Mental models and human reasoning

To be rational is to be able to reason. Thirty years ago psychologists believed that human reasoning depended on formal rules of inference akin to those of a logical calculus. This hypothesis ran into difficulties, which led to an alternative view: reasoning depends on envisaging the possibilities consistent with the starting point--a perception of the world, a set of assertions, a memory, or some mixture of them. We construct mental models of each distinct possibility and derive a conclusion from them. The theory predicts systematic errors in our reasoning, and the evidence corroborates this prediction. Yet, our ability to use counterexamples to refute invalid inferences provides a foundation for rationality. On this account, reasoning is a simulation of the world fleshed out with our knowledge, not a formal rearrangement of the logical skeletons of sentences.     

Changes in analogical reasoning in adulthood

This study sought to investigate adult intellectual development through an analysis of a particular type of cognitive ability, verbal analogical reasoning. The performance of 60 individuals between the ages of 20 and 79 was compared on 100 verbal analogies. The subjects consisted of six groups of ten individuals each (five males and five females), matched as a group for education and gender. Solution times and error rates served as the dependent measures. Results showed that there was a significant trend for the older subjects (60- and 70-year-olds) to be slower than the young subjects (20-, 30-, 40-, and 50-year-olds), but not necessarily more error prone. These data suggest that verbal analogical reasoning changes with age. Supplemental data demonstrated a change in other abilities as well (i.e., decline in perceptual-motor speed and spatial skill).     

Education debate: clinical diagnostic reasoning

Whilst it is clear that experienced clinicians adopt a rational approach of diagnosis, the logic of their clinical reasoning has been difficult to define. I outline here an approach based on the four categories of a complete diagnosis: Anatomical diagnosis (system involved); Pathological diagnosis (nature of the condition); Physiological diagnosis (functional consequences) and Aetiological diagnosis (background cause). Each phrase of the history and examination data is assigned to one or other of these categories as the case unfolds, with interpretations and interactions allowing sub‐conclusions that gradually build to a final clinical diagnosis overall. The system has the advantage of facilitating a diagnosis individualized to the patient, rather than to some previously learned diagnostic ‘checklist’. As such, it should provide an advance over current problem‐based approaches to clinical diagnosis.     

Belief discrepancy reasoning in the elderly

The development of belief discrepancy reasoning, or how people evaluate disagreeing others, was examined with forty-four college and elderly respondents. Dogmatism and IQ measures were also administered. The results showed that the elderly were significantly lower in belief discrepancy reasoning and higher in dogmatism than the college sample, despite statistically greater IQ for the former sample and controls for education. For belief discrepancy, the elderly sample did not evidence intolerance, but rather relativism and open-mindedness toward disagreeing others. Implications for the construct validation of belief discrepancy and senescent intolerance are discussed.     

Diagnostic dilemma

In those issues in which our regular Case of the Month does not appear, The Green Journal will present a Diagnostic Dilemma—an electrocardiogram or radiograph, or both, with a brief case history—as a challenge for our readers to solve. The correct answer appears on page 741. If you would like to contribute a Diagnostic Dilemma, please submit a high-quality copy of the electrocardiogram or radiograph with a brief synopsis (fewer than 250 words) of the case to the editorial office of The American Journal of Medicine.     

Diagnostic dilemma

In those issues in which our regular Case of the Month does not appear, The Green Journal will present a Diagnostic Dilemma-an electrocardiogram and/or radiograph with a brief case history-for our readers to solve. The correct answer appears on p. 511 of this issue.If you would like to contribute a Diagnostic Dilemma, please submit a high-quality copy of the EKG or radiograph with a brief synopsis (<250 words) of the case to The American Journal of Medicine's editorial office.     

Diagnostic imaging

Physical techniques have always had a key role in medicine, and the second half of the 20th century in particular saw a revolution in medical diagnostic techniques with the development of key imaging instruments: x-ray imaging and emission tomography (nuclear imaging and PET), MRI, and ultrasound. These techniques use the full width of the electromagnetic spectrum, from gamma rays to radio waves, and sound. In most cases, the development of a medical imaging device was opportunistic; many scientists in physics laboratories were experimenting with simple x-ray images within the first year of the discovery of such rays, the development of the cyclotron and later nuclear reactors created the opportunity for nuclear medicine, and one of the co-inventors of MRI was initially attempting to develop an alternative to x-ray diffraction for the analysis of crystal structures. What all these techniques have in common is the brilliant insight of a few pioneering physical scientists and engineers who had the tenacity to develop their inventions, followed by a series of technical innovations that enabled the full diagnostic potential of these instruments to be realised. In this report, we focus on the key part played by these scientists and engineers and the new imaging instruments and diagnostic procedures that they developed. By bringing the key developments and applications together we hope to show the true legacy of physics and engineering in diagnostic medicine.