form of an object from single views or from the continuously transforming two-dimensional projections of an object rotating in depth. The present work reports that 16-week-old infants can perceive three-dimensional form from transforming optical projections, but not from single or multiple static views of an object. In a habituation-of-looking-time procedure, infants in a kinetic condition were shown videotapes of one of two three-dimensional objects continuously rotating, on alternate trials, around two different axes of rotation in depth. Infants in two other conditions saw successive static views taken from the same rotation sequences. After habituation, perception of three-dimensional form was tested by presenting the same three-dimensional form moving around a new axis of rotation in depth and a different three-dimensional form moving around the same, new axis. Infants shown continuously transforming displays generalized habituation to the same object and dishabituated dramatically to the new object, whereas infants in the two static conditions showed no differential responding to the test objects as a function of habituation object. Kinetic information seems to be primary in the development of three-dimensional form perception.

The memory effect of visual perception of three-dimensional form.

The memory effect of visual perception of three-dimensional form.

The kinetic depth effect.

The problem of how three-dimensional form is perceived in spite of the fact that pertinent stimulation consists only in two-dimensional retinal images has been only partly solved. Much is known about the impressive effectiveness of binocular disparity. However, the excellent perception of threedimensional form in monocular vision has remained essentially unexplained. It has been proposed that some patterns of stimulation on the retina give rise to three-dimensional experiences, because visual processes differ in the spontaneous organization that results from certain properties of the retinal pattern. Rules of organization are supposed to exist according to which most retinal projections of three-dimensional forms happen to produce three-dimensional percepts and most retinal images of flat forms lead to flat forms in experience also. This view has been held mainly by gestalt psychologists. Another approach to this problem maintains that the projected stimulus patterns are interpreted on the basis of previous experience, either visual