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

Effects of task and age on the magnitude and structure of force fluctuations: insights into underlying neuro-behavioral processes

BACKGROUND

The present study aimed at characterizing the effects of increasing (relative) force level and aging on isometric force control. To achieve this objective and to infer changes in the underlying control mechanisms, measures of information transmission, as well as magnitude and time-frequency structure of behavioral variability were applied to force-time-series.

RESULTS

Older adults were found to be weaker, more variable, and less efficient than young participants. As a function of force level, efficiency followed an inverted-U shape in both groups, suggesting a similar organization of the force control system. The time-frequency structure of force output fluctuations was only significantly affected by task conditions. Specifically, a narrower spectral distribution with more long-range correlations and an inverted-U pattern of complexity changes were observed with increasing force level. Although not significant older participants displayed on average a less complex behavior for low and intermediate force levels. The changes in force signal's regularity presented a strong dependence on time-scales, which significantly interacted with age and condition. An inverted-U profile was only observed for the time-scale relevant to the sensorimotor control process. However, in both groups the peak was not aligned with the optimum of efficiency.

CONCLUSION

Our results support the view that behavioral variability, in terms of magnitude and structure, has a functional meaning and affords non-invasive markers of the adaptations of the sensorimotor control system to various constraints. The measures of efficiency and variability ought to be considered as complementary since they convey specific information on the organization of control processes. The reported weak age effect on variability and complexity measures suggests that the behavioral expression of the loss of complexity hypothesis is not as straightforward as conventionally admitted. However, group differences did not completely vanish, which suggests that age differences can be more or less apparent depending on task properties and whether difficulty is scaled in relative or absolute terms.

Age and verbal fluency: the mediating effect of speed of processing

Background and Purpose

Cognitive decline is a function of normal aging; however, the effect of age on various domains is differential. This study examined the effect of age on verbal fluency and showed how speed of processing modifies fluency performance in healthy older adults compared to younger individuals.

Methods

Three age groups, 62 young (17–40 years), 30 middle-aged (41–59 years), and 38 older adults (60–78 years), were studied using the Controlled Oral Word Association Test, National Adult Reading Test, and speed-of-processing composite score. The study examined the effect of age on fluency before and after controlling for processing speed and intelligence quotient.

Results

The young group performed better than the older group on category fluency as measured by animal category (p < .001) and on processing speed composite score (p < .001). However, the older group performed better than the young group on the National Adult Reading Test (p < .05) and on letter fluency after controlling for the decline in processing speed (p < .05). Processing speed had a significant effect on both category and letter fluency (p < .01) in older adults.

Conclusions

This study suggests that aging adversely affects some but not all cognitive domains and that age-related decline in processing speed contributes to age-related changes in fluency.

Combining movement kinematics, efficiency functions, and Brinley plots to study age-related slowing of sensorimotor processes: insights from Fitts' task

BACKGROUND

Measurement of changes in human information-processing capacities underlying slowing of sensorimotor processes is an important challenge for aging research. Methods exist to estimate the magnitude of slowing and variability coefficients, but attempts to apply them in motor tasks have been scarce. In the present experiment we combined movement kinematic analysis, efficiency functions and Brinley plot to assess age-related slowing and variability of sensorimotor processes in a discrete Fitts' aiming task.

OBJECTIVES

(1) Quantifying slowing and variability for the different sensorimotor processes involved in aiming movements, and (2) determining whether changes occurred continuously over time by comparing different age groups.

METHODS

29 participants (24-90 years) divided into four age groups were tested. Target size manipulation resulted in three levels of difficulty. Total movement time, durations of the first and secondary movement phases and related variability were analyzed. Fitts and Brinley regression functions were calculated on the basis of the different movement variables.

RESULTS

Only older participants were slower than the three younger age groups. For this group, age-difficulty effect was observed for total movement times, but analyses showed that only the secondary movement phase slowed multiplicatively. Additive and proportional increases in variability were also observed in older participants for the first and secondary movement phases, respectively. For the secondary movement phase, estimated slowing coefficients were comparable to those reported in cognitive literature. In addition, Brinley analyses showed that variability increased more than movement time in the secondary movement phase.

DISCUSSION

Combination of the different methods of analysis allowed a precise assessment of the locus of slowing and variability of sensorimotor processes in the different movement phases. Results showed that significant changes in both slowing and variability of the different processes occurred late in life. Our findings also suggest that slowing could result from age-induced increase in noise produced by the neural system. Finally, the present results raise the question of whether age-related slowing and increase in variability observed in both cognitive and sensorimotor domains share common causes in the central nervous system.

Electrophysiological evidence for aging effects on local contextual processing

We used event-related potentials to investigate how aging affects local contextual processing. Local context was defined as the occurrence of a short predictive series of visual stimuli before delivery of a target event. Stimuli were presented to either the left or right visual field and consisted of 15% targets (downward facing triangle) and 85% of equal numbers of three types of standards (triangles facing left, upwards and right). Recording blocks consisted of targets preceded by either randomized sequences of standards or by sequences including a three-standard predictive sequence signaling the occurrence of a subsequent target event. Subjects pressed a button in response to targets. Predictive local context affected target detection by reducing the duration of stimulus evaluation compared to detection of non-predictive random targets comparably for both young and older adults, as shown by a P3b latency shift. The peak of an earlier latency context positivity, which was seen only in the predicted compared to the random target condition, was prolonged in the older population compared to young adults. Finally, older subjects elicited a late sustained positivity in the predictive condition, not seen in the younger subjects. Taken together, these findings suggest that local contextual effects on target detection processes are altered with age.

Age differences in implicit interference

We assessed age differences in interference effects in priming by using fragment completion. In Experiment 1, noninterfering filler words preceded critical targets at study, and priming was age invariant. In Experiment 2, the same target items had interfering competitors at the beginning of the list, such that both the target and the competitor were legitimate solutions to a fragment. Having two responses to a cue was disruptive for older adults, but not for younger adults. Younger and older adults differ in their susceptibility to interference in implicit tasks, and interference may play a role in influencing the magnitude of age differences in priming.

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.

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.

Developmentally impaired processing speed decreases more than normally with age

Several studies show that although function may recover after brain damage the insult can nevertheless cause accelerated deterioration in old age. This has been interpreted as indicating reduced neuronal capacity to counteract age-related decline with plastic changes. Psychosocial and compensatory factors obscure the neuronal explanation. Since the speed of processing sequential temporal information is impaired in developmental dyslexia, we investigated its dependence on age (20-59 years) in psychosocially comparable groups of dyslexic and fluent readers using six tasks. Processing speed was impaired in dyslexia and decreased with age. The decrement was faster in dyslexic than normal readers in processing periodic stimuli. No exacerbation occurred in reading and other experiential factors. Our results, therefore, support the neuronal explanation.

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.

Cortical instability and the mechanism of mania: a neural network simulation and perceptual test

BACKGROUND

A previous neural network simulation suggested that manic states arise from excessive levels of noise that destabilize neural representations. The Necker cube stick figure provides a simple perceptual task that assesses stability of gestalt-type representations.

METHODS

A neural network was developed that included a simulation of the Necker cube task. Noise was added to induce maniclike jumps from one representation to another. A parallel study of Necker cube perception was conducted with 16 patients diagnosed with manic-spectrum disorder, 18 patients with schizophrenia, and 19 normal control subjects. Cognitive speed and rate of indiscriminate responses were assessed using an auditory continuous performance task.

RESULTS

During processing of the "Necker cube" stimulus, the reversal rate of the noise-destabilized "manic" network was increased by 30%. In the human subject study, the median score of Necker cube reversal rates for manic-spectrum patients was roughly twice that of normal control subjects and patients with schizophrenia. Accelerated reversal rates in the manic-spectrum group were not attributable to excessive cognitive speed or higher rates of indiscriminate responses.

CONCLUSIONS

The two studies, considered together, support the hypothesis that excessive cortical noise destabilizes neural representations in manic-spectrum patients.

Age differences and changes in midline-crossing inhibition in the lower extremities

BACKGROUND

The effects of crossing the body midline on the lower extremities of individuals 65 years of age and older was investigated.

METHODS

The subjects were 10 individuals 65-79 years of age, 10 individuals 80 years and older, and 10 individuals 20-35 years. The total testing phase consisted of 2 sets of 30 trials per leg on 2 days. The subjects performed trials that involved movements ipsilaterally, contralaterally, and directly in front of the anterior superior iliac crest of the leg being tested. Reaction time and movement time scores were recorded.

RESULTS

Individuals 65 years of age and older were found to exhibit slower reaction times to movements in a contralateral direction when compared with movements made in the ipsilateral direction whereas individuals 80 years of age and older were also found to exhibit slower reaction times to movements in a contralateral direction when compared with movements made in the midline and ipsilateral direction.

CONCLUSIONS

These findings indicate that the effects of midline-crossing inhibition on the lower extremities reemerge in individuals 65 years and older, whereas in early development this effect disappears by 8 or 9 years of age.

The exhaustive additivity displayed by nitrous oxide has implications for cognitive-energetical theory

The cognitive-energetical approach, which relies on the discrete stage model of additive factors logic, asserts that basal energetical mechanisms such as arousal act via particular information processing stages. The anaesthetic gas nitrous oxide (N(2)O) produces additivity at four of the five perceptual and central stages, but its effect on the remaining stage, feature extraction, is unknown. We investigated this stage using 12 subjects who performed a visual oddball experiment in which two levels of stimulus quality, three levels of breathing mixture (air, 25% and N(2)O, 35%) and three levels of stimulus probability were combined factorially. Reaction time (RT) and P300 were collected simultaneously. The RT results showed additivity between N(2)O, stimulus quality and probability. P300 latency also showed additivity between N(2)O and stimulus quality. Since the discrete stage model cannot easily account for the exhaustive additivity displayed by N(2)O on perceptual and central stages, we performed a continuous cascade model simulation to determine whether it is better able to account for this phenomenon. We found that exhaustive additivity could be reproduced by adding a time delay to the activation rate of the first stage, which we interpreted as evidence that N(2)O causes slowing prior to stage processing. To account for these results, we propose a two-tiered energetical model in which a lower GABAergic reticular system (influenced by N(2)O) modulates the activity of upper 'arousal-like' multidimensional ascending thalamocortical systems. The applicability of this model to drugs such as the barbiturates, the benzodiazepines and ethanol, as well as the aging process, is discussed.