Some thoughts on neurocognitive slowing

Speeding-up while growing-up: Synchronous functional development of motor and non-motor processes across childhood and adolescence

Describing the maturation of information processing in children is fundamental for developmental science. Although non-linear changes in reaction times have been well-documented, direct measurement of the development of the different processing components is lacking. In this study, electromyography was used to quantify the maturation of premotor and motor processes on a sample of 114 children (6–14 years-old) and 15 adults. Using a model-based approach, we show that the development of these two components is well-described by an exponential decrease in duration, with the decay rate being equal for the two components. These findings provide the first unbiased evidence in favour of the common developmental rate of nonmotor and motor processes by directly confronting rates of development of different processing components within the same task. This common developmental rate contrasts with the differential physical maturation of region-specific cerebral gray and white matter. Tentative paths of interpretation are proposed in the discussion.

Aging induced loss of complexity and dedifferentiation: consequences for coordination dynamics within and between brain, muscular and behavioral levels

Growing evidence demonstrates that aging not only leads to structural and functional alterations of individual components of the neuro-musculo-skeletal system (NMSS) but also results in a systemic re-organization of interactions within and between the different levels and functional domains. Understanding the principles that drive the dynamics of these re-organizations is an important challenge for aging research. The present Hypothesis and Theory paper is a contribution in this direction. We propose that age-related declines in brain and behavior that have been characterized in the literature as dedifferentiation and the loss of complexity (LOC) are: (i) synonymous; and (ii) integrated. We argue that a causal link between the aforementioned phenomena exists, evident in the dynamic changes occurring in the aging NMSS. Through models and methods provided by a dynamical systems approach to coordination processes in complex living systems, we: (i) formalize operational hypotheses about the general principles of changes in cross-level and cross-domain interactions during aging; and (ii) develop a theory of the aging NMSS based on the combination of the frameworks of coordination dynamics (CD), dedifferentiation, and LOC. Finally, we provide operational predictions in the study of aging at neural, muscular, and behavioral levels, which lead to testable hypotheses and an experimental agenda to explore the link between CD, LOC and dedifferentiation within and between these different levels.

Age-related dedifferentiation of cognitive and motor slowing: insight from the comparison of Hick-Hyman and Fitts' laws

The present study aimed to determine whether the general slowing hypothesis (GSH) could be extended to the motor domain by comparing cognitive and motor age-related slowing. To achieve this objective, we compared the slopes of Hick–Hyman’s law and Fitts’ law, in young and older adults. The general hypothesis was that, due to the dedifferentiation of cognitive and motor neural resources during aging, the slopes of Hick–Hyman’s law and Fitts’ law should become closer, if not similar, in older adults. Ten young adults (mean age = 26 ± 3 years) and 14 older adults (mean age = 78 ± 7 years) participated in the experiment. They had to perform a discrete rapid-aiming task and a reaction time (RT) task. In the aiming task, five index of difficulty (ID) levels were used (from three to seven bits by increments of 1.0 bit). Task difficulty was scaled via the manipulation of target distance from home position. In the RT task, five IDs were selected: 0, 1, 2, 3, and 4 bits, with incompatible S–R associations. RT and movement times were recorded. Efficiency and Brinley regression functions were calculated. Age-related slowing ratios were estimated. Response times increased in both tasks in older adults. The slopes of Hick–Hyman’s law and Fitts’ law were steeper in older adults than in young participants. In young participants, the slope of Hick–Hyman’s law was smaller than that of Fitts’ law. In older adults, no difference was found. Slowing ratios observed in both tasks were equivalent. The present results extended the GSH to the motor domain. They suggested that, due to dedifferentiation of cognitive and motor neural resources, decrease in processing speed acts as a common cause to behavioral slowing in both cognitive and motor tasks.

Age-related differences in reaction time task performance in young children

Performance of reaction time (RT) tasks was investigated in young children and adults to test the hypothesis that age-related differences in processing speed supersede a "global" mechanism and are a function of specific differences in task demands and processing requirements. The sample consisted of 54 4-year-olds, 53 5-year-olds, 59 6-year-olds, and 35 adults from Russia. Using the regression approach pioneered by Brinley and the transformation method proposed by Madden and colleagues and Ridderinkhoff and van der Molen, age-related differences in processing speed differed among RT tasks with varying demands. In particular, RTs differed between children and adults on tasks that required response suppression, discrimination of color or spatial orientation, reversal of contingencies of previously learned stimulus-response rules, and greater stimulus-response complexity. Relative costs of these RT task differences were larger than predicted by the global difference hypothesis except for response suppression. Among young children, age-related differences larger than predicted by the global difference hypothesis were evident when tasks required color or spatial orientation discrimination and stimulus-response rule complexity, but not for response suppression or reversal of stimulus-response contingencies. Process-specific, age-related differences in processing speed that support heterochronicity of brain development during childhood were revealed.

Syntactic processing with aging: an event-related potential study

To assess age-related changes in simple syntactic processing with normal aging, event-related brain potentials (ERPs) elicited by grammatical number violations as individuals read sentences for comprehension were analyzed. Violations were found to elicit a P600 of equal amplitude and latency regardless of an individual's age. Instead, advancing age was associated with a change in the scalp distribution of the P600 effect, being less asymmetric and more frontal (though still with a parietal maximum) in older than younger adults. Our results thus show that the brain's response to simple syntactic violations, unlike those reported for simple binary categorizations and simple semantic violations, is neither slowed nor diminished in amplitude by age. At the same time, the brain's processing of these grammatical number violations did engage at least somewhat different brain regions as a function of age, suggesting a qualitative change rather than any simple quantitative change in speed of processing.

Developmental trends in simple and selective inhibition of compatible and incompatible responses

This study examined age-related change in the ability to inhibit responses using two varieties of the stop signal paradigm. Three age groups (29 7-year-olds, 24 10-year-olds, and 28 young adults) performed first on a visual choice reaction task in which the spatial mapping between the go signal and response was varied between blocks. The choice task was then complicated by randomly inserting a visual stop signal on 30% of the trials. In the simple stop signal paradigm, the stop signal required the inhibition of the planned response. In the selective stop signal paradigm, the stop signal required response inhibition only when the stop signal was presented at the same side as the instructed response to the go signal. The results showed that simple stopping was faster than selective stopping and that selective, but not simple, stopping of incompatible responses was slower than stopping of compatible responses. Brinley plot analysis yielded linear functions relating children's latencies to adults' latencies. Analysis of shared variance indicated that developmental change in the speed of selective stopping continued to be significant even when the effect associated with simple stopping was removed. This pattern of findings is discussed vis-à-vis notions of global versus specific developmental trends in the speed of information processing.

Visual Word Recognition of Single-Syllable Words

Speeded visual word naming and lexical decision performance are reported for 2428 words for young adults and healthy older adults. Hierarchical regression techniques were used to investigate the unique predictive variance of phonological features in the onsets, lexical variables (e.g., measures of consistency, frequency, familiarity, neighborhood size, and length), and semantic variables (e.g. imageahility and semantic connectivity). The influence of most variables was highly task dependent, with the results shedding light on recent empirical controversies in the available word recognition literature. Semantic-level variables accounted for unique variance in both speeded naming and lexical decision performance, level with the latter task producing the largest semantic-level effects. Discussion focuses on the utility of large-scale regression studies in providing a complementary approach to the standard factorial designs to investigate visual word recognition.

Process-specific slowing with advancing age: evidence derived from the analysis of sequential effects

In the current study we examined the generalized slowing hypothesis on the mechanisms underlying sequential effects in serial two-choice reaction time tasks. For young adults, sequential effects of conditions with a high and a low stimulus presentation rate respectively pointed to an automatic and an expectancy mechanism. Older adults' low presentation rate data corroborated the general slowing hypothesis for expectancy, whereas the high presentation rate results did not. The observation of a differential influence of age on the automatic and the expectancy mechanism poses a problem for notions assuming that higher level processes are more vulnerable to advancing age than lower level processes.

Older age, traumatic brain injury, and cognitive slowing: some convergent and divergent findings

Reaction time (RT) meta-analyses of cognitive slowing indicate that all stages of processing slow equivalently and task independently among both older adults (J. Cerella & S. Hale, 1994) and adults who have suffered a traumatic brain injury (TBI; F. R. Ferraro, 1996). However, meta-analyses using both RT and P300 latency have revealed stage-specific and task-dependent changes among older individuals (T. R. Bashore, K. R. Ridderinkhof, & M. W. van der Molen, 1998). Presented in this article are a meta-analysis of the effect of TBI on processing speed, assessed using P300 latency and RT, and a qualitative review of the literature. They suggest that TBI induces differential slowing. Similarities in the effects of older age and TBI on processing speed are discussed and suggestions for future research on TBI-induced cognitive slowing are offered.

The ability to activate and inhibit speeded responses: separate developmental trends

When children grow older they respond faster and are less susceptible to interference caused by task-irrelevant information. These observations suggested the hypothesis that a global mechanism may account for developmental change in the speed of responding and that inhibitory function may underlie the ability to activate speeded responses. The current study examined these issues by comparing the performance of 4 age groups (5-, 8-, and 11-year-olds and young adults) on a battery of 6 speeded performance tasks, 4 of which required the inhibition of response activation. An analysis of reaction and inhibition times supported a hypothesis of generalized developmental changes in response activation, but revealed a less pronounced development of inhibition. A nonselective mechanism of response inhibition seems to be fully developed during early childhood.

Age-related slowing of control processes: evidence from a response coordination task

Normal aging is associated with slowing of performance mostly due to a slowed functioning of central response-related processes. In this paper we set out to discover whether slowing occurs also when the process controlling the coordination of responses is engaged by the task. To this end, we compared the mean-reaction time performance of two groups of subjects (young vs. elderly) in single- and dual-task experimental paradigm. The response coordination process is required only by the dual-task paradigm. The results indicate that, in the dual-task situation, the elderly are markedly slower than young subjects. The eventual relevance of information-processing speed in determining the cognitive performance of the elderly is considered in the discussion of the results.

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.

Is the age-complexity effect mediated by reductions in a general processing resource?

The rate of information processing, as revealed in measures of reaction time, slows with advancing age and this slowing is most evident as processing complexity increases. This phenomenon, known as the Age-Complexity effect, has been attributed to general changes in the speed of processing that affect all components of processing indiscriminantly, both within and across tasks in a particular processing domain. That the slowing is thought to be task- and process-independent has led to the additional inference that it reflects reductions in a general processing resource. On the basis of converging evidence identified in a review of both behavioral and chronopsychophysiological studies, we argue that the slowing induced by older age is not generalized, but rather is both task-dependent and process-specific and, as such, cannot be explained in terms of a diminished general processing resource. We close by speculating that elements of the age-induced slowing can be interpreted within the context of the cognitive-energetical model.

Age comparisons of serial position effects in short-term memory

Memory for serial position in four-item lists of words or abstract designs was tested at retention intervals of 5-25 seconds in two subject groups, aged 25-35 and 60-75 years; accuracy and choice reaction times (RT) were recorded. Increasing the retention interval transformed the serial position curve from recency to primacy but produced no overall reduction in memory performance in terms of accuracy. RTs varied as a function of both serial position and retention interval. Under all conditions the memory of older subjects was less accurate and they exhibited longer RTs compared to young subjects, but the age differences did not interact with list position or retention interval for either response indicator. The results suggest that age differences in memory can be explained by a single factor of mental speed limiting encoding efficiency and affecting decision times.

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.

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

Meta-analyses of age effects on processing speed suggest a single, global mechanism underlying developmental speeding and slowing in the elderly. Myerson, Hale, Wagstaff, Poon and Smith (1990) proposed an information loss model assuming that a constant amount of information is lost at each processing step in all age groups whereas the rate of information loss differs between age groups. In this study, a series of simulations has been conducted comparing global versus local information loss. This has been outcomes of these deterministic and stochastic varieties of the information loss model. The outcomes of these comparisons were consistently negative; the information loss model fails to discriminate between global and local age effects on the reaction process. The simulations were followed by a discussion of Hohle's (1967) scheme for investigating selective age effects on processing speed. It was concluded that the combined approach of stage and distribution analysis of the reaction process augmented with psychophysiological time markers provides a powerful tool for the study of life-span changes in processing speed.