A theory is proposed to account for some of the age-related differences reported in measures of Type A or fluid cognition. The central hypothesis in the theory is that increased age in adulthood is associated with a decrease in the speed with which many processing operations can be executed and that this reduction in speed leads to impairments in cognitive functioning because of what are termed the limited time mechanism and the simultaneity mechanism. That is, cognitive performance is degraded when processing is slow because relevant operations cannot be successfully executed (limited time) and because the products of early processing may no longer be available when later processing is complete (simultaneity). Several types of evidence, such as the discovery of considerable shared age-related variance across various measures of speed and large attenuation of the age-related influences on cognitive measures after statistical control of measures of speed, are consistent with this theory.

http://www.anitacrawley.net/Resources/Articles/salthouse%20The%20Processing%20Speed%20Theory%20of%20Adult%20Age%20Differences%20in%20Cognition.pdf

The processing-speed theory of adult age differences in cognition.

https://www.absch.cl/w/images/gallery/sports_conference_2015/docs/Development_of_cognitive.pdf

Development of cognitive control and executive functions from 4 to 13 years: Evidence from manipulations of memory, inhibition, and task switching

Normal Cognitive Aging

Is there a biology of intelligence which is characteristic of the normal human nervous system?" Here we review 37 modern neuroimaging studies in an attempt to address this question posed by Halstead (1947) as he and other icons of the last century endeavored to understand how brain and behavior are linked through the expression of intelligence and reason. Reviewing studies from functional (i.e., functional magnetic resonance imaging, positron emission tomography) and structural (i.e., magnetic resonance spectroscopy, diffusion tensor imaging, voxel-based morphometry) neuroimaging paradigms, we report a striking consensus suggesting that variations in a distributed network predict individual differences found on intelligence and reasoning tasks. We describe this network as the Parieto-Frontal Integration Theory (P-FIT). The P-FIT model includes, by Brodmann areas (BAs): the dorsolateral prefrontal cortex (BAs 6, 9, 10, 45, 46, 47), the inferior (BAs 39, 40) and superior (BA 7) parietal lobule, the anterior cingulate (BA 32), and regions within the temporal (BAs 21, 37) and occipital (BAs 18, 19) lobes. White matter regions (i.e., arcuate fasciculus) are also implicated. The P-FIT is examined in light of findings from human lesion studies, including missile wounds, frontal lobotomy/leukotomy, temporal lobectomy, and lesions resulting in damage to the language network (e.g., aphasia), as well as findings from imaging research identifying brain regions under significant genetic control. Overall, we conclude that modern neuroimaging techniques are beginning to articulate a biology of intelligence. We propose that the P-FIT provides a parsimonious account for many of the empirical observations, to date, which relate individual differences in intelligence test scores to variations in brain structure and function. Moreover, the model provides a framework for testing new hypotheses in future experimental designs.

/pdf/the-parieto-frontal-integration-theory-p-fit-of-intelligence-2kp9bfy1c3.pdf

The Parieto-Frontal Integration Theory (P-FIT) of intelligence: converging neuroimaging evidence.

Motor function involves complex physiologic processes and requires the integration of multiple systems, including neuromuscular, musculoskeletal, and cardiopulmonary, and neural motor and sensory-perceptual systems. Motor-functional status is indicative of current physical health status, burden of disease, and long-term health outcomes, and is integrally related to daily functioning and quality of life. Given its importance to overall neurologic health and function, motor function was identified as a key domain for inclusion in the NIH Toolbox for Assessment of Neurological and Behavioral Function (NIH Toolbox). We engaged in a 3-stage developmental process to: 1) identify key subdomains and candidate measures for inclusion in the NIH Toolbox, 2) pretest candidate measures for feasibility across the age span of people aged 3 to 85 years, and 3) validate candidate measures against criterion measures in a sample of healthy individuals aged 3 to 85 years (n = 340). Based on extensive literature review and input from content experts, the 5 subdomains of dexterity, strength, balance, locomotion, and endurance were recommended for inclusion in the NIH Toolbox motor battery. Based on our validation testing, valid and reliable measures that are simultaneously low-cost and portable have been recommended to assess each subdomain, including the 9-hole peg board for dexterity, grip dynamometry for upper-extremity strength, standing balance test, 4-m walk test for gait speed, and a 2-minute walk test for endurance.

https://n.neurology.org/content/neurology/80/11_Supplement_3/S54.full.pdf

Cognition assessment using the NIH Toolbox

In six experiments, subjects read narratives describing varying spatial scenes with more than one point of view. They were probed with questions about objects located in six directions from each character’s point of view. Subjects’ response times were consistent with a one place-one perspective rule. They seemed to form separate mental models for separate places and to take a character’s perspective when there was only one relevant character in a scene, but they seemed to take a neutral perspective when there was more than one probed point of view, rather than switch perspectives.

https://link.springer.com/content/pdf/10.3758/BF03199583.pdf

Switching points of view in spatial mental models.

Previous research has yielded conflicting results regarding the relationship between adult age and the ability to divide attention between two concurrent tasks. At least some of the inconsistency is probably attributable to methodological variations, such as the manner in which divided-attention ability has been assessed, how single-task performance has been considered, and the degree of control over relative emphasis placed on each task. Two experiments employing procedures sensitive to these concerns were conducted in which a speeded decision task was performed during the retention interval of a letter-memory task. The results of both experiments indicated that there were relatively few age-related influences on dual-task performance vis-a-vis those on single-task performance.

Aging of attention: Does the ability to divide decline?

Two studies were conducted to investigate the aspect(s) of processing involved in the hypothesized speed mediation of adult age differences in memory. Both studies involved a serial memory task in which information was to be recalled either in the original order of presentation, or in a reordered sequence. Results from both studies indicated that taskspecific processing durations were slower among older adults thon among loung adults, but that the attenuation of the age-related variance in memory was nearly as great after statistical control of a task-independent speed measure as after conlrol of nsk-specffic speed measures. These findings are consistent with the hypothesis that a substantial proportion of the adult age-related differences in memory is associated with a decrease with increased age in the speed of executing many cognitive processes, and not simply the speed of one or two specific processes. 'JHE goal of the studies described in this report was to r investigate how processing speed contributes to the relations between age and memory. The relations of interest have been documented. and some initial evidence relevant to this issue has been provided, with data from earlier research (Salthouse, 1983, in press). The memory tasks in the previous studies were free recall of two lists of, l2 unrelated nouns presented auditorily at a rate of -2 seconds/word, and paired associatc recall <lf six pairs of unrelated nouns also presented at -2 secondsiword. The speed measures were derived from three paper-and-pencil tests of perceptual speed; digit symbol substitution, letter comparison, and pattern comparison. The average of the z-scores in the three tests served as a composite index of the speed with which the individual could execute elementary operations. The results of these earlier studies are summarized in Table I . Notice that in the first study there was a large attenuation of the age-related variance in the memory measures when the variance associated with the processing speed measure was statistically controlled (i.e., 87o/o attenuation with free recall, from an R' for age of . 162-.O2l , and 857o attenuation with paired associates, from an R2 for age of .162-.024). An extreme-groups design was used in the second study, which resulted in larger age-related effects than those in the first study because of the omission of the variance associated with the intermediate ages. [The memory data were not reported in the Salthouse (1993) article, but most of the subjects from the second study in that project performed these tasks after completing the tasks reported in the article.l The speed and memory tasks were identical to those of the first study, but also included were measures of associational fluency that might be expected to be important in the performance of many memory tasks if effectiveness of elaborative encoding is related to the number of relevant associations that can be produced in a limited time. The measures were from tasks requiring the generation of as many words as possible, beginning with one of two stems (pro- and sub-) or ending with one of two terminations (-ay and -ow), and the average of the z-scores in the two tasks served as the measure of associational fl uency. It is apparent in the bottom panel of Table l that the major findings of the first study were replicated, as there was 9l7o attenuation of the age-related variance in free recall performance and 88o/o attenuation of the age-related variance in paired associates performance after control of the same composite speed measure. However, it was surprising that the attenuation of the age-related variance in memory was smaller after control of the presumably more specific fluency measure than after control of the more general speed measure; that is, only 44.5o/o attenuation with fiee recall performance and 37 .l%o attenuation with paired associates performance. Taken together, the results of these earlier studies suggest that processing speed, as indexed by various perceptual comparison tasks, is involved in the mediation of age differences in memory, and that the speed influence appears to be fairly general, in that it does not seem to be restricted to measures postulated to reflect memory-relevant processes. The existence of significant residual age-related variance even when the variation in speed is controlled indicates that other factors also contribute to the age differences evident in these tasks. Nevertheless, the discovery that influences independent of speed are associated with <157o of the total agerelated variance for free recall and paired associate measures of memory suggests that some aspect of speed plays a major role in the relations between age and memory. The purpose of the current project was to conduct a more detailed examination of the relation between speed and memory with a simpler task in which it might be possible to identify the mechanisms responsible for the apparent speed mediation of age-related differences in memory. The research strategy consisted of three distinct steps or phases. The first step was to determine the amount of age-related variance in the criterion measure of memory before and after controlling the variance in an index of processing speed derived from independent tasks. The goal of these analyses

Influence of Task-Specific Processing Speed on Age Differences in Memory

A fundamental issue in research on individual differences is the type of evidence sufficient to justify an inference of selective or distinct deficits in relevant theoretical processes. It is proposed that an important consideration is the extent to which the individual differences in 1 variable are independent of those in another variable. Specifically, the suggestion presented here is that a strong conclusion of selective impairment requires evidence that there is significant group-related variance in 1 variable after the variance in the other relevant variable is controlled. Furthermore, an inference that the groups are equivalent on a particular theoretical process requires evidence that the variable presumed to reflect that process has sufficient unique variance to justify the claim that a distinct process is being assessed. The proposed methods are illustrated with two studies comparing adults of different ages in mental arithmetic tasks.

Interpretation of differential deficits: the case of aging and mental arithmetic.

Participants in two studies conducted by Salthouse (in press) were called 2 to 182 days after participation and asked to describe the activities that they had performed in the previous study. Hierarchical regression analyses were used to examine the prediction of activity recall from age, speed, and retention interval. Overall, age was associated with 20% of the variance in activity recall, and retention interval was associated with 19%, but there was no significant interaction of age and retention interval. When perceptual speed was entered into the regression equation before age, the age-related variance was reduced by 70%. A small, but statistically significant, amount of age-related variance in activity memory remained after controlling for speed and retention interval.

Adult age differences in long-term memory for performed activities.

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