Inducing the return of automaticity in gait after stroke through distractions that force the act of walking into the background.
By Mike Studer, PT, DPT, MHS, NCS, CEEAA, CWT, CSST, FAPTA, and Robert Winningham, PhD
Expect this article about post-stroke dual task rehabilitation to surprise, inform, and help to improve your efforts in restoring functional ambulation for persons recovering from stroke. We expect you to learn why and how to use dual task interference (DTI) or cognitive-motor training to help people recover better after a stroke. It may be easiest to understand why we use DTI if we frame it as a constraint. Yes, that’s right, a constraint…similar to using a sling on a less-impaired arm to “force” a more involved arm to be chosen, used, and stimulated to recover.
Imagine it. Place a constraint on your patient’s attention, by using a distraction…causing a person recovering from stroke to reprogram a motor task to operate without as much attentional resources. Movement such as walking must be able to survive in the background without attention, as a “motor memory” or what is scientifically known as a procedural memory.
Accessing Procedural Memories
Among the related questions that we will answer for post-stroke dual task rehabilitation include, “How did walking become procedural?” or “How do we access these memories and motor skills after stroke or injury?” and finally, “How many repetitions of a task are needed to make it ‘automatic’ again after stroke?” Our most pressing and practical question at hand is, “How can rehabilitation interventions most effectively encourage the return of procedural memories?”
Know that the terms automatic, automatized, or expressing that a person has automaticity, are synonymous with having a procedural memory. As for the first question—”How does a movement become procedural?”—we are aware that the procedural memory centers (PMCs) develop in any skill (functional, vocational, craft, or athletic) when we have interest, repetitions, and a demand (stimulus) that the movement operate without full attention. In walking, we need two essential ingredients.
First, we need an environment that allows for predictable locomotion as a primary means of transit (ie, repetitions and a surface with minimal variability). Second, we need an attentional demand (DTI), such as texting, cleaning glasses, counting money, assessing a dynamic environment, engaging in conversation, or preparing for an upcoming interview. Neuroplasticity (learning) comes when sufficient demand pushes the organization of the motor control of gait into the PMCs.
Our recognizable “walk” does evolve during developmental years and, barring injury or change in somatotype (eg, significant weight gain or loss), remains relatively constant through our adult years. To the good fortune of most PwS, the primary PMCs are spared. It is far less likely that a stroke will impact the basal ganglia (BG) or cerebellum, leaving this pathway to access walking intact.
Redefining “Their Walk”
A common problem for most PwS is the reverse: creating movement with conscious attention, generated from the primary motor cortex. So, thinking about moving (internal focus) is often more challenging than moving without thinking (external or goal-directed focus). Walking toward a destination, with a list of items to retrieve from that shelf, is an example of goal-directed movement with DTI. Recognizing that the PMCs largely remain intact leaves therapists and PwS alike with the problem of reclaiming automaticity. This requires neuroplasticity, which includes making and growing new connections as well as reorganization of responsibilities.
PwS can reorganize and redefine “their walk” in the face of a changing set of resources as compared to what they had pre-stroke (hemiplegia, sensory impairments, abnormal tone). Compensated gait can be healthy, automatic, and reliable again. Recall that having a reliable and predictable walk poses a very low demand on attentional resources and is therefore preferable to either of the alternatives of: 1) variable gait that is unpredictable or 2) most every step requiring conscious control to initiate, monitor, and terminate.
Redeveloping Automaticity: Repetitions and Dual Tasking
How many repetitions of a task are needed to make the behavior “automatic” again after stroke? Is there a dosage of intensity that would make repetitions more effective? How can we ensure that DTI will promote carryover in way of tolerance for distractions, or an improved procedural encoding of gait again?
While dual-task demands are everywhere, no two people should be affected by the same environmental and task demands in the same manner. This variability is due to: 1) their past experiences with the proposed task or related tasks; 2) their relative automaticity in a primary motor task (influencing the cognitive resources available); and 3) each person’s tolerance for a specific mode of distraction (eg, cognitive, motor, visual, or auditory). Each person has an individual skill set with both biological and experiential (nature and nurture) influence.
There is clear evidence for the functional significance of DTI on gait speed, fall frequency, and independence in gait after stroke. Subsequently, there is clear evidence for the efficacy of cognitive-motor training to promote automaticity in PwS. However, the present science does not easily translate into applications, objective tests, or justifications of skilled care.
Applying the Science
While many of these studies have included sufficient numbers of repetitions, they have not always applied sufficient intensity and quite likely insufficient dosage. Dosage built in frequency, intensity, type, and time (FITT principle)56, as well as those principles cited of neuroplasticity and motor learning57,58, lead us to the understanding that it is not the sheer numbers of repetitions or minutes-spent in dual task training, but rather the level of rigor, complexity, challenge, intensity, and ultimately interest (engagement), which has the opportunity to make each repetition meaningful and sufficient to induce measurable change.
Recent studies in stroke rehabilitation have improved the delivery of intensity and respect for the presence of error (difficulty). Kleim and Jones 2008 found that dual task training delivered at a rigorous level induces neuroplasticity when the complexity and intensity are adequate.58 Gait training with dual task overlay is complex, by application, but only intense when applied relative to the learner’s capabilities and readiness.58
As for the application of dual task training, therapists must conduct their efforts in motor learning for the primary task of gait, with a consideration for both individualizing and later integrating dual task overlay. This must be carried out using reasonable expectations based on lesion size and location, age, learning style, and personality.59-69 As McIsaac and colleagues21 wrote, “In aging and disease states, declines in sensorimotor and cognitive functions may lead to reduced postural reserve and cognitive reserve creating overall greater demands for attention to the task.”
While all dual-tasking must be proportional to capabilities, success rates, and personal tolerance as noted above, we must recognize additional trends by diagnosis and age. Therapists must watch for signs of DT overload, including agitation, pathway deviation, foot clearance, steps to turn, dramatic reductions in gait velocity, poor sequencing of assistive device, and increased losses of balance requiring assistance. As stroke is not a heterogeneous condition, clinicians should not assume that all groups have a timetable upon which they are “ready” for dual task interference to be introduced.
Clinical applications of DT training are only as sophisticated as the evidence to date. As it is functionally relevant to focus on ambulation, the task specific nature of DT practice in the clinic often stops there, meaning that the distraction should have specificity, relevance, and person-based interest. Asking patients to perform mathematical calculations, spell words backwards, or name state capitals are cognitive tasks that many clinicians have applied. However, these distractions may not be as intuitive to the learner as they can feel contrived, lacking functional significance and failing to fully engage PwS as they are left to ask two questions that they should not have to face:
1) “Why am I doing this?” and, 2) “Am I improving?”
As we mature in DT applications, clinicians can be seen incorporating cell phones; pulling items from a purse, wallet, or pocket; recalling information delivered prior-to and after a primary task (requiring cognitive rehearsal during); utilizing obstacles for visual distraction; and overlaying relevant auditory distractions during the motor task. When a person endures the overtraining or loading of DT, it is important for them to see and feel the “why.”
As for the second question, we land squarely at the feet of gamification. PwS should know their functional measurements that reflect their capacity to tolerate distractions in activities that reflect their lives, in real numbers. This leaves people with an opportunity to both see their improvement, and to compete against an established baseline. For the sake of this brief article, these are the essential ingredients affording gamification, elevating intensity, and increasing the likelihood of neuroplastic change.
This may leave us with a final question: “How_ _can rehabilitation interventions most effectively encourage the return of procedural memories?” In all, the best DT training takes into consideration the following:
1) Patient’s relative experience or level of automaticity with the primary gait task. Is the patient using a new assistive device? New footwear? Will distractions interfere with motor learning?14,21,23
2) Transfer of training (what are and how can training imitate the environmental demands for this person?42,43)
3) Lesion location/type (what strengths and limitations are superimposed neurologically by the stroke?74)
4) Patient tolerance of error and need for success—consider personality. Will this person improve or become more frustrated by the DT loading?43
5) Specificity. Exposure to one condition/environment of gait or modality of DT condition should not be expected to transfer to skill (tolerance) in another.42
6) Intensity. For dual task experiences to induce change and stimulate procedural processing of a primary task, they must be of sufficient challenge to offer a therapeutic dosage.42,76
7) Autonomy. Has this person been given an opportunity to voice their typical routines, skills, and preferences—as well as their preferred level of challenge?
8) Safety (perceived). Intensity, error (consequence), and ultimately carryover are impacted by patients’ perception of safety. Recall that fear is a cognitive distractor. Using a safety harness or body weight support as a safety net can mitigate some of these concerns as patients engage in their initial DT experiences.
9) Measurement. As stated above, gamification can enhance engagement and intensity. Intensity is required for neuroplasticity. Measure patient performance in single task and immediately follow this with dual task. Share numbers. Remeasure. Compete.
10) Awareness. The ultimate indicator for DT prognosis in recovery. Does this person:
a. Recognize dual task conflict? Are they able to perceive and independently recognize reduction in primary performance?
b. Recognize as they are being distracted?
c. Independently re-prioritize attention for their own safety, attempting to extinguish or filter-out distractions?
It is through these 10 considerations that we can both guide our dual task intervention and individualize care, providing each person the greatest opportunity to recover.
For stroke survivors, the evidence is irrefutable and conclusive; dual task gait training can be and often is beneficial for when adhering to principles of task specificity and intensity at the least. Many authors have postulated the mechanism by which this is true, with the most common theme being one of motor learning, specifically engaging the learner to re-automatize the primary task of walking, by organizing the effort of gait on external feedback. In other words, gait training by itself may be beneficial, yet this approach allows the learner to internalize the focus of attention on the movement itself. Dual task training forces an external focus of attention, which has proven to be a superior form of training for stroke and many other impaired and un-impaired (athletics, developmental learning, etc) conditions.75,81,82
Evidence suggests that stroke survivors can make new procedural memories. The extent to which these memories are identical to pre-stroke patterns of gait, or are well-reinforced and novel iterations of post-stroke gait, is based on the type of stroke, the location of the stroke, access to rehabilitation, comorbidities, social support, personal traits, and many more factors, as suggested by the International Classification of Functioning.85 Creating dual task interference during gait training has the proven capacity to take the recovery of gait from a conscious-control frontal lobe process and make it subcortical again.
Limitations of this line of research to date can be found in the lack of respect for principles of task specificity and intensity. Additionally, most dual task research has been designed to prove the presence of dual task cost, or its relationship to fall risk, rather than the potential benefits in applications in rehabilitating the automaticity of gait. As noted above, it is time to mature from the notion of rehabilitating dual task tolerance in the activity of gait, to the more sophisticated and functionally relevant notion of rehabilitating gait, through the application of dual task interference. Readers may utilize the 10 recommendations above to improve their efficacy of DT interventions.
Mike Studer, PT, DPT, MHS, NCS, CEEAA, CWT, CSST, FAPTA, is the owner of Northwest Rehabilitation Associates in Salem, Ore. He is also an adjunct professor at Oregon State University’s DPT program in Bend, Ore, where he leads the coursework on motor control and assists the national network of neurologic PT residencies (Neuroconsortium). He is also part of the clinical team for SMARTfit.
Robert Winningham, PhD, has more than 25 years of experience researching human memory and has largely focused on older adults and ways to enhance their mental functioning and quality of life. He currently serves as provost and vice president for Academic Affairs at Western Oregon University, where he has been a professor of Psychology and Gerontology, chair of the Behavioral Sciences Division, and interim dean of the College of Liberal Arts and Sciences. He is also part of the clinical team for SMARTfit. For more information, contact [email protected].
The following companies provide products that are useful in treating stroke and neurological conditions:
Allard USA Inc
Biodex Medical Systems Inc
Bionik Laboratories Corp
CIR Systems Inc/GAITRite
1. [Benjamin EJ, Blaha MJ, Chiuve SE, et al. on behalf of the American Heart Association Statistics Committee and Stroke Statistics Subcommittee. Heart disease and stroke statistics—2017 update: a report from the American Heart Association. Circulation. 2017; 135: e229-e445. CITATION 2 J Am Heart Assoc. 2016 Nov 14; 5(11). pii: e004282.](https://www.ncbi.nlm.nih.gov/pubmed/27930356) 2. [Medford-Davis LN, Fonarow GC, Bhatt DL, et al. Impact of Insurance Status on Outcomes and Use of Rehabilitation Services in Acute Ischemic Stroke: Findings From Get With The Guidelines-Stroke. J Am Heart Assoc. 2016; 5. pii: e004282.](https://jaha.ahajournals.org/content/5/11/e004282) 3. [Caleo M. Rehabilitation and plasticity following stroke: Insights from rodent models. Neuroscience. 2015; 311: 180-194.](https://www.ncbi.nlm.nih.gov/pubmed/26493858) 4. [Jones TA. Motor compensation and its effects on neural reorganization after stroke. Nat Rev Neurosci. 2017; 18: 267-280.](https://www.ncbi.nlm.nih.gov/pubmed/28331232) 5. [Levin MF, Kleim JA, Wolf SL. What do motor “recovery” and “compensation&” mean in patients following stroke? Neurorehabil Neural Repair. 2009; 23: 313-319.](https://www.ncbi.nlm.nih.gov/pubmed/19118128) 6. [Squire L. Memory systems of the brain: A brief history and current perspective. Neurobiology Of Learning And Memory [serial online]. 2004; 82: 171-177.](https://www.ncbi.nlm.nih.gov/pubmed/15464402) 7. [Roy S, Park N. Effects of dividing attention on memory for declarative and procedural aspects of tool use. Memory & amp; Cognition [serial online]. 2016; 44: 727-739.](https://www.ncbi.nlm.nih.gov/pubmed/26951117) 8. [Moscovitch M, Nadel L, Winocur G, Gilboa A, Rosenbaum R. The cognitive neuroscience of remote episodic, semantic and spatial memory. Current Opinion In Neurobiology [serial online]. 2006; 16: 179-190.](https://www.ncbi.nlm.nih.gov/pubmed/16564688) 9. [Scoville W, Milner B. Loss of recent memory after bilateral hippocampal lesions. Journal Of Neurology, Neurosurgery & amp; Psychiatry [serial online]. 1957; 20: 11-21.](https://www.ncbi.nlm.nih.gov/pubmed/13406589) 10. [Middleton E, Schwartz M. Errorless learning in cognitive rehabilitation: A critical review. Neuropsychological Rehabilitation [serial online]. 2012; 22: 138-168.](https://www.ncbi.nlm.nih.gov/pubmed/22247957) 11. [Orrell A, Eves F, Masters R. Motor learning of a dynamic balancing task after stroke: implicit implications for stroke rehabilitation. Physical Therapy [serial online]. 2006; 86: 369-380.](https://www.ncbi.nlm.nih.gov/pubmed/16506873) 12. [Kal E, Winters M, Scherder E, et al. Is Implicit Motor Learning Preserved after Stroke? A Systematic Review with Meta-Analysis. Plos One [serial online]. 2016; 11: e0166376.](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5161313/) 13. [Lee KB, Kim JS, Hong BY,etal. Clinical recovery from stroke lesions and related outcomes. J Clin Neurosci. 2017; 37: 79-82.](https://www.jocn-journal.com/article/S0967-5868(16)30446-5/abstract) 14. [Takakusaki K. Functional Neuroanatomy for Posture and Gait Control. Journal Of Movement Disorders [serial online]. 2017; 10: 1-17.](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5288669/) 15. [Killeen T, Easthope CS, Demkó L, et al. Minnimum toe clearance: probing the neural control of locomotion. Sci Rep. 2017; 7: 1922.](https://www.ncbi.nlm.nih.gov/pubmed/28507300) 16. [Ashby FG, Crossley MJ. Automaticity and multiple memory systems. Wiley Interdiscip Rev Cogn Sci. 2012; 3: 363-376.](https://www.ncbi.nlm.nih.gov/pubmed/26301468) 17. [Ericsson KA. Expertise and individual differences: the search for the structure and acquisition of experts’ superior performance. Wiley Interdiscip Rev Cogn Sci. 2017; 8.](https://wires.wiley.com/WileyCDA/WiresArticle/wisId-WCS1382.html) 18. [Clark DJ. Automaticity of walking: functional significance, mechanisms, measurement and rehabilitation strategies. Frontiers in Human Neuroscience. 2015; 9: 246.](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4419715/) 19. [Galit Yogev G, Hausdorff JM, Giladi N. The Role of Executive Function and Attention in Gait. Mov Disord. 2008; 23: 329–472.](https://www.ncbi.nlm.nih.gov/pubmed/18058946) 20. [Springer S, Giladi N, Peretz C, Yogev G, Simon ES, Hausdorff JM. Dualtasking effects on gait variability: the role of aging, falls, and executive function. Mov Disord. 2006; 21: 950–957.](https://www.ncbi.nlm.nih.gov/pubmed/16541455) 21. [McIsaac T, Lamberg E, Muratori L. Building a Framework for a Dual Task Taxonomy. BioMed Research International. 2015.](https://www.hindawi.com/journals/bmri/2015/591475/) 22. [Brown SW1, Collier SA, Night JC. Timing and executive resources: dual-task interference patterns between temporal production and shifting, updating, and inhibition tasks. J Exp Psychol Hum Percept Perform. 2013; 39: 947-963.](https://www.ncbi.nlm.nih.gov/pubmed/23127475) 23. [Wayne PM, Hausdorff JM, Lough M, et al. Tai Chi Training may Reduce Dual Task Gait Variability, a Potential Mediator of Fall Risk, in Healthy Older Adults: Cross-Sectional and Randomized Trial Studies. Frontiers in Human Neuroscience. 2015; 9: 332.](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4460804/) 24. [Sarkar M1, Fletcher D. Psychological resilience in sport performers: a review of stressors and protective factors. J Sports Sci. 2014; 32: 1419-1434.](https://www.ncbi.nlm.nih.gov/pubmed/24716648) 25. [Hsu C, Lin L, Wu S. The effects of spaced retrieval training in improving hyperphagia of people living with dementia in residential settings. Journal Of Clinical Nursing [serial online]. 2017; 26: 3224-3231.](https://onlinelibrary.wiley.com/doi/10.1111/jocn.13671/full) 26. [Zmily A, Mowafi Y, Mashal E. Study of the usability of spaced retrieval exercise using mobile devices for Alzheimer’s disease rehabilitation. JMIR Mhealth And Uhealth [serial online]. 2014; 2: e31.](https://www.ncbi.nlm.nih.gov/pubmed/25124077) 27. [Wonsetler EC, Bowden MG. A systematic review of mechanisms of gait speed change post-stroke. Part 1: spatiotemporal parameters and asymmetry ratios. Top Stroke Rehabil. 2017; 24: 435-446.](https://www.ncbi.nlm.nih.gov/pubmed/28220715) 28. [Srivastava A1, Taly AB, Gupta A, Kumar S, Murali T. Bodyweight-supported treadmill training for retraining gait among chronic stroke survivors: A randomized controlled study. Ann Phys Rehabil Med. 2016; 59: 235-241.](https://www.ncbi.nlm.nih.gov/pubmed/27107532) 29. [Bang DH, Shin WS. Effects of robot-assisted gait training on spatiotemporal gait parameters and balance in patients with chronic stroke: A randomized controlled pilot trial. Neuro Rehabilitation. 2016; 38: 343-349.](https://www.ncbi.nlm.nih.gov/pubmed/27061162) 30. [Horak F, King L, Mancini M. Role of body-worn movement monitor technology for balance and gait rehabilitation. Phys Ther. 2015; 95: 461-470.](https://www.ncbi.nlm.nih.gov/pubmed/25504484) 31. [Schenck C, Kesar TM. Effects of unilateral real-time biofeedback on propulsive forces during gait. J Neuroeng Rehabil. 2017; 14: 52.](https://jneuroengrehab.biomedcentral.com/articles/10.1186/s12984-017-0252-z) 32. [Xiao X, Lin Q, Lo WL, Mao YR, et al. Cerebral Reorganization in Subacute Stroke Survivors after Virtual Reality-Based Training: A Preliminary Study. Behav Neurol. 2017; 2017: 6261479.](https://www.hindawi.com/journals/bn/2017/6261479/) 33. [Boisgontier MP, Beets IA, Duysens J, Nieuwboer A, Krampe RT, Swinnen SP. Age-related differences in attentional cost associated with postural dual tasks: increased recruitment of generic cognitive resources in older adults. Neurosci Biobehav Rev. 2013; 37: 1824-1837.](https://www.ncbi.nlm.nih.gov/pubmed/23911924) 34. [Redfern MS, Chambers AJ, Jennings JR, Furman JM. Sensory and motoric influences on attention dynamics during standing balance recovery in young and older adults. Exp Brain Res. 2017; 235: 2523-2531.](https://www.ncbi.nlm.nih.gov/pubmed/28528460) 35. [Giladi N, Nieuwboer A. Understanding and treating freezing of gait in parkinsonism, proposed working definition, and setting the stage. Mov Disord. 2008; 23: S423–S425.](https://www.ncbi.nlm.nih.gov/pubmed/18668629) 36. [Yang L, He C, Pang MY. Reliability and Validity of Dual-Task Mobility Assessments in People with Chronic Stroke. PLoS One. 2016; 11.](https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0147833) 37. [Malcay O, Grinberg Y, Berkowitz S, Hershkovitz L, Kalron A. Cognitive-motor interference in multiple sclerosis: What happens when the gait speed is fixed? Gait Posture. 2017; 57: 211-216.](https://www.ncbi.nlm.nih.gov/pubmed/28667902) 38. [Foerde K, Poldrack R, Knowlton B. Secondary-task effects on classification learning. Memory & amp; Cognition [serial online]. 2007; 35: 864-874.](https://www.ncbi.nlm.nih.gov/pubmed/17910172) 39. [Roche R, Commins S, Mara S, et al. Concurrent task performance enhances low-level visuomotor learning. Perception & amp; Psychophysics [serial online]. 2007; 69: 513-522.](https://www.ncbi.nlm.nih.gov/pubmed/17727104) 40. [Fritz N, Cheek F, Nichols-Larsen D. Motor-Cognitive Dual-Task Training in Neurologic Disorders: A Systematic Review. Journal of Neurologic Physical Therapy. 2015; 39: 142-153.](https://www.ncbi.nlm.nih.gov/pubmed/26079569) 41. [Plummer P, & Osborne MB. What Are We Attempting to Improve When We Train Dual-Task Performance?. Journal of Neurologic Physical Therapy. 2015; 39: 154-155.](https://www.ncbi.nlm.nih.gov/pubmed/26050072) 42. [Patel P, Bhatt T. Task matters: influence of different cognitive tasks on cognitive-motor interference during dual-task walking in chronic stroke survivors. Top Stroke Rehabil. 2014; 21: 347–357.](https://www.ncbi.nlm.nih.gov/pubmed/25150667) 43. [Studer MT, McIsaac T, Whetten B, Fritz N. Advancing the clinical application of dual tasking: Individualizing the cognitive, auditory, visual, and manual distraction taxonomy. American Physical Therapy Association Combined Sections Meeting, San Antonio, TX. February 2017.](http://www.austinpublishinggroup.com/physical-medicine/fulltext/pmr-v4-id1125.php) 44. [Cho KH, Lee HJ, Lee WH. Test-retest reliability of the GAITRite walkway system for the spatio-temporal gait parameters while dual-tasking in poststroke patients. Disabil Rehabil. 2015; 37: 512–516.](https://www.ncbi.nlm.nih.gov/pubmed/24957081) 45. [Tsang CS, Liao LR, Chung RC, Pang MY. Psychometric properties of the Mini-Balance Evaluation Systems Test (Mini-BESTest) in communitydwelling individuals with chronic stroke. Phys Ther. 2013; 93: 1102–1115.](https://www.ncbi.nlm.nih.gov/pubmed/23559522) 46. [Al-Yahya E, Dawes H, Smith L. Cognitive motor interference while walking: A systematic review and meta-analysis. Neurosci Biobehav Rev. 2011; 35: 715–728.](https://www.ncbi.nlm.nih.gov/pubmed/20833198) 47. [Plummer-D’Amato P, Altmann LJ, Saracino D, Fox E, Behrman AL, Marsiske M. Interactions between cognitive tasks and gait after stroke: a dual task study. Gait Posture. 2008; 27: 683–688.](https://www.ncbi.nlm.nih.gov/pubmed/17945497) 48. [Shumway-Cook A, Woollacott M, Kerns KA, Baldwin M. The effects of two types of cognitive tasks on postural stability in older adults with and without a history of falls. J Gerontol A Biol Sci Med Sci. 1997; 52: M232-240.](https://www.ncbi.nlm.nih.gov/pubmed/9224435) 49. [Shumway-Cook A, Woollacott M. Attentional demands and postural control: the effect of sensory context. J Gerontol A Biol Sci Med Sci. 2000; 55: M10- 16.](https://www.ncbi.nlm.nih.gov/pubmed/10719767) 50. [Shumway-Cook ONE MORE](http://www.austinpublishinggroup.com/physical-medicine/fulltext/pmr-v4-id1125.php) 51. [Yang L, He C, Pang MYC. Reliability and Validity of Dual-Task Mobility Assessments in People with Chronic Stroke. Tremblay F, ed. PLoS ONE. 2016; 11: e0147833.](https://www.ncbi.nlm.nih.gov/pubmed/26808662) 52. [Menant JC, Schoene D, Sarofim M, Lord SR. Single and dual task tests of gait speed are equivalent in the prediction of falls in older people: a systematic review and meta-analysis. Ageing Res Rev. 2014; 16: 83–104.](https://www.ncbi.nlm.nih.gov/pubmed/24915643) 53. [Muir-Hunter SW, Wittwer JE. Dual-task testing to predict falls in communitydwelling older adults: a systematic review. Physiotherapy. 2016; 102: 29–40.](https://www.ncbi.nlm.nih.gov/pubmed/26390824) 54. [Eggenberger P, Tomovic S, et al. Older adults must hurry at pedestrian lights! A cross-sectional analysis of preferred and fast walking speed under singleand dual-task conditions. PLOS. 2017; 12: e0182180.](https://www.ncbi.nlm.nih.gov/pubmed/28759587) 55. [Altmann LJP, Stegemöller E, Hazamy AA, et al. Unexpected Dual Task Benefits on Cycling in Parkinson Disease and Healthy Adults: A Neuro- Behavioral Model. Wang K, ed. PLoS ONE. 2015; 10: e0125470.](https://www.ncbi.nlm.nih.gov/pubmed/25970607) 56. [Billinger SA, Boyne P, Coughenour E, et al. Does aerobic exercise and the FITT principle fit into stroke recovery? Curr Neurol Neurosci Rep. 2015; 15: 519.](https://www.ncbi.nlm.nih.gov/pubmed/25475494) 57. [Boyne P, Dunning K, Carl D, et al. High-Intensity Interval Training and Moderate-Intensity Continuous Training in Ambulatory Chronic Stroke: Feasibility Study. Phys Ther. 2016; 96: 1533-1544.](https://www.ncbi.nlm.nih.gov/pubmed/27103222) 58. [Kleim JA, Jones TA. Principles of experience-dependent neural plasticity: implications for rehabilitation after brain damage. J Speech Lang Hear Res. 2008; 51: S225-239.](https://www.ncbi.nlm.nih.gov/pubmed/18230848) 59. [Plummer P, Zukowski LA, Giuliani C, Hall AM, Zurakowski D. Effects of Physical Exercise Interventions on Gait-Related Dual-Task Interference in Older Adults: A Systematic Review and Meta-Analysis. Gerontology. 2015; 62: 94-117.](https://www.ncbi.nlm.nih.gov/pubmed/25721432) 60. [Chawla S, Walia M, Behari M, et al. Effect of type of secondary task on cued gait on people with idiopathic Parkinson’s disease. J Neurosci Rural Practice. 2014; 5: 18–23.](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3985349/) 61. [Beurskens R, Bock O. Age-related deficits of dual-task walking: a review. Neural Plast. 2012; 2012: 131608.](https://www.hindawi.com/journals/np/2012/131608/) 62. [Menant JC, Schoene D, Sarofim M, Lord SR. Single and dual task tests of gait speed are equivalent in the prediction of falls in older people: a systematic review and meta-analysis. Ageing Res Rev. 2014; 16: 83–104.](https://www.ncbi.nlm.nih.gov/pubmed/24915643) 63. [Montero-Odasso M, Verghese J, Beauchet O, Hausdorff JM. Gait and cognition: a complementary approach to understanding brain function and the risk of falling. J Am Geriatr Soc. 2012; 60: 2127–2136.](https://www.ncbi.nlm.nih.gov/pubmed/23110433) 64. [R. Galletly and S. G. Brauer. “Does the type of concurrent task affect preferred and cued gait in people with Parkinson’s disease?&” Australian J Physiother. 2005; 51: 175–180.](https://www.ncbi.nlm.nih.gov/pubmed/16137243) 65. [Kemper S, Herman RE, Lian CHT. The costs of doing two things at once for young and older adults: talking while walking, finger tapping, and ignoring speech or noise. Psych and Aging. 2003; 18: 181–192.](https://www.ncbi.nlm.nih.gov/pubmed/12825768) 66. [Chawla S, Walia M, Behari M, et al. Effect of type of secondary task on cued gait on people with idiopathic Parkinson’s disease. J Neurosci Rural Practice. 2014; 5: 18–23.](https://www.ncbi.nlm.nih.gov/pubmed/24741243) 67. [Beurskens R, Bock O. Age-related deficits of dual-task walking: a review. Neural Plast. 2012; 2012: 131608.](https://www.hindawi.com/journals/np/2012/131608/) 68. [Menant JC, Schoene D, Sarofim M, Lord SR. Single and dual task tests of gait speed are equivalent in the prediction of falls in older people: a systematic review and meta-analysis. Ageing Res Rev. 2014; 16: 83–104.](https://www.ncbi.nlm.nih.gov/pubmed/24915643) 69. [Montero-Odasso M, Verghese J, Beauchet O, Hausdorff JM. Gait and cognition: a complementary approach to understanding brain function and the risk of falling. J Am Geriatr Soc. 2012; 60: 2127–2136.](https://www.ncbi.nlm.nih.gov/pubmed/23110433) 70. [Galletly R, Brauer SG. Does the type of concurrent task affect preferred and cued gait in people with Parkinson’s disease? Austral J Physiother. 2005; 51: 175–180.](https://www.ncbi.nlm.nih.gov/pubmed/16137243) 71. [Rosso AL, Cenciarini M, Sparto PJ, Loughlin PJ, Furman JM, Huppert TJ. Neuroimaging of an attention demanding dual-task during dynamic postural control. Gait Posture. 2017; 57: 193-198.](https://www.ncbi.nlm.nih.gov/pubmed/28662465) 72. [Schättin A, Arner R, Gennaro F, de Bruin ED. Adaptations of Prefrontal Brain Activity, Executive Functions, and Gait in Healthy Elderly Following Exergame and Balance Training: A Randomized-Controlled Study. Frontiers in Aging Neuroscience. 2016; 8: 278.](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5120107/) 73. [Wang X-Q, Pi Y-L, Chen B-L, et al. Cognitive motor interference for gait and balance in stroke: a systematic review and meta-analysis. European Journal of Neurology. 2015; 22: 555-e37.](https://www.ncbi.nlm.nih.gov/pubmed/25560629) 74. [Lee KB, Kim JS, Hong BY, Lim SH. Clinical recovery from stroke lesions and related outcomes. J Clin Neurosci. 2017; 37: 79-82.](https://www.jocn-journal.com/article/S0967-5868(16)30446-5/abstract) 75. [An HJ, Kim JI, Kim YR, Lee KB, Kim DJ, Yoo KT, et al. The Effect of Various Dual Task Training Methods with Gait on the Balance and Gait of Patients with Chronic Stroke. Journal of Physical Therapy Science. 2014; 26: 1287– 1291.](https://www.ncbi.nlm.nih.gov/pubmed/25202199) 76. [Merzenich M. Experience-Dependent Adult Cortical Plasticity. III STEP Conference. APTA. Salt Lake City, UT. 2005.](http://www.austinpublishinggroup.com/physical-medicine/fulltext/pmr-v4-id1125.php) 77. [Kleim JA. 2005. Principles of experience-dependent neural plasticity: Implications for rehabilitation after brain damage. III STEP Conference. APTA. Salt Lake City, UT.](http://www.austinpublishinggroup.com/physical-medicine/fulltext/pmr-v4-id1125.php) 78. [Gordon Choi Y1, Qi F, Gordon J, Schweighofer N. Performance-based adaptive schedules enhance motor learning. J Mot Behav. 2008; 40: 273- 280.](https://www.ncbi.nlm.nih.gov/pubmed/18628104) 79. [Winstein C, Lewthwaite R, Blanton SR, Wolf LB, Wishart L. Infusing motor learning research into neurorehabilitation practice: a historical perspective with case exemplar from the accelerated skill acquisition program. J Neurol Phys Ther. 2014; 38: 190-200.](https://www.ncbi.nlm.nih.gov/pubmed/24828523) 80. [Nepveu JF, Thiel A, Tang A, Fung J, Lundbye-Jensen J, Boyd LA. A Single Bout of High-Intensity Interval Training Improves Motor Skill Retention in Individuals With Stroke. Neurorehabil Neural Repair. 2017; 31: 726-735.](https://www.ncbi.nlm.nih.gov/pubmed/28691645) 81. [Lewthwaite R, Wulf G. Optimizing motivation and attention for motor performance and learning. Curr Opin Psychol. 2017; 16: 38-42.](https://www.ncbi.nlm.nih.gov/pubmed/28813352) 82. [Sarkar M1, Fletcher D. Psychological resilience in sport performers: a review of stressors and protective factors. J Sports Sci. 2014; 32: 1419-1434.](https://www.ncbi.nlm.nih.gov/pubmed/24716648) 83. [Fulk G, He Y, Boyne P, Dunning K. Predicting Home and Community Walking Activity Poststroke. Stroke. 2017; 48: 406-411.](https://www.ncbi.nlm.nih.gov/pubmed/28057807) 84. [Fulk G. Personal communication. 2017.](http://www.austinpublishinggroup.com/physical-medicine/fulltext/pmr-v4-id1125.php) 85. [Hurst R. The international disability rights movement and the ICF. Disability and Rehabilitation. 2003; 25: 572-576.](https://www.ncbi.nlm.nih.gov/pubmed/12959330)