Dual-task costs while walking increase in old age for some, but not for other tasks: an experimental study of healthy young and elderly persons
© Bock; licensee BioMed Central Ltd. 2008
Received: 11 February 2008
Accepted: 13 November 2008
Published: 13 November 2008
It has been suggested in the past that the ability to walk while concurrently engaging in a second task deteriorates in old age, and that this deficit is related to the high incidence of falls in the elderly. However, previous studies provided inconsistent findings about the existence of such an age-related dual-task deficit (ARD). In an effort to explain this inconsistency, we explored whether ARD while walking emerges for some, but not for other types of task.
Healthy young and elderly subjects were tested under five different combinations of a walking and a non-walking task. The results were analysed jointly with those of a previous study from our lab, such that a total of 13 task combinations were evaluated. For each task combination and subject, we calculated the mean dual-task costs across both constituent tasks, and quantified ARD as the difference between those costs in elderly and in young subjects.
An analysis of covariance yielded no significant effects of obstacle presence and overall task difficulty on ARD, but a highly significant effect of visual demand: non-walking tasks which required ongoing visual observation led to ARD of more than 8%, while those without such requirements led to near-zero ARD. We therefore concluded that the visual demand of the non-walking task is critical for the emergence of ARD while walking.
Combinations of walking and concurrent visual observation, which are common in everyday life, may contribute towards disturbed gait and falls during daily activities in old age. Prevention and rehabilitation programs for seniors should therefore include training of such combinations.
Human gait deteriorates in old age. Walking speed and the stability of the walking pattern decrease [1–3], and the incidence of falls increases dramatically: about 25% of the 70 year olds, 35% of the 75 year olds, and 50% of the over 80 year olds fall at least once per year [4–6]. Many of these falls don't result in physical injury, but they often have negative psychosocial consequences such as fear of falling, self-imposed inactivity, dependence on others , and ultimately, admittance into nursing homes . To counteract this downward spiral, it is important to understand the reasons why locomotion is degraded in the elderly and, based on this understanding, to develop efficient prevention and rehabilitation programs.
Previous studies proposed various explanations for gait impairments in old age, such as reduced sensory functions, muscle weakness, and slowdown of psychomotor processing [reviews in [7, 9, 10]], as well as a reduced ability to perform two tasks concurrently [11, 12]. Our present work focuses on the latter explanation. According to this view, elderly persons are at a particular risk of falling when they move through their home while talking to a friend on the phone, walk down a street while mentally rehearsing the shopping list, cross a roadway while watching for traffic, etc. Indeed, a number of studies provided experimental evidence that seniors have more problems than younger persons to perform two tasks concurrently [13–16]. This age-related dual-task deficit (ARD) has been attributed to the shrinkage of prefrontal brain areas in old age [17–19], since those areas are strongly related to executive functions – such as the management of multiple-tasks [17, 20].
Most previous studies documented ARD using tasks which required manual and/or verbal responses; their findings are therefore not necessarily generalizable to locomotion. Other authors included a task which required a postural response, such as maintenance of steady stance [21–23], or recovery of stance after a perturbation [24, 25]; those authors observed ARD as well. Yet other work included walking as a task, but unfortunately, the resultant data are inconclusive. Some of the latter studies compared single- and dual-task performance on only one of the two concurrent tasks, and thus confounded ARD with task priority: a larger dual-task decrement of seniors on the registered task may not reflect ARD, but rather seniors' higher priority for the non-registered task . Other authors avoided this design flaw, but yielded discrepant results: some observed no ARD while walking [27, 28], while others reported substantial ARD while walking [29, 30]. This discrepancy is probably not explainable by between-study differences of task difficulty, since ARD is un related to the difficulty of walking and non-walking tasks [13, 29, 30]. The emergence of ARD while walking therefore seems to depend on some specific task characteristics, present only in a part of the above studies.
In search for those characteristics, our group has recently compared eight different combinations of a walking and a non-walking task , and found ARD for only one of them. This combination differed from the other ones in three respects: subjects had to walk on a treadmill rather than on solid ground, they had to avoid obstacles while walking, and had to engage in ongoing visual observation of the non-walking task. It remained open in the above study which of these differences was responsible for the emergence of ARD, and the present work was therefore designed to find out.
Eighteen younger (24.3 ± 3.5 years of age, 9 female and 9 male) and fifteen older subjects (67.2 ± 3.6 years of age, 7 female and 8 male) participated in Exp. A. Sixteen younger (22,4 ± 1.6 years of age, 6 female and 10 male) and sixteen older subjects (66.1 ± 3.7 years of age, 6 female and 10 male) participated in Exp. B. All elderly subjects lived independently in the community, and exhibited no signs of cognitive or sensorimotor deficits except corrected vision and hearing. No subject had been involved in sensorimotor research before. All subjects signed an informed consent statement before participating in this study, which was pre-approved by the author's Ethics committee.
Experiment A was designed to find out whether the use of a treadmill was essential for the emergence of ARD in our previous study. Furthermore, we wanted to find out whether ongoing visual observation but not visual memory was crucial. Subjects therefore walked on solid ground while avoiding obstacles, engaged in a visual checking task, and/or kept a visual scene in memory. The walking and each non-walking task were administered separately as well as concurrently.
For task walk o , an obstacle parcours was laid out in a 2.2 m wide hallway. Paper sheets of 60 cm width and 21 cm length were distributed along the floor at center-to-center distances of 1.8*λ, 3.5* λ, 5.5* λ, 3.5* λ, 1.5* λ, 5.5* λ, and 1.5* λ, where λ denotes the mean step length of a given subject, as determined prior to the experiment. We found in preliminary tests that this obstacle layout is complex enough to disturb the gait rhythm, but simple enough to be negotiated by elderly persons without help. Subjects started to walk two steps in front of the first obstacle, and finished one step behind the last. They walked at their preferred speed, and all succeeded in not touching the obstacles. We quantified their performance as mean walking speed from the last footfall before the second obstacle until the first footfall after the last obstacle.
In task check gw , subjects held a clipboard in their left, and a pen in their right hand. A paper sheet on the clipboard displayed pairs of boxes, arranged in three columns of 25 rows. One box of each pair was grey and the other white, and their order (grey-white versus white-grey) varied randomly between pairs. A new paper sheet with a different order of pairs was used for each task repetition. Subjects were instructed to scan the paper from top to bottom, column by column, and to check off the grey box of the first pair, the while box of the second, the grey box of the third, the white box on the fourth, etc. We quantified their performance as the number of boxes checked correctly within 20 s of quiet stance (single-task condition), or during negotiation of the obstacle parcours (dual-task condition).
In task memo, subjects inspected for 20 s a drawing which showed a familiar scene, such as children at play. Afterwards, they stood still for 20 s (single-task condition) or negotiated the obstacle parcours (dual-task condition), and were then asked ten questions about the drawing such as "how many toy trucks did you see?". Their performance was scored as number of correct responses. A new drawing was used for each task repetition.
Each subject participated in the single-task conditions walk o , check gw , and memo, and in the dual-task conditions walk o +check gw , and walk o +memo. Each condition was repeated three times, and the average score across repetitions was used for further analyses. The order of conditions varied randomly between subjects. The experiment took about 30 minutes, including instructions and other preliminary activities.
Experiment B was designed to find out whether the emergence of ARD depended on the use of obstacles in walk o , and/or on rule switching in check gw . We therefore administered the additional tasks walk, where subjects walked down an obstacle-free hallway at preferred speed for the same distance as in Exp. A, and check g , where subjects checked off just the grey boxes in all grey-and-white pairs. Performance was quantified as the mean walking speed from the second to the second-to-last step, and as the number of boxes checked correctly within 20 s. Each subject participated in two repetitions of walk, check g , walk o , check gw , walk+check g , walk+check gw , walk o +check g , and walk o +check gw , with the order of conditions varying randomly between subjects. The experiment took about 45 minutes, including instructions and other preliminary activities.
To quantify subjects' ability for executing two tasks concurrently, we calculated for each subject and task the dual-task costs DTC according to the customary formula 
DTC [%] = 100 * (single-task score - dual-task score)/single-task score
Dual-task costs of the constituent tasks in Exp. A and B.
walko + memo
-1.21 ± 5.71
1.22 ± 6.20
3.84 ± 12.95
6.78 ± 15.91
22.46 ± 8.58
28.64 ± 11.11
28.86 ± 11.67
39.44 ± 20.71
walk + check/g
11.20 ± 6.37
13.84 ± 7.87
0.44 ± 12.00
14.53 ± 17.31
walk + checkgw
16.02 ± 8.11
16.96 ± 10.61
1.34 ± 17.25
10.61 ± 29.00
walko + check/g
16.35 ± 7.19
18.34 ± 9.15
28.07 ± 12.82
44.81 ± 10.68
walko + checkgw
23.83 ± 8.32
26.85 ± 13.80
28.77 ± 16.36
39.36 ± 24.11
Subjects' performance in Exp. B is illustrated in the right part of Fig. 1. Again, older subjects performed generally less well than younger ones. Walking speed was comparable in walk and walk o , and decreased somewhat when a second task was added. Checking performance was better in check g than in check gw , decreased slightly when walk was added, and more distinctly when walk o was added. In accordance with these observations, two-way ANOVAs yielded significant effects of Age on walking speed (F(1,30) = 5.83; p < 0.05), performance in check g (F(1,30) = 25.36; p < 0.001), and in check gw (F(1,30) = 45.22; p < 0.001). We also found significant effects of Condition on walking speed (F(5,150) = 70.93; p < 0.001), performance in check g (F(2,60) = 106,80; p < 0.001), and in check gw (F(2,60) = 37.21; p < 0.001). All Age*Condition interactions were again non-significant. The corresponding DTC scores are summarized in the bottom part of Tab. 1. They are substantial, except when younger subjects performed one of the checking tasks in combination with obstacle-free walking. Again, elderly subjects had larger DTC than younger ones, but unlike in Exp. A, the group difference now became significant for two task combinations.
Summary of experimental tasks used in our previous study.
walk at preferred speed down a 2.2 m wide hallway, or along a 0.8 m wide circular path
walk at preferred speed along a 0.2 m wide circle
walk at maximum speed along a 0.2 m wide circle
walk on a treadmill (elderly 0.8, younger 1.2 m/s), while obstacles appear at unknown intervals
percent of obstacles negotiated without contact
spell a word of 18–21 letters
number of correctly spelled letters per 20 s
hear names of 10 geometrical shapes while walking, and repeat them afterwards
number of correctly repeated shapes
close nine different buttons on a jacket, open them, close them again, etc.
number of completed button actions per 120 s
press knob when a dot appearing in a random-dot pattern forms a square with three pre-existing dots
percent and RT of hits, percent of correct rejections
Mean DTC for the five rightmost task combinations in Fig. 2 were generally higher in elderly than in younger subjects. This age difference was significant in t-tests for walk + check g (t = 2.92, p < 0.01), walk o +check g (t = 3.14, p < 0.01), and walk o +check gw (t = 2.67, p < 0.01), but not walk o +memo (t = 0.98, p > 0.05) and walk+check gw (t = 1.07, p > 0.05). Not surprisingly, this pattern of findings on mean DTC is quite comparable to that on task-specific DTC shown in Tab. 2. The only exception is walk o +check gw , where the age effect was significant for mean but not for task-specific DTC; this is so because data from two experiments were merged to calculate mean DTC, which increased the sample size, and thus also increased the power of statistical testing.
where is the average across all younger subjects in task combination k. The resultant ARD scores were submitted to an analysis of covariance, with the between-factors Obstacles (yes/no) and ongoing Visual Observation (yes/no). The following tasks were deemed to require ongoing visual observation: detect, check g , and check gw . To guard against possible effects of overall task difficulty, we included as a covariate. Since the age of elderly subjects differed between task combinations (mean age ranged from 65,0 to 70,7 years), we also included each senior's actual age as a covariate.
The analysis yielded a significant effect only for the factor Visual Observation (F(1,204) = 13.45; p < 0.001), not for Obstacles (F(1,204) = 2.65; p > 0.05), the interaction term (F(1,204) = 0.19; p > 0.05), the covariate Difficulty (F(1,204) = 2.89; p > 0.05), nor the covariate Age (F(1,204) = 0.87; p > 0.05). On the average, task combinations with low visual-observation requirements in the non-walking task had a mean ARD of -0.76%, while those with high visual-observation requirements had a mean ARD of 8.53%.
The purpose of the present study was to compare the dual-tasking ability of young and elderly subjects under different combinations of a walking and a non-walking task, in order to determine which task characteristics favor the emergence of age-related dual-task deficits (ARD). Based on our previous work , we postulated that ARD may depend critically on the use of a treadmill for walking, the presence of obstacles in the walking path, and/or the need for ongoing visual observation in the non-walking task (see Introduction).
Our data from Exp. A and B clearly show that a treadmill is not critical, since ARD were significant in three out of five task combinations even though subjects walked on solid ground. The data from both experiments further suggest that the presence of obstacles is not critical either: as shown in Fig. 2, dual-task costs increased in the presence of obstacles by a comparable amount in both age groups, and the difference between older and younger subjects therefore remained virtually unchanged (cf. walk o and walk). This observation is supported by a statistical analysis of all 13 task combinations from our present and previous study , which yielded no significant effect of the factor Obstacles on ARD. The same analysis also yielded no significant effect of the covariate Task Difficulty. Our findings therefore confirm previous reports, according to which ARD is not consistently related to the complexity of walking and non-walking tasks [13, 29, 30].
The above analysis yielded a significant effect only for the factor Visual Observation: non-walking tasks which required ongoing visual observation led to ARD of more than 8%, while those without such requirements led to near-zero ARD. Our data therefore suggest that visual demand of the non-walking task is critical for the emergence of ARD while walking. This conclusion could explain the conflicting results of previous authors. Some earlier studies combined walking with a complex visual-imagery task; mean dual-task costs in those studies were substantially higher in elderly than in young subjects [29, 30]. Other work combined walking with active listening, or with simple reactions to clearly perceptible acoustic or visual signals; in that case, mean dual-task costs were comparable in healthy seniors and in young subjects [27, 28, 34]. Thus, non-walking tasks with high, but not those with lower demand for visual processing produced ARD, in accordance with our present conclusion. Additional, indirect support for our conclusion is provided by experiments which combined a postural rather than locomotor task with five different non-postural tasks: there, ARD was limited to non-postural tasks with high visual requirements . Our conclusion is also in agreement with the finding that in elderly subjects, body stability is related to visuospatial but not to other cognitive demands [35–37]
To understand why visual demand of the non-walking task is crucial for the emergence of ARD while walking, it should be noted that locomotion is visually demanding as well, since body stability and heading are constantly adjusted with the help of optic flow  and visual position cues . The observed deficits could therefore reflect a general problem of seniors to process two sources of visual information at the same time. Indeed, available literature documents several potential reasons for the existence of such a problem. First, old age is characterized by an increase of saccadic latency  and a decrease of the useful field of view , which could impair seniors' ability to rapidly shift their gaze back and forth between two concurrent tasks. Second, walking becomes increasingly dependent on vision with advancing age , possibly due to a reduced proprioceptive and vestibular sensitivity [review in [43, 44]]; this could increase the competition between walking and another visually demanding task for visual processing resources . Third, executive functions of the prefrontal cortex decay in old age [review in [18, 45]], which could reduce the ability to quickly alternate between the central processing of two visual tasks. Available literature argues against gaze shifting ability as the sole explanation, since substantial ARD was observed even when the non-walking task required visual imagery rather than actual viewing [29, 30]. Further research is needed to reliably determine the validity of each above interpretation.
The critical role of vision proposed in the present study is of relevance for many everyday-life scenarios. For example, elderly subjects may have no more problems than younger ones to walk down the street while listening to music, but they may experience difficulties to walk down the street while observing the display in shop windows. In fact, seniors may have a high risk of falling in the latter scenario, since degraded performance on walking with a concurrent visually demanding task is a known predictor of falls in the elderly [46, 47]. This differential vulnerability of seniors to scenarios with high versus low visual demand should be taken into account when designing prevention and rehabilitation programs for the elderly.
It should be noted, however, that visual demand may not be the only critical factor for falls in healthy seniors. A range of other predictors not addressed in our study has been identified in literature, such as visual, vestibular, and proprioceptive sensitivity, muscle strength, psychomotor speed, sensorimotor coordination, executive functions, self-efficacy, as well as exposure to slipping and tripping hazards [reviews in [7, 9, 10, 48]]. Additional predictors may exist in seniors suffering from cognitive or sensorimotor dysfunctions: such persons show ARD while walking even if the non-walking task has low visual demand [34, 49, 50]. Our present findings therefore don't argue against the utility of training programs aimed at those predictors, but rather underline the role of one particular training component.
In an analysis of 13 combinations between a walking and a non-walking task, we found that dual-task performance is degraded in the elderly for non-walking task which require ongoing visual observation. Such task combinations are common in everyday life, and may therefore contribute to the incidence of falls in seniors. Prevention and rehabilitation programs for the elderly should take this age-related deficit into account, and specifically train participants on task combinations such as walking while adjusting a TV set via remote control, balancing on one leg while reading, standing up and walking while carrying a cup of water , etc. Such training is likely to be successful, since seniors' dual-tasking abilities are known to improve by practice [16, 32].
Thanks are due to Ch. Steinweg for assistance in data collection and analysis, as well as to K. Engelhard and P. Guardiera for help in the re-analysis of data from our previous study.
- Hausdorff J, Edelberg H, Mitchell S, Goldberger A, Wei J: Increased gait unsteadiness in community-dwelling elderly fallers. Arch Phys Med Rehabil 1997, 78: 278-83. 10.1016/S0003-9993(97)90034-4View ArticlePubMedGoogle Scholar
- Grabiner P, Biswas S, Grabiner M: Age-related changes in spatial and temporal gait variables. Arch Phys Med Rehabil 2001, 82: 31-35. 10.1053/apmr.2001.18219View ArticlePubMedGoogle Scholar
- Winter D, Patla A, Frank J, Walt S: Biomechanical walking pattern changes in the fit and healthy elderly. Phys Ther 1990, 70: 340-347.PubMedGoogle Scholar
- Campbell A, Reineken J, Allan B, Martinez G: Falls in old age: a study of frequency and related clinical factors. Age Ageing 1981, 10: 264-70. 10.1093/ageing/10.4.264View ArticlePubMedGoogle Scholar
- van Bemmel T, Vandenbroucke J, Westendorp R, Gussekloo J: In an observational study elderly patients had an increased risk of falling due to home hazards. J Clin Epidemiol 2005, 58: 63-67. 10.1016/j.jclinepi.2004.06.007View ArticlePubMedGoogle Scholar
- Tinetti M, Baker D, McAvay G, Claus E, Garrett P, Gottschalk M, Koch M, Trainor K, Horwitz R: A multifactorial intervention to reduce the risk of falling among elderly people living in the community. New England J Med 1994, 331: 821-27. 10.1056/NEJM199409293311301View ArticleGoogle Scholar
- Tinetti M, Speechley M: Prevention of falls among the elderly. N E J Med 1989, 320: 1055-1059.View ArticleGoogle Scholar
- Smallegan M: How families decide on nursing home admission. Geriatr Consult 1983, 1: 21-24.Google Scholar
- van Dieen J, Pijnappels M, Bobbert M: Age-related intrinsic limitations in preventing a trip and regaining balance after a trip. Safety Sci 2005, 43: 437-53.View ArticleGoogle Scholar
- Lajoie Y, Gallagher S: Predicting falls within the elderly community: comparison of postural sway, reaction time, the Berg balance scale and the Activities-specific Balance Confidence (ABC) scale for comparing fallers and non-fallers. Arch Gerontol Geriatr 2004, 38: 1-26. 10.1016/S0167-4943(03)00082-7Google Scholar
- Woolacott M, Shumway-Cook A: Attention and the control of posture and gait: a review of an emerging area of research. Gait Posture 2002, 16: 1-14. 10.1016/S0966-6362(01)00156-4View ArticleGoogle Scholar
- Chen H, Schultz A, Ashton-Miller J, Giordani B, Alexander N, Guire K: Stepping over obstacles: Divided attention impairs performance of old more than young subjects. J Gerontol A Biol Sci Med Sci 1996, 51: M116-122.View ArticlePubMedGoogle Scholar
- Verhaeghen P, Steitz D, Sliwinski M, Cerella J: Aging and Dual-Task Performance: A Meta-Analysis. Psychol Aging 2003, 18: 443-60. 10.1037/0882-79184.108.40.2063View ArticlePubMedGoogle Scholar
- McDowd J, Craik F: Effects of aging and task difficulty on divided attention performance. J Exp Psychol Hum Percept Perform 1988,14(2):267-280. 10.1037/0096-15220.127.116.117View ArticlePubMedGoogle Scholar
- Göthe K, Oberauer K, Kliegl R: Age differences in dual-task performance after practice. Psychology Aging 2007, 22: 596-606. 10.1037/0882-7918.104.22.1686View ArticlePubMedGoogle Scholar
- Bherer L, Kramer A, Peterson M, Colcombe S, Erickson K, Becic E: Training Effects on Dual-Task Performance: Are There Age-Related Differences in Plasticity of Attentional Control? Psychol Aging 2005, 20: 695-709. 10.1037/0882-7922.214.171.1245View ArticlePubMedGoogle Scholar
- Gunning-Dixon F, Raz N: Neuroanatomical correlates of selected executive functions in middle-aged and older adults: a prospective MRI study. Neuropsychologia 2003, 41: 1929-41. 10.1016/S0028-3932(03)00129-5View ArticlePubMedGoogle Scholar
- Raz N: Aging of the brain and its impact on cognitive performance: Integration of structural and functional findings. In The Handbook of Aging and Cognition. Edited by: Craik F, Salthouse T. Erlbaum: Hillsdale, NJ; 2000:1-90.Google Scholar
- West R: An application of prefrontal cortex function theory to cognitive aging. Psychol Bull 1996, 120: 272-92. 10.1037/0033-2909.120.2.272View ArticlePubMedGoogle Scholar
- Stuss D, Benson D: The frontal lobes. New York: Raven Press; 1986.Google Scholar
- Shumway-Cook A, Woolacott M: Attentional demands and postural control: The effects of sensory context. J Gerontol Med Sci 2000, 55A: M10-M16.Google Scholar
- Teasdale N, Bard C, LaRue J, Fleury M: On the cognitive penetrability of posture control. Exp Aging Res 1993, 19: 1-13. 10.1080/03610739308253919View ArticlePubMedGoogle Scholar
- Maylor EA, Wing AM: Age differences in postural stability are increased by additional cognitive demands. J Gerontol B Psychol Sci Soc Sci 1996,51(3):P143-P154.View ArticlePubMedGoogle Scholar
- Stelmach GE, Zelaznik HN, Lowe D: The influence of aging and attentional demands on recovery from postural instability. Aging 1990, 2: 155-161.PubMedGoogle Scholar
- Rankin J, Woollacott M, Shumway-Cook A, WBrown J: A neuromuscular analysis of the influence of a cognitive task on postural stability in young and older adults. J Gerontol A Biol Sci Med Sci 2000, 55: M112-19.View ArticlePubMedGoogle Scholar
- Damos D: Dual-task methodology: Some common problems. In Multiple Task Performance. Edited by: Damos D. Taylor & Francis, Ltd.: London; 1991:101-120.Google Scholar
- Lajoie Y, Teasdale N, Bard C, Fleury M: Upright standing and gait: Are there changes in attentional requirements related to normal aging? Exp Aging Res 1996, 22: 185-198. 10.1080/03610739608254006View ArticlePubMedGoogle Scholar
- Sparrow W, Begg R, Parker S: Aging effects on visual reaction time in a single task condition and when treadmill walking. Motor Control 2006,10(3):201-211.PubMedGoogle Scholar
- Lindenberger U, Marsiske M, Baltes P: Memorizing while walking: Increase in dual-task costs from young adulthood to old age. Psychol Aging 2000, 15: 417-436. 10.1037/0882-79126.96.36.1997View ArticlePubMedGoogle Scholar
- Li K, Lindenberger U, Freund A, Baltes P: Walking while memorizing: Age-related differences in compensatory behavior. Psychol Sci 2001, 12: 230-237. 10.1111/1467-9280.00341View ArticlePubMedGoogle Scholar
- Bock O, Engelhard K, Guardiera P, Allmer H, Kleinert J: Gerontechnology and human cognition. IEEE Eng Med Biol Magazine 2008, 27: 23-28. 10.1109/MEMB.2008.919497View ArticleGoogle Scholar
- McDowd J: The effects of age and extended practice on divided attention performance. J Gerontol 1986, 41: 764-769.View ArticlePubMedGoogle Scholar
- Somberg BL, Salthouse TA: Divided attention abilities in young and old adults. J Exp Psychol: Hum Percept Perform 1982, 8: 651-663. 10.1037/0096-15188.8.131.521Google Scholar
- Springer S, Giladi N, Peretz C, Yogev G, Simon E, Hausdorff J: Dual-Tasking Effects on Gait Variability: The Role of Aging, Falls, and Executive Function. Movement Disorders 2006, 21: 950-57. 10.1002/mds.20848View ArticlePubMedGoogle Scholar
- Faulkner K, Redfern M, Cauley J, Landsittel D, Studenski S, Rosano C, Simonsick E, Harris T, Shorr R, Ayonayon H, Newman A: Multitasking: Association between poorer performance and a history of recurrent falls. J Am Geriatr Soc 2007, 55: 570-76. 10.1111/j.1532-5415.2007.01147.xView ArticlePubMedGoogle Scholar
- Hausdorff J, Yogev G, Springer S, Simon E, Giladi N: Walking is more like catching than tapping: gait in the elderly as a complex cognitive task. Exp Brain Res 2005, 164: 541-48. 10.1007/s00221-005-2280-3View ArticlePubMedGoogle Scholar
- Jamet M, Deviterne D, Gauchard G, G Vançon, Perrin P: Higher visual dependency increases balance control perturbation during cognitive task fulfilment in elderly people. Neurosci Letters 2004, 359: 61-64. 10.1016/j.neulet.2004.02.010View ArticleGoogle Scholar
- Nomura Y, Mulavara A, Richards J, Brady R, Bloomberg J: Optic flow dominates visual scene polarity in causing adaptive modification of locomotor trajectory. Brain Res Cogn Brain Res 2005, 25: 624-31. 10.1016/j.cogbrainres.2005.08.012View ArticlePubMedGoogle Scholar
- Rushton S, Harris J, Lloyd M, Wann J: Guidance of locomotion on foot uses perceived target location rather than optic flow. Curr Biol 1998, 8: 1191-94. 10.1016/S0960-9822(07)00492-7View ArticlePubMedGoogle Scholar
- Abel L, Troost B, Dell'Osso L: The effects of age on normal saccadic characteristics and their variability. Vision Res 1983, 23: 33-37. 10.1016/0042-6989(83)90038-XView ArticlePubMedGoogle Scholar
- Ball K, Beard B, Roenker D, Miller R, Griggs D: Age and visual search: expanding the useful field of view. J Opt Soc Am A 1988, 5: 2210-19. 10.1364/JOSAA.5.002210View ArticlePubMedGoogle Scholar
- Anderson PA, Nienhuis B, Mulder T, Hulstijn W: Are older adults more dependent on visual information in regulating self-motion than younger adults? J Motor Behav 1998, 30: 104-113.View ArticleGoogle Scholar
- Shaffer S, Harrison A: Aging of the somatosensory system: a translational perspective. Phys Ther 2007, 87: 193-207. 10.2522/ptj.20060083View ArticlePubMedGoogle Scholar
- Sloane P, Baloh R, Honrubia V: The vestibular system in the elderly: Clinical implications. Am J Otolaryngol 1989, 10: 422-29. 10.1016/0196-0709(89)90038-0View ArticlePubMedGoogle Scholar
- Rhodes M: Age-related differences in performance on the Wisconsin card sorting test: a meta-analytic review. Psychol Aging 2004, 19: 482-94. 10.1037/0882-79184.108.40.2062View ArticlePubMedGoogle Scholar
- Lundin-Olsson L, Nyberg L, Gustafson Y: Attention, frailty, and falls: The effect of a manual task on basic mobility. J Am Geriat Soc 1998, 46: 758-761.View ArticlePubMedGoogle Scholar
- Toulotte C, Thevenon A, Watelain E, Fabre C: Identification of healthy elderly fallers and non-fallers by gait analysis under dual-task conditions. Clin Rehabil 2006, 20: 269-76. 10.1191/0269215506cr929oaView ArticlePubMedGoogle Scholar
- Holtzer R, Friedman R, Lipton R, Katz M, Xue X, Verghese J: The Relationship Between Specific Cognitive Functions and Falls in Aging. Neuropsychol 2007, 21: 540-48. 10.1037/0894-4220.127.116.110View ArticleGoogle Scholar
- Lundin-Olsson L, Nyberg L, Gustafson Y: "Stops walking when talking" as a predictor of falls in elderly people. The Lancet 1997, 349: 616. 10.1016/S0140-6736(96)10338-XView ArticleGoogle Scholar
- Cocchini G, Della Sala S, Logie R: Dual-task effects of walking while talking in Alzheimer's disease. La Revue Neurologique 2004, 160: 74-80. 10.1016/S0035-3787(04)70951-0View ArticleGoogle Scholar
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.