Combining reaction-time distributions to conserve shape.

To improve the estimate of the shape of a reaction-time distribution, it is sometimes desirable to combine several samples, drawn from different sessions or different subjects. How should these samples be combined? This paper provides an evaluation of four combination methods, two that are currently in use (the bin-means histogram, often called "Vincentizing", and quantile averaging) and two that are new (linear-transform pooling and shape averaging). The evaluation makes use of a modern method for describing the shape of a distribution, based on L-moments, rather than the traditional method, based on central moments.

Sex differences in the effects on the brain of early cognitive stimulation.

A study by Farah and colleagues (2021) of the effects on the adult brain of a cognitively intense early childhood experience revealed large effects, but primarily in the brains of male subjects, while causing equally large increases of childhood IQ in males and females. The present analysis advances and tests a conjecture about one reason for the sex difference. Among the control subjects, the summed volume of four small regions of the cortex, associated with language and cognitive processes, is proportionally larger in females.

Randomized Manipulation of Early Cognitive Experience Impacts Adult Brain Structure.

Does early exposure to cognitive and linguistic stimulation impact brain structure? Or do genetic predispositions account for the co-occurrence of certain neuroanatomical phenotypes and a tendency to engage children in cognitively stimulating activities? Low socioeconomic status infants were randomized to either 5 years of cognitively and linguistically stimulating center-based care or a comparison condition. The intervention resulted in large and statistically significant changes in brain structure measured in midlife, particularly for male individuals. These findings are the first to extend the large literature on cognitive enrichment effects on animal brains to humans, and to demonstrate the effects of uniquely human features such as linguistic stimulation.

In defence of high-speed memory scanning.

Unlabelled: This paper reviews some of the evidence that bears on the existence of a mental high-speed serial exhaustive scanning process (SES) used by humans to interrogate the active memory of a set of items to determine whether it contains a test item. First proposed in the 1960s, based on patterns of reaction times (RTs), numerous later studies supported, elaborated, extended, and limited the generality of SES, while critics claimed that SES never occurred, that predictions from SES were violated, and that other mechanisms produced the RT patterns that led to the idea. I show that some of these claims result from ignoring variations in experimental procedure that produce superficially similar but quantitatively different RT patterns and that, for the original procedures, the most frequently repeated claims that predictions are violated are false.

Sequential processes and the shapes of reaction time distributions.

It is sometimes suggested that reaction time (RT) distributions have the same shape across conditions or groups. In this note we show that this is highly unlikely if the RT is the sum of the stochastically independent durations of 2 or more stages (sequential processes) (a) that are influenced selectively by different factors, or (b) 1 of which is influenced selectively by some factor. We provide an example of substantial shape differences in RT data from a flash-detection experiment, data that have been shown to satisfy requirement (a).

Modular processes in mind and brain.

One approach to understanding a complex process starts with an attempt to divide it into modules·, sub-processes that are independent in some sense, and have distinct functions. In this paper, I discuss an approach to the modular decomposition of neural and mental processes. Several examples of process decomposition are presented, together with discussion of inferential requirements.

Nutritional supplements and infection in the elderly: why do the findings conflict?

Background: Most of the randomized placebo-controlled trials that have examined the clinical effects of multivitamin-mineral supplements on infection in the elderly have shown no significant effect. The exceptions are three such trials, all using a supplement with the same composition, and all claiming dramatic benefits: a frequently cited study published in 1992, which reported a 50% reduction in the number of days of infection (NDI), and two 2002 replication studies. Questions have been raised about the 1992 report; a second report in 2001 based on the same trial, but describing effects of the supplement on cognitive functions, has been retracted by Nutrition.

The time of consciousness and vice versa.

The temporal granularity of consciousness may be far less fine than the real-time information processing mechanisms that underlie our sensitivity to small temporal differences. It is suggested that conscious time perception, like space perception, is subject to errors that belie a unitary underlying representation. E.