On the discrimination between global and local trend hypotheses of life-span changes in processing speed

Differential Age Effects on Semantic and Syntactic Priming

Adult age differences in the processing of semantic and syntactic information during language comprehension were investigated in a lexical decision task in which the target word was preceded by a sentence fragment. Sentence fragment and target were presented visually and made up either a correct or an incorrect sentence containing either a semantic violation (selectional restriction violation) or a syntactic violation (subcategorisation violation). Experiment 1 revealed a differential age effect for the processing of syntactic, but not for the processing of semantic violations. Experiment 2, using visually degraded targets, demonstrated that this differential effect was independent of peripheral processing aspects, such as visual encoding. Experiment 3 including a neutral baseline condition revealed that the differential age effect on syntactic processing was due to controlled rather than to automatic aspects of priming, as it was observed for the cost component, but not for the bene”t component. Experiment 4 revealed that this effect was independent of the timing parameters used for stimulus presentation. It appears that age can have differential effects on specific cognitive domains, such as syntax and semantics. This may be attributable to the amount of controlled processes involved in syntactic and semantic priming.

Aging, focus switching, and task switching in a continuous calculation task: evidence toward a new working memory control process

This study examined switching of the focus of attention in working memory in relation to global task switching in a continuous calculation task using two rules (midpoint and up-and-down) in a group of 25 younger adults and a group of 23 older adults. Age differences emerged in accuracy when participants worked on two strings simultaneously (necessitating a focus switch); focus switching did not interact with age in the response time domain. No age differences were obtained for global task switching. Ex-Gaussian decomposition showed a shift due to focus switching in all parameters, but a shift in leading edge only for task switching. The results suggest that task switching and focus switching rely on different processes, and that there is a specific age-related deficit in focus switching.

Mean response times, variability, and skew in the responding of ADHD children: a response time distributional approach

Response time (RT) distributions from three fixed foreperiod conditions (2, 4, and 8 s) in a warned four-choice RT task were obtained for a group of boys with attention-deficit/hyperactivity disorder, combined type (ADHD; n = 17) and for two groups of normal control boys (age-matched, n = 18, and younger-aged, n = 10). Quantitative measures of distributional shape were derived by fitting the ex-Gaussian distributional model to the individual RT data. Statistical results indicate that the ADHD distributions differ from the age-matched control distributions with respect to the size of the tail (larger for the ADHD boys), but differ from the younger control distributions with respect to the location of the leading edge (slower for the younger control boys). Receiver operating characteristic (ROC) results reveal that the ex-Gaussian exponential component is highly diagnostic of the ADHD boys.

Cortical and cognitive development in 4th, 8th and 12th grade students. The contribution of speed of processing and executive functioning to cognitive development

This study investigated cortical/cognitive relations in 30 4th, 8th and 12th grade students. All students were administered the Figural Intersection Test, a measure of cognitive development, and performed, three times with different targets, an event-related potential (ERP) oddball/selective-attention task. Two independent factors emerged from the ERP task that predicted development--speed of processing (P300 latency to Block 1 targets) and maturation of executive functioning (a composite ERP variable calculated as the ratio of RT and P300 latency divided by the accuracy to Block 2 targets). These two variables loaded on orthogonal factors in a principal components analysis, and were the only variables included in a stepwise regression of physiological variables on cognitive development. Speed of processing is modulated by myelination and synaptogenesis, and executive functioning is modulated by maturation of the frontal system. These electrophysiological markers could index these cortical transformations underlying cognitive development.

Mental resources, processing speed, and inhibitory control: a developmental perspective

The present article addresses the claim that the speed of information processing qualifies as a processing resource. This claim contends that age-related changes in processing speed pertain to all cognitive processes to the same proportional degree. That is, processing speed is compared to the clock speed of a microcomputer: as young children's clock speed increases, the speed of processing in all cognitive processes increases until the adult level is reached. Re-analyses of recent behavioral and psychophysiological data provide evidence against the notion that development is characterized by an increase in children's global clock speed, and refute the claim that processing speed operates as a mental resource on which all cognitive processes depend to the same extent. Rather, the results emphasize the role of inhibitory control in cognitive development, and we consider the relevance of inhibitory development to the issue of age-related changes in processing capacity.

Testing the global-slowing hypothesis: are alcohol's effects on human performance process-specific or task-general?

In an interesting recent meta-analysis, Maylor and Rabbitt (1993) suggested that alcohol's effects on human performance may not be process- or stage-specific, but reflect a general, undifferentiated, cognitive slowing. According to this view, performance is globally slowed by a constant multiplicative fraction (b), such that the longer a process takes without alcohol on board (a -), the more it will be slowed by alcohol (a +). In summary: RTa+ = b b (RTa-). In this sense, the effects of alcohol are determined simply by the duration of a process or stage--not by its function or content--and attempts to map the effects of alcohol to specific cognitive operations are essentially futile. This global-slowing hypothesis entails, then, (i) that the function relating RTa+ to RTa- will be linear and increasing; (ii) that the value of b will be significantly greater than 1.0; and (iii) that all experimental factors which increase the complexity (hence, duration) of a task or stage will interact with alcohol. In this study we tested the global-slowing hypothesis directly using fixed set, varied set and concurrent sets item-recognition paradigms. All three tasks showed convincing additivity between alcohol and other key experimental factors which affect response latency (e.g., setsize, response type); there was no hint of any of the spectrum of significant interactions predicted by the global-slowing hypothesis. A meta-analysis of varied set latencies, analogous to Maylor and Rabbitt's, yielded a reasonably linear alcohol/no-alcohol function, but with a slope constant (b) less than 1.0. In all, the data provided little support for the global-slowing hypothesis.

Some thoughts on neurocognitive slowing

An historical review of the use of Brinley analyses in reaction time studies of age-related cognitive slowing is presented. The debate between critics and supporters of this procedure is discussed. It is concluded that the debate has served to sharpen our understanding of when and how this analytic procedure should be used. It is also argued that our insights into mental slowing may be deepened by studying this phenomenon using cognitive psychophysiological methods.