Individual differences in decision speed have been regarded as direct reflections of a "primitive" functional neurophysiological characteristic, which affects performance on all cognitive tasks and so may be regarded as the "biological basis of intelligence", or of age-related changes in mental abilities. More detailed analyses show that variability within an experimental session (WSV) is a stable individual difference characteristic and that mean choice reaction times (CRTs) are gross summary statistics that reflect variability, rather than maximum speed of performance. A total of 98 people aged from 60 to 80 years completed 36 weekly sessions on six different letter categorization tasks. After effects of practice and of circadian variability had been eliminated, individuals with lower scores on the Cattell Culture Fair intelligence test had slower CRTs and greater WSV on all tasks. A simulation study showed that the greater WSVs of low Cattell scorers led directly to the significantly greater variability of their mean CRTs from session to session. However because CRTs on tasks co-varied from session to session it was apparent that, besides being affected by WSV, individuals' between-session variabilities (BSVs) also vary because of state changes that affect their performance from day to day. It seems that both variability in performance from trial to trial during a session and variability in average performance from day to day are correlated, stable, individual difference characteristics that vary inversely with intelligence test performance. Methodological consequences of these results for interpretations of age-related cognitive changes, for variability between as well as within individuals, for individual differences in decision speed, and for circadian variability in performance are discussed.

Individual differences in decision speed have been regarded as direct reflections of a "primitive" functional neurophysiological characteristic, which affects performance on all cognitive tasks and so may be regarded as the "biological basis of intelligence", or of age-related changes in mental abilities. More detailed analyses show that variability within an experimental session (WSV) is a stable individual difference characteristic and that mean choice reaction times (CRTs) are gross summary statistics that reflect variability, rather than maximum speed of performance. A total of 98 people aged from 60 to 80 years completed 36 weekly sessions on six different letter categorization tasks. After effects of practice and of circadian variability had been eliminated, individuals with lower scores on the Cattell Culture Fair intelligence test had slower CRTs and greater WSV on all tasks. A simulation study showed that the greater WSVs of low Cattell scorers led directly to the significantly greater variability of their mean CRTs from session to session. However because CRTs on tasks co-varied from session to session it was apparent that, besides being affected by WSV, individuals' between-session variabilities (BSVs) also vary because of state changes that affect their performance from day to day. It seems that both variability in performance from trial to trial during a session and variability in average performance from day to day are correlated, stable, individual difference characteristics that vary inversely with intelligence test performance. Methodological consequences of these results for interpretations of age-related cognitive changes, for variability between as well as within individuals, for individual differences in decision speed, and for circadian variability in performance are discussed.

Ethanol can be converted to heavy diesel ethers and jet fuel precursor olefins through sequential Guerbet coupling and dehydration.

Elevated pancreatic β-cell cholesterol levels impair insulin secretion and reduce plasma insulin levels. This study establishes that low plasma insulin levels have a detrimental effect on two major insulin target tissues: adipose tissue and skeletal muscle. Mice with increased β-cell cholesterol levels were generated by conditional deletion of the ATP-binding cassette transporters, ABCA1 and ABCG1, in β-cells (β-DKO mice). Insulin secretion was impaired in these mice under basal and high-glucose conditions, and glucose disposal was shifted from skeletal muscle to adipose tissue. The β-DKO mice also had increased body fat and adipose tissue macrophage content, elevated plasma interleukin-6 and MCP-1 levels, and decreased skeletal muscle mass. They were not, however, insulin resistant. The adipose tissue expansion and reduced skeletal muscle mass, but not the systemic inflammation or increased adipose tissue macrophage content, were reversed when plasma insulin levels were normalized by insulin supplementation. These studies identify a mechanism by which perturbation of β-cell cholesterol homeostasis and impaired insulin secretion increase adiposity, reduce skeletal muscle mass, and cause systemic inflammation. They further identify β-cell dysfunction as a potential therapeutic target in people at increased risk of developing type 2 diabetes.

Donald Broadbent's work in developing and validating his Cognitive Failures Questionnaire (CFQ) incidentally contributed to our understanding of what self-assessment questionnaires (SAQs) can tell us about the nature of cognitive changes that occur in old age, and their effects on people's everyday lives. The literature on use of SAQs in age comparisons is reviewed in the context of this work, as is new empirical evidence that older people complain of general loss of memory efficiency but, paradoxically, report fewer lapses than young adults on the CFQ and other SAQs. These new data provide a basis for discussion of the reliability and consistency of SAQs and of their validity as tools to explore a wide range of changes associated with cognitive ageing: objective changes in cognitive ability and in objective functional competence; changes in people's understanding of their own cognitive processes, in their knowledge of cognitive and mnemonic strategies, and in their abilities to make use of these strategies; the extent to which responses given by older and younger adults reflect emotional and personality variables such as depression, anxiety, neuroticism, extraversion, and perceived locus of control. Self-reports by elderly adults on the CFQ, and other SAQs, simultaneously provide so many different kinds of information about the changes they experience, and about their attitudes and adaptations to old age, that apparently straightforward analyses give misleading answers. Methodological precautions are suggested for determining which questions can, and are, being asked and which analyses may, and which cannot, answer them. Donald Broadbent understood that however thoughtfully laboratory tasks are designed a n d interpreted, they are not good predictors of performance in demanding work environments such as automobile production lines. To study individual differences in error-proneness in these complex situations, he developed an exceptionally well designed and standardized self-assessment questionnaire (SAQ), the Cognitive Failures Questionnaire (CFQ: Broadbent, Cooper, Fitzgerald and Parkes, 1982). P. Rabbitt et al.During the next decade he and his associates used this questionnaire to discover what people's self-reports could tell them about their objective competence. For Cognitive Gerontologists, well designed SAQs (such as the CFQ) seem to be uniquely useful tools to discover what changes in cognitive efficiency people experience as they grow old, and how these changes affect their daily lives. However, experience has shown that interpretation of SAQ data is difficult because people's answers to SAQs simultaneously tell us a variety of very different things. They offer clues about their objective competencies and weaknesses, but also about their levels of self-confidence, anxiety, and depression; the extent of their knowledge and insight about their own abilities; their knowledge and beliefs about how their memories work; their insights into how they may improve their efficiency; and their relative vulnerabili...