On the Functional Role of Implicit Visual Memory for the Adaptive Deployment of Attention Across Scenes

Although very little visual information is explicitly retained across views, some continuity of processing is afforded by implicit visual memory traces of previous views. These memory traces interact with attentional mechanisms to guide eye movements, cognition, and action. Two different memory mechanisms are described here. First, the deployments of focal attention and eye movements are facilitated towards recently attended features and locations (priming of popout). Second, attention is guided by implicit memory traces of specific visual contexts experienced in the past (contextual cueing). Compared to the visual memory tapped by change blindness tasks, the implicit memory mechanisms of priming of popout and contextual cueing do not require conscious intervention and may exhibit greater memory capacity, longer durability, and higher discriminability. Thus, these implicit traces of past views guide attention and eye movements to allow for effective access (indexing) to a scene's details, hence providing context and continuity to ongoing interactions with the perceptual world.     

Role of conditioned reinforcers in the initiation,maintenance and extinction of drug-seeking behavior

The development of a secondary reinforcer as a result of associating a neutral stimulus (buzzer) with intravenous (IV) doses of morphine was studied in rats. Secondary reinforcement developed in the absence of physical dependence and followed the association of the stimulus with either response-contingent or non-contingent injections of morphine. Strength of the conditioned reinforcer, measured in terms of responding on a lever for the stimulus plus infusion of saline solution, was proportional to the unit dosage of morphine employed in pairings of buzzer and drug. When extinction of the lever-press response for IV morphine was conducted (by substituting saline for morphine solution) in the absence of the conditioned reinforcing stimulus, it was seen later that the stimulus could still elicit lever responses, until it too had been present for a sufficient interval of non-reinforced responding. Similarly, extinction of the response for morphine by blocking its action with naloxone in the absence of the stimulus did not eliminate the conditioned reinforcement. Another study showed that a passive, subcutaneous (SC) dose of morphine served to maintain lever-pressing on a contingency of buzzer plus sahne infusion. Furthermore, the stimuli resulting from the presence of morphine (after a SC injection) were able to reinstate the lever-responding with only the buzzer-saline contingency when such responses had previously been extinguished. Moreover, it was shown thatd-amphetamine could restore responding under the same conditions, and that morphine could also do so for rats in which the primary reinforcer had beend-amphetamine. It is suggested that animal data such as these show that procedures designed for the elimination of human drug-taking behavior must take into account secondary reinforcers as well as the primary reinforcer(s).     

Experiences of being homeless or at risk of being homeless among Canadian youths

A qualitative study was undertaken with four groups--immigrants, youths, Aboriginal people, and landlords--in order to explore, compare, and contrast diversity issues among the homeless population and those at risk of homelessness in a larger Canadian city (Calgary, Alberta) with a smaller city (Lethbridge, Alberta), to better understand their and to needs make recommendations for improvement in service delivery and policy formation. This paper focuses on the findings from our sample of youths who shared information on a range of factors that contributed to their being homeless or at risk of being homeless. The youths in this study also shared their positive as well as negative experiences with educators, peers, family members, and social service providers. Canada's homeless include growing numbers of young people, families, women, and members of various ethnic communities, including Aboriginal people and immigrants. Today it is no longer possible to articulate a single silhouette of the homeless, but rather a diversity of profiles is needed. It was in the light of this reality that a study, "Diversity Among the Homeless and Those At Risk," was carried out. It was undertaken with four groups--immigrants, youths, Aboriginal people, and landlords.