Karen Z. H. Li

Walking While Memorizing: Age-Related Differences in Compensatory Behavior

This study investigated predictions of the life-span theory of selection, optimization, and compensation, focusing on different patterns of task priority during dual-task performance in younger and older adults. Cognitive (memorizing) and sensorimotor (walking a narrow track) performance were measured singly, concurrently, and when task difficulty was manipulated. Use of external aids was measured to provide another index of task priority. Before dual-task testing, participants received extensive training with each component task and external aid. Age differences in dual-task costs were greater in memory performance than in walking, suggesting that older adults prioritized walking over memory. Further, when given a choice of compensatory external aids to use, older adults optimized walking, whereas younger adults optimized memory performance. The results have broad implications for systemic theories of cognitive and sensorimotor aging, and the costs and benefits of assistive devices and environmental support for older populations.

Comparing the effects of aging and background noise on short-term memory performance

Paired associate recall was tested as a function of serial position for younger and older adults for five word pairs presented aurally in quiet and in noise. In Experiment 1, the addition of noise adversely affected recall in young adults, but only in the early serial positions. Experiments 2 and 3 suggested that the recall of older adults listening to the words in quiet was nearly equivalent to that of younger adults listening in noise. In Experiment 4, we determined the signal-to-noise ratio (S/N) such that, on average, younger and older adults were able to correctly hear the same percentage of words when words were presented one at a time in noise. In Experiment 5, younger adults were tested under this S/N. Compared with older adults from Experiment 3, younger adults in this experiment recalled more words at all serial positions. The results are interpreted as showing that encoding in secondary memory is impaired by aging and noise either as a function of degraded sensory representations, or as a function of reduced processing resources.

Visual search across the life span.

Gains and losses in visual search were studied across the life span in a representative sample of 298 individuals from 6 to 89 years of age. Participants searched for single-feature and conjunction targets of high or low eccentricity. Search was substantially slowed early and late in life, age gradients were more pronounced in conjunction than in feature search, and all age groups were uniformly affected by eccentricity manipulations. However, developmental and aging trends were distinctly asymmetrical: Childrens performance was particularly affected by the mere presence of distractors; whereas in late life, performance was particularly impaired on target-absent trials and with increasing numbers of distractors. The implications for life span theories of cognitive and attentional development and for cognitive-speed and inhibitory-control accounts are discussed.

Benefits of Cognitive Dual-Task Training on Balance Performance in Healthy Older Adults

BACKGROUND There is growing evidence of the involvement of executive control in the maintenance of balance in old age. We examined whether healthy older adults who completed five sessions of nonmotor cognitive dual-task training would show significant improvements on measures of dual-task standing balance and mobility, compared with an untrained control group. METHODS Twenty healthy older adults were assigned to either training or control groups. In the pre- and post-training sessions, all participants performed tests of cognition, balance, and mobility (single-support balance, dynamic posturography, sit-to-stand, 40-foot walk) under single- and dual-task conditions. The training group completed five sessions of cognitive dual-task training spaced at least 2 days apart. The two tasks involved making two-choice decisions to visually presented stimuli. Participants completed multiple blocks of single-task (task A or B, blockwise) and mixed (A, B, or A + B) trials in each training session. RESULTS The training group showed significant improvements in body sway during single-support balance and center of gravity alignment during double-support dynamic balance. The control group showed no appreciable improvements. CONCLUSIONS This study is the first to demonstrate training-related benefits to gross motor performance stemming from cognitive dual-task training. The results support the view that motor control in aging is influenced by executive control and have implications for theories of cognitive training and transfer.

Distractibility, circadian arousal, and aging: A boundary condition?

Two studies assessed the presence of a synchrony effect between peak circadian arousal and time of testing for both older and younger adults. Participants performed a reading aloud task that included distracting words that were either present or absent and, if present, were either thematically related or unrelated to the target text. As well, the distracting material was presented in either spatially predictable or unpredictable locations. In each experiment, older and younger adults were tested at optimal versus nonoptimal times. Both experiments showed age differences in susceptibility to distraction, replicating earlier findings (e.g., M. C. Carlson, L. Hasher, R. T. Zacks, & S. L. Connelly, 1995). Neither showed differences due to time of testing, suggesting a boundary condition for cognitive disruptions associated with circadian arousal patterns.

Selective Attention Impairments in Alzheimer's Disease: Evidence for Dissociable Components

Tasks emphasizing 3 different aspects of selective attention-inhibition, visuospatial selective attention, and decision making-were administered to subjects with mild Alzheimers disease (AD) and to healthy elderly control (HEC) subjects to determine which components of selective attention were impaired in AD subjects and whether selective attention could be dissociated into different components. The tasks were administered with easy versus hard levels of difficulty to assess proportional slowing as the key variable across tasks. The results indicated that the inhibitory and visual search tasks showed greater proportional slowing in subjects with AD than in HEC subjects, and that the task involving inhibition was significantly more affected in subjects with AD. Furthermore, there were no significant intertask correlations, and the results cannot be explained simply in terms of generalized cognitive slowing. These results provide evidence that inhibition is the most strikingly affected aspect of selective attention that is observed to be impaired in early stages of AD.

An Ecological Approach to Studying Aging and Dual-Task Performance.

An aspect of executive functioning observed to decline with normative and nonnormative aging is the control of attention when performing concurrent tasks. Previous research directed at localizing the underlying processes that might lead to such decline (e.g., reduced attentional capacity, attentional flexibility), has mostly used artificial laboratory tasks tapping into novel and unpracticed skills. Our approach emphasizes the ecological relevance of concurrent tasks for individuals of different age groups. In this context we highlight the interacting effects of specific losses in cognitive ability on the one hand, and compensatory resource allocation on the other. This perspective is informed by the Selection, Optimization, and Compensation (SOC) model of adaptive development advanced by Baltes and Baltes (1990), in which adaptation to losses can involve compensatory behaviors or a revision of goal or task priorities. After reviewing the basic literature on aging and cognitive dual-task performance, we discuss the case of dual-task cognitive and sensorimotor performance. There, studies show that healthy older adults selectively prioritize sensorimotor performance (walking, balance) over cognitive performance (memory encoding, response selection). This pattern appears to generalize to special populations of less cognitively intact older adults. Compensatory behavior focusing on the prioritized task provides further evidence of qualitatively different approaches to dual-task performance in older adults. The data reviewed prompt a reconsideration of our definitions of successful dual-task performance, and more generally, of intellectual status (intelligence) in old age. Aging and dual-task performance 3 “... cognitive aging researchers can accept the reality of declining cognitive powers stemming from the reduced efficiency of the brain but at the same time look for means by which older adults can best hold the negative effects of aging at bay and optimize the mental capacities they possess.” Salthouse & Craik (2002, p. 701) A pervasive challenge of modern adult life is to satisfy numerous demands within a constrained period of time. The simultaneous performance of two or more tasks such as driving and conversing (e.g., Strayer & Johnson, 2000), walking and talking (Kemper, Herman, & Lian, 2003), or listening while note-taking (Tun & Wingfield, 1995), constitutes a cognitive dual-task situation in which attention must be divided. Questionnaire data indicate that older adults rate the difficulty of everyday divided attention activities higher than do younger adults, whereas younger adults report a higher frequency of engaging in dual-task situations compared to older adults (Tun & Wingfield, 1995). The majority of age-comparative studies of divided attention performance concur with the subjective report data (for reviews, see Hartley, 1992; Kramer & Larish, 1996; McDowd, Vercruyssen, & Birren, 1991; McDowd & Shaw, 2000). The importance of dual-task functioning for independent living in old age, coupled with the general trend of age-related declines in such performance, has prompted a steady output of empirical work on this topic since the early 1960s (e.g., Broadbent & Heron, 1962). As with many other areas of cognitive aging research (Craik & Salthouse, 2000), substantial efforts have been devoted to understanding how and why age-related loss in dual-task performance is observed, but less work has been done to understand how such age deficits can be ameliorated (but see Kramer, Larish, & Strayer, 1995). Further, Aging and dual-task performance 4 little is known about the development of cognitive adaptations that may occur in midlife and beyond, in response to normative cognitive declines. Our approach to cognitive aging research (loss-plus-compensation) acknowledges both the reduction of efficiency and the compensatory means, as alluded to in our opening quotation. In this context we highlight the interacting effects of specific losses in cognitive ability on the one hand, and compensatory resource allocation on the other. This perspective is informed by the Selection, Optimization, and Compensation (SOC) model of adaptive development advanced by Baltes and Baltes (1990), in which adaptation to losses can involve compensatory behaviors or a revision of goal or task priorities. In this chapter, we first review central findings and theoretical models of aging and dual-task performance. We then discuss the importance of considering a more holistic or ecological approach to studying dual-task performance, illustrating with recent findings from the domain of concurrent cognitive and sensorimotor dual-task performance. Finally, we propose ways in which our loss-plus-compensation perspective might be applicable to models of individual and pathological differences in cognitive processing. There, we argue that taking a developmental approach to studying cognitive deficits associated with clinical conditions would help clarify debates concerning causality vis à vis symptomatology and cognitive status. What processing limitations are known? With few exceptions, investigations of aging and dual-task performance have been cross-sectional in design, with standard convenience samples of young adults in their 2 and 3 decades, and older adults in their 6 and 7 decades. The standard method of investigation involves measuring performance on each single task condition (Task A, Task B) and on the dual-task condition (Task A&B) to determine the degree to which Aging and dual-task performance 5 Task A and B performance decreases under dual-task conditions compared to their respective single-task baseline levels (dual-task costs; DTCs). Figure 1 illustrates the derivation of absolute and proportional dual-task costs. ----Insert Figure 1 about here ----Early empirical observations. Broadbent and Heron (1962) tested concurrent visual search of specified digits and auditory detection of repeated letters, finding age-related deficits in the auditory task but age-equivalence in the visual task. Talland (1962) reported a similar pattern using concurrent motor tasks (bead manipulation and rapid button pressing) such that older adults showed DTCs only on the second task, relative to young adults. Two subsequent studies juxtaposed simultaneous auditory and visual presentations of digits (McGhie, Chapman, & Lawson, 1965) or alternating digits and letters (Broadbent & Gregory, 1965). Both studies reported substantial age-related decreases in dual-task performance in both tasks. As noted by McDowd et al. (1991), older adults in these early studies appear to show some evidence of focusing on one task at the expense of the other. By modern standards, these studies lack the control of temporal parameters associated with some more recent work, allowing more opportunities for older adults to sequentialize or switch between tasks rather than concurrently perform both tasks. Processing resource explanations. Subsequent dual-task research focused more on specifying the processes responsible for age-related differences in dual-task performance. Wright’s (1981) investigation of concurrent digit span and verbal reasoning showed increasing age effects as a function of task complexity, which she attributed to decreasing general processing resources. Aging and dual-task performance 6 A more specific resource reduction approach has been taken by Salthouse and colleagues, who have argued that reductions in general processing speed result in lower dual-task performance because of the added processing stages required to carry out two tasks instead of one. Somberg and Salthouse (1982) prompted several important considerations by arguing that previous studies had not taken into account the age differences inherent under single-task conditions. In one experiment involving simultaneous visual target detection, they first calibrated single-task difficulty to ensure equivalent accuracy levels across individuals and age groups (Expt. 1). In a second experiment involving simultaneous tone detection and sequential digit keying, they computed relative, or proportional DTCs by computing the absolute difference in single versus dual-task performance, then dividing by single-task performance. Using these two methods of controlling for variations in single-task performance, Somberg and Salthouse reported age-invariance in DTCs. A subsequent study (Salthouse, Rogan, & Prill, 1984) produced an important caveat: Using more complex tasks than before, Salthouse et al. (1984) reported greater DTCs in older than younger participants, even when task difficulty was individually calibrated. As well, with these more controlled stimuli, Salthouse and colleagues demonstrated that young and older adults were similar in their ability to shift their attentional emphasis across tasks when instructed to by using proportions or ratios as goals (e.g., 25:75, 50:50, 75:25; see also Crossley & Hiscock, 1992). Salthouse’s early dual-task findings provoked a more direct examination of the effects of task complexity (McDowd & Craik, 1988). Using auditory 2-choice reaction time (RT) and visual 4-choice RT tasks, McDowd and Craik manipulated the depth of processing (perceptual or semantic) required to make the decisions in each task (Expt. Aging and dual-task performance 7 1). These increases in complexity had interacting effects with age when calculated as absolute, but not relative, DTCs (see also Baron & Mattila, 1989). In a second experiment using different visual and auditory tasks, they found that manipulations of difficulty had comparable effects on young and older adults. Taken together, these experiments yield mixed support for the complexity hypothesis, although they demonstrate a clear age-related decline in dual-task performance. Lorsbach and Simpson (1988) also introduced a manipulation of complexity by varying depth of processing. Participants made same-different judgments to letter pairs o

Predicting memory completeness and accuracy: Emotion and exposure in repeated autobiographical recall

Using a repeated testing procedure modified for an autobiographical event, individuals provided narrative accounts of their memory for the announcement of the verdict in a widely publicized murder trial. The goal of the study was to determine whether different factors would predict initial versus final recall performance. Ratings of negative emotional reaction during the event predicted initial amount recalled, and frequency of exposure to the event predicted final amount recalled. Judged completeness of recall and phenomenological ratings of the vividness of the memory were also related to final amount recalled. The measured variables were unrelated to recall accuracy. Examining memory over repeated recall attempts offers a fruitful way to examine processes in autobiographical memory. Copyright

Attentional requirements of walking according to the gait phase and onset of auditory stimuli

A dual-task paradigm was used to examine the influence of an attention demanding cognitive task on each phase of gait. Twenty-three participants (aged 18-27) walked on a treadmill at a 20% increase of their self-selected speed, either alone or while performing a cognitive task. Muscle activity was measured with electromyography (iEMG) for eight muscles of the dominant leg. The cognitive task consisted of subtracting one (EASY) or seven (HARD) from orally presented numbers. Reaction time (RT) and accuracy were recorded. iEMG events were selected according to stimulus onset (0-150 ms, 150-300 ms and 300-450 ms) prior to phases of gait (double-leg stance, single-leg stance and swing). There was a decrease in iEMG amplitude of fibularis longus (p=.013) and a trend in the same direction for vastus lateralis (p=.065) while walking and performing the cognitive task. When stimulus onset was considered, iEMG of medial gastrocnemius (p=.021) and lateral gastrocnemius (p=.004) were reduced during single-leg stance, when stimuli occurred between 300 and 450 ms prior to this phase. Cognitive performance was affected by task difficulty (RT, accuracy) and by dual-task load (RT). Dual-task costs were observed in both the motor and the cognitive tasks, suggesting that walking requires attention. There was a specific moment (300 ms after stimulus onset) during single-leg stance when dual-task costs were most pronounced, corroborating supraspinal involvement in the control of normal walking. Time-based approaches should be considered when analyzing attentional demands of a dynamic task such as gait.

Dual-Task Performance Reveals Increased Involvement of Executive Control in Fine Motor Sequencing in Healthy Aging

The purpose of the current study was to examine the role of executive control in fine motor sequencing using a motor-cognitive dual-task paradigm. Younger and older adults performed a sequential tapping task separately and concurrently with a semantic judgment task (Experiment 1) and a mental arithmetic task (Experiment 2). Experiment 1 established that under low cognitive load, older adults were slower and less accurate in sequential tapping than younger adults. Load was manipulated in Experiment 2, and across mental arithmetic difficulty levels, older adults were less accurate in sequential tapping when performing mental arithmetic than younger adults. At the highest difficulty level, both groups suffered performance costs. In line with gross motor research, these findings suggest a role for executive functions in fine motor performance in old age.