Lisa Jenkins

Converging Evidence That Visuospatial Cognition Is More Age-Sensitive Than Verbal Cognition

In 3 separate experiments, the same samples of young and older adults were tested on verbal and visuospatial processing speed tasks, verbal and visuospatial working memory tasks, and verbal and visuospatial paired-associates learning tasks. In Experiment 1, older adults were generally slower than young adults on all speeded tasks, but age-related slowing was much more pronounced on visuospatial tasks than on verbal tasks. In Experiment 2, older adults showed smaller memory spans than young adults in general, but memory for locations showed a greater age difference than memory for letters. In Experiment 3, older adults had greater difficulty learning novel information than young adults overall, but older adults showed greater deficits learning visuospatial than verbal information. Taken together, the differential deficits observed on both speeded and unspeeded tasks strongly suggest that visuospatial cognition is generally more affected by aging than verbal cognition.

Individual and developmental differences in working memory across the life span

The effects of secondary tasks on verbal and spatial working memory were examined in multiple child, young adult, and older adult samples. Although memory span increased with age in the child samples and decreased with age in the adult samples, there was little evidence of systematic change in the magnitude of interference effects. Surprisingly, individuals who had larger memory spans when there was no secondary task showed greater interference effects than their age-mates. These findings are inconsistent with the hypothesis that age and individual differences in working memory are due to differences in the ability to inhibit irrelevant information, at least as this hypothesis is currently formulated. Moreover, our results suggest that different mechanisms underlie developmental and individual differences in susceptibility to interference across the life span. A model is proposed in which memory span and processing speed both increase with development but are relatively independent abilities within age groups.

Analysis of group differences in processing speed: Brinley plots, Q-Q plots, and other conspiracies.

Researchers in a growing number of areas (including cognitive development, aging, and neuropsychology) use Brinley plots to compare the processing speed of different groups. Ratcliff, Spieler, and McKoon (2000) argued that a Brinley plot is a quantile—quantile (Q—Q) plot and that therefore Brinley plot regression slopes measure standard deviation ratios rather than relative speed of processing. We show that this argument is incorrect. Brinley plots, by definition, are not Q—Q plots; the former are based on unranked data and the latter are based on ranked data. Furthermore, the relationship between standard deviation ratios and slopes is a general property of regression lines and has no implications for the use of Brinley plot regression slopes as processing speed measures. We also show that the relative speed interpretation of Brinley plot slopes is strongly supported by converging evidence from a metaanalysis of visual search, mental rotation, and memory scanning in young and older adults. As to Ratcliff et al.’s hypothesis that age differences in response time are attributable to greater cautiousness on the part of the elderly, rather than true processing speed differences, this hypothesis has been extensively tested in previous studies and found wanting.

The difference engine: a model of diversity in speeded cognition.

A theory of diversity in speeded cognition, the difference engine, is proposed, in which information processing is represented as a series of generic computational steps. Some individuals tend to perform all of these computations relatively quickly and other individuals tend to perform them all relatively slowly, reflecting the existence of a general cognitive speed factor, but the time required for response selection and execution is assumed to be independent of cognitive speed. The difference engine correctly predicts the positively accelerated form of the relation between diversity of performance, as measured by the standard deviation for the group, and task difficulty, as indexed by the mean response time (RT) for the group. In addition, the difference engine correctly predicts approximately linear relations between the RTs of any individual and average performance for the group, with the regression lines for fast individuals having slopes less than 1.0 (and positive intercepts) and the regression lines for slow individuals having slopes greater than 1.0 (and negative intercepts). Similar predictions are made for comparisons of slow, average, and fast subgroups, regardless of whether those subgroups are formed on the basis of differences in ability, age, or health status. These predictions are consistent with evidence from studies of healthy young and older adults as well as from studies of depressed and age-matched control groups.

The Role of Metals in the Hydrolytic Cleavage of DNA and RNA

Abstract The nucleic acids RNA and DNA consist of nucleoside building blocks joined by phosphodiester linkages. Phosphodiesters are generally inert to hydrolytic cleavage under physiological conditions because their negative charge disfavors nucleophilic attack. However, the hydrolytic scission of phosphodiester linkages is an important and common biological process, and can occur rapidly in the presence of appropriate catalysts such as ribozymes and nuclease enzymes. Metals play an important role in this process. Several possible modes of action can be invoked for metal-promoted phosphate ester hydrolysis, including Lewis acid catalysis, Br⊘nsted base catalysis by metal-bound hydroxides, nucleophilic catalysis by metal-bound hydroxides, Br⊘nsted acid catalysis by metal-bound water, and electrostatic stabilization of transition states by positively charged metal ions. Here we critically discuss the roles of metals in the hydrolytic cleavage of nucleic acids and related model substrates.

General Slowing of Lexical and Nonlexical Information Processing in Dementia of the Alzheimer Type

Individuals with very mild and mild dementia of the Alzheimer type (DAT) and age-matched controls performed three lexical and three nonlexical speeded information-processing tasks. The DAT group was slower than the control group on all six tasks. As predicted by general slowing (Nebes & Brady, 1992), most main effects of task condition were accompanied by Group × Condition interactions. That is, as task complexity increased, the response times (RTs) of the DAT group increased more than the RTs of the control group. Multitask regression analyses confirmed the existence of general slowing in DAT, such that the DAT group took approximately 1.8 times as long to process information as the controls on all six tasks. Importantly, lexical and nonlexical processing speed were equivalently affected by DAT. This pattern was observed both in very mild and mild DAT, although the degree of general slowing increased with the severity of the dementia.

Catalytic hydrolysis of 2′,3′-cyclic adenosine monophosphate by aqua(2,2′:6′,2″-terpyridine)copper(II): breakdown of the analogy between activated phosphodiesters and RNA

Aqua(2,2′:6′,2″-terpyridine)copper(II) catalyses the hydrolysis of 2′,3′-cyclic adenosine monophosphate, but does not hydrolyse the ‘activated’ substrate bis(p-nitrophenyl) phosphate indicating that the latter is not a reliable model for biological phosphoric ester hydrolysis.