Rigid and non-rigid kinetic depth effect with rotating discrete helices

Summary To examine the conditions in which human observers fail to recover the rigid structure of a three-dimensional object in motion we used simulations of discrete helices with various pitches undergoing either pure rotation in depth (rigid stimuli) or rotation plus stretching (non-rigid stimuli). Subjects had either to rate stimuli on a rigidity scale (Experiments 1 and 2) or to judge the amount of rotation of the helices (Experiments 3 and 4). We found that perceived rigidity depended on the pitch of the helix rather than on objective non-rigidity. Furthermore, we found that helices with a large pitch/radius ratio were perceived as highly non-rigid and that their rotation was underestimated. Experiment 5 showed that the detection of a pair of dots rigidly related (located on. the helix) against a background of randomly moving dots is easier at small phases in which the change of orientation across frames is also small. We suggest that this is because at small phases the grouping of dots in virtual lines does occur and that this may be an important factor in the perceived nonrigidity of the helices.This research was supported by MPI 60% (1987, 1988) and CNR (1986), 1987, 1988) grants to Clara Casco and Sergio Roncato and Grant CNR 90.01603.PS93 to Giorgio Ganis.     

Reconsidering Intentions

This paper argues that the principles of instrumental rationality apply primarily to extended action through time. Most philosophers assume that rational requirements and principles govern in the first instance momentary mental states, as opposed to governing extended intentional actions directly. In the case of instrumental rationality, the relevant mental states or attitudes would typically be preferences, decisions, or intentions. In fact, even those who recognize the extended nature of our agency still assume that rational requirements apply primarily to mental states at a moment in time. Such views try to do justice to the extended nature of our agency by postulating rational requirements that apply in the first instance to plans, policies, and intentions more generally. The paper focuses on the central case of requirements and reasons governing the reconsideration of intentions and argues that these requirements or reasons are either superfluous or invalid. I argue that a proper conception of instrumental reasoning that applies directly to actions turn out to have surprising consequences. In fact, this conception allows us to see that policies, projects and the like are best understood as instances of extended actions, and that the instrumental requirements that apply to projects and policies are exactly the same as the instrumental requirements that apply to ordinary extended actions. Finally, I argue that the resulting theory of instrumental rationality is a significant improvement over theories that rely on principles governing intentions.     

Differences in protective factors of substance use in early and middle adolescence

This study focuses on possible differences in protective factors of substance use in early and middle adolescence. These possible differences are analysed by means of the same structural equation model applied to two different samples of adolescents: the first sample is made up of 450 adolescents, ages 12 to 14 years, and second of 203 adolescents, ages 15 to 17 years. The results indicate that adequate family communication is a protective factor in both samples, whereas high social self-esteem is proposed as a risk factor in middle adolescence. The adolescent's family self-esteem and attitudes towards authority are also relevant factors in both samples. These results may have important implications in the development of future intervention programmes.     

AIDS‐NGOs and political participation: Brazilian and Canadian experiences

Non‐governmental organizations (AIDS‐NGO) are an instrument of political pressure and assistance, often serving as a life reconstruction aid for people living with HIV/AIDS. In this case study, we analyze data from historical documents, in‐depth interviews, and questionnaires obtained from participants and community agents in two AIDS‐NGOs: one in Canada (NGO‐Ca), and another in Brazil (NGO‐Br). Despite contextual differences, both NGOs are involved in a fight against stigma and discrimination that may aggravate existing social exclusion. Variances in political participation are nevertheless evident. In NGO‐Ca, efforts are directed towards maintaining and consolidating human and social rights. In NGO‐Br, the primary goal is building these. In NGO‐Ca, the participant is part of a structured organization where he or she receives the required supports; the NGO is thus a service provider. Conversely, in NGO‐Br, the participant is both the actor and author of collectively constructed supportive actions. It is hoped that the lessons learned from this limited case study will assist in the strengthening of AIDS‐NGO organization and activity, particularly in the developing world context. Copyright © 2008 John Wiley & Sons, Ltd.     

Paradoxical sleep deprivation impairs acquisition, consolidation, and retrieval of a discriminative avoidance task in rats

The aim of the present study was to investigate the effects of paradoxical sleep deprivation (PSD) for 96 h on the learning/memory processes in rats submitted to the plus-maze discriminative avoidance task (PM-DAT), which simultaneously evaluates learning, memory, anxiety and motor function. Four experiments were performed in which rats were submitted to: (1) post-training and pre-test PSD; (2) post-training or pre-test PSD; (3) pre-training PSD or pre-training paradoxical sleep (PS) rebound (24 h) and (4) pre-test PSD rebound. Concerning Experiment I, post-training and pre-test PSD induced memory deficits, an anxiolytic-like behavior and an increase in locomotor activity. In Experiment II, both post-training PS-deprived and pre-test PS-deprived groups showed memory deficits per se. However, only the pre-test PS-deprived animals presented anxiolytic-like behavior and increased locomotor activity. In Experiment III, pre-training PS-deprived rats showed learning and memory deficits, anxiolytic-like behavior and increased locomotor activity. A 24h-sleep recovery period after the PSD abolished the learning and memory deficits but not anxiety and locomotor alterations. Finally, sleep rebound did not modify acquisition (Experiment III) and retrieval (Experiment IV). This study strengthened the critical role of paradoxical sleep (but not sleep rebound) in all the phases of learning and memory formation. In addition, it suggests that PSD effects on acquisition and consolidation do not seem to be related to other behavioral alterations induced by this procedure.     

Spatial negative priming in bilingualism

Balanced bilinguals have been shown to have an enhanced ability to inhibit distracting information. In this study, we investigated the hypothesis that the bilinguals’ efficiency in inhibitory control can be advantageous in some conditions, but disadvantageous in others—for example, negative priming conditions, in which previously irrelevant information becomes relevant. Data collected in a target-stimulus locating task from 29 early bilingual adults and 29 age-matched monolinguals showed that the bilinguals’ greater inhibition of irrelevant spatial information (i.e., the position of a distractor stimulus) resulted in a smaller effect of the distractor presence (i.e., a smaller difference in error rates in trials with and without distractors) and a larger negative priming effect (i.e., a larger difference between the error rates shown in trials wherein the target position corresponded to the position of the previous-trial distractor and trials wherein the target was presented in a previously vacant position). These findings support the hypothesis of specific nonlinguistic cognitive effects of bilingualism on inhibitory control functions, which are not necessarily reflected in cognitive advantages.     

Dissociation between appearance and location within visuo-spatial working memory

Previous research has demonstrated separation between systems supporting memory for appearance and memory for location. However, the interpretation of these results is complicated by a confound occurring because of the simultaneous presentation of objects in multiple-item arrays when assessing memory for appearance and the sequential presentation of items when assessing memory for location. This paper reports an experiment in which sequential or simultaneous modes of presentation were factorially manipulated with memory for visual appearance or memory for location. Spatial interference (tapping) or visual interference (dynamic visual noise) were presented during retention. Appearance versus location interacted with the type of interference task, but mode of presentation did not. These results are consistent with the view that different subsystems within visuo-spatial working memory support memory for appearance and memory for location.     

Role reversal changes during the ontogeny of play fighting in male rats: Attack vs. defense

From weaning until sexual maturity, the rates at which young male rats hold each other supine during play fighting appear to become progressively asymmetrical. These changes have been previously thought to reflect an initial lack of dominance and a later development of dominance-subordinance relationships. In this paper it is shown that pairs of male rats exhibit asymmetries in playful attack and playful defense throughout development. The changes, resulting in greater asymmetry of pinning rates, are shown to result from age-dependent changes in defensive tactics; the relationship, therefore, remains constant while the form of the behavior changes. Furthermore, it is not the animals showing the highest rates of playful attack who become dominant in older ages.