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PubMed1990

Focused attention in three-dimensional space.

The size of focused attention was assessed within a three-dimensional display. Subjects viewed random-dot stereogram displays in which they responded differentially to vertical and horizontal bars. Adjacent noise elements either were identical to the response target or specified the opposite response. The position of the noise elements was varied in depth according to binocular disparity. Interference by incompatible noise elements decreased with depth separation between the noise elements and response target. In addition, interference was greater for noise elements that were more distant from the observer than from the response target than it was for noise elements that were closer to the observer than to the response target. The implications of these results for a viewer-centered representation of focused attention in depth are discussed.

Adult↗
PubMed1991

Recovery of 3-D shape from deforming contours.

Three experiments were conducted to examine the accuracy of 3-D shape recovery from deforming-contour displays. The displays simulated silhouettes of ellipsoids rotating about a vertical axis. Subjects judged the horizontal cross-section of the ellipsoids. The shape of the ellipsoid, the position of the axis of rotation, and the type of projection were manipulated in Experiment 1. The results indicated relatively accurate shape recovery when the major axis of the ellipsoid was small. In Experiment 2, the shape of the ellipsoid and the velocity and curvature of the contour were manipulated. When the rate of deformation of curvature was decreased, more eccentric shapes were reported. In Experiment 3, the shape of the object and the amount of simulated rotation were manipulated. Subjects made both shape and extent of rotation judgments. The results showed that eccentricity of shape responses could be accurately predicted from rotation responses, suggesting that the recovery of 3-D shape from smooth, deforming contours is dependent on the perceived extent of rotation.

Depth Perception↗
PubMed1991

Three-dimensional Müller-Lyer illusion.

Three-dimensional (3-D) variants of the Müller-Lyer pattern were created to address the question of where along the path of information flow in the visual system the illusion might occur. These variants, which yielded a robust illusion, included dihedral angles in place of the arrowheads of the classical pattern. The enormous difference in the shape of the resulting retinal image, compared with that of the classical pattern, makes it difficult to explain the present illusion by resorting to image-processing theories such as selective filtering (Ginsburg, 1984, 1986) or depth processing (Gregory, 1963, 1966, 1968). It was also shown that this 3-D illusion is homologous with the classical illusion, and that the two may thus share a common causal mechanism. A new type of 3-D figure, which yielded the same retinal image as did the classical pattern, was then employed. However, since the figure was 3-D, its shape in spatial coordinates was very different compared to that of the classical pattern. The magnitude of the illusion obtained with this figure was half that of the classical pattern. This finding suggests that the illusion might be caused by processes that occur after the computation of depth. All three experiments indicated that the illusion may be produced later in the processing stream than has previously been suggested.

Depth Perception↗
PubMed1992

Strength of visual interpolation depends on the ratio of physically specified to total edge length.

We report four experiments in which the strength of edge interpolation in illusory figure displays was tested. In Experiment 1, we investigated the relative contributions of the lengths of luminance-specified edges and the gaps between them to perceived boundary clarity as measured by using a magnitude estimation procedure. The contributions of these variables were found to be best characterized by a ratio of the length of luminance-specified contour to the length of the entire edge (specified plus interpolated edge). Experiment 2 showed that this ratio predicts boundary clarity for a wide range of ratio values and display sizes. There was no evidence that illusory figure boundaries are clearer in displays with small gaps than they are in displays with larger gaps and equivalent ratios. In Experiment 3, using a more sensitive pairwise comparison paradigm, we again found no such effect. Implications for boundary interpolation in general, including perception of partially occluded objects, are discussed. The dependence of interpolation on the ratio of physically specified edges to total edge length has the desirable ecological consequence that unit formation will not change with variations in viewing distance.

Adult↗
PubMed1996

Gravitational acceleration as a cue for absolute size and distance?

When an object's motion is influenced by gravity, as in the rise and fall of a thrown ball, the vertical component of acceleration is roughly constant at 9.8 m/sec2. In principle, an observer could use this information to estimate the absolute size and distance of the object (Saxberg, 1987a; Watson, Banks, von Hofsten, & Royden, 1992). In five experiments, we examined people's ability to utilize the size and distance information provided by gravitational acceleration. Observers viewed computer simulations of an object rising and falling on a trajectory aligned with the gravitational vector. The simulated objects were balls of different diameters presented across a wide range of simulated distances. Observers were asked to identify the ball that was presented and to estimate its distance. The results showed that observers were much more sensitive to average velocity than to the gravitational acceleration pattern. Likewise, verticality of the motion and visibility of the trajectory's apex had negligible effects on the accuracy of size and distance judgments.

Acceleration↗
PubMed1994

Cross-modal compatibility effects with visual-spatial and auditory-verbal stimulus and response sets.

Within the visual-spatial and auditory-verbal modalities, reaction times to a stimulus have been shown to be faster if salient features of the stimulus and response sets correspond than if they do not. Accounts that attribute such stimulus-response compatibility effects to general translation processes predict that similar effects should occur for cross-modal stimulus and response sets. To test this prediction, three experiments were conducted examining four-choice reactions with (1) visual spatial-location stimuli assigned to speech responses, (2) speech stimuli assigned to keypress responses, and (3) symbolic visual stimuli assigned to speech responses. In all the experiments, responses were faster when correspondence between salient features of the stimulus and response sets was maintained, demonstrating that similar principles of translation operate both within and across modalities.

Auditory Perception↗
PubMed1990

Monocular stereopsis with and without head movement.

Random dots moving with various velocity gradients were presented to observers; the motion was yoked to head movement in one condition and to no head movement in another. In Experiment 1, 12 observers were shown motion gradients with sine, triangle, sawtooth, and square waveforms with amplitudes (equivalent disparities) of 12' and 1 degrees 53'. In Experiment 2, 48 observers were shown only the sinewave or square-wave gradient of 1 degrees 53' disparity either with or without head movement so that the observers' expectation to see depth in one condition did not transfer to another. The main findings were: (1) with 12' disparity, the head-movement condition produced perceived depth but almost no perceived motion, whereas the no-head-movement condition produced both perceived depth and perceived motion; (2) with 1 degrees 53' disparity, both conditions produced perceived depth and perceived motion; and (3) when the expectation to see depth was removed, the no-head-movement condition with the square-wave gradient produced no perceived depth, only motion. We suggest that monocular stereopsis with head movement can be achieved without perception of motion but monocular stereopsis without head movement requires perception of motion.

Attention↗
PubMed1989

Color correspondence in apparent motion.

To maintain figural identity during motion perception, the visual system must match images over space and time. Correct matching requires a metric for identifying "corresponding" images, those representing the same physical object. To test whether matching is based on achromatic (black/white) polarity and chromatic (red/green) color, observers viewed an ambiguous motion display and judged the path of apparent motion. Matching preserved black/white identity regardless of whether frames were viewed binocularly or dichoptically. Red/green identity was also preserved, but coherence of motion depended in part on the number of frames in the motion sequence and on the background luminance. These results suggest that correspondence is computed by a weighted metric containing terms for image features coded early in visual processing.

Color Perception↗
PubMed1989

The vista paradox: a natural visual illusion.

Suppose an observer views a distant object through a window in the far wall of a room or corridor--a visual scene constituting a vista. If the observer moves toward the window, then the distant object will shrink in apparent size and appear farther away. These effects are paradoxical, because the distant object appears smaller as its visual angle increases. The vista paradox occurs under many other real-world conditions, such as viewing a distant object while moving out of the mouth of a valley, or driving across a topographic crest. In the present study, framing effects and the equidistance tendency are considered as possible factors. However, an explanation based on the dynamic relationship between the visual angle of the framing portion of a vista and the visual angle of a distant object appears more promising.

Adult↗
PubMed1989

Examination of apparent extent as an explanation of the Poggendorff effect.

The explanation of apparent misalignment in the Poggendorff figure, based on underestimation of the intertransversal distance, was investigated in two experiments. In Experiment 1, subjects judged the intertransversal distance in the traditional Poggendorff figure and two of its variants. The size of the acute angle and the intertransversal distance were manipulated. Half of the subjects made the judgments with the method used by Wilson and Pressey (1976) and the other half made their judgments with the method used by Greist-Bousquet and Schiffman (1981). The results indicated that perceived intertransversal distance was greater with the former method. In Experiment 2, subjects adjusted the transversals to apparent collinearity in the same displays as were used in Experiment 1. The collinearity judgments were transformed to allow comparison with the results of Experiment 1. Comparison of the collinearity judgments with the distance judgments indicated that they did not follow similar trends. For each Poggendorff variant, proportional distance judgments increased as the size of the acute angle increased, and decreased as the intertransversal distance increased. Collinearity judgments did not vary as a function of intertransversal distance. As the size of the acute angle increased, collinearity judgments increased for two of the Poggendorff variants but decreased for the third. It was concluded that the findings did not support the explanation of apparent misalignment based on underestimation of the intertransversal distance.

Adult↗
PubMed1989

2-D contour perception resulting from kinetic occlusion.

Kinetic occlusion, the progressive deletion or accretion of texture elements as one surface covers or uncovers another, has been shown to be an important source of information for determining depth order. In the present study, the importance of this information for 2-D contour perception was examined. In Experiment 1, subjects were asked to discriminate four different target shapes defined solely by kinetic occlusion. Discrimination increased with an increase in texture density and velocity, with density as the major factor. In Experiment 2, the targets were defined by static untextured regions as well as by kinetic occlusion. Overall, accuracy was similar to that found in Experiment 1, indicating that the presence of static information had little impact on accuracy. In Experiment 3, subjects were unable to discriminate among the four targets when presented with static versions of the displays used in Experiment 2. The results from these experiments indicate that kinetic occlusion can be used for discrimination of different 2-D shapes and that density has a more important role in determining accuracy than velocity.

Adult↗