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 comment on ‘some standard errors in item response theory’

In maximum likelihood estimation the standard error of the location parameter of the three parameter logistic model can be large, due to inaccurate estimation of the lower asymptote. Thissen and Wainer who demonstrated this effect, suggested that the introduction of a prior distribution for the lower asymptote might alleviate the problems. Here it is demonstrated in some detail that the standard error of the location parameter can be made acceptably small in this way.The author thanks Pieter Vijn for his helpful comments.     

Linear relations amongk sets of variables

A family of solutions for linear relations amongk sets of variables is proposed. It is shown how these solutions apply fork=2, and how they can be generalized from there tok3.The family of solutions depends on three independent choices: (i) to what extent a solution may be influenced by differences in variances of components within each set; (ii) to what extent the sets may be differentially weighted with respect to their contribution to the solution—including orthogonality constraints; (iii) whether or not individual sets of variables may be replaced by an orthogonal and unit normalized basis.Solutions are compared with respect to their optimality properties. For each solution the appropriate stationary equations are given. For one example it is shown how the determinantal equation of the stationary equations can be interpreted.     

Abnormal and normal obsessions

Three related, exploratory studies were carried out in order to ascertain the occurrence and nature of normal obsessions, and to relate them to abnormal obsessions. The subjects included 8 obsessional patients, and up to 124 non-clinical subjects.Broadly, the findings were that normal obsessions are a common experience and they resemble the form of abnormal obsessions. They also show some notable similarities of content. However normal and abnormal obsessions differ in several respects, including frequency, duration, intensity and consequences, among others.With repeated practice, the frequency, duration and discomfort of obsessions are observed to decrease. Overall, the findings are considered to be consistent with the noxious stimulus cum habituation theory.     

Insulin and glucagon as determinants of body weight set point and microregulation in rats

Seven adult male rats were observed for body weight and microregulation (feeding, drinking, and running patterns) after manipulation of insulin and glucagon levels. They received three injections per day for 3 days each week of 3 U of protamine zinc insulin, .25 mg of zinc glucagon, 50 microgram of protamine zinc somatostatin (SRIF), or protamine zinc vehicle. Diabetes was then induced with an iv injection of streptozotocin (65 mg/kg), and the injection schedule was repeated after the full diabetic syndrome emerged. In all rats whose insulin levels were increased relative to glucagon levels, body weight increased; in those whose glucagon levels were increased relative to insulin levels, body weight decreased. All injections except vehicle reduced meal sizes in both normal and diabetic rats, but only insulin increased the frequency of feeding. These effects could be predicted by the glucostatic theory of food intake regulation and are thus interpreted as supportive of this theory. These results also support the hypothesis that the relative concentration of insulin to glucagon is a regulator of body weight set point.     

Foreign Investments in Southern Africa

“If one believes in the Prince of Peace one must stop committing crimes in the name of the Prince of Peace. The Christian Church still rules this world, it still has the power to change the structure of South Africa.” James Baldwin in his address to the Fourth Assembly of the World Council of Churches, Uppsala, 1968.     

A speech-rate intelligibility threshold for speeded and time-compressed connected speech

An automated threshold method has been developed for determining the maximum rate of speech understood by individual listeners. Two experiments were undertaken to determine whether the threshold was related to the comprehension of speech or to speech intelligibility. The first experiment compared thresholds of two types of rapid speech reportedly different in intelligibility: simple speeded speech and speech compressed by the sampling method. The second experiment sought to determine the relationship of the threshold to traditional comprehension measures. The results are discussed in terms of the intelligibility and comprehensibility of speech.     

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.     

Avoidance of pain of unpredictable intensity

Unpredictability of the intensity of an aversive event might be an important factor in producing negative effects of the event, especially if the UCS becomes stronger than could have been expected. The present experiment tested the hypothesis that unpredictability of intensity of a painful stimulus contributes to avoidance behaviour. The experiment was concealed in a shock working-up procedure, which was done to assess the pain level subjects were willing to tolerate in a subsequent experiment. The experimental subjects, who received an unannounced sudden increase of the pain stimulus during the working-up procedure, tolerated less pain on a subjective as well as on an objective level (avoidance of high levels of pain) than the control subjects, who received the stimuli in a predictable pattern. The results support the hypothesis that unpredictability of intensity of an aversive event contributes to avoidance behaviour.