The visual perception of velocity

Summary In this section it is concluded that velocity is perceived directly and is dynamically conditioned by the structure and general properties of the visual field in which the movement occurs. The visual perception of velocity follows dynamic laws that are not immediately deducible from the velocity of the stimulus as physically defined. No physiological theory is offered but it is pointed out that the theory of physiological Gestalten is essentially correct in its basic assumptions concerning the perception of movement.The investigation has bearing on the problems of movement thresholds, movement after-images and the perception of time.This paper is abridged from a thesis presented to the faculty of the graduate school of Yale University in partial fulfilment of the requirements for the degree of Doctor of Philosophy. The study was started in the Psychological Institute of the University of Berlin in 1926–1927 and completed at Yale University in 1928–1929. The work at Berlin, which has been already reported [cf. J. F. Brown, Über gesehene Geschwindigkeit. Psychol. Forschg 10, 84–101 (1927)] was largely exploratory in nature; that at Yale was undertaken to fill the gaps in the experimental series and to control more completely the causal factors. For clarity of exposition the previously reported data are included here so far as necessary. The writer is indebted to Professor W. Köhler of the University of Berlin for suggesting the problem, and to Professors R. P. Angier, R. Dodge, and L. T. Spencer of Yale University for many valuable suggestions. He wishes also to express his thanks to the subjects who served in the experiments.     

The perception of three-dimensional solids

Arising from the discussion of differences between three- and two-dimensional perceptual objects in relation to current theories, an attempt is made to extend the traditional type of shape-constancy investigation into the realm of three-dimensional solids. For this purpose a specially constructed “solid” is made to undergo progressive physical changes of shape while being compared, under controlled conditions, with various stationary two-dimensional projections.

The results indicate that three-dimensional solids possess perceptual properties not shared by simple surfaces or representational projections. It is suggested that changes in the magnitude and sign of the constant errors obtained under certain conditions can be explained only on the assumption that subjects react to the stimulus in terms of some conceptual schema, or reference frame, involving mental processes other than those of perception.     

Haptic perception of texture gradients

To pick up 3-D aspects of pictures is arguably the most difficult problem concerning tactile pictorial perception by the blind. The aim of the experiments reported was to examine the potential utility of texture gradients in this context. Since there is no theoretical basis for predicting absolute values of 3-D properties from 2-D patterns read by the finger pads, the abilities of participants to perceive gradients lying between known maxima and minima were assessed. Experiment 1 involved blindfolded sighted participants making verbal magnitude estimations of texture-gradient magnitudes corresponding to plane surfaces at different slants. In experiment 2 the participants' task was to orient a surface at a slant corresponding to the texture gradients depicted tactually, and experiment 3 required early-blind participants to attempt the same task. The results revealed that participants can scale the magnitudes of texture gradients with high precision and that they can also accurately produce surface slants from depictions, providing the extreme conditions are clearly defined and there are opportunities for learning. Texture gradients appear as informative to the blind as they do to the sighted. To what extent these data can be generalised to other gradients and textures or to other projections of 3-D scenes remains to be investigated.     

Cognitive biases in the perception of discrimination: The importance of format

Previous work has shown that people seem less able to perceive sex discrimination on a personal level than on a societal level. The present experiment was performed to test the hypothesis that this phenomenon is in part an information-processing bias; that is, the perception of discrimination is more difficult when one makes case-by-case comparisons than when one encounters information in aggregate form. The experiment demonstrated the importance of formatting for the perception of discrimination. Among subjects with little or no emotional investment in the issue of sex discrimination, the format of the pertinent information has a large effect on information processing: subjects perceived less discrimination when they encountered the relevant information in little chunks than when they saw the total picture at a single shot.     

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.     

Three gradients and the perception of flat and curved surfaces

Researchers of visual perception have long been interested in the perceived slant of a surface and in the gradients that purportedly specify it. Slant is the angle between the line of sight and the tangent to the planar surface at any point, also called the surface normal. Gradients are the sources of information that grade, or change, with visual angle as one looks from one's feet upward to the horizon. The present article explores three gradients--perspective, compression, and density--and the phenomenal impression of flat and curved surfaces. The perspective gradient is measured at right angles to the axis of tilt at any point in the optic array; that is, when looking down a hallway at the tiles of a floor receding in the distance, perspective is measured by the x-axis width of each tile projected on the image plane orthogonal to the line of sight. The compression gradient is the ratio of y/x axis measures on the projected plane. The density gradient is measured by the number of tiles per unit solid visual angle. For flat surfaces and many others, perspective and compression gradients decrease with distance, and the density gradient increases. We discuss the manner in which these gradients change for various types of surfaces. Each gradient is founded on a different assumption about textures on the surfaces around us. In Experiment 1, viewers assessed the three-dimensional character of projections of flat and curved surfaces receding in the distance. They made pairwise judgments of preference and of dissimilarity among eight stimuli in each of four sets. The presence of each gradient was manipulated orthogonally such that each stimulus had zero, one, two, or three gradients appropriate for either a flat surface or a curved surface. Judgments were made were made for surfaces with both regularly shaped and irregularly shaped textures scattered on them. All viewer assessment were then scaled in one dimension. Multiple correlation and regression on the scale values revealed that greater than 98% of the variance in scale values was accounted for by the gradients. For the flat surfaces a mean of 65% of the variance was accounted for by the perspective gradient, 28% by the density gradient, and 6% by the compression gradient. For curved surfaces, on the other hand, a mean of 96% of the variance was accounted for by the compression gradient, and less than 2% by either the perspective gradient or the density gradient.(ABSTRACT TRUNCATED AT 400 WORDS)     

A counterexample to the rigidity assumption in the visual perception of structure from motion

It has been proposed that the human visual system prefers perceptions of objects that are rigid or undergo minimum form change. A counterexample is presented in which a rigid two-dimensional figure rotating in the frontal plane is perceived as a distorting three-dimensional shape. It is argued that this perception results from the stimulation of automatic processes for perceiving size change, and that these processes are not subject to a general rigidity assumption.     

The importance of social factors is a matter of perception

Caucasian female faces were randomly assigned to participants' in- or out-group following false feedback on a personality inventory. Participants recognised in-group faces better than out-group faces, but they showed no evidence of category-contingent opposing aftereffects. We conclude that the explanatory power of social-cognitive models will be enhanced when they are integrated with models of perceptual expertise.     

The perception of depth and slant from texture in three-dimensional scenes.

The perception of depth and slant in three-dimensional scenes specified by texture was investigated in five experiments. Subjects were presented with computer-generated scenes of a ground and ceiling plane receding in depth. Compression, convergence, and grid textures were examined. The effect of the presence or absence of a gap in the center of the display was also assessed. Under some conditions perceived slant and depth from compression were greater than those found with convergence. The relative effectiveness of compression in specifying surface slant was greater for surfaces closer to ground planes (80 degrees slant) than for surfaces closer to frontal parallel planes (40 degrees slant). The usefulness of compression was also observed with single-plane displays and with displays with surfaces oriented to reduce information regarding the horizon.     

Rotation reveals the importance of configural cues in handwritten word perception

A dramatic perceptual asymmetry occurs when handwritten words are rotated 90 ° in either direction. Those rotated in a direction consistent with their natural tilt (typically clockwise) become much more difficult to recognize, relative to those rotated in the opposite direction. In Experiment 1, we compared computer-printed and handwritten words, all equated for degrees of leftward and rightward tilt, and verified the phenomenon: The effect of rotation was far larger for cursive words, especially when they were rotated in a tilt-consistent direction. In Experiment 2, we replicated this pattern with all items being presented in visual noise. In both experiments, word frequency effects were larger for computer-printed words and did not interact with rotation. The results suggest that handwritten word perception requires greater configural processing, relative to computer print, because handwritten letters are variable and ambiguous. When words are rotated, configural processing suffers, particularly when rotation exaggerates the natural tilt. Our account is similar to theories of the “Thatcher illusion,” wherein face inversion disrupts holistic processing. Together, the findings suggest that configural, word-level processing automatically increases when people read handwriting, as letter-level processing becomes less reliable.     

The role of three-dimensional depth cues in infants' perception of partly occluded objects

Newborn infants were familiarized to a three dimensional display consisting of a rod which moved behind a central occluder, so that only the top and bottom of the rod were visible. The infants' eyes were 38 cm from the rod and the occluder was 15 cm in front of the rod, a separation intended to ensure that the gap between the two was detected by the infants. On subsequent test trials the infants looked longer at a complete rod than at two rod pieces, suggesting that the hidden unity, or completeness of the rod had not been perceived. In a study by Johnson and Náñez (in press), using computer. generated stimuli, 4 month olds perceived the hidden unity of a similar display presented on a VDU in the complete absence of three. dimensional depth cues. Taken together, these findings suggest that, for these displays, perception of three. dimensional depth cues is not necessary for the detection of the unity of partially hidden objects. It is suggested that age changes in early infancy in the perception of occluded objects may result either from the emergence of abilities to perceive objects from kinematic information or from the emergence of sensitivity to that information itself.     

The effect of movement velocity on form perception: geometric illusions in dynamic displays

We investigated the effects of movement velocity on the perception of simple geometric trajectories. We show that when an ellipse is traced by the continuous displacement of a spot against an empty background, the subjective aspect ratio (R = vertical axis/horizontal axis) of the figure depends on the law of motion of the spot. If the tangential velocity of the spot is constant, very large and subject-specific biases emerge in the perception of the aspect ratio. If the tangential velocity of the spot is made equal to that of an elliptic motion with aspect ratio R less than 1, and resulting from the vectorial composition of two harmonic functions (Lissajous motion) there is a general trend to perceive the ellipse as being flatter than in reality. The effect, however, is not symmetric: when the velocity follows a Lissajous modulation with R greater than 1, highly significant biases are still present in most subjects, but no common trend emerges from the experimental population. The results are discussed in the context of recent findings on the relationship between form and kinematics in spontaneous human movements.