Instance theory predicts categorization decisions in the absence of categorical structure: A computational analysis of artificial grammar learning without a grammar.

Theories of categorization have historically focused on the stimulus characteristics to which people are sensitive. Artificial grammar learning (AGL) provides a clear example of this phenomenon, with theorists debating between knowledge of rules, fragments, whole strings, and so on as the basis of categorization decisions (i.e., stimulus-driven explanations). We argue that this focus loses sight of the more important question of how participants make categorization decisions on a mechanistic level (i.e., process-driven explanations). To address the problem, we derived predictions from an instance-based model of human memory in a pseudo-AGL task in which all study and test strings were generated randomly, a task that stimulus-driven explanations of AGL would have difficulty accommodating. We conducted a standard AGL experiment with human participants using the same strings. The model's predictions corresponded to participants' decisions well, even in the absence of any experimenter-generated structure and regardless of whether test stimuli contained any incidental structure. We argue that theories of categorization ought to continue shifting towards the goal of modeling categorization at the level of cognitive processes rather than primarily attempting to identify the stimulus characteristics to which participants are drawn.

Shallow Value Weighting Predicts Problem Gambling: A Parameter Estimation Analysis Using Cumulative Prospect Theory.

Problem gambling is a non-substance-based addictive disorder that can cause significant distress and dramatic consequences. Despite extensive research in neuroscience and clinical/social psychology, few contributions have been made from formal models of behavioural economics. We apply Cumulative Prospect Theory (CPT) to provide a formal analysis of cognitive distortions in problem gambling. In two experiments, participants made decisions between pairs of gambles and completed a standard gambling assessment. We estimated the parameter values specified by CPT for each participant and used those estimates to predict gambling severity. In Experiment 1, severe gambling behaviour was associated with a shallow valuation curve, a reversal of loss aversion, and decreased influence of subjective value on decisions (i.e., more noise or variability in preference). Experiment 2 replicated the effect of shallow valuation but did not demonstrate reversed loss version or noisier decisions. Neither experiment provided evidence of differences in probability weighting. We explore implications of the findings and conclude that problem gambling at least partially reflects a fundamental distortion to subjective valuation.

Trends in infections and antibiotic usage in a community hospital.

The results of a physician-performed prevalence survey of infections and antibiotic use at the Salt Lake City LDS Hospital in 1984 were compared with results of surveys done in 1971 and 1979. The hospital census and length of stay declined in successive surveys, contributing to the changes observed. Community-acquired infections were more prevalent in 1984 than in the previous surveys, whereas hospital-acquired infections were seen with similar frequencies. Among hospital-acquired infections, lower respiratory tract and soft-tissue infections were more prevalent in 1984. Gram-negative bacilli accounted for 34% of hospital-acquired infections in 1984 versus rates of 60% or more found in the 1970s. Although the overall prevalences of antibiotic use were similar in the three surveys, the proportion attributed to cephalosporins increased from 17.5% (1971) to 49.2% (1979) and 59.1% (1984). Antibiotic prophylaxis was less frequent in 1984 (14.4%) than in 1979 (24.1%) and reversed the trend found after 1971 (11.0%). Despite extensive educational efforts since the prevalence survey of 1979, perioperative antibiotics were used for durations longer than 48 hours after surgery in 43% of the patients receiving such prophylaxis in 1984. The LDS Hospital has adopted a restrictive antibiotic formulary in part as a result of the present survey.