Perceptual Categorization: Connectionist Modelling and Decision Rules

Although it is currently popular to model human associative learning using connectionist networks, the mechanism by which their output activations are converted to probabilities of response has received relatively little attention. Several possible models of this decision process are considered here, including a simple ratio rule, a simple difference rule, their exponential versions, and a winner-take-all network. Two categorization experiments that attempt to dissociate these models are reported. Analogues of the experiments were presented to a single-layer, feed-forward, delta-rule network. Only the exponential ratio rule and the winner-take-all architecture, acting on the networks' output activations that corresponded to responses available on test, were capable of fully predicting the mean response results. In addition, unlike the exponential ratio rule, the winner-take-all model has the potential to predict latencies. Further studies will be required to determine whether latencies produced under more stringent conditions conform to the model's predictions.     

“To hope was to expect”: The impact of perspective taking and forecast type on wishful thinking

When forecasting future outcomes, people tend to believe that the outcomes they want to happen are also likely to happen. Despite numerous attempts, few systematic factors have been identified that consistently and robustly reduce wishful thinking (WT) effects. Using elections and sporting event outcomes as contexts, three experiments examined whether taking the perspective of a political rival or opposing fan reduced WT effects. We also examined whether making deliberative (vs. intuitive-based) forecasts was associated with lower WT effects. Online adult samples of U.S. citizens from Mechanical Turk and U.S. college students provided their preferences and forecasts for the U.S. presidential election (Experiments 1 and 2) and a sports competition outcome (Experiment 3). Critically, some participants received perspective taking prompts immediately before providing forecasts. First, results revealed reductions in WT effects when participants engaged in perspective taking. Interestingly, this effect only emerged when intuitive-based forecasts were made first (Experiment 3). Second, intuitive-based forecasts revealed stronger evidence of WT effects. Finally, we found that perspective taking and forming forecasts deliberately promoted a shift in focus away from preferences and toward a consideration of the relative strengths and weaknesses of the entities (i.e., candidates and teams). Theoretical implications for understanding WT effects and applied implications for developing interventions are discussed.     

Cardiovascular reactivity to psychological stress in aerobically trained versus untrained mild hypertensives and normotensives

Cardiovascular reactivity to video game and mental arithmetic stressors was compared among three groups of men: aerobically trained mild hypertensives, untrained mild hypertensives, and a comparison group of untrained normotensives. Relative to the untrained hypertensives, the trained hypertensives reacted to the video game with marginally smaller systolic blood pressure and diastolic blood pressure, but there were no significant differences between these groups in reactivity during the mental arithmetic task. Comparisons between each hypertensive group and the normotensive group showed that blood pressure (BP) reactivity of normotensives during the video game was generally similar to that of trained hypertensives but smaller than that of untrained hypertensives. These results indicate that aerobic training, which has been found to reduce resting BP in mild hypertensives, may also exert a favorable impact in reducing cardiovascular reactivity of hypertensives during some stressful situations.     

Adaptation to displacing prisms in human infants.

This research reports a first attempt to study adaptation to laterally displacing prisms in human infants of ages six to ten months. Twenty infants were tested over four days under conditions similar to those used in adult adaptation studies. Evidence was found of vigorous adaptation when infants were exposed to base-right prisms under conditions of active exposure. Detailed consideration is given to the conditions and methods of studying adaptation in infants and implications for adult studies.