Geometric and featural representations in semantic concepts

We explore the adequacy of two types of similarity representation in the context of semantic concepts. To this end, we evaluate different categorization models, assuming either a geometric or a featural representation, using categorization decisions involving familiar and unfamiliar foods and animals. The study aims to assess the optimal stimulus representation as a function of the familiarity of the stimuli. For the unfamiliar stimuli, the geometric categorization models provide the best account of the categorization data, whereas for the familiar stimuli, the featural categorization models provide the best account. This pattern of results suggests that people rely on perceptual information to assign an unfamiliar stimulus to a category but rely on more elaborate conceptual knowledge when assigning a familiar stimulus.     

Interacting noradrenergic and corticosteroid systems shift human brain activation patterns during encoding

Emotionally arousing experiences are usually well retained, an effect that depends on the release of adrenal stress hormones. Animal studies have shown that corticosterone and noradrenaline – representing the two main stress hormone systems – act in concert to enhance memory formation by actions involving the amygdala, hippocampus and prefrontal cortex (PFC). Here we test whether interactions between these two stress hormone systems also affect human memory formation as well as the associated pattern of brain activation. To this end, forty-eight male human subjects received hydrocortisone, yohimbine or both before presentation of emotional and neutral pictures. Activity in the amygdala, hippocampus and PFC was monitored with functional Magnetic Resonance Imaging (fMRI) during encoding of these stimuli, when hormonal levels were elevated. Memory performance was tested 1 week later. We investigated whether an increased level of one of the two hormone systems would lead to differential effects compared to the combined application of the drugs on brain activation and memory performance. We report that the application of cortisol led to an overall enhancing effect on recognition memory, with no significant additional effect of yohimbine. However, during encoding the brain switched from amygdala/hippocampus activation with either hormone alone, to a strong deactivation of prefrontal areas under the influence of the combination of both exogenous hormones. Although we did not find evidence that exogenous stimulation of the noradrenergic and corticosteroid systems led to significant interaction effects on memory performance in this experiment, we conclude that stress hormone levels during encoding did differentially determine the activation pattern of the brain circuits here involved.     

Psychosocial forces and neural mechanisms in disease: Defining the question and collecting the evidence

Adapted from the Samuel Novey Lecture in Psychological Medicine, The Johns Hopkins University School of Medicine, November 12, 1981.     

An Experiment in Judging Personalities

Use of the semantic differential technique has largely been restricted to “paper and pencil” settings and student populations. In this study, adult respondents in an interview setting were asked to evaluate two concepts—use of lake (a) as a source of electric power and (b) as a recreational area—by means of eight seven-point scales. Results indicated considerable conceptscale interaction, suggesting that Osgood's interpretation of the semantic differential may be restricted by both technique of data collection and subpopulation. Respondent hostility might be an intervening variable. The semantic differential technique appeared to yield a preliminary evaluation of the two concepts, suggesting its use as an indicator of orientation.