Discrimination of 3-D shape and 3-D curvature from motion in active vision

We examined the ability of human observers to discriminate between different 3-D quadratic surfaces defined by motion, and with head position fed back to the stimulus to provide an up-to-date dynamical perspective view. We tested whether 3-D shape or 3-D curvature would affect discrimination performance. It appeared that discrimination of 3-D quadratic shape clearly depended on shape but not on the amount of curvature. Even when the amount of curvature was randomized, subjects’ performance was not altered. On the other hand, the discrimination of 3-D curvature clearly depended linearly on curvature with Weber fractions of 20% on the average and, to a small degree, on 3-D shape. The experiment shows that observers can easily separate 3-D shape and 3-D curvature, and that Koenderink’s shape index and curvedness provide a convenient way to specify shape. These results warn us against using just any arbitrary 3-D shape in 3-D shape perception tasks and indicate, for example, that emphasizing 3-D shape in computer displays by exaggerating curvature does not have any effect.     

A new axiomatization of portfolio theory

An axiomatization proposed by Coombs 1974 is shown to be insufficient for the representation of gambles in a risk × expected value space as described by Portfolio Theory. A new axiom system is given which is necessary and sufficient for this representation, and which implies the old axiomatization.     

Stimulus-governance and the hyperkinetic syndrome

The hypothesis that hyperkinetic children are stimulusgoverned was tested. In a sample of 39 nonmedicated hyperkinetic boys 26 were found to be stimulus-governed. In a control sample of 20 nonmedicated boys 6 were found to be stimulus-governed. An association was found between the hyperkinetic syndrome and stimulusgovernance. The hypothesis is raised that response to methylphenidate is related to stimulusgovernance. Several issues raised by the research are discussed.This research was supported in part by a grant from Bloemendaal Psychiatric Hospital, The Hague, The Netherlands. The authors wish to thank Mr. E. M. Ockhorst, for constructing the KFA-testing equipment, and Mr. R. Reyneart, for helping with the computer analysis. An earlier draft of the paper was presented at the European Conference of Neuropsychology, sponsored by the International Neuropsychology Society, at Oxford University, England.     

Acquired aphasia with convulsive disorders in children: a case study with a seven-year follow-up.

In a 7-year follow-up a case of the “syndrome of acquired aphasia with convulsive disorder” is described. In particular, attention is paid to EEG patterns and linguistic analysis. Although seizures have been controlled medically and EEG abnormalities have tended to improve, no close parallel improvement has been observed in the patient's language disorders.     

Interrelation of the effects of binocular disparity and perspective cues on judgments of depth and height

The effects of binocular disparity (aniseikonia) and perspective cues operating together on judgments of depth and height were studied, both when these stimulus variables operated in the same direction and when they were in conflict. Both depth cues were effective upon the perception of depth and height. The effects of binocular disparity and perspective cues upon perceived depth were found to be additive. The effects of these depth cues upon perceived height showed some interaction in the sense that, operating together, the effect of the perspective cue was stronger than the separate effect of the perspective cue, both when binocular disparity and perspective cues operated in the same direction and when they were in conflict. This interactive effect increased with increasing strength of the perspective cues. The size-distance invariance hypothesis was confirmed under the present experimental conditions. By a causal analysis of inference, this invariant relation could be explained in the following way: both the perceived depth and the perceived height of the sides of the patterns were directly determined by binocular disparity and perspective cues, but the perceived height was also indirectly determined through change of perceived depth. A direct causal relation between perceived depth and perceived height was found.     

Neon color spreading and structural information measures

This article presents a study on Van Tuijl’s (1975) neon effect. The neon effect can be described as an illusory spreading of color around the colored elements of an otherwise black line pattern. The observer has a strong impression of colored light projected onto a lattice of black lines. The hypothesis is advanced that the neon effect will only result if the structural relationships between black and colored line elements in the pattern are such that a neon interpretation is the most efficient interpretation that can be given of the pattern. The necessity of this approach to the neon phenomenon emanates from the inadequacy of alternative, more simple, explanations, such as aberrations of peripheral perceptual mechanisms or the presence in the pattern of easily definable stimulus features. To subject the hypothesis proposed above to experimental test, a precise quantification of its central concept, the efficiency of pattern interpretations, is needed. To that end, Leeuwenberg’s (1971) coding language for sequential patterns is introduced. By means of the coding language, pattern interpretations can be represented in a pattern code, the length of which is inversely proportional to the efficiency of the interpretation coded. Several possible interpretations of color differences between the elements of line patterns are discussed, and it is shown how the efficiency of each of them can be determined. Next, in two experiments, the efficiency of the neon interpretationrelative to that of alternative interpretations of color differences in line patterns is varied, by manipulating the structural relations between black and colored line elements, and the dependency of the neon effect on the relative efficiency of the neon interpretation is demonstrated. Implications of the findings are discussed.     

Reactions to receiving expected and unexpected help from a person who violates or does not violate a norm

Different factors may affect reciprocity and attraction to an aid-giver. Sixty white South African high school students participated in a “record contest”. Hints provided by the quizmaster enabled them to win a prize. His help was expected or unexpected and, in providing this help, the quizmaster either did or did not violate a specific norm against doing so. It was predicted that recipients of unexpected help would display more reciprocity than recipients of expected help, but that the aid-giver would be derogated only when he behaved in both an unexpected and counternormative way and that, in general, attraction and reciprocity would be unrelated. These hypotheses were supported. They suggest that reciprocity is normally not mediated by attraction and that neither expectancy violation nor counternormative behavior will be itself produce derogation of an aid-giver. They further suggest recipients of unexpected help probably feel more obliged to repay an aid-giver than do recipients of expected help.     

Local homogeneity in latent trait models. A characterization of the homogeneous monotone irt model

The stochastic subject formulation of latent trait models contends that, within a given subject, the event of obtaining a certain response pattern may be probabilistic. Ordinary latent trait models do not imply that these within-subject probabilities are identical to the conditional probabilities specified by the model. The latter condition is called local homogeneity. It is shown that local homgeneity is equivalent to subpopulation invariance of the model. In case of the monotone IRT model, local homogeneity implies absence of item bias, absence of item specific traits, and the possibility to join overlapping subtests. The following characterization theorem is proved: the homogeneous monotone IRT model holds for a finite or countable item pool if and only if the pool is experimentally independent and pairwise nonnegative association holds in every positive subpopulation.This research was supported by the Dutch Interuniversity Graduate School of Psychometrics and Sociometrics. The authors wish to thank two reviewers for their thorough comments.     

Goal attainment scaling: An idiosyncratic method to assess treatment effectiveness in agoraphobia

Goal attainment scaling (GAS) is an individually tailored way to measure treatment gains, using a highly standardized procedure. An advantage of the method is that it takes into account individual characteristics of the patients, and at the same time the data are suitable for quantitative analysis and comparable across patients. Despite the wide acceptance and use of the method in the evaluation of psychotherapy, data on its psychometric properties are rather scarce. In the current study, GAS was used as one of several outcome measures in a research project on the effectiveness of various treatments for panic disorder with agoraphobia. Guidelines for GAS are presented as well as data on the reliability and validity of the procedure. Results indicate that the procedure is reliable, valid, and sensitive to the improvement of patients during treatment. Comparison of GAS with standardized measures revealed considerable concordance, although the clinical end status of patients diverged somewhat dependent on the measure considered.     

Is the brain an effective Turing machine or a finite-state machine?

Summary A theorem presented by Hornik, Stinchcombe, and White (1989) suggested the possibility that connectionist networks could be effectively Turing machines. Levelt (1990) argued that the theorem of Hornik et al. only implies that networks are finite-state machines and are therefore not capable of generating the very unlimited productivity of symbol systems. Yet it can be argued that all real machines, including the brain, are finite-state machines. If so, no real machine actually possesses the very unlimited productivity of symbol systems. So any model of actual behaviour should capture the limitations on productivity inherent in the situation. Thus connectionist networks can be valuable models in psychology, precisely because they are finite-state machines.