The perception of surface curvature from optical motion

Observers viewed the optical flow field of a rotating quadric surface patch and were required to match its perceived structure by adjusting the shape of a stereoscopically presented surface. In Experiment 1, the flow fields included rigid object rotations and constant flow fields with patterns of image acceleration that had no possible rigid interpretation. In performing their matches, observers had independent control of two parameters that determined the surface shape. One of these, called the shape characteristic, is defined as the ratio of the two principle curvatures and is independent of object size. The other, called curvedness, is defined as the sum of the squared principle curvatures and depends on the size of the object. Adjustments of shape characteristic were almost perfectly accurate for both motion conditions. Adjustments of curvedness, on the other hand, were systematically overestimated and were not highly correlated with the simulated curvedness of the depicted surface patch. In Experiment 2, the same flow fields were masked with a global pattern of curl, divergence, or shear, which disrupted the first-order spatial derivatives of the image velocity field, while leaving the second-order spatial derivatives invariant. The addition of these masks had only negligible effects on observers’ performance. These findings suggest that observers’ judgments of three-dimensional surface shape from motion are primarily determined by the second-order spatial derivatives of the instantaneous field of image displacements.     

Overestimation of base-rate differences in complex perceptual categories

The optimality of multidimensional perceptual categorization performance was examined for several base-rate ratios, for both integral and separable dimension stimuli, and for complex category structures. In all cases, the optimal decision bound was highly nonlinear. Observers completed several experimental sessions, and all analyses were performed at the single-observer level using a series of nested models derived from decision-bound theory (Maddox, 1995; Maddox & Ashby, 1993). In every condition, all observers were found to be sensitive to the base-rate manipulations, but the majority of observers appeared to overestimate the base-rate difference. These findings converge with those for cases in which the optimal decision bound was linear (Maddox, 1995) and suggest that base-rates are learned in a similar fashion regardless of the complexity of the optimal decision bound. Possible explanations for the consistent overestimate of the base-rate difference are discussed. Several continuous-valued analogues of Kruschke’s (1996) theory of base-rate learning with discrete-valued stimuli were tested. These models found some support, but in all cases were outperformed by a version of decision-bound theory that assumed accurate knowledge of the category structure and an overestimate of the base-rate difference.     

Evidence for an equality heuristic in social decision making

Subjects read a story in which five business partners needed to allocate the profits and expenses of the partnership in a fair and reasonable manner. Each of the partners worked independently and produced different gross incomes between $140 and $285. The gross incomes were to be divided into expenses and profits. Subjects were asked to fill in fair allocations in an accounting ledger. Three factors were manipulated: the target of the allocation task (either the expenses or the profits), the causal attributions for the differences in gross incomes (internal, external, or both), and whether the subjects were asked to fill in both columns (expenses and profits) or just one.

The results supported the hypothesis that the subjects heuristically used equality to make their allocations. Over 70% of the subjects allocated at least one column equally (although the frequency of equality use varied as a function of both the target of the allocation and the attribution given). Subjects allocated the target columns equally more often than non-target columns, even though equality for one column implied inequality for the other. The use of equality was also sensitive to the attribution given for the performance differences. Differences due to external factors, i.e., the number of people showing up at the market, produced the most equal allocations of profits (with unequal expenses) while the internal attribution produced the highest proportion of equal expense allocations (with unequal profits).     

OPEN ENVIRONMENT DESIGN FOR INFANT AND TODDLER DAY CARE

Group care settings for dependent people must be organized to facilitate delivery of responsive care and to prevent inadvertant neglect or deliberate abuse. Accordingly, in an infant and a toddler day-care center, an open environment was examined as a means to increase the visibility of children to staff and of staff-child interactions to the supervisor, and to investigate potential adverse effects of the open environment on infants' and toddlers' activities. These studies demonstrated that: (1) an open environment markedly decreased the amount of time a child could not be seen by any adult and the amount of time staff members' activities were not visible to the supervisor, and markedly reduced the effort required to supervise those who were not immediately visible; (2) an open environment did not adversely affect the sleep of either infants or toddlers; and (3) an open environment is as conducive to small group pre-academic activities with toddlers as is a separate room. These studies convinced us that infant and toddler day care can and should be accomplished in an open environment.     

Additional evidence for veridicality of perceptions based on physiognomic cues.

This study was designed to determine whether veridical interpersonal perceptions can be found on the basis of physiognomic cues. 21 male and female college students attempted to identify the correct social category [honor student, active or inactive in extracurricular events, and beauty queen (for female stimulus persons) or athlete (for male stimulus persons)] of 44 photographed male and female stimulus persons. Results demonstrated considerable veridicality, especially by male judges and of stimulus persons occupying categories which imply physical attributes.     

Comments on Richard Jeffrey

In this commentary, after first summarizing the three major theses of Jeffrey's paper ‘Probability and Falsification: Critique of the Popper Program’, and sketching out what I take to be his central argument, I criticize Jeffrey on two grounds. The first is that he has failed to explain why his version of Bayesianism provides us with better theories upon which to make decisions; the second is that he has offered a theory about decision-making that by-passes the important question: How can we make more rational decisions?     

A proposal for handling missing data

A method for dealing with the problem of missing observations in multivariate data is developed and evaluated. The method uses a transformation of the principal components of the data to estimate missing entries. The properties of this method and four alternative methods are investigated by means of a Monte Carlo study of 42 computer-generated data matrices. The methods are compared with respect to their ability to predict correlation matrices as well as missing entries. The results indicate that whenever there exists modest intercorrelations among the variables (i.e., average off diagonal correlation above .2) the proposed method is at least as good as the best alternative (a regression method) while being considerably faster and simpler computationally. Models for determining the best alternative based upon easily calculated characteristics of the matrix are given. The generality of these models is demonstrated using the previously published results of Timm.