Visual perception of surface curvature: psychophysics of curvature detection induced by motion parallax

The continuous approach to optic-flow processing shows that the curvature of a moving surface is related to a second spatial derivative of the velocity field, the spin variation (Droulez & Cornilleau-Pérès, 1989). With this approach as a theoretical framework, visual sensitivity to the curvature of a cylinder in motion was measured using a task of discrimination between cylindrical and planar patches. The results confirm the predictions suggested by the theory: (1) Sensitivity to curvature was always greater when the cylinder axis and the frontal translation were parallel than when they were orthogonal. The ratio of curvature detection thresholds in the two cases was between 1.3 and 2.5; the value predicted from the spin variation theory is about 2. (2) Sensitivity to curvature increased strongly with the velocity of the motion but was only weakly affected by its amplitude and the duration of viewing for the range of values used in our experiments.     

Semantic congruity effects in perceptual comparisons

Semantic congruity effects occur when, as in Experiment 1, for example, the time to select the shorter of two relatively short lines is faster than the time to select the longer; conversely, selection of the longer of two relatively long lines is faster than selection of the shorter. Semantic congruity effects are also demonstrated in experiments requiring comparisons of the heaviness of weights (Experiment 2) and horizontal extent (Experiment 3). In Experiment 1, the magnitude of the semantic congruity effect was larger under conditions emphasizing accuracy rather than speed and when the comparison was difficult. In fact, when comparisons were errorless, the effect was minimal (20 msec), thereby replicating previous failures to obtain the effect with supraliminal perceptual comparisons (Banks, Mermelstein, & Yu, 1982; Marschark & Paivio, 1981; Petrusic & Baranski, 1988a). In confirmation of Henmon's (1911) introspective analyses of psychophysical comparisons, Experiments 2 and 3 extend the range of the semantic congruity effect to include judgments of confidence. However, in each of the three experiments, semantic congruity effects were not evident with the response-accuracy measure. Finally, using highly confusable stimuli, in Experiment 3 the magnitude of the semantic congruity effect was shown to be larger for error than for correct response times. The implications of these findings for a decisional locus of the effect and for the semantic coding theory are discussed.     

Normal cerebrospinal fluid findings in spinal tumors--an analysis of 503 cases

Till now almost nothing has been published about normal liquor findings in spinal cord tumours. Out of 503 cases there were normal findings of total proteins and cells in 30 cases (6 per cent). A connection with the severity of the compression-syndrome was not evident. Nevertheless liquor examinations are important in diseases of the medulla spinalis. This is especially useful in the differential diagnostical demarcation of inflammable spinal cord diseases, accompanying reactions or bleedings into the spinal channel.     

Objective and simulated stimulation: an empirical study of the effect of indirect suggestion on motor behavior

In an experimental investigation it is demonstrated that motor behavior-in contrast to the opinion forwarded in the literature-is not only elicitable by means of direct persuasion, but also to a great extend by mere indirect suggestion, (feigning of stimuli). A differential investigation of these effects provided evidence that reactions to feigned stimuli are highly person specific and relatively homogenous concerning the respective instruments whereas objective stimuli lead to reactions relatively specific for the respective instrument applied. The findings are interpreted as an analog on to placebo-effects in the area of motor behavior. Their extend may be seen as an argument for a stronger concern with subjective reaction tendencies in this field.     

Feelings of attachment to siblings and well-being in later life

On the basis of an adult model of sibling attachment, I hypothesized that the well-being of older persons depends on their perception of the closeness of the sibling bond, on their perception of any disruption of that bond, and on the sex combination of the siblings being considered. In all, 83 persons, aged 61 to 91 years, were interviewed about their relationships with each of their living siblings. They rated their feelings of closeness, conflict or rivalry, and indifference to the sibling. A measure of depression was used as the indicator of well-being. Separate correlational analyses were carried out for the four sex combinations of siblings. Closeness of the bond to a sister (by both men and women) was related to less depression. Also, women's perceptions of conflict and indifference in their relationships with sisters were related to increased depression. Findings are interpreted in terms of attachment theory and sex role expectations.     

Patterns of movement in the first 6 months of life: new directions

The field of infant perceptual development has relied heavily on the preferential-looking and habituation paradigms. Despite the obvious advantages of employing standardized methodologies, there is a need to study how perceptual variables give rise to and guide action beginning in the neonatal period. It is argued here that, in the first 5 months of life, it is important to distinguish reflexive patterns of movement from voluntary and cortically controlled patterns. Some criteria are defined. This paper describes three experiments which utilized movement counters to record developmental changes in the frequency and synchrony of limb movements in infants under 5 months. The results show that there is a general increase in frequency of limb movements from 1 to 5 months, but with a plateau or even a decrease in activity from the middle of the third month to the end of the fourth month. It was also demonstrated that synchrony scores (co-activation) for pairs of limbs showed significant increases from 1 month to 5 months. Finally, in all three experiments the presentation of an attractive toy resulted in suppression of activity. The results of the three experiments are interpreted to measure a gradual increase in cortically controlled movement patterns.     

Topographic electroencephalographic alpha in recovered depressed elderly

Late-middle-aged and elderly normal volunteers with past histories of Major Depression according to the Diagnostic and Statistical Manual of Mental Disorders (third edition-revised) criteria were compared with sex- and age-matched control subjects using topographic electroencephalographic (EEG) indices. Healthy, euthymic recovered depressed subjects showed greater alpha amplitudes than controls. Delta, theta, and beta amplitudes did not reliably distinguish the groups. Considered in the context of previous research indicating that actively depressed subjects exhibit elevated EEG alpha compared to controls, these findings raise questions concerning state and trait conceptualizations of depression and EEG alpha.     

Eyewitness accuracy and confidence: within- versus between-subjects correlations

Previous researchers using between-subjects comparisons have found eyewitness confidence and accuracy to be only negligibly correlated. In this study, we examined the predictive power of confidence in within-subject terms. Ninety-six subjects answered, and made confidence ratings for, a series of questions about a crime they witnessed. The average between-subjects and within-subject accuracy-confidence correlations were comparably low: r = .14 (p less than .001) and r = .17 (p less than .001), respectively. Confidence is neither a useful predictor of the accuracy of a particular witness nor of the accuracy of particular statements made by the same witness. Another possible predictor of accuracy, response latency, correlated only negligibly with accuracy (r = -.09 within subjects), but more strongly with confidence (r = -.27 within subjects). This pattern was obtained for both between-subjects and within-subject comparisons. The theoretical and practical implications of these results are discussed.