The role of occlusion cues in apparent motion

Classical apparent motion stimuli exhibit an inherent ambiguity with respect to the onsets and offsets of the stimulus elements. Sigman and Rock (1974, Perception 3 9-28) presented evidence suggesting that occlusion cues are used to resolve this ambiguity. We present results from experiments designed to further test predictions of this hypothesis. As expected, we found that the apparent motion of a target stimulus is suppressed when a 'moving' occluder is positioned such that it rationalises the onsets and offsets of the stimulus elements constituting the target. Somewhat unexpectedly, though, we also observed a slight tendency for motion suppression under conditions where the target was only partially occluded. The expected motion suppression occurred both with solid occluders and purely virtual Kanizsa-like occluders, although it was not always observed in the latter case. Motion suppression was found to occur over a wide range of stimulus onset asynchronies. Finally, we used binocular disparity cues to test the occlusion account of the motion suppression phenomenon against an alternative explanation in terms of attentional factors. The results are in clear favour of the occlusion account.     

Stuck in the middle: the many moral challenges with bariatric surgery

Bariatric surgery is effective on short- and medium-term weight loss, reduction of comorbidities, and overall mortality. A large and increasing portion of the population is eligible for bariatric surgery, which increases instant health care costs. A review of the literature identifies a series of ethical challenges: unjust distribution of bariatric surgery, autonomy and informed consent, classification of obesity and selecting assessment endpoints, prejudice among health professionals, intervention in people's life-world, and medicalization of appearance. Bariatric surgery is particularly interesting because it uses surgical methods to modify healthy organs, is not curative, but offers symptoms relief for a condition that it is considered to result from lack of self-control and is subject to significant prejudice. Taking the reviewed ethical issues into account is important when meeting persons eligible for bariatric surgery, as well as in the assessment of and decision making on surgery for obesity.     

The tight coupling between category and causal learning

The main goal of the present research was to demonstrate the interaction between category and causal induction in causal model learning. We used a two-phase learning procedure in which learners were presented with learning input referring to two interconnected causal relations forming a causal chain (Experiment 1) or a common-cause model (Experiments 2a, b). One of the three events (i.e., the intermediate event of the chain, or the common cause) was presented as a set of uncategorized exemplars. Although participants were not provided with any feedback about category labels, they tended to induce categories in the first phase that maximized the predictability of their causes or effects. In the second causal learning phase, participants had the choice between transferring the newly learned categories from the first phase at the cost of suboptimal predictions, or they could induce a new set of optimally predictive categories for the second causal relation, but at the cost of proliferating different category schemes for the same set of events. It turned out that in all three experiments learners tended to transfer the categories entailed by the first causal relation to the second causal relation.     

Strength contributions from precipitates

A theory for the strength contribution from precipitates is developed based on the statistical particle-size and shape distributions and the corresponding obstacle strengths. The generic case of spherical precipitates and the special case of needle-shaped precipitates in the 6xxx aluminium alloy series are considered. It is accounted for that the largest precipitates are stronger and at the same time, intersect a larger number of slip planes than the smaller ones. For a considered peak aged AA6082, the improved model gives a 59% higher strength, which fits the experiments well without the need of previously introduced calibration parameter for the mean effective particle spacing in the slip plane.