Global Switch Cost as an Index for Concussion Assessment
Global Switch Cost as an Index for Concussion Assessment
Purpose: The objective of this study is to determine the stability and sensitivity of a dual-task (DT) methodology that can be used to assess the effects of concussion in athletes.
Methods: Fifty-nine healthy young adults (Mage = 20.32 ± 1.84 yr, 19 males) who volunteered to participate completed auditory switch tasks that varied in length (30, 40, and 60 items) at baseline, 1 wk later, and approximately 7 months later. During sessions 2 and 3, the participants completed one of three switch tasks while concurrently performing a modified Harvard Step Test. Global switch cost indices and percentage error were calculated for each switch task. The stability reliability of the global switch cost indices was assessed under single-task conditions, and the sensitivity of the global switch costs to interference effects was assessed under DT conditions.
Results: The stability reliability was 0.64, 0.84, and 0.83 for the 30-, 40-, and 60-item tests, respectively. ANOVA revealed a main effect for condition (single task vs DT) for both global switch costs (F(1,55) = 44.53, P < 0.0001) and percentage error (F(1,56) = 64.69, P < 0.001). The magnitude of the global switch cost interference effects was nearly identical across the three DT conditions.
Conclusions: The current concussion testing models test athletes' cognitive and physical function in isolation. The stability reliability of the global switch cost index obtained under DT conditions suggests that it may be a useful measure for clinicians. The DT paradigm presents another test methodology that may be useful for making return-to-play decisions as part of a comprehensive concussion management plan.
Decisions concerning an athlete's return to play (RTP) after a concussion are made on the basis of multiple indices. Over the past decade, neuropsychological testing has increasingly become part of the concussion assessment and in making RTP decisions. Several computer-based neuropsychological test batteries have been developed and marketed for evaluation of concussion effects. The advantage of computerized testing has been purported to be that the tests provide fine-grain analyses of basic cognitive functions such as visual scanning, information processing speed, executive function, and memory. Typically, baseline measures of athlete's performance on these test batteries are obtained before beginning a sport season and compared with test performance after a concussive event. The athlete's cognitive function may be assessed at multiple time points to track recovery, and the interpretation of these data can be used as part of the RTP decision. Recently, the merits of this approach have been questioned, particularly in terms of the sensitivity and reliability of the tests used.
The dual-task (DT) testing method has been proposed as a complementary approach to assess the effects of concussion in athletes. Researchers have shown that specific combinations of motor-control tests and cognitive tests lead to changes in performance of one or both tasks. Reduced performance observed during DT conditions is typically explained in terms of limitations of attentional resources. Theorists hypothesize that individuals' attentional resources are fixed and that concurrent performance of multiple tasks draws on limited resources to the point that reductions in performance are observed. Numerous studies have examined the challenges that can arise when individuals are asked to perform a cognitive task and a sensorimotor task simultaneously. The majority of recent studies used cognitive tests of executive function, which is thought to be particularly sensitive to the effects of concussion, and sensorimotor tests that involve balance or gait. The results obtained from research conducted to assess age-related differences in these DT studies suggest that balance and locomotion, which have traditionally been seen as reflexive, is influenced by higher CNS control systems and draws on attentional resources. Older adults, for example, who are characterized as having fewer attentional resources than younger adults, tend to use strategies in which locomotion and balance control are prioritized over cognitive test performance.
The behavioral characteristics of concussed athletes (e.g., difficulties in balance control, mental confusion, and difficulties in short-term or working memory) have lead us to consider the merits of the DT approach to evaluate recovery from brain injury and in making safe RTP decisions. However, although theories of attention have been bolstered by the findings of DT studies, several factors impede the translation of laboratory-based DT methods to assess concussed athletes. Lacking is a "gold standard" measure of DT interference that provides adequate sensitivity and reliability. The cognitive tests and motor tests used in previous studies vary widely, and none of the protocols describe measures that can be adapted and used to estimate the magnitude of DT interference caused by concussion. In addition, absent from prior research studies are data concerning the stability of an individual's cognitive test performed over the time ranges that are necessary for tracking recovery from concussion and making RTP decisions. The paucity of test–retest reliability data has also been noted for the existing neuropsychological test batteries often used to assist into RTP decisions.
As a prelude to assessing concussed individuals, we have developed a DT method that uses a single test of executive function—the switch task. Executive functions are hypothesized to reflect the operations of three component processes that, together, regulate complex, goal-oriented actions: response inhibition, working memory, and switching. The switch task requires participants to perform different tasks that alternate the response sets associated with specific stimuli. For example, in the present study, if a letter followed a number, the participant was required to make discriminations based on an alphabetic decision rule; when a number followed a letter, the discriminations were made via a numeric decision rule. The response time (RT) measured after an alternation provides a switch cost index, which is taken to reflect the changes in the attention-demanding mental processes required to abandon one response set and to reconfigure a different response set. The switch-task protocol has been used in three DT experiments performed in our laboratory designed to assess interference between balance control and cognitive test performance in nonconcussed young adults. The balance control in each of these experiments was measured via standardized instrumentation, which provided measures of changes in postural control in response to systematic variation of somatosensory input. A visual switch task was used by Broglio et al., whereas auditory switch tasks were used in studies conducted by May et al. and Resch et al. The switch tasks were introduced shortly after balance perturbation and concluded before the end of the balance period. Dual-task interference, indexed by switch-task performance, was observed in all the experiments. However, the switch tasks used in these studies differed in length, and it was unclear if the number of alternation trials might affect the sensitivity of the cognitive test and whether the within-session reliability remained consistent across multiple trials. Also unknown was the stability reliability of switch-task performance under single-task (ST) and DT conditions. The present study was designed to address these issues. Young, nonconcussed adults performed switch tasks that differed in the number of alternation trials under ST and DT conditions. In addition, the stability reliability was measured after 1 wk and approximately 7 months.
Abstract and Introduction
Abstract
Purpose: The objective of this study is to determine the stability and sensitivity of a dual-task (DT) methodology that can be used to assess the effects of concussion in athletes.
Methods: Fifty-nine healthy young adults (Mage = 20.32 ± 1.84 yr, 19 males) who volunteered to participate completed auditory switch tasks that varied in length (30, 40, and 60 items) at baseline, 1 wk later, and approximately 7 months later. During sessions 2 and 3, the participants completed one of three switch tasks while concurrently performing a modified Harvard Step Test. Global switch cost indices and percentage error were calculated for each switch task. The stability reliability of the global switch cost indices was assessed under single-task conditions, and the sensitivity of the global switch costs to interference effects was assessed under DT conditions.
Results: The stability reliability was 0.64, 0.84, and 0.83 for the 30-, 40-, and 60-item tests, respectively. ANOVA revealed a main effect for condition (single task vs DT) for both global switch costs (F(1,55) = 44.53, P < 0.0001) and percentage error (F(1,56) = 64.69, P < 0.001). The magnitude of the global switch cost interference effects was nearly identical across the three DT conditions.
Conclusions: The current concussion testing models test athletes' cognitive and physical function in isolation. The stability reliability of the global switch cost index obtained under DT conditions suggests that it may be a useful measure for clinicians. The DT paradigm presents another test methodology that may be useful for making return-to-play decisions as part of a comprehensive concussion management plan.
Introduction
Decisions concerning an athlete's return to play (RTP) after a concussion are made on the basis of multiple indices. Over the past decade, neuropsychological testing has increasingly become part of the concussion assessment and in making RTP decisions. Several computer-based neuropsychological test batteries have been developed and marketed for evaluation of concussion effects. The advantage of computerized testing has been purported to be that the tests provide fine-grain analyses of basic cognitive functions such as visual scanning, information processing speed, executive function, and memory. Typically, baseline measures of athlete's performance on these test batteries are obtained before beginning a sport season and compared with test performance after a concussive event. The athlete's cognitive function may be assessed at multiple time points to track recovery, and the interpretation of these data can be used as part of the RTP decision. Recently, the merits of this approach have been questioned, particularly in terms of the sensitivity and reliability of the tests used.
The dual-task (DT) testing method has been proposed as a complementary approach to assess the effects of concussion in athletes. Researchers have shown that specific combinations of motor-control tests and cognitive tests lead to changes in performance of one or both tasks. Reduced performance observed during DT conditions is typically explained in terms of limitations of attentional resources. Theorists hypothesize that individuals' attentional resources are fixed and that concurrent performance of multiple tasks draws on limited resources to the point that reductions in performance are observed. Numerous studies have examined the challenges that can arise when individuals are asked to perform a cognitive task and a sensorimotor task simultaneously. The majority of recent studies used cognitive tests of executive function, which is thought to be particularly sensitive to the effects of concussion, and sensorimotor tests that involve balance or gait. The results obtained from research conducted to assess age-related differences in these DT studies suggest that balance and locomotion, which have traditionally been seen as reflexive, is influenced by higher CNS control systems and draws on attentional resources. Older adults, for example, who are characterized as having fewer attentional resources than younger adults, tend to use strategies in which locomotion and balance control are prioritized over cognitive test performance.
The behavioral characteristics of concussed athletes (e.g., difficulties in balance control, mental confusion, and difficulties in short-term or working memory) have lead us to consider the merits of the DT approach to evaluate recovery from brain injury and in making safe RTP decisions. However, although theories of attention have been bolstered by the findings of DT studies, several factors impede the translation of laboratory-based DT methods to assess concussed athletes. Lacking is a "gold standard" measure of DT interference that provides adequate sensitivity and reliability. The cognitive tests and motor tests used in previous studies vary widely, and none of the protocols describe measures that can be adapted and used to estimate the magnitude of DT interference caused by concussion. In addition, absent from prior research studies are data concerning the stability of an individual's cognitive test performed over the time ranges that are necessary for tracking recovery from concussion and making RTP decisions. The paucity of test–retest reliability data has also been noted for the existing neuropsychological test batteries often used to assist into RTP decisions.
As a prelude to assessing concussed individuals, we have developed a DT method that uses a single test of executive function—the switch task. Executive functions are hypothesized to reflect the operations of three component processes that, together, regulate complex, goal-oriented actions: response inhibition, working memory, and switching. The switch task requires participants to perform different tasks that alternate the response sets associated with specific stimuli. For example, in the present study, if a letter followed a number, the participant was required to make discriminations based on an alphabetic decision rule; when a number followed a letter, the discriminations were made via a numeric decision rule. The response time (RT) measured after an alternation provides a switch cost index, which is taken to reflect the changes in the attention-demanding mental processes required to abandon one response set and to reconfigure a different response set. The switch-task protocol has been used in three DT experiments performed in our laboratory designed to assess interference between balance control and cognitive test performance in nonconcussed young adults. The balance control in each of these experiments was measured via standardized instrumentation, which provided measures of changes in postural control in response to systematic variation of somatosensory input. A visual switch task was used by Broglio et al., whereas auditory switch tasks were used in studies conducted by May et al. and Resch et al. The switch tasks were introduced shortly after balance perturbation and concluded before the end of the balance period. Dual-task interference, indexed by switch-task performance, was observed in all the experiments. However, the switch tasks used in these studies differed in length, and it was unclear if the number of alternation trials might affect the sensitivity of the cognitive test and whether the within-session reliability remained consistent across multiple trials. Also unknown was the stability reliability of switch-task performance under single-task (ST) and DT conditions. The present study was designed to address these issues. Young, nonconcussed adults performed switch tasks that differed in the number of alternation trials under ST and DT conditions. In addition, the stability reliability was measured after 1 wk and approximately 7 months.
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