Joan McDowd

11 – Inhibitory processes in cognition and aging

Publisher Summary This chapter reviews a number of studies that have implications for the inhibitory decline hypothesis. Available data suggest that at several levels of information processing in the nervous system, older adults show evidence of a deficit in inhibitory function. Although the evidence is not unequivocal, the following generalization can be made: older adults are less selective information processors than are younger adults. In a variety of situations ranging from elicitation of a brain-stem reflex to the execution of higher language functions, in which both relevant and irrelevant information are available for processing, older adults are more likely to process both classes of information, rather than restricting processing to the most relevant information. The theoretical notion of an inhibitory deficit has been applied with some success in accounting for empirical observations, both in direct tests with models that specifically invoke inhibitory function and less direct tests with tasks for which inhibitory processes are assumed to be relevant.

Understanding verbal fluency in healthy aging, Alzheimer’s disease, and Parkinson’s disease

OBJECTIVE Verbal fluency measures are frequently part of batteries designed to assess executive function (EF), but are also used to assess semantic processing ability or word knowledge. The goal of the present study was to identify the cognitive components underlying fluency performance. METHOD Healthy young and older adults, adults with Parkinsons disease, and adults with Alzheimers disease performed letter, category, and action fluency tests. Performance was assessed in terms of number of items generated, clustering, and the time course of output. A series of neuropsychological assessments were also administered to index verbal ability, working memory, EF, and processing speed as correlates of fluency performance. RESULTS Findings indicated that regardless of the particular performance measure, young adults performed the best and adults with Alzheimers disease performed most poorly, with healthy older adults and adults with Parkinsons disease performing at intermediate levels. The exception was the action fluency task, where adults with Parkinsons disease performed most poorly. The time course of fluency performance was characterized in terms of slope and intercept parameters and related to neuropsychological constructs. Speed of processing was found to be the best predictor of performance, rather than the efficiency of EF or semantic knowledge. CONCLUSIONS Together, these findings demonstrate that the pattern of fluency performance looks generally the same regardless of how performance is measured. In addition, the primary role of processing speed in performance suggests that the use of fluency tasks as measures of EF or verbal ability warrants reexamination.

The Role of Visual Attention in Predicting Driving Impairment in Older Adults

This study evaluated the role of visual attention (as measured by the DriverScan change detection task and the Useful Field of View Test [UFOV]) in the prediction of driving impairment in 155 adults between the ages of 63 and 87. In contrast to previous research, participants were not oversampled for visual impairment or history of automobile accidents. Although a history of automobile accidents within the past 3 years could not be predicted using any variable, driving performance in a low-fidelity simulator could be significantly predicted by performance in the change detection task and by the divided and selection attention subtests of the UFOV in structural equation models. The sensitivity and specificity of each measure in identifying at-risk drivers were also evaluated with receiver operating characteristic curves.

Inhibition and aging: similarities between younger and older adults as revealed by the processing of unattended auditory information.

The ability to selectively attend to an auditory stimulus appears to decline with age and may result from losses in the ability to inhibit the processing of irrelevant stimuli (i.e., the inhibitory deficit hypothesis; L. Hasher & R. T. Zacks, 1988). It is also possible that declines in the ability to selectively attend are a result of age-related hearing losses. Three experiments examined whether older and younger adults differed in their ability to inhibit the processing of distracting stimuli when the listening situation was adjusted to correct for individual differences in hearing. In all 3 experiments, younger and older adults were equally affected by irrelevant stimuli, unattended stimuli, or both. The implications for auditory attention research and for possible differences between auditory and visual processing are discussed.

An overview of attention: behavior and brain.

The purpose of this review is to provide an overview of attention as it has been studied in the field of psychology. Broad themes in terms of theory are highlighted, focusing on concepts of attentional resources and attentional effort. In addition, a functional approach to understanding attention is presented, describing attention in terms of the task contexts in which it may operate: selective attention, divided attention, attention switching, and sustained attention. Factors promoting and impairing good task performance in each of these contexts are introduced. Posners attentional network and Mesulams attentional matrix are also briefly reviewed in support of the point that attentional functions appear to be distributed throughout the human brain. Topics covered provide a foundation for understanding attention and its role in everyday behavior, as well as a rubric for thinking about and understanding attentional behavior that would be useful in practice.

Revealing Language Deficits Following Stroke: The Cost of Doing Two Things at Once

ABSTRACT The costs of doing two things were assessed for a group of healthy older adults and older adults who were tested at least 6 months after a stroke. A baseline language sample was compared to language samples collected while the participants were performing concurrent motor tasks or selective ignoring tasks. Whereas the healthy older adults showed few costs due to the concurrent task demands, the language samples from the stroke survivors were disrupted by the demands of doing two things at once. The dual task measures reveal long-lasting effects of strokes that were not evident when stroke survivors were assessed using standard clinical tools.

Simulator Driving Performance Predicts Accident Reports Five Years Later

L. Hoffman, J. M. McDowd, P. Atchley, and R. A. Dubinsky (2005) reported that visual and attentional impairment (measured by the Useful Field of View test and DriverScan) and performance in a low-fidelity driving simulator did not predict self-reported accidents in the previous 3 years. The present study applied these data to predict accidents occurring within a subsequent 5-year period (N = 114 older adults, 75% retention rate). Multivariate path models revealed that accidents in which the driver was at least partially at fault were significantly more likely in persons who had shown impaired simulator performance. These results suggest that even low-fidelity driving simulators may be useful in predicting real-world outcomes.

The association between verbal memory, processing speed, negative symptoms and functional capacity in schizophrenia

The aim of this paper is to explore the links among verbal memory, processing speed, negative symptoms, and functional capacity, using structural equation modeling techniques. Model A is a multiple regression model with cognitive and symptom variables as predictors and functional capacity as the latent outcome variable. Model B consists of three two mediator models that assess the ability of each variable to mediate the effect of the other variable on outcome conditional on the inclusion of the other mediator in the model. Ninety-eight community-dwelling patients with schizophrenia (mean age=35.8years, S.D.=10.1) participated in the study. Results indicate that verbal memory, processing speed and negative symptoms significantly contributed to functional status. Verbal memory was at least partially mediated by processing speed in its effect on outcome, while the impact of processing speed on outcome was mediated by both verbal memory and negative symptoms. The influence of negative symptoms on functional capacity was partially mediated by processing speed. These findings enrich our understanding of the direct and indirect effects of these three interrelated variables and provide a basis for the development of intervention strategies.

Balance and gait of adults with very mild Alzheimer disease.

Background and Purpose:Studies have shown that adults with Alzheimer disease (AD) have gait and balance deficits; however, the focus has been on those with mild to severe disease. The purpose of this study was to determine whether balance and gait deficits are present in those with very mild AD. Methods:Thirteen adults (72.9 ± 4.7 years old) with very mild AD and 13 age-matched (72.6 ± 4.6 years old) and sex-matched (10 males and 3 females) participants in a control group without AD performed balance and gait tests. All participants were living in the community and independent in community ambulation. Results:Participants with very mild AD had shorter times in tandem stance with eyes open (P < 0.001) and with eyes closed (P = 0.007) compared with participants in the control group. Those with AD also took longer to complete the Timed “Up & Go” Test (P < 0.001). Gait deficits were found for those with AD as demonstrated by slower velocities in the 10-m walk at a comfortable pace (P = 0.029) and on an instrumented walkway (P < 0.001). Stance times were longer for those with AD (P < 0.001) and step length was shorter (P = 0.001). There were no group differences in the 10-m walk at a fast pace. The gait velocity of participants in the control group was faster on the instrumented walkway than in the 10-m walk at a comfortable pace (P = 0.031). In contrast, the gait velocity of those with AD was significantly slower on the instrumented walkway than in the 10-m walk at a comfortable pace (P = 0.024). Discussion:Balance and gait deficits may be present in those in the very early stages of AD. Novel surfaces may affect gait speed in those with very mild AD. Identifying mobility deficits early in the progression of AD may provide an opportunity for early physical therapy intervention, thus promoting continued functional independence. Conclusions:Adults in the very early stages of AD may show signs of balance and gait deficits. Recognition of these problems early with subsequent physical therapy may slow the progression of further balance and gait dysfunction.

Processing Speed Mediates Gender Differences in Memory in Schizophrenia

The primary aim of this study was to examine whether processing speed mediates the association between gender and episodic memory in schizophrenia. Participants were 51 female and 51 male outpatients comparable on demographic, clinical, and cognitive variables. Memory tests included both verbal and visual measures. Both groups scored below the normative mean of the memory and processing speed tests, except that females performed slightly above the mean on face recognition. Females outperformed males on verbal memory, visual recognition, and processing speed. Mediation regression analyses showed processing speed mediated immediate and delayed recall for both verbal and visual memory measures. Thus processing speed appears to be a critical variable for understanding cognitive deficits in schizophrenia and may be an important target for cognitive rehabilitation.