The role of direction information in the perception of geometric optic flow components

Theoretically, optic flow, an important source of information for the perception of locomotion and three-dimensional structure of the environment, is described in terms of divergence, curl, and shear components. We measured how the detection of the type of flow field depends on directional information. We manipulated the local directions by rotating them through an angle x relative to the original direction (i.e., the direction of motion at that locus in an unaltered flow field). The results of the first experiments showed that divergence, curl, and shear can be detected even if the directional range of the individual motion vectors is as broad as 180 degrees. Subsequent experiments revealed that the detection of the geometric components of the optic flow field is merely based on the integration of a few (10% of vectors) local directions correctly (within 10 degrees of original direction) specifying the type of flow field. Other directions are irrelevant to this process. This is actually what one would expect if the optic flow is analyzed by special purpose mechanisms that detect and process the geometric components on the basis of the integration of motion information. The results indicate that as far as they integrate motion information, detectors for divergence, curl, and shear operate in a similar manner. Implications of the results for modeling such mechanisms are discussed.     

Occlusion cues contribute to orientation judgments of occlusion-defined contours

Occlusion cues defining a contour in a 2-D stimulus pattern were shown to contribute to the accuracy of orientation judgments of that contour. The stimulus pattern was altered so that the occlusion cues became ambiguous, by introducing a textured background suggesting transparency of the stimulus pattern. Orientation judgments then became significantly less accurate. This finding shows that occlusion cues in 2-D patterns can be behaviorally relevant, in addition to generating the subjective percept commonly known as an illusory contour. The disruptive effect of the textured background on orientation judgments remained when no texture elements were present in the vicinity of the contour. This suggests that the generation of occlusion-defined contours relies as much on an evaluation of the surfaces at either side of the contour as being opaque as it does on local encoding of occlusion cues close to the contour. Finally, orientation sensitivity measured with contours defined by other than occlusion cues was not altered after the introduction of a textured background.     

Condom use by prostitutes: behavior,factors and considerations

119 female prostitutes were interviewed over the period July 1990-March 1991 about their sex behavior and condom use, their working attitude, and perception of risk in an attempt to combine qualitative and quantitative research methods to gain insight into the determinants of condom use in prostitution by putting high or low risk taking behavior into context. The participants were recruited from different regions of the Netherlands, of mean age 29.8 years, and had been working in the field for an average 6.8 years. Most of the 28% of participants who did not have Dutch nationality were from Germany or Latin America. Health locus of control and attributions concerning an unpleasant proceeding of client contacts were assessed by means of item lists. Prostitutes were identified as either consistent condom users, selective risk takers, or risk takers. Consistent condom users used condoms on all occasions, selective risk takers used condoms for vaginal sex with all but a few selected clients, and risk takers seeing no possibility of consistently getting clients to use a condom for vaginal sex used condoms the least frequently. 78% were consistent users, 11% were selective risk takers, and 11% were risk takers. Protection behavior was found to be linked to working attitude. Condom use is most likely among women with a moderately positive, yet businesslike, working attitude, and least likely among those with a negative working attitude and when there is no positive identification with the professional group. It appears that health locus of control is of no influence on protection style, but risk takers attribute an unpleasant proceeding of client contacts significantly more to powerlessness and helplessness. The authors conclude that the objective situation of women influences condom use at least as strongly as subjective motivations.     

The Men's Adult Life Experiences Inventory: an instrument for assessing developmental concerns of middle age

This article describes the development and testing of a new 97-item self-report instrument assessing the frequency and intensity of 11 developmentally related domains of concerns of middle-aged men. These include relationships (child, parents, wife, friends), job, health, sex, leisure, death, pressures of time, and self-reflection. The psychometric properties of the instrument, as well as potential uses, are discussed.     

Attribution of leadership in a resource management situation

In a resource management game we investigated how regular group members respond to a leader who promotes group success or fails to do so, while operating in a predictable or totally unpredictable environment. The subjects (N = 110) were confronted with a bogus leader who purportedly took decisions on behalf of the whole group. Performance of the leader and Predictability of the environment were manipulated by means of a 2 × 2 factorial design. As predicted, a failing leader received weaker endorsement than a successful leader (Performance main effect). The Performance × Predictability interaction effect was ascribed to two circumstances: (a) As predicted by the attributional approach of leadership (Calder, 1977; Pfeffer, 1977), endorsement of a successful leader was weaker in the Unpredictable than in the Predictable environment. However, (b) endorsement of a failing leader was not significantly weaker in the Predictable than in the Unpredictable environment. Additional data showed that regular group members' attributions played a mediating role.     

Stimulating the demand for dental care: An application of Ajzen and Fishbein's theory of reasoned action

Ajzen and Fishbein's attitude-behaviour model was applied to the problem of stimulating the demand for dental care, Subjects were 329 members of Amsterdam health insurance companies. They had not received regular dental treatment and/or a certificate of dental fitness for at least two and a half years. Applying for treatment and acquiring a dental certificate were the behavioural measures. The effectiveness of the communication based on Ajzen and Fishbein's model was compared with the effectiveness of messages based on the Health-Belief model and the notion that knowledge of Rights and Obligations is a prerequisite for seeking dental care. Results lend support to the validity of the Ajzen and Fishbein model. Relationships between the components of the model are moderate to strong, both before and after subjects were exposed to the message. The message proved effective in changing beliefs about seeking dental treatment. Ajzen and Fishbein's claim that their approach has exclusive merits, however, was refuted. A differential effectiveness of the three messages was absent. In all, 47.4 per cent applied for treatment. No control subjects applied. Fifteen months later 70 per cent of the applicants had obtained a dental certificate. Contrary to our expectations, a condition of no-message application-form- only proved equally effective as the message conditions.     

What happens to information to be suppressed in working-memory tasks? Short and long term effects

The study explored, from an individual differences point of view, what happens to information to be suppressed in a working-memory task at short and long term. In particular, it was examined whether control mechanisms of irrelevant information in working memory imply their complete elimination from working memory or just the modulation of their activation. To this end, we compared the fate of irrelevant information in groups of subjects with high and low reading comprehension (Experiments 1 and 2) and subjects with high and low working memory (Experiments 1, 2, 3, and 4). All the experiments presented a working-memory task devised by De Beni, Palladino, Pazzaglia, and Cornoldi (1998), which required participants to process lists of words, to tap when a word from a particular category was presented, and then to recall only the last items in each list. Results confirmed that participants with high reading comprehension also have higher working memory and make less intrusion errors due to irrelevant items that have to be processed but then discarded. Furthermore, it was found that participants with low working memory have slightly better implicit (Experiment 1) and explicit memory (Experiments 3 and 4) of highly activated irrelevant information. Nevertheless, in a long-term recognition test, participants with high and low reading comprehension/working memory presented a similar pattern of memory for different types of irrelevant information (Experiment 2), whereas in a short-term memory recognition test, low-span participants presented a facilitation effect in the time required for the recognition of highly activated irrelevant information (Experiment 4). It was concluded that efficient working-memory performance is related to the temporary reduction of activation of irrelevant information but does not imply its elimination from memory.     

Présentation

Sans résumé