Chapter 4 Discussions
4.4 Methodological Issues
First, in the current experimental paradigm, a force-matching task with 50% MVC
force was used as the suprapostural task. In order to choose an adequate level of force
target, we executed a pilot study to examine the variability of force output in different
force-intensity and the effects of force-intensity on postural balance. With the same
apparatus and postural-suprapostural task design as the current experiment, twelve
healthy right-handed volunteers (4 males, 8 females; mean age: 24.5 ± 3.0 years)
without past neurological or neuromuscular impairment were recruited to perform a
force-matching task with 25%, 50% and 75% of MVC force while standing on a
41
stabilometer with keeping their balance at 50% of the maximal anterior tilt angle. The
twelve subjects of the pilot study were different to that of the main experiment. Subjects
were instructed to performed both postural and force-matching tasks as precision as
possible with providing online visual feedback of both targets and their performance.
Coefficient of variance of peak precision grip force (CV_PPF) and postural error were
measured in each condition. A one-way repeated-measures analysis of variance with
Bonferroni adjustments were used to contrast force-matching variability (CV_PPF) and
postural error differences among 25%, 50%, and 75% of MVC force conditions. The
level of significance was set as p < 0.05. ANOVA statistics suggested that CV_PPF
differed among the force-intensity conditions (F
2, 22
= 24.18, p < 0.01), and CV_PPF wasgreatest in the 25% MVC condition (p < 0.01)(Figure 14 (a)). ANOVA statistics also
suggested that the postural error was not significantly different among three
force-intensity conditions (F
2, 22
= 0.03, p = .97)(Figure 14 (b)). These facts indicated thatpostural error was not significantly affected by force-intensity of the force-matching
task and force-matching with 50% or 75% of MVC force would have less
within-subject variability of force output. Also, Slifkin and Newell (1999) reported that optimal
signal to noise ratio is in about 50% of maximal force output that subjects can
produce.
62
Besides, for avoiding possible fatigue effect result from higherforce-intensity output (75% of MVC), we chose the 50% of MVC force as the target of the
42
force-matching task in the main experiment.
Second, the experiments were conducted in two separate days with one-week apart
in order to avoid the potential fatigue or learning effect. In this study, participants of
both younger and older groups were assigned to either the PF or SF conditions on the
first experimental day and executed the other condition on the second experimental day.
On the first experimental day, half participants in both age groups were assigned to the
PF condition and the others were assigned to the SF condition. Moreover, all behavioral
parameters of postural-suprapostural task were normalized to their corresponding
control task measured in the same experimental day, avoiding the results from the effect
of different baseline conditions between two experimental days. In order to test the
potential learning effect, all behavioral parameters, including normalized postural error,
normalized postural ApEn, normalized matching error, and normalized
force-matching RT, were compared between the participants who conduct the SF condition on
the first experimental day and the participants who conduct the PF condition on the first
experimental day via student t-test. The results showed no significant difference
between these two groups in both conditions (Table 2), indicating there was no
significant learning effect on behavioral performance.
Third, both younger and older adults performed the same postural task and
suprapostural task in the present study. The task difficulty may be different between the
43
younger and older adults since older adults might have less capability of balance control
or force scaling than younger adults.
52,61
And the differences of relative task difficultymight vary central resource allocation and affect the optimal strategy selection and
performance of postural and suprapostural tasks. However, we could not quantify the
real perception of task difficulty in postural and suprapostural task for younger and
older adults and it is beyond the scope of this study. Further investigation is needed by
considering different task difficulty level of postural and suprapostural tasks.
44
Chapter 5 Conclusion
This study first presented three ERP components (P1, N1, and P2) in a
postural-suprapostural task with a perceptual-motor goal to investigate the effects of
task prioritization in younger and older adults. Significant task prioritization benefit was
found with SF strategy, with better task accuracy and attentional resource allocation. In
healthy older adults, P1 positivity was enhanced for achieving optimal postural and
force-matching performance, especially under the SF condition. Our behavioral and
neurophysiological data suggested that SF strategy may be the adequate strategy for
both younger and older adults in a postural-suprapostural task, with more automatic
postural control and optimal resource allocation between postural and suprapostural
tasks (Figure 15). However, neurological disease is a critical factor to affect
postural-suprapostural performance, especially for balance control. Some researchers argued that
posture-first might be a safe strategy for patients with Parkinson’s disease. Therefore,
the appropriateness of task priority strategy in patients with neurological disease, such
as Parkinson’s disease, requires further investigation for providing optimal attentional
strategy clinically.
45
References
1. Woollacott 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.
2. Riley MA, Stoffregen TA, Grocki MJ, Turvey MT. Postural stabilization for the
control of touching. Hum Mov Sci 1999;18:795-817.
3. Huxhold O, Li SC, Schmiedek F, Lindenberger U. Dual-tasking postural control:
Aging and the effects of cognitive demand in conjunction with focus of
attention. Brain Res Bull 2006;69:294-305.
4. Stoffregen TA, Smart LJ, Bardy BG, Pagulayan RJ. Postural stabilization of
looking. J Exp Psychol Hum Percept Perform 1999;25:1641-58.
5. Yogev-Seligmann G, Hausdorff JM, Giladi N. Do we always prioritize balance
when walking? Towards an integrated model of task prioritization. Mov Disord
2012;27:765-70.
6. Mitra S, Fraizer EV. Effects of explicit sway-minimization on postural–
suprapostural dual-task performance. Hum Mov Sci 2004;23:1-20.
7. Pellecchia GL. Postural sway increases with attentional demands of concurrent
cognitive task. Gait Posture 2003;18:29-34.
8. Mitra S. Adaptive utilization of optical variables during postural and
suprapostural dual-task performance: Comment on Stoffregen, Smart, Bardy,
46
and Pagulayan (1999). J Exp Psychol Hum Percept Perform 2004;30:28-38.
9. Papegaaij S, Taube W, Baudry S, Otten E, Hortobágyi T. Aging causes a
reorganization of cortical and spinal control of posture. Front Aging Neurosci
2014;6:28.
10. Shumway-Cook A, Woollacott MH. Motor control: translating research into
clinical practice. Philadelphia: Wolters Kluwer Health/Lippincott Williams &
Wilkins; 2012:223-45.
11. Brown LA, Sleik RJ, Polych MA, Gage WH. Is the prioritization of postural
control altered in conditions of postural threat in younger and older adults? J
Gerontol A Biol Sci Med Sci 2002;57:M785-M92.
12. Borel L, Alescio-Lautier B. Posture and cognition in the elderly: Interaction and
contribution to the rehabilitation strategies. Neurophysiol Clin 2014;44:95-107.
13. Lacour M, Bernard-Demanze L, Dumitrescu M. Posture control, aging, and
attention resources: Models and posture-analysis methods. Neurophysiol Clin
2008;38:411-21.
14. Mitra S. Postural costs of suprapostural task load. Hum Mov Sci
2003;22:253-70.
15. Bernard-Demanze L, Dumitrescu M, Jimeno P, Borel L, Lacour M. Age-related
changes in posture control are differentially affected by postural and cognitive
47
task complexity. Curr Aging Sci 2009;2:135-49.
16. Siu K-C, Woollacott MH. Attentional demands of postural control: The ability to
selectively allocate information-processing resources. Gait Posture
2007;25:121-6.
17. Jehu DA, Desponts A, Paquet N, Lajoie Y. Prioritizing attention on a reaction
time task improves postural control and reaction time. Int J Neurosci
2015;125:100-6.
18. Kelly VE, Eusterbrock AJ, Shumway-Cook A. Factors influencing dynamic
prioritization during dual-task walking in healthy young adults. Gait Posture
2013;37:131-4.
19. Yogev-Seligmann G, Rotem-Galili Y, Mirelman A, Dickstein R, Giladi N,
Hausdorff JM. How does explicit prioritization alter walking during dual-task
performance? Effects of age and sex on gait speed and variability. Phys Ther
2010;90:177-86.
20. Yogev-Seligmann G, Rotem-Galili Y, Dickstein R, Giladi N, Hausdorff JM.
Effects of explicit prioritization on dual task walking in patients with Parkinson's
disease. Gait Posture 2012;35:641-6.
21. Doumas M, Krampe RT. Ecological relevance determines task priority in older
adults’ multitasking. J Gerontol B Psychol Sci Soc Sci 2013;70(3):377-85.
48
22. Krampe RT, Schaefer S, Lindenberger U, Baltes PB. Lifespan changes in
multi-tasking: Concurrent walking and memory search in children, young, and older
adults. Gait Posture 2011;33:401-5.
23. Tsang PS. Ageing and attentional control. Q J Exp Psychol (Hove) 2012;66:
1517-47.
24. Malcolm BR, Foxe JJ, Butler JS, De Sanctis P. The aging brain shows less
flexible reallocation of cognitive resources during dual-task walking: a mobile
brain/body imaging (MoBI) study. Neuroimage 2015;117:230-42.
25. Hollman JH, Kovash FM, Kubik JJ, Linbo RA. Age-related differences in
spatiotemporal markers of gait stability during dual task walking. Gait Posture
2007;26:113-9.
26. 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;52A:M232-M40.
27. Siu K-C, Chou L-S, Mayr U, Donkelaar Pv, Woollacott MH. Does inability to
allocate attention contribute to balance constraints during gait in older adults? J
Gerontol A Biol Sci Med Sci 2008;63:1364-9.
28. Weeks D, Forget R, Mouchnino L, Gravel D, Bourbonnais D. Interaction
between attention demanding motor and cognitive tasks and static postural
49
stability. Gerontology 2003;49:225-32.
29. Bloem BR, Grimbergen YAM, van Dijk JG, Munneke M. The “posture second”
strategy: A review of wrong priorities in Parkinson's disease. J Neurol Sci
2006;248:196-204.
30. Hartley AA. Age differences in dual-task interference are localized to
response-generation processes. Psychol Aging 2001;16:47-54.
31. Kasper RW, Cecotti H, Touryan J, Eckstein MP, Giesbrecht B. Isolating the
neural mechanisms of interference during continuous multisensory dual-task
performance. J Cogn Neurosci 2014;26:476-89.
32. Huang CY, Hwang IS. Behavioral data and neural correlates for postural
prioritization and flexible resource allocation in concurrent postural and motor
tasks. Hum Brain Mapp 2013;34:635-50.
33. De Sanctis P, Butler JS, Malcolm BR, Foxe JJ. Recalibration of inhibitory
control systems during walking-related dual-task interference: A mobile
brain-body imaging (MOBI) study. Neuroimage 2014;94:55-64.
34. Luck SJ. Introduction to the event-related potential technique (2nd edition).
Cambridge, MA, USA: The MIT Press; 2014:71-100.
35. Nash AJ, Fernandez M. P300 and allocation of attention in dual-tasks. Int J
Psychophysiol 1996;23:171-80.
50
36. Kida T, Kaneda T, Nishihira Y. Modulation of somatosensory processing in dual
tasks: an event-related brain potential study. Exp Brain Res 2012;216:575-84.
37. Little CE, Woollacott M. EEG measures reveal dual-task interference in postural
performance in young adults. Exp Brain Res 2015;233:27-37.
38. Vogel EK, and Steven J. Luck. The visual N1 component as an index of a
discrimination process. Psychophysiology 2000;37:190-203.
39. Näätänen R. Attention and brain function. Hillsdale, N.J.: L. Erlbaum; 1992.
40. Navon D. Exploring two methods for estimating performance tradeoff. Bull.
Psychon. Soc. 1990;28:155-7.
41. Szameitat AJ, Schubert T, Müller KU, Von Cramon DY. Localization of
executive functions in dual-task performance with fMRI. Cognitive
Neuroscience, Journal of 2002;14:1184-99.
42. Schubert T, Szameitat AJ. Functional neuroanatomy of interference in
overlapping dual tasks: an fMRI study. Brain Res Cogn Brain Res
2003;17:733-46.
43. Zanone PG, Monno A, Temprado JJ, Laurent M. Shared dynamics of attentional
cost and pattern stability. Hum Mov Sci 2001;20:765-89.
44. Huang CY, Zhao CG, Hwang IS. Neural basis of postural focus effect on
concurrent postural and motor tasks: Phase-locked electroencephalogram
51
responses. Behav Brain Res 2014;274:95-107.
45. Pincus S. Approximate entropy (ApEn) as a complexity measure. Chaos
1995;5:110-7.
46. Pincus SM. Approximate entropy as a measure of system complexity. Proc Natl
Acad Sci U S A 1991;88:2297-301.
47. Donker S, Roerdink M, Greven A, Beek P. Regularity of center-of-pressure
trajectories depends on the amount of attention invested in postural control. Exp
Brain Res 2007;181:1-11.
48. Burcal CJ, Drabik EC, Wikstrom EA. The effect of instructions on postural–
suprapostural interactions in three working memory tasks. Gait Posture
2014;40:310-4.
49. Wulf G, McNevin N, Shea CH. The automaticity of complex motor skill
learning as a function of attentional focus. Q J Exp Psychol A 2001;54:1143-54.
50. Boisgontier MP, Beets IAM, 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;37:1824-37.
51. Kuczyński M, Szymańska M, Bieć E. Dual-task effect on postural control in
high-level competitive dancers. J Sports Sci 2011;29:539-45.
52
52. Hillyard SA, Vogel EK, Luck SJ. Sensory gain control (amplification) as a
mechanism of selective attention: electrophysiological and neuroimaging
evidence. Philos Trans R Soc Lond B Biol Sci 1998;353:1257-70.
53. Luck SJ, Heinze HJ, Mangun GR, Hillyard SA. Visual event-related potentials
index focused attention within bilateral stimulus arrays. II. Functional
dissociation of P1 and N1 components. Electroencephalogr Clin Neurophysiol
1990;75:528-42.
54. Heinze HJ, Luck SJ, Mangun GR, Hillyard SA. Visual event-related potentials
index focused attention within bilateral stimulus arrays. I. Evidence for early
selection. Electroencephalogr Clin Neurophysiol 1990;75:511-27.
55. Magill RA. Motor learning and control : concepts and applications. New York:
McGraw-Hill; 2011:198-9.
56. Hülsdünker T, Mierau A, Neeb C, Kleinöder H, Strüder HK. Cortical processes
associated with continuous balance control as revealed by EEG spectral power.
Neurosci Lett 2015;592:1-5.
57. Jones L. Force matching by patients with unilateral focal cerebral lesions.
Neuropsychologia 1989;27:1153-63.
58. Kida T, Nishihira Y, Hatta A, et al. Resource allocation and somatosensory P300
amplitude during dual task: effects of tracking speed and predictability of
53
tracking direction. Clin Neurophysiol 2004;115:2616-28.
59. Serrien DJ, Ivry RB, Swinnen SP. Dynamics of hemispheric specialization and
integration in the context of motor control. Nat Rev Neurosci 2006;7:160-6.
60. Lijffijt M, Lane SD, Moeller FG, Steinberg JL, Swann AC. Trait impulsivity and
increased pre-attentional sensitivity to intense stimuli in bipolar disorder and
controls. J Psychiatr Res 2015;60:73-80.
61. Latash ML. Neurophysiological basis of movement. Champaign, IL: Human
Kinetics; 2008:279-87.
62. Slifkin AB, Newell KM. Noise, information transmission, and force variability. J
Exp Psychol Hum Percept Perform 1999;25:837-51.
54
Figures
Figure 1. Thinking process of the study.
55
Figure 2. Experimental setup of the study.
56
Figure 3. Flow diagram of the study.
57
Time(s)
0 5 10 15 20 25 30
Time(s)
0 5 10 15 20 25 30
Figure 4. Visual information for the PF and SF conditions. (PF: posture-first; SF:
supraposture-first)
PF condition
SF condition
target line of stabilometer movement and force-matching
performance of stabilometer movement
performance of force-matching
58
Figure 5. Means and standard errors of absolute (upper) and normalized (lower) postural error of younger and older groups in the SF and PF conditions. (PF:
posture-first; SF: supraposture-first)(*p < 0.05)
59
Figure 6. Means and standard errors of absolute (upper) and normalized (lower) ApEn of younger and older groups in the SF and PF conditions. (PF:
posture-first; SF: supraposture-first)(*p < 0.05)
60
Figure 7. Means and standard errors of absolute (upper) and normalized (lower) force-matching error of younger and older groups in the SF and PF conditions.
(PF: posture-first; SF: supraposture-first)(*p < 0.05)
61
Figure 8. Means and standard errors of absolute (upper) and normalized (lower) force-matching RT of younger and older groups in the SF and PF conditions. (PF: posture-first; SF: supraposture-first)
62
Figure 9. Typical ERP waveforms of (a) younger group and (b) older group in postural-suprapostural tasks
63
Younger Group Older Group
P1
__64
Figure 10. Task prioritization effect on ERP waveforms of (a) N1 amplitude of younger group, (b) P2 amplitude of younger group, (c) P1 amplitude of older group, (d) N1 amplitude of older group, and (e) P2 amplitude of older group in postural-suprapostural tasks.
65
Younger Group Older Group
P1
__66
Figure 11. Task prioritization effect on grand-averaged ERP topological plots of (a) N1 amplitude of younger group, (b) P2 amplitude of younger group, (c) P1
amplitude of older group, (d) N1 amplitude of older group, and (e) P2 amplitude of older group in postural-suprapostural tasks. Filled squares represent the electrode had a significant difference in ERP amplitudes between the SF and PF conditions in ERP amplitudes (p < 0.05).
67
Figure 12. Age effect on grand-averaged ERP topological plots of (a) N1 amplitude in the PF condition, (b) P2 amplitude in the PF condition, (c) N1 amplitude in the SF condition, and (d) P2 amplitude in the SF condition in postural-suprapostural tasks. Filled squares represent the electrode had a significant difference in ERP amplitudes between the SF and PF conditions in ERP amplitudes (p < 0.05).
68
80.00/89.00 ms90.00/99.00 ms 100.00/109.00 ms 110.00/119.00 ms 120.00/129.00 ms 130.00/139.00 ms140.00/149.00 ms 150.00/159.00 ms 160.00/169.00 ms 170.00/179.00 ms 180.00/189.00 ms190.00/199.00 ms 200.00/209.00 ms 210.00/219.00 ms 220.00/229.00 ms
80.00/89.00 ms90.00/99.00 ms 100.00/109.00 ms 110.00/119.00 ms 120.00/129.00 ms 130.00/139.00 ms140.00/149.00 ms 150.00/159.00 ms 160.00/169.00 ms 170.00/179.00 ms 180.00/189.00 ms190.00/199.00 ms 200.00/209.00 ms 210.00/219.00 ms 220.00/229.00 ms 80.00/89.00 ms90.00/99.00 ms 100.00/109.00 ms 110.00/119.00 ms 120.00/129.00 ms 130.00/139.00 ms140.00/149.00 ms 150.00/159.00 ms 160.00/169.00 ms 170.00/179.00 ms 180.00/189.00 ms190.00/199.00 ms 200.00/209.00 ms 210.00/219.00 ms 220.00/229.00 ms 80.00/89.00 ms90.00/99.00 ms 100.00/109.00 ms 110.00/119.00 ms 120.00/129.00 ms 130.00/139.00 ms140.00/149.00 ms 150.00/159.00 ms 160.00/169.00 ms 170.00/179.00 ms 180.00/189.00 ms190.00/199.00 ms 200.00/209.00 ms 210.00/219.00 ms 220.00/229.00 ms
T a sk P ri o ri ti za ti o n Effect P F SF
Y oung
er Older
Age Effect
+6.0 +5.1 +4.1 +3.2 +2.3 +1.3 +0.4 -0.6 -1.5 -2.4 -3.4 -4.3 -5.3 -6.2 -7.1 -8.1 -9.0
69
Figure 13. Population means of topological plots of all task priority condition (PF and SF conditions) and age groups (younger and older groups) in
postural-suprapostural tasks.
70
Figure 14. Force CV and postural error of pilot study.
71
Figure 15. Graphic summary of the study.
72
Tables
Table 1. Baseline characteristics of the participants.
Younger Group (n=16) Older Group (n=16)
Age (yrs) 24.4 ± 4.6 69.1 ± 2.7
Gender, M/F 8/8 6/10
Height (cm) 168.7 ± 9.3 155.9 ± 7.6 Weight (kg) 64.4 ± 14.0 60.1 ± 9.2
MMSE score - 29.3 ± 1.5
73
Table 2. Comparison of collected normalized postural error, postural ApEn, force-matching error, and force-force-matching RT between the first and second experimental days.
NFRT: normalized force-matching reaction time
74
Appendices
Appendix 1. Mini Mental State Examination (MMSE).
75
76
77
78
Appendix 2. Approved document form the research ethics board at the National Taiwan University Clinical Trail Center.