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Mediators between age & cognitive function (Neurobiological…
Mediators between age & cognitive function
Limited Time mechanism: assembly line
external time window that determines how well you will perform
issue when relevant cognitive operations are executed too slowly to be successfully completed in the available time -> the quality of the "product" will likely be impaired
Task difficulty
low level: the determinant of differences in performance is the speed of performance
high level: complexity effect
Simultaneity mechanism: Juggler
internal speed of processing determines your performance
relevant information may no longer be available when it is needed because information decreases in availability over time (it decays)
slow processing reduces the amount of simultaneously available information needed for high level processing
like juggling because complex activities require synchronization if constituent tasks and synchronization is easier when th erelevant operations can be executed rapidly
Processing Speed Theory (Salthouse)
Assumptions
Fundamental: Major factor that contributes to age-related memory/cognition changes is the reduction in speed
1) Performance in many cognitive tasks is limited by general processing constraints.
2) Speed of processing is a critical processing constraint associated with increased age
Hypotheses & Statistical Methods
Hypothesis 1: Age-related slowing isn't simply attributable to specific & independent processing deficits. There are common/general age-related influences that contribute to measures of processing speed
Implication 1: It should be possible to predict age-differences in particular speed measures from knowledge of age differences in other speed measures (supported)
Analyses of Systematic Relations (age comparative data): eg. use the performance of young adults & the systematic relations from a set of variables to predict the mean values of older adults in a given condition -> there are indeed systematic relations between mean times of young & old adults
Implication 2: Age-related influences on different speed measures are not independent and they share age-related variance (supported)
Statistical Control Procedures (method of quality control), usage of hierarchical regression & correlation to find the proportion of age-related variance shared with controlled and criterion variables
Structural Equation Model
Hypothesis 2: Processing speed functions as a mediator of the relations between age & measures of cognitive functioning
Path Analysis: strong relation between age & speed (motor, perceptual), moderate relation between speed & measures of cognitive functioning (eg.study time, decision accuracy, decision time), weak relation between age & measures of cognitive functioning
slow speed also affects the quality of cognitive processing (decision accuracy)
Path analyses show the importance of balance between data-driven & hypothesis-driven approach
Hypothesis 3: The limited & simultaneity mechanisms are primarily responsible for the relations between speed & cognitive fucntioning
limited time: manipulate the amount of time available to process a stimulus
simultaneity: working memory tasks to assess the amount of simultaneously available information
Age-related slowing in not...
uniform: age-related effects can vary in magnitude because of other influences
unitary: there is not a single speed factor
universal: some measures may not exhibit age-related slowing, not every measure is affected by general influences
Evidence of age-related slowing: correlation of age & measures of speed is ca. .45
tasks to measure it should be cognitively simple to be sure that time differences are because of speed (best to use multiple measures)
What other factors mediate the relationship?
storage capacity
coordination effectiveness
white matter deterioration/integrity
processing efficiency (related to speed)
Neurobiological underpinnings of cognitive speed
Mean Diffusivity increase (represents the average rate of water diffusion regardless of directionality): higher values reflect high rate of diffusion & poor local WM integrity
Anterior posterior gradient of WM integrity: anterior section of corpus callous more susceptible to aging compared to posterior section
Fractional anisotropy decrease (reflects how direction specific the diffusion of water is): higher values would reflect intact WM integrity & consistent diffusion orientation
PASA (posterior anterior shift in aging): increased activity in anterior regions to compensate for posterior changes & loss of function. Anteior regions start to be more and more engaged but they are also less & less efficient (less automated & need additional cognitive resources)
structural changes in GM & WM, where white matter deterioration contributes to disconnection among distributed networks
Salami's findings contradict Salthouse's Theory
Salthouse states that there are general factors that contribute to age-related decline. He states that results from certain measures can tell us something about the results on other measures.
Salami's study shows that there are also local & more specific influences in some measures. For example, there was a typical age-related cognitive decline in block design, letter digit & episodic memory, but there was no age effect on the fluency task.
Parallels between TBI & Aging
Diffuse axonal injury can affect the speed of information processing
the "general factor" might be the same for TBI & older adults
People suffering fromTBI could potentially recover but older adults experience multiple other age-related processes that dictate their state/level of functioning