How much information about meaning is contained in the statistical structure of the environment? LSA is a theoretical and practical tool that is challenging previous notions about what is contained in the statistical structure of the environment. This paper examines what kind of category knowledge can be obtained from the environment using LSA. In particular, two experiments are conducted with LSA to test what kind of category structure it embodies. LSA ratings about the relatedness of categories to their properties are compared with human judgments regarding the centrality of properties to the categories. LSA is found to capture aspects of property centrality for some object and event categories. However, it is found to only capture those aspects related to typicality: how often do members of the category have that property? LSA fails to capture other aspects of centrality that can be found in human category judgments. Thus, it appears that humans do bring other constraints to bear in shaping their categories.

Previous psychological research about scientific discovery has often focused on subjects' heuristics for discovering simple concepts with one relevant dimension or a few relevant dimensions with simple two-way interactions. This p^er presents results from an experiment in which subjects had to discover a concept involving complex three-way interactions on a multi-valued output by running experiments in a computerized microworld. Twenty-two C M U undergraduates attempted the task, of which sixteen succeeded, in an average of 85 minutes. The analyses focus on three strategies used to regulate task complexity. First, subjects preferred depth-first to breadth-first search, with successful subjects regulating the number of features varied from experiment to experiment most effectively. Second, subjects systematically regulated the length of their experiments. Third, a new explicit search heuristic (Put Upon Stack Heuristic) used by successful subjects is described.

Other-generated hypotheses are often considered easier to test than self-generated hyptitheses. T o determine the precise effects of other-generated hypotheses, w e propose three kinds of effects and describe a study designed to test for these effects of hypothesis source. T h e three kinds of effects considered are: (i) hypothesis plausibility changes, (ii) skepticism changes, and (iii) process changes. Forty-two undergraduate subjects were given a microworld discovery task called Milktruck. Subjects either had to generate their o w n initial hypothesis or were given the most frequently generated hypothesis. It w a s found that the other- generated hypothesis lead to m o r e thorough investigation of hypotheses resulting in a decrease in false terminations with incorrect solutions. T h e results suggested these effects were caused by an increjise in skepticism rather than changes in hypothesis plausibility or process changes.

One of the most frequently mentioned sources of scientific hypotheses is analogy. Despite attractiveness of this mechanism of discovery, there has been but a small success in demonstrating that people actually use analogies while solving problems. The study reported below attempted to foster analogical U-ansfer in a scientific discovery task. Subjects worked on two problems that had the same type of underlying mechanism. On day 1, subjects discovered the mechanism that controls virus reproduction. On day 2, subjects returned to work on a problem in molecular genetics that had a similar underlying mechanism. The results showed that experience at discovering the virus mechanism did facilitate performance on the molecular genetics task. However, the verbal protocols do not indicate that subjects analogically mapped knowledge from the virus to the genetics domain. Rather, experience with the virus problem appeared to prime memory. It is argued that analogical mapping can be used flexibly in scientific discovery contexts and that primed knowledge structures can also provide access to relevant information when analogical mapping fails.