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Two experiments were conducted to assess the extent of potential experimental demand characteristics inherent in the image-scanning paradigm. The results of the first "mental travel" experiment that pitted verbal versus imagery coding showed that (a) the positive correlation between physical distance and reaction time was replicated, and (b) when given a choice, subjects' reaction times varied as a function of verbal codes rather than imagery. To isolate the effects due to demand constraints from those produced by mode dominance, a nonexperiment in which subjects received only a description of the image-scanning procedure was conducted. Results demonstrated that subjects were capable of predicting the reaction time results for both verbal and imagery codes. The presence of experimental demand in the image-scanning paradigm necessitates caution when structural interpretations of visual images are considered.

In June 2013, the American Academy of Arts and Sciences (AAAS) released The Heart of the Matter, a report on the continuing indispensable role of the humanities and social sciences in meeting major global challenges and urgent national goals. Commissioned by a bipartisan group of senators and representatives and involving more than fifty AAAS members from various sectors—including academia, business, government, the arts, and the media—the report called for renewed commitment to the humanities and social sciences. More specifically, it called for leadership collaborations across a wide array of sectors to meet the urgent goals of: educating Americans . . .

The difficulty of four binary conceptual rules (conjunctive, disjunctive, conditional, and biconditional) was assessed using the rule-learning paradigm in a variety of stimulus populations. Decreasing the number of unique stimuli representing each truth-table class had a facilitative effect on learning the conditional and biconditional rules. Manipulating the relative frequency of truth-table classes changed the difficulty of particular truth-table classes but had no effect on overall measures of performance. It was suggested that either increasing the occurrence of a difficult stimulus or simplifying that stimulus facilitates learning. Furthermore, changes in relative frequency affect the stability of preexperimental biases, and changes in complexity affect choice of strategy. Based on the finding that rule learning was a function of preexperimental bias, a multibiased modification of the Sawyer-Johnson rule-difficulty model was developed and tested. An additional finding was that preexperimental bias may be affected by the specific relevant attributes used to assess it.A binary conceptual rule is a plan for partitioning a population of stimuli into two discrete groups based on the presence or absence of two particular attributes. If there are two attributes and each can either be present or absent, then four situations are possible: Both attributes can be present (truth-table class TT), just one present (TF), just the other present (FT), or neither present (FF). A binary rule is a system whereby, based on its truth-table class, a stimulus is assigned one of two pos-

2011 marks the 175th anniversary of the United States National Library of Medicine (NLM) that traces its origins to 1836 and the commitment of the second US Army Surgeon General, Thomas Lawson (1789–1861), to purchase books and journals for active-duty medical officers. The occasion affords an opportunity to focus on the contributions of the NLM to the history of medicine and public health, and to look forward into the digital world of the twenty-first century as the NLM joins with like-minded institutions, scholars, educators, writers, students, and others to expand knowledge of medical and public health history for the advancement of scholarship across the disciplines and for the education of the general public. As more audiences become interested in medical and public health history, opportunities abound to broaden and deepen understanding of the past, present, and future of medicine and public health in order to help refine critical thinking about medicine and science, promote deeper understanding of medical and scientific concepts, and generally humanise medicine and public health by revealing the implications of disease and healthcare for individuals and communities in the United States and around the world.