A growing body of evidence supports the notion that walking is not an automatic activity. Research using dual-task paradigms suggest an associated cognitive cost and links to executive function.1–3 Dual-task approaches, which involve the pairing of a primary task with a secondary task, are frequently used to examine the attentional or cognitive requirements of walking.3,4 Attention, which is seen as one specific element of executive function,5–7 is important to the acquisition of environmental information needed to guide and proactively adapt walking. Changes in primary and/or secondary task performance, arising from simultaneous task completion, indicates that an activity has a cognitive cost and/or is attentionally demanding.8,9 Work by Wright and Kemp10 demonstrated the attentional requirements of walking with an assistive device by utilizing a dual-task task paradigm involving the measurement of changes in probe voice reaction time. Walking with and without an assistive device were the primary tasks. The secondary task, which was performed both alone as a single task and in combination with the primary walking tasks, involved responding verbally to an auditory stimulus. Differences in single and dual-task verbal response time provided support for the increased attentional requirements of walking with an assistive device.
Researchers have utilized a variety of secondary motor and cognitive tasks in combination with walking.1,3 Increasing gait variability, delayed motor reaction time, reduced capacity for communication, and altered cognitive task performance in both young and older adults have all been reported when cognitive or motor tasks are completed concurrently with walking.4,11–17 Performing a cognitive task while walking results in gait changes that are potentially destabilizing for older adults.18–20 Research also shows that walking imposes a greater cognitive burden on older adults when compared to younger adults.4,21,22 For older adults, the reported consequences of walking while concurrently performing another task are often markers for increased fall risk.18,19,23–25 Falling while walking is a common occurrence.26,27
On an annual basis, more than a third of older community-dwelling adults fall.28,29 The consequences can be life altering. After a fall, 20% to 30% of older adults experience injury, such as lacerations/contusions, fractures, or head trauma.30–32 Fall-related injuries lead to a decline in function, reduced quality of life, institutionalization, and increased mortality.31,33–36 The psychological consequences, which includes fear of falling, results in activity restrictions that further increase fall risk.37–39 The consequences of falling and the growing population of older adults in the United States highlight the need to fully explore all of the risk factors that contribute to falls, including those that may be gender specific.
Age-specific changes in gait and rates of falling are different for older men and women. Older women fall more frequently than older men and are more likely to experience injury.26,32,36,40 Gender differences in preferred gait speed, cadence, and other temporal and distance measures have been reported.41 Some of the reported gait differences that are markers for increased fall risk are also seen when cognitive or motor tasks are performed concurrently with walking.42 The underlying causes of gender-specific changes in gait may also be the same factors that increase the attentional requirements of walking.43–45 Therefore, it would be informative to have a better understanding of gender differences related to how older men and women allocate attention to walking. Gender-specific differences in the capacity to either allocate attention while walking or perform other tasks simultaneously when walking could possibly account for differences in the rate of falls among older men and women. Differences in how older men and women allocate attention to walking have not been explored in the literature. The purpose of this study was to use a dual-task voice reaction time paradigm to examine gender-specific differences in the attentional demands of walking in older adults.
Twenty-nine community-dwelling older men (mean age = 78.39 ± 6.06 years) and 33 women (mean age = 78.90 ± 6.41 years) participated in the study. On the basis of self-report, all were independent in both household and community ambulation, which was a requirement to participate in the study. Participant exclusion criteria included (1) reported active musculoskeletal pain localized to the back or lower extremity on the day of testing that limited ability to ambulate; (2) any self-reported medical history of central nervous system involvement; (3) use of any assistive or orthotic devices for ambulation; (4) inability to hear the auditory tone used for the dual-task stimulus; (5) required physical assistance to restore balance during the standing and walking trials; or (6) the rest needed between any ambulation trial exceeded 2 minutes. The study received institutional review board approval, and all participants provided informed consent prior to study entry.
Attentional allocation was examined by measuring the time required to respond verbally to a piezo-electric tone (RadioShack Model 273-054; RadioShack, Fort Worth, Texas) presented under single- and dual-task conditions. The instrumentation used to measure voice reaction time (VRT) consisted of a signal board, constructed by the principle investigator, a digital stop clock (Lafayette Instruments Model 54035; Lafayette Instrument Company, Lafayette, Indiana), a voice-activated relay switch (Lafayette Instruments Model 63040), and a wireless FM microphone system (RadioShack Model 32-1221). A button on the signal board, when pressed, simultaneously activated the auditory stimulus and the digital stop clock. The wireless 49.00 Hz FM microphone system transmitted the verbal response to the voice-activated relay switch that was attached to and stopped the digital clock. The timer provided a digital readout of VRT in milliseconds. The sensitivity of the microphone system and the voice-activated relay switch were both modified as necessary to account for differences in the volume of the participant's voice and to minimize the possibility of extraneous noise triggering the digital stop clock.
Two infrared photocell switches (Lafayette Instruments Model 63501IR) and a digital timer (Lafayette Instruments Model 54035A) were used to measure single- and dual-task gait velocity. The switches were placed parallel to the participant's path of travel and separated by a distance of 3.0 m. Walking past the switches activated and stopped the attached digital timer. The time elapsed was used to calculate gait velocity. Walking velocity from the single-task walking trials was compared with the dual-task condition to determine whether primary task performance (walking) was altered to improve secondary task performance (response to the auditory stimulus). The validity of the dual-task reaction time paradigm requires the participant to maintain primary task performance when presented with the secondary task stimulus.8,46,47 The triggering and switch activation mechanisms were hidden at all times from the participant's view to prevent priming or the anticipation of the presentation of the auditory signal from cues within the environment.
Data collection required approximately 45 minutes and occurred in a room free from noise and distractions located on the campus of Widener University. After being screened for the study's inclusion and exclusion criteria, the participants completed the following balance measures: the Functional Reach Test (FRT), the Timed Get-up and Go Test (TUG), and the Activities-specific Balance Confidence (ABC) Scale. The FRT was developed as a quick balance screen for older adults.48,49 To complete the test, the shoulder of the dominant upper extremity is flexed to the height of the acromion and the participant is instructed to reach forward, as far as possible, without taking a step. A meter stick attached to a wall at the height of the acromion measures distance reached. Developed as a performance-based measure of functional mobility and balance impairment for older individuals, the TUG requires the participant to rise from a chair, walk 3.0 m at preferred pace to a mark placed on the floor and turn around, walk back to the starting point, and return to sitting in the chair.50,51 The test is scored by measuring the amount of time required for completion. The ABC was used to examine self-perceptions of mobility confidence for walking and standing activities.52,53 Balance confidence is determined by averaging the scores on each of the items which are demarcated into 10% increments ranging from 0% to 100%. Higher scores indicate greater confidence in mobility.53
Voice reaction time was measured under 3 task conditions: sitting in a chair, standing without upper extremity support, and while walking on a level surface. Voice reaction time in sitting established baseline single-task performance and was always the first task condition completed. The participants were instructed to vocalize the letter “B,” as quickly as possible, whenever the auditory tone was presented. A total of 15 trials were performed. The first 5 trials were used to set the sensitivity of the VRT measurement system. Once ideal sensitivity was determined, the auditory stimulus was presented 10 more times by the researcher using random delays between trials.
After establishing baseline single-task VRT performance in sitting, the order of completion of the 2 remaining task conditions was randomly determined to minimize the effects of order. When measuring VRT in standing, participants assumed their preferred posture. Similar to sitting, a total of 15 trails were completed. The first 5 trials were used to re-check the function of the system to make sure the transfer to standing did not alter the microphone position and settings. Prior to the start of the trial, a reminder to vocalize the letter “B,” as quickly as possible, in response to the auditory tone was provided. Data from the remaining trials were used to calculate mean standing VRT.
When measuring VRT during walking, participants were instructed to ambulate at their usual or preferred pace along a 7.0 m path. No specific instructions were given regarding task prioritization. The infrared photocell sensors marked the middle portion of the walkway and was not only used to determine gait velocity but also provided reference points for the researcher to randomly present the auditory stimulus. The first and last 2.0 m of the walkway provided space for acceleration to preferred walking velocity and deceleration, respectively. Participants were informed that the auditory stimulus would not be presented during the first 5 walking trials. Gait data collected during those initial trials established single-task walking performance. Data generated were also used to ensure that the participants maintained primary task performance and did not elect to change the manner of walking to improve response time to the auditory stimulus that was presented in the dual-task condition. Upon completing the initial level walking trials, participants were told that the dual-task stimulus would be presented during some of the remaining 10 walking trials but were unaware that the tone would not be presented every trial. Catch trials were included in the 10 remaining trials to prevent stimulus anticipation that could potentially enhance secondary task performance.47,54 Stimulus and catch trial presentation order was randomly determined at the start of the study.
Measures of balance were examined descriptively using means and standard deviations and an independent sample t test was used to compare the groups. A 2 (gender) by 2 (single- versus dual-task walking velocity) analysis of variance (ANOVA) with repeated measures on the last factor was conducted to explore between- and within-group differences in walking velocity. This analysis was performed to ensure that the participants maintained primary walking task performance during the dual-task condition. A 2 (gender) by 3 (task condition) ANOVA with repeated measures on the last factor was implemented to examine between- and within-group differences in VRT to determine the attentional requirements of walking. Statistical significance was set at P ≤ .05 for all primary analyses and SPSS version 17 (SPSS Inc, Chicago, Illinois) was used. Post hoc differences were explored using a Bonferroni procedure to reduce the possibility of a chance finding and the creation of a type I error.
Tables 1 and 2 provide a summary of the group demographics for age, measures of balance, and walking velocity. Both groups were similar in age, and measures of balance fell within the expected range for nondisabled older adults with low fall risk.48,55–58 There was no statistically significant difference between the groups based on age (t 60 = 0.33, P = .745). In general, the means revealed that women participants scored lower than men on all balance measures (Table 1). Men took less time to complete the TUG and also scored higher on the ABC Scale indicating greater confidence in mobility. Overall, scores on the ABC Scale indicate retention of high to moderate levels of physical function typical for older adults who remain active in the community.59 However, the groups did not differ significantly on both the TUG (t 60 = 1.17, P = .245) and the ABC (t 60 = 1.25, P = .745). The only statistically significant between-group difference for balance was found for the FRT, where men participants reached significantly farther (t 60 = 2.18, P = .034).
Gender Differences in the Attentional Requirements of Walking
The descriptive statistics revealed changes in VRT that corresponded to increasing functional task complexity (Figure 1). The means indicate that sitting and standing VRT were faster than walking VRT for both groups. Voice reaction time for men and women were similar in sitting. Standing VRT was slightly faster than sitting for both groups (10 milliseconds for men versus 2.5 milliseconds for women) and men participants responded a little quicker than women (444.90 milliseconds versus 452.09 milliseconds). When walking, VRT became longer for both groups and men responded faster than women. The results from the 2 (gender) by 3 (task condition) ANOVA revealed a significant main effect for task condition (F 2,59 = 16.24, P < .001); the main effect of gender (F 1,60 = .190, P = .665) and the interaction of group with task (F 2,59 = 0.632, P = .433) were both not statistically significant. Post hoc analysis of the main effects of task revealed that there were no statistically significant differences (P = .833) between sitting (n = 62, mean = 454.68, SD = 116.89 milliseconds) and standing (n = 62, mean = 448.36, SD = 108.37 milliseconds) VRT. However, walking VRT (n = 62, mean = 524.25, SD = 131.71 milliseconds) was significantly longer than both sitting (P < .001) and standing (P < .001) VRT. The pattern of statistically significant differences in VRT for the post hoc analysis of the main effect of task indicated that the attentional requirements of walking was significantly greater than both sitting and standing. There were no statistically significant differences in VRT for any of the task conditions based on gender (Figure 1).
Single- and Dual-Task Gait Performance
Means and standard deviations for walking velocity are summarized in Table 2. Ambulation velocity was within the expected norms for nondisabled older adults.60 The means revealed that men walked slightly slower than women for both the single- and dual-task conditions. Men walked slightly faster under the dual-task condition than under the single-task condition. The opposite pattern was seen for the women participants who walked slightly slower in the dual-task condition. However, the differences seen between the single- and dual-task conditions may not be meaningful given that the differences did not exceed the minimal detectable change reported in the literature.61 The results of the 2 (gender) by 2 (single- versus dual-task walking velocity) ANOVA revealed that the main effects for gender (F 1,59 = 0.915, P = .343) and task (F 1,59 = 0.097, P = .757) were both not statistically significant; the interaction of gender with task was also not statistically significant (F 1,59 = 1.461, P = .232). The findings indicate that primary task performance, which was walking, was not altered during the dual-task condition to improve secondary task performance on the VRT task. Men and women were similar in their walking velocity.
The study results demonstrate that the attentional demands of walking in a closed environment within a laboratory setting are not different for older adult men and women who are independent in community mobility. When sitting in a chair with back support, older men and women had similar response times (Figure 1) for the baseline single-task VRT condition. The transition from sitting to standing can be assumed to provide a greater balance challenge but did not seem to increase the associated attentional demands of task performance on the basis of the observed differences in VRTs. There were no significant task and gender differences in sitting and standing VRTs. Given the participants' functional capacity based on walking velocity, measures of balance, and self-reported independence in community ambulation, the postural challenge posed by standing on a stable surface without challenge was not sufficient to increase the attentional demands of the task. However, the combinations of more challenging standing balance and cognitive tasks have been shown to increase the attentional demands of standing in older adults.62,63
When examining walking, older men, on average, had a faster VRT than older women; however, those differences did not reach the level of statistical significance. This finding indicates a similar capacity for the allocation of attention to the task of walking on a level surface for the study participants who were not disabled and had low fall risk and who reported being independent in community ambulation. Gender differences might be expected if there were significant differences seen in gait performance, balance, and mobility confidence, which could affect attentional allocation. While older men did reached significantly farther on the FRT, other measures of balance were different but not significantly better based on gender. Older men and women with a similar functional level do not differ in how much attention is required to walk on a level surface.
The results from the examination of between-task differences in VRT clearly indicate that walking had an associated cognitive cost for the study participants. When compared with sitting and standing, walking VRT was significantly longer for both older men and women (Figure 1). Thus, confirmation is provided for what has been previously reported in the literature by other authors who have used dual-task reaction time paradigms.64,65 The importance of the finding relates to potential impact of not having sufficient attentional resources to respond to other environmental stimuli that could contribute to a fall. While the current study was conducted in a laboratory setting, walking in a more open environment, such as in the community, is a more complex task that requires the acquisition of information from a variety of sources to guide ongoing motor actions.66,67 Tripping is a frequent source of falls in older adults.28,29,40,68,69 One plausible explanation is the failure to perceive an environmental feature as having the potential for causing instability or even a fall. Relative to younger adults, older adults frequently allocate greater attention to walking tasks that can lead to delays in responding to environmental features that can cause a loss of balance. Chen and colleagues70 suggest that a 50 or 100 milliseconds delay in responding to an obstacle appearing in the path of travel reduces the chance of successful negotiation. The destabilizing effects of having to complete one or more concurrent tasks while walking, such as talking or engaging in a cognitive task, when add to baseline level of attention required only to walk, may explain why tripping is a frequent cause of falls in older adults or the increased difficulty when walking in an environment containing multiple obstacles. A reduced capacity to direct and divide attention to perform multiple concurrent tasks is associated increased fall risk.3,13,71–73
There were no statistically significant differences in gait velocity when comparing men to women and between the single- and dual-task conditions. Older men in the study walked slower than older women. Gait velocity findings indicated that both groups maintained primary task performance, which was walking, when presented with the secondary dual-task stimulus. Altering walking performance to improve reaction time to the auditory stimulus can make the results difficult to interpret because of the switch in attentional focus.46,47,74 Given the single- and dual-task walking velocity findings, it is a reasonable assumption that VRT changes reflect the increased attentional demands of walking. The robustness of the finding underscores the importance the participants may have placed on walking safely. The participants could have adopted “a posture first strategy,” where attentional priority or focus is prudently shifted to walking to ensure stability.63,75
The application of the findings from this study is limited to community-dwelling older adults who are independent in ambulation. Given the expected level of function for someone residing in the community, there may not be significant differences in the attentional requirements of walking based on gender. More substantial differences based on gender may present when either examining groups of older adults with impairments and whose physiological level of function limit access to community or those who are frail or transitioning to frailty. These groups are more likely to fall while walking and physiological gender differences, such as strength, activity levels, body mass, or flexibility, may make the task of walking more difficult and therefore more attentionally demanding.76–78 Among frail older adults, increased attention during gait has been linked to increased fall risk and limitations in mobility.79–82 Recent work has also suggested a link between changes in executive function and attentional allocation for walking and falls in older adults.42,73,83
What merits additional investigation and cannot be ruled out as influencing how attention was allocated for the level walking task implemented in this study are changes in vision, altered somatosensory function, variations in physical activity levels, and possible early changes in executive function in the older adult group. These factors were not explored in the current study but can potentially influence gait performance and the level of attention that must be allocated during walking.42,73,76–78,83 While the participants were all, by self-report, independent in community ambulation, there could have been underlying mild changes in executive function that would have influenced the study outcome.
While dual-task probe reaction time paradigms have been shown to a valid indicator of attentional cost, exploring the effects of the secondary cognitive task on walking performance is also indicated as a future direction of study. A complimentary dual-task approach to what was implemented in this study involves an examination changes in walking performance arising from the concurrent and continuous performance of a cognitive or mental task while walking. The focus of this approach is on changes in walking, such as reductions in gait speed or increasing stride and stance variability, arising out of the concurrent performance of a cognitive task. This line of work has demonstrated that performing a concurrent cognitive task while walking leads to increased gait variability.11,12,84 Typical cognitive tasks include counting or spelling words backwards, and memory, or mental manipulations involving spatial areas of the brain. Older men and women may perform cognitive tasks differently, which could potentially lead to destabilizing gait alterations that are associated with falls and a different study outcome.
The study findings provide insight into age-specific attentional requirements of walking based on gender for nondisabled older adults. On the basis of the dual-task paradigm used, older men and women who are independent in community ambulation demonstrate a similar capacity to allocate attention when walking. The results of the study are consistent with previous reports in the literature indicating that walking is an attentional demanding task for older adults. Additional investigation exploring the capabilities of older adults who are more functionally limited is necessary to see how gender might influence the attentional requirements of walking.
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