Myron L. Braunstein

Exploring predecisional behavior: An alternative approach to decision research☆

Abstract A trend in the study of decision behavior is the increased emphasis being placed on understanding the psychological processes underlying observed judgments or choices. Unfortunately, the input-output analyses that have been used by most decision researchers do not appear fully adequate to develop and test process models of decision behavior. It is argued that data collection methods are needed that will yield data on predecisional behavior in order to identify what information a decision maker has and how it is being processed. Two such process tracing methods, verbal protocol analysis and the analysis of information acquisition behavior, which should be especially valuable in decision research are illustrated and discussed. The process tracing approach appears to be a valuable complement to more traditional model fitting approaches to the study of decision behavior. The value of a multimethod approach is also illustrated and discussed.

Induced self-motion in central vision.

Previous research on visually induced self-motion found that stimulation of the central visual field (up to 30 degrees in diameter) results in perceived object motion while self-motion requires peripheral stimulation. In the present study, perceived self-motion was induced with a radially expanding pattern simulating observer motion through a space filled with dots, with visual angles of 7.5 degrees, 10.6 degrees, 15 degrees, and 21.2 degrees. Speed and texture density were also varied. The duration of reported self-motion (a) decreased with increased speed, (b) failed to increase with increased visual angle, and (c) decreased with visual angle at the highest speed level. In a second experiment, subjects rated the perceived depth of the displays. The speed and speed/area interaction effects on judged depth matched those found for induced self-motion. These results suggest an extension of the focal/ambient theory: In addition to a more primitive ambient processing mode that requires peripheral vision, there is a higher level system concerned with ambient processing that functions in the central visual field and uses more complex stimulus information, such as internal depth represented in a radially expanding pattern.

Risky choice: An examination of information acquisition behavior

The monitoring of information acquisition behavior, along with other process tracing measures such as response times, was used to examine how individuals process information about gambles into a decision. Subjects indicated preferences among specially constructed three-outcome gambles. The number of alternatives available was varied across the sets of gambles. A majority of the subjects processed information about the gambles in ways inconsistent with compensatory models of risky decision making, such as information integration (Anderson & Shanteau, 1970). Furthermore, the inconsistency between observed information acquisition behavior and such compensatory rules increased as the choice task became more complex. Alternative explanations of risky choice behavior are considered.

Parts of Visual Objects: An Experimental Test of the Minima Rule

Three experiments were conducted to test Hoffman and Richardss (1984) hypothesis that, for purposes of visual recognition, the human visual system divides three-dimensional shapes into parts at negative minima of curvature. In the first two experiments, subjects observed a simulated object (surface of revolution) rotating about a vertical axis, followed by a display of four alternative parts. They were asked to select a part that was from the object. Two of the four parts were divided at negative minima of curvature and two at positive maxima. When both a minima part and a maxima part from the object were presented on each trial (experiment 1), most of the correct responses were minima parts (101 versus 55). When only one part from the object—either a minima part or a maxima part—was shown on each trial (experiment 2), accuracy on trials with correct minima parts and correct maxima parts did not differ significantly. However, some subjects indicated that they reversed figure and ground, thereby changing maxima parts into minima parts. In experiment 3, subjects marked apparent part boundaries. 81% of these marks indicated minima parts, 10% of the marks indicated maxima parts, and 9% of the marks were at other positions. These results provide converging evidence, from two different methods, which supports Hoffman and Richardss minima rule.

Shape and depth perception from parallel projections of three-dimensional motion.

Parallel projections of dots on the surface of a transparent sphere rotating about a vertical axis provide strong impressions of depth and spherical shape. The hypothesis was tested that these impressions are the result of three perceptual heuristics: (a) The sinusoidal projected velocity function of each dot in the horizontal dimension tends to be perceived as a rotary motion in depth; (b) the projected velocity gradient in the vertical dimension is perceived as curvature in depth; and (c) the simultaneously visible fields of dots moving in opposite directions are perceived as surfaces separated in depth. When each factor was varied independently, all three significantly affected judgments of spherical shape and depth. Similar results were obtained with cylinders. The first factor was more important for shape judgments; the second was generally more important for depth judgments. These results, together with those of earlier studies in which these factors led to similar effects for different stimuli and transformations, suggest that these are general principles applicable to the perception of structure from both rigid and nonrigid motion.

Discriminating rigid from nonrigid motion: Minimum points and views

Theoretical investigations of structure from motion have demonstrated that an ideal observer can discriminate rigid from nonrigid motion from two views of as few as four points. We report three experiments that demonstrate similar abilities in human observers: In one experiment, 4 of 6 subjects made this discrimination from two views of four points; the remaining subjects required five points. Accuracy in discriminating rigid from nonrigid motion depended on the amount of nonrigidity (variance ofthe interpoint distances overviews) in the nonrigid structure. The ability to detect a rigid group dropped sharply as noise points (points not part of the rigid group) were added to the display. We conclude that human observers do extremely well in discriminating between nonrigid and fully rigid motion, but that they do quite poorly at segregating points in a display on the basis of rigidity.

Velocity gradients and relative depth perception

The effectiveness of velocity gradients in providing relative depth information was assessed using random dot patterns translating horizontally. The gradients simulated two planes meeting at a horizontal line at the center, and subjects judged whether the center was the nearest or farthest part of the display. Accuracy increased with maximum dot speed, exceeding 90% in conditions combining the highest speed (10.4o/sec) and longer of two display durations (10 sec) with unrestricted fixation. Separate experiments examined a rotational component perceived in the motion of the planes and the latency in reporting a rigid organization of the displays. Possible reasons for the chance accuracy found by Farber and McConkie (1979) and alternative explanations of the effect of maximum dot speed on accuracy are discussed. A model is presented that accounts for the effects of dot speed and display duration on the accuracy of relative depth judgments.

Recovery of 3-D shape from binocular disparity and structure from motion

Four experiments were conducted to examine the integration of depth information from binocular stereopsis and structure from motion (SFM), using stereograms simulating transparent cylindrical objects. We found that the judged depth increased when either rotational or translational motion was added to a display, but the increase was greater for rotating (SFM) displays. Judged depth decreased as texture element density increased for static and translating stereo displays, but it stayed relatively constant for rotating displays. This result indicates that SFM may facilitate stereo processing by helping to resolve the stereo correspondence problem. Overall, the results from these experiments provide evidence for a cooperative relationship between. SFM and binocular disparity in the recovery of 3-D relationships from 2-D images. These findings indicate that the processing of depth information from SFM and binocular disparity is not strictly modular, and thus theories of combining visual information that assume strong modularity-or-independence cannot accurately characterize all instances of depth perception from multiple sources.

Recovering viewer-centered depth from disparity, occlusion, and velocity gradients

Two experiments were conducted to assess the effects of corresponding and conflicting binocular and monocular information on the recovery of depth order (signed depth). Subjects viewed displays in which the same or opposite depth orders were indicated by disparity and occlusion, in one experiment, or by disparity and velocity gradients, in a second experiment. The same 36 subjects, 17 who had failed a Random Dot E test and 19 who had passed, were run in both experiments. When binocular and monocular information indicated conflicting depth orders, most subjects responded in accordance with the monocular information on some trials in both experiments. This was true even for a subgroup who always responded in accordance with the stereoscopic information on control trials that did not provide monocular information for depth order. For this subgroup, the impact of conflicting monocular information in the velocity gradient task correlated with performance on the uncrossed version of the Random Dot E test. We also found that some subjects who failed static tests of stereoscopic depth perception could respond accurately to continuously changing disparities.

The use of occlusion to resolve ambiguity in parallel projections

Previous research has shown that the three-dimensional structure of an object usually can be perceived when viewing a parallel projection of the object rotating in depth. Accurate judgments of direction of rotation, however, have been found only with polar projections. The present study demonstrated that accurate direction judgments can occur with parallel projections if occlusion is included in the displays. The stimuli were parallel projections of pentagonal texture elements on the surface of a rotating sphere. In one condition, the elements were occluded as they rounded the edge of an opaque sphere. In another condition, elements on the far surface of a transparent sphere were occluded by elements on the near surface. Accuracy of direction judgments was consistently high in the first condition and increased monotonically with element size in the second condition, from chance to over 80% correct. The relationship of these results to the general issue of perceptually combining structure in depth information from one source with relative distance information from another source is discussed.