. 2017 Aug 1;4(4):041403. doi: 10.1117/1.NPh.4.4.041403

Table 1.

Overview about the population, study designs, and data processing steps of reviewed fNIRS studies (note that the number of trials is reported per condition).


First author	– Population ( $n = number of participants$ ; $age in years \pm SD$ )	1. Baseline condition	1. DPF
	• Conditions	2. Baseline duration	2. Data processing (filtering)
		3. Number of trials and duration	3. Final data processing
		4. Rest phase duration	4. Activation parameters
		4. Rest phase duration	5. Time used for analysis
Al-Yahya et al.⁶⁵	– Stroke patients ( $n = 19$ ; $59.61 \pm 15.03$ )	1. Quiet standing	1. Age-dependent value ( $4.99 + 0.067 \times {age}^{0.814}$ )
	– Healthy old adults ( $n = 20$ ; $54.35 \pm 9.38$ )	2. 25 to 45 s (randomized order)	2. LPF at 0.67 Hz
	• DTW vs. NW	3. $5 \times$ ; 30 s	3. Baseline correction; averaging
		4. 25 to 45 s (between trials / randomized order)	4. Oxy- and deoxyHb
		4. 25 to 45 s (between trials / randomized order)	5. 6 to 16 s after task begin
Atsummori et al.⁶⁹	– Healthy young adults ( $n = 6$ ; $29.7 \pm 3.3$ )	1. Quiet standing	1. Constant value (no details reported)
	• DTW vs. NW	2. 5 s before task begin	2. Not reported
		3. $5 \times$ (DTW) / $6 \times$ (NW); 10 s	3. Baseline correction; averaging
		4. 20 s at beginning	4. Oxy- and deoxyHb
		4. 20 s at beginning	5. 6 s after task begin/ending
Basso-Moro et al.⁹⁸	– Healthy young adults ( $n = 16$ ; $29 \pm 4.8$ )	1. Quiet standing	1. Age-dependent value ( $4.99 + 0.067 \times {age}^{0.814}$ )
	• Perturbations in semivirtual reality with increasing difficulty	2. Last 30 s (of 2 min)	2. LPF at 0.1 Hz
		3. $7 \times$ ; 45 s	3. Averaging
		4. 2 min after block	4. Oxy- and deoxyHb
		4. 2 min after block	5. Last 10 s of perturbation
Beurskens et al.¹⁰⁵	– Healthy young adults ( $n = 15$ ; $24.5 \pm 3.3$ )	1. Sitting on chair	1. Constant value (6.0)
	– Healthy old adults ( $n = 10$ ; $71.0 \pm 3.8$ )	2. 30 s	2. HRF-filter; wavelet MDL detrending algorithm
	• DTW vs. NW	3. $2 \times$ ; 30 s	3. Moving standard deviation and spline interpolation, baseline correction, canonical HRF
		4. Not reported	4. Oxy- and deoxyHb
		4. Not reported	5. Entire task time
Caliandro et al.⁷⁰	– Patients with ataxic gait ( $n = 14$ ; 27 to 71)	1. Quiet standing	1. Constant value (5.93)
	– Healthy controls ( $n = 20$ ; 32 to 65)	2. Last 10 s of standing	2. LPF at 0.1 Hz
	• Patients vs. HC	3. $1 \times$ ; 10 m	3. Baseline correction; averaging
		4. Not relevant	4. OxyHb
		4. Not relevant	5. Entire task time expect of first 5 s
Caliandro et al.⁷¹	– Patients with ataxic gait ( $n = 19$ ; 31 to 70)	1. Quiet standing	1. Constant value (5.93)
	– Healthy controls ( $n = 15$ ; 36 to 73)	2. Last 10 s of standing	2. LPF at 0.1 Hz
	• Patients vs. HC	3. $2 \times$ ; 10 m	3. Baseline correction; averaging
		4. 30 min between trials	4. OxyHb
		4. 30 min between trials	5. Entire task time expect of first 5 s
Clark et al.⁶⁶	– Older persons with mobility and somatosensory deficits ( $n = 14$ ; $77.1 \pm 5.56$ )	1. Quiet standing	1. N/A
	• Walking in normal shoes vs. texture insoles vs. barefoot vs. DTW	2. 10 s immediately before task	2. No filter
		3. $5 \times$ walking laps with 18 m (overground); 60 to 120 s (treadmill)	3. Averaging
		4. 2 min after task	4. TOI
		4. 2 min after task	5. Entire task phase
Clark et al.⁸⁶	– Older adults with mild mobility deficits ( $n = 16$ ; $77.2 \pm 5.6$ )	1. Quiet standing	1. N/A
	• NW vs. DTW	2. 10 s immediately before task	2. No filter
		3. $5 \times$ walking laps with 18 m	3. Averaging
		4. 2 min after task	4. TOI
		4. 2 min after task	5. 10 s before task begin (preparation phase) and in steady phase/transition phase excluded
Doi et al.⁷²	– Adults with mild cognitive impairment ( $n = 16$ ; $75.4 \pm 7.2$ )	1. Quiet standing	1. N/A (arbitrary unit)
	• NW vs. DTW	2. 10 s before walking	2. LPF at 0.05 Hz; linear fitting on baseline data
		3. $3 \times$ ; 20 s	3. Averaging
		4. 30 s between trials	4. OxyHb
		4. 30 s between trials	5. Entire task period
Eggenberger et al.⁶⁸	– Healthy old adults (dancing: $n = 19$ ; $72.8 \pm 5.9$ ; balance: $n = 14$ ; $77.8 \pm 7.4$ )	1. Walking at $2 km / h$	1. N/A (absolute values)
	• Dancing vs. balancing (before and after intervention)	2. Middle 40 s (of 1 min)	2. 60 s moving average: motion artifact correction (oxyHb: $> 2.5$ and $< - 2.5 μ M / deoxyHb$ : $> 1.5$ and $< - 1.5 μ M$ excluded); visual inspection of data
		3. $8 \times$ ; 30 s	3. Averaging
		4. 30 s between trials (walking at $2 km / h$ )	4. OxyHb
		4. 30 s between trials (walking at $2 km / h$ )	5. 1 to 7 s = acceleration phase; 10 to 25 s = steady state walking phase; 26 to 34 s = deceleration phase; 35 to 46 s = drop phase
Ferrari et al.⁹⁹	– Healthy, young adults ( $n = 22$ ; $26.5 \pm 4.0$ )	1. Quiet standing	1. Age-dependent value ( $4.99 + 0.067 \times {age}^{0.814}$ )
	• Balancing in semivirtual reality	2. Last 30 s (of 2 min)	2. LPF at 0.1 Hz
		3. $2 \times$ ; 9 min	3. Averaging
		4. 2 min after block	4. Oxy- and deoxyHb
		4. 2 min after block	5. 30 s per task
Fraser et al.⁶³	– Healthy young adults ( $n = 19$ ; $21.83 \pm 1.92$ )	1. Quiet standing	1. Constant value (no details reported)
	– Healthy old adults ( $n = 14$ ; $66.85 \pm 5.26$ )	2. 5 s	2. No filter
	• NW vs. single cognitive task vs. easy DTW vs. hard DTW	3. Walking: $2 \times$ ; 2 min; single cognitive task: $4 \times$ ; 75 s; DTW $4 \times$ ; 2 min (for each dual-task condition)	3. Averaging
		4. 30 to 60 s between trials	4. Oxy- and deoxyHb
		4. 30 to 60 s between trials	5. Entire task period
Fujimoto et al.¹⁰²	- Patients with subcortical stroke ( $n = 20$ ; $60.2 \pm 9.5$ )	1. Quiet standing	1. N/A (arbitrary unit)
	• Postural test before/after rehabilitation	2. Time before next perturbation (ERD)	2. HPF at 0.01 Hz; PCA
		3. $15 \times$ ; 1 s	3. Two parameter gamma HRF
		4. 5 to 15 s between trials (randomized)	4. Oxy- and deoxyHb
		4. 5 to 15 s between trials (randomized)	5. Around perturbations
Fujita et al.¹⁰¹	– Healthy, young adults (low span group: $n = 13$ ; $24.0 \pm 3.1$ / high span group: $n = 16$ ; $22.5 \pm 3.6$ )	1. Quiet standing	1. N/A (arbitrary unit)
	• Single- and dual-task mono- or bipedal standing	2. 10 s	2. LPF at 0.5 Hz; HPF at 0.01 Hz; 5 s moving average
		3. $3 \times$ ; 20 s	3. Baseline normalization, baseline correction, averaging
		4. 10 s between trials	4. OxyHb
		4. 10 s between trials	5. Entire task time
Harada et al.⁵³	– Healthy, old adults ( $n = 15$ ; $63 \pm 4$ )	1. Quiet standing	1. N/A (arbitrary unit)
	• Low vs. high gait capacity group at different speeds	2. 10 s before walking	2. HPF at 0.03 Hz
		3. $3 \times$ ; 60 s	3. Baseline normalization; averaging
		4. 40 s between trials	4. OxyHb
		4. 40 s between trials	5. 20 s after target speed
Helmich et al.¹⁰⁸	– Young, concussed adults with persistent postconcussive symptoms ( $n = 7$ ; $29 \pm 15$ )	1. N/A	1. Constant value (6.0)
	– Young, concussed adults with minor postconcussive symptoms ( $n = 13$ ; $26 \pm 7$ )	2. N/A	2. LPF at 0.1 Hz; HPF at 0.001 Hz; spline interpolation; visual inspection
	– Healthy, young adults ( $n = 10$ ; $27 \pm 8$ )	3. $10 \times$ ; 10 s	3. Normalization; averaging
	• Comparison of three groups during standing on different surfaces (stable vs. instable) and sensory conditions (eyes closed vs. eyes open vs. blurred vision)	4. No rest between trials	4. Oxy- and deoxyHb
		4. No rest between trials	5. Entire task time
Hernandez et al.⁸²	– Healthy old adults ( $n = 8$ ; $61 \pm 4$ )	1. Quiet standing	1. Constant value (6.0)
	– Patients with multiple sclerosis ( $n = 8$ ; $57 \pm 5$ )	2. 10 s before walking (counting silently in steps of 1)	2. LPF at 0.14 Hz; noisy channels excluded (dark current condition or saturation); visual inspected
	• Comparison of healthy adults and patients with multiple sclerosis during NW and DTW	3. $3 \times$ walking loops (= $6 \times$ straight walks a 14 ft.)	3. Baseline normalization; averaging
		4. At least 10 s after trial	4. OxyHb
		4. At least 10 s after trial	5. Entire task time
Herold et al.¹⁰⁰	– Healthy young adults ( $n = 10$ ; 25; 21 to 47)	1. Quiet standing	1. N/A (arbitrary unit)
	• Standing vs. balancing on balance board	2. 30 s before task	2. 5.0 s moving average; LPF at 0.5 Hz; HPF at 0.01 Hz; PCA ( $r = 0.25$ )
		3. $3 \times$ ; 30 s	3. Averaging
		4. 30 s after trial	4. Oxy- and deoxyHb
		4. 30 s after trial	5. Middle 20 s
Holtzer et al.⁷³	– Healthy, young adults ( $n = 11$ ; 19 to 29)	1. Quiet standing	1. Constant value (6.0)
	– Healthy, old adults ( $n = 11$ ; 69 to 88)	2. 5 s before walking	2. LPF at 0.14 Hz; combined principal and independent component analysis
	• DTW vs. NW vs. standing/comparison between cohorts	3. $3 \times$ walking loops (= $6 \times$ straight walks a 15 ft.)	3. Baseline normalization; averaging
		4. Not reported	4. OxyHb
		4. Not reported	5. Old 4 s / young 3.5 s
Holtzer et al.⁷⁴	– Nondemented older adults ( $n = 318$ ; $76.66 \pm 6.7$ )	1. Quiet standing	1. Constant value (6.0)
	• DTW vs. NW vs. standing	2. 10 s (counting silently forward in steps of 1)	2. LPF at 0.14 Hz; noisy channels excluded (dark current condition or saturation); visual inspected
		3. $3 \times$ walking loops (= $6 \times$ straight walks a 14 ft.) / standing for 30 s	3. Baseline normalization; averaging
		4. “Short break” reported	4. OxyHb
		4. “Short break” reported	5. Entire task time
Holtzer et al.⁸⁴	– Nondemented older adults ( $n = 348$ ; $76.8 \pm 6.8$ )	1. Quiet standing	1. Constant value (6.0)
	– Older adults with low perceived stress ( $n = 147$ ; $76.72 \pm 6.87$ )	2. 10 s (counting silently forward in steps of 1)	2. LPF at 0.14 Hz; noisy channels excluded (dark current condition or saturation); visual inspected
	– Older adults high perceived stress ( $n = 171$ ; $76.58 \pm 6.37$ )	3. $3 \times$ walking loops (= $6 \times$ straight walks a 14 ft.) / standing for 30 s	3. Baseline normalization; averaging
	• DTW vs. NW vs. standing/comparison between cohorts	4. “Short break” reported	4. OxyHb
	• DTW vs. NW vs. standing/comparison between cohorts	4. “Short break” reported	5. Entire task time
Holtzer et al.⁷⁵	– Nondemented older adults (total: $n = 236$ ; $75.5 \pm 6.49)$	1. Quiet standing	1. Constant value (6.0)
	– Healthy older adults ( $n = 167$ ; $74.43 \pm 6.04$ )	2. 10 s (counting silently forward in steps of 1)	2. LPF at 0.14 Hz; noisy channels excluded (dark current condition or saturation); visual inspected
	– Older adults with peripheral NGA ( $n = 40$ ; $77.03 \pm 6.27$ )	3. $3 \times$ walking loops (= $6 \times$ straight walks a 14 ft.) / standing for 30 s	3. Baseline normalization; averaging
	– Older adults with central NGA ( $n = 29$ ; $79.59 \pm 7.38$ )	4. “Short break” reported	4. OxyHb
	• DTW vs. NW vs. standing/comparison between cohorts	4. “Short break” reported	5. Entire task time
Holtzer et al.⁸⁵	– Older adults with low perceived fatigue ( $n = 160$ ; $76.20 \pm 6.64$ )	1. Quiet standing	1. Constant value (6.0)
	– Older adults with high perceived fatigue ( $n = 154$ ; $77.41 \pm 6.66$ )	2. 10 s (counting silently forward in steps of 1)	2. LPF at 0.14 Hz; noisy channels excluded (dark current condition or saturation); visual inspected
	• DTW vs. NW vs. standing/comparison between cohorts	3. $3 \times$ walking loops (= $6 \times$ straight walks a 14 ft.) / standing for 30 s	3. Baseline normalization; averaging
		4. “Short break” reported	4. OxyHb
		4. “Short break” reported	5. Entire task time
Huppert et al.⁹¹	– Healthy young adults ( $n = 10$ ; 21 to 47)	1. Quiet standing	1. Not relevant (image reconstruction)
	• Stepping reaction task	2. Time before next trial (4 to 8 s, random order)	2. Discrete cosinus transform term ( $0 - 1 / 120 Hz$ ); visual inspected
		3. $8 \times$ blocks a $32 \times$ trials	3. Gamma-variant HRF; averaging
		4. 4 to 8 s between trials (random order) / few minutes after 2 to 3 scans	4. Oxy- and deoxyHb
			5. Entire task phase
Karim et al.⁹⁷	– Healthy young adults ( $n = 9$ ; 18 to 42)	1. Quiet standing	1. Not relevant (image reconstruction)
	• Video game with balance task	2. 60 s (pre- and posttask)	2. Cosinus transform term (0 to $1 / 120 Hz$ ); visual inspected
		3. $6 \times$ beginner / $8 \times$ advanced level; 30 to 60 s	3. Boxcar HRF; averaging
		4. 30 s between trials	4. Oxy- and deoxyHb
		4. 30 s between trials	5. Entire task phase
Karim et al.⁹²	– Healthy young adults ( $n = 15$ ; $28 \pm 9$ )	1. Quiet standing	1. Not relevant (image reconstruction)
	• SOT conditions	2. 45 s before trial	2. Cosinus transform term (0 to $1 / 120 Hz$ )
		3. $2 \times; 45 s$	3. Gamma-variant HRF; averaging
		4. 60 s after trial / 2 min after two scans	4. Oxy- and deoxyHb
		4. 60 s after trial / 2 min after two scans	5. Entire task phase
Kim et al.¹⁰⁶	– Healthy young adults ( $n = 14$ ; $30.06 \pm 4.53$ )	1. Not reported	1. Not reported
	• Stepping (ST) vs. Treadmill walking (TW) vs. robot-assisted walking (RAW)	2. Not reported	2. Gaussian smoothing; wavelet MDL algorithm
		3. $5 \times$ ; 30 s (ST, TW); 60 s (RAW)	3. Canonical HRF
		4. 15 s at begin and end; 30 s between trials (ST, TW) / 60 s at begin and end; 45 s between trials (RAW)	4. OxyHb
			5. Entire task time
Koenraadt et al.⁵⁴	– Healthy, young adults ( $n = 11 / 23 \pm 4$ )	1. Quiet standing	1. N/A (arbitrary unit)
	• Precision walking vs. NW	2. 25 to 35 s	2. LPF at 1.25 Hz; HPF at 0.01 Hz; superficial interference with LPF at 1 Hz; short separation channels (1 cm)
		3. $10 \times$ ; 35 s	3. Baseline normalization; averaging
		4. 25 to 35 s before/after trial / 3 min after 10 trials	4. Oxy- and deoxyHb
		4. 25 to 35 s before/after trial / 3 min after 10 trials	5. 12.5 s in task phase
Kurz et al.⁵⁵	– Healthy, young adults ( $n = 13$ ; $23.7 \pm 1.4$ )	1. Quiet standing	1. N/A (arbitrary unit)
	• Forward vs. backward walking	2. 2.5 s before walking	2. HPF at 0.01 Hz; 5 s moving average; PCA ( $r = 0.25$ )
		3. $10 \times$ ; 30 s	3. Baseline correction; averaging
		4. 30 s between trials	4. Oxy- and deoxyHb
		4. 30 s between trials	5. Entire task phase
Kurz et al.⁵⁶	– Children with spastic diplegic cerebral palsy ( $n = 4$ ; $11.0 \pm 4$ )	1. Quiet standing	1. N/A (arbitrary unit)
	– Healthy children ( $n = 8$ ; $13.2 \pm 3$ )	2. 2.5 s before walking	2. HPF at 0.01 Hz; 5 s moving average; PCA ( $r = 0.25$ )
	• Patients vs. HC	3. $10 \times$ ; 30 s	3. Baseline correction; averaging
		4. 30 s between trials	4. OxyHb
		4. 30 s between trials	5. Entire task phase
Lin et al.¹⁰³	– Healthy middle-aged adults ( $n = 15$ ; $46 \pm 11$ )	1. Quiet standing	1. N/A (image reconstruction)
	– Healthy old adults ( $n = 15$ ; $73 \pm 5$ )	2. 40 s before trial	2. Autoregressive model with prewhitened iterative reweighted least squares algorithm
	• Middle-aged vs. old adults (different balance conditions)	3. $4 \times$ ; 40 s	3. HRF; averaging
		4. 1 min between trials	4. Oxy- and deoxyHb
		4. 1 min between trials	5. Entire task phase
Lin and Lin⁷⁹	– Healthy young adults ( $n = 24$ ; 20 to 27)	1. Quiet standing	1. Age-dependent value ( $4.99 + 0.067 \times {age}^{0.814}$ )
	• DTW vs. NW	2. 20 s	2. LPF at 0.2 Hz
		3. $1 \times$ ; 60 s	3. Baseline correction
		4. 20 s before/after task / 2 min after two trials	4. OxyHb
		4. 20 s before/after task / 2 min after two trials	5. Entire task phase
Lu et al.⁷⁶	– Healthy young adults ( $n = 17$ ; $23.1 \pm 1.5$ )	1. Quiet standing	1. Constant value (6.0)
	• DTW vs. NW	2. 5 s before walking	2. Bandpass filter (LPF at 0.01 Hz; HPF at 0.2 Hz); PCA; spike rejection (channels with > CV 15% rejected/channels with CV > 10% for further analysis)
		3. $3 \times$ ; 60 s	3. Averaging
		4. 60 s between trials	4. Hbdiff (oxyHb–deoxyHb)
		4. 60 s between trials	5. Early phase (5 to 20 s after task begin); late phase (21 to 50 s after task begin)
Mahoney et al.⁹³	– Healthy, nondemented older adults ( $n = 126$ ; $74.41 \pm 6.12$ )	1. Quiet standing	1. Constant value (6.0)
	– Older adults wild mild Parkinson symptoms ( $n = 117$ ; $77.50 \pm 6.72$ )	2. First 2 s	2. LPF at 0.14 Hz; visual inspected
	– Patients with Parkinson disease ( $n = 26$ ; $81.23 \pm 5.93$ )	3. 10 s	3. Baseline normalization; averaging
	• Patients vs. HC (standing while counting silently in steps of 1)	4. “Short break” reported	4. OxyHb
		4. “Short break” reported	5. Entire task phase
Maidan et al.⁹⁰	– Parkinson patients with FOG ( $n = 11$ ; $66.2 \pm 10.0$ )	1. Walking	1. Age-dependent value ( $4.99 + 0.067 \times {age}^{0.814}$ )
	– Healthy controls ( $n = 11$ ; $71.2 \pm 6.0$ )	2. 6 s before FOG	2. LPF at 0.14 Hz
	• Patients vs. HC (walking; turning)	3. 6 s walking with 180 deg turn	3. Baseline correction; averaging
		4. 2 min between tasks	4. OxyHb
		4. 2 min between tasks	5. Defined time period around FOG event ( $prior = - 6$ to $- 3 s$ / $before = - 3$ to 0 / $during = 0$ to 3 s)
Maidan et al.⁸⁰	– Healthy, older adults ( $n = 38$ ; $70.4 \pm 0.9$ )	1. Quiet standing	1. Age-dependent value ( $4.99 + 0.067 \times {age}^{0.814}$ )
	– Parkinson patients ( $n = 68$ ; $71.7 \pm 1.1$ )	2. 5 s before task	2. Bandpass filter (LPF at 0.01 Hz and HPF at 0.14 Hz), wavelet filter; CBSI
	• DTW vs. NW vs. obstacle negotiation	3. $5 \times$ ; 30 s	3. Baseline correction; averaging
		4. 20 s after trial / between trials on individual needs	4. OxyHb
		4. 20 s after trial / between trials on individual needs	5. Entire task phase
McKendrick et al.⁸⁸	– Healthy, young adults ( $n = 13$ ; 22; 19 to 31)	1. Sitting (for sitting condition) and standing (for walking condition)	1. Constant value (5.94)
	• Sitting vs. walking indoors vs. walking outdoors (all conditions while performing secondary task)	2. 10 s	2. LPF at 0.1 Hz; visual inspected
		3. $16 \times$ ; 120 s (sitting) / $8 \times$ ; a 120 s (per walking condition)	3. Baseline correction
		4. 5 min between walking conditions	4. Oxy- and deoxyHb
		4. 5 min between walking conditions	5. Entire task time
Meester et al.⁵⁷	– Young, healthy adults ( $n = 17$ ; $27.8 \pm 6.3$ )	1. Quiet standing	1. Age-dependent value ( $4.99 + 0.067 \times {age}^{0.814}$ )
	• DTW vs. NW	2. Middle 10 s of rest	2. LPF at 0.67 Hz; 4 s moving average; visual inspected
		3. $5 \times$ ; 30 s	3. Averaging
		4. 20 to 40 s between trials	4. OxyHb
		4. 20 to 40 s between trials	5. Middle 10 s of task
Metzger et al.⁶⁴	– Healthy young adults ( $n = 12$ ; 27.6; 19 to 39)	1. Quiet standing	1. N/A (arbitrary unit)
	• DTW vs. NW	2. 10 s at begin	2. 5 s moving average; CBSI
		3. $4 \times$ ; 45 s	3. Averaging; baseline correction
		4. 15 s after trial	4. Oxy- and deoxyHb
		4. 15 s after trial	5. Entire task time
Mihara et al.⁵⁸	– Stroke patients with ataxic gait ( $n = 12$ ; $52.7 \pm 16.9$ , 12 to 74)	1. Quiet standing	1. N/A (arbitrary unit)
	– Healthy controls ( $n = 11$ ; $42.6 \pm 11.6$ , 30 to 70)	2. 6 s before walking	2. Not reported
	• Patients vs. HC	3. $3 \times$ ; 60 s (HC); 30 s (patients)	3. Baseline correction; averaging
		4. 15 s before/after walking	4. OxyHb
		4. 15 s before/after walking	5. Acceleration phase = 6 s after starting treadmill; steady phase = 6 s during steady speed
Mihara et al.⁹⁴	– Healthy young adults ( $n = 15$ ; $29.4 \pm 6.7$ )	1. Quiet standing	1. N/A (arbitrary unit)
	• Warned before perturbations vs. baseline; unwarned before perturbations vs. baseline; warned vs. unwarned	2. Time before next perturbation (ERD)	2. HPF at 0.05 Hz
		3. 20 to $30 \times$ ; 1 s	3. Gaussian HRF; averaging
		4. 5 to 20 s between trials (randomized) / 4 to 5 min after block	4. OxyHb
			5. Around perturbation
Mihara et al.⁹⁵	– Stroke patients ( $n = 20$ ; $61.6 \pm 11.9$ )	1. Quiet standing	1. N/A (arbitrary unit)
	• Balance perturbations	2. Time before next perturbation (ERD)	2. HPF at 0.03 Hz
		3. $15 \times$ ; 1 s	3. Two-parameter gamma HRF
		4. 5 to 15 s between trials (randomized)	4. OxyHb
		4. 5 to 15 s between trials (randomized)	5. Around perturbations
Mirelman et al.⁷⁷	– Young, healthy adults ( $n = 23$ ; $30.9 \pm 3.7$ )	1. Quiet standing	1. Age-dependent value ( $4.99 + 0.067 \times {age}^{0.814}$ )
	• Standing vs. DTS vs. NW vs. DTW	2. 20 s before walking	2. LPF at 0.14 Hz; continuous wavelet transform
		3. $5 \times$ ; 30 m	3. Baseline correction; averaging
		4. 20 s before/after trial	4. OxyHb
		4. 20 s before/after trial	5. Entire task phase
Miyai et al.¹⁰⁷	– Healthy young adults ( $n = 8$ ; $35 \pm 8$ , 24 to 56)	1. Quiet standing	1. N/A (arbitrary unit)
	• NW vs. standing	2. 30 s	2. HPF at 0.03 Hz
		3. $5 \times$ ; 30 s	3. Linear interpolation; averaging
		4. 30 s between trials	4. Oxy- and deoxyHb
		4. 30 s between trials	5. Entire task phase
Miyai et al.⁶¹	– Stroke patients ( $n = 6$ ; $57 \pm 13$ )	1. Quiet standing	1. N/A (arbitrary unit)
	• Walking with mechanical assistance vs. walking with facilitation technique	2. Middle 20 s	2. HPF at 0.03 Hz
		3. $4 \times$ ; 30 s	3. Linear interpolation; baseline correction; averaging
		4. 30 s between trials	4. OxyHb
		4. 30 s between trials	5. Last 20 s of task phase
Miyai et al.⁶⁰	– Stroke patients ( $n = 8$ ; $57 \pm 12$ )	1. Quiet standing	1. N/A (arbitrary unit)
	• Before/after 2 months rehabilitation	2. Middle 20 s	2. HPF at 0.03 Hz
		3. $4 \times$ ; 30 s	3. Linear interpolation; baseline correction; averaging
		4. 30 s between trials	4. OxyHb
		4. 30 s between trials	5. Last 20 s of task phase
Miyai et al.⁵⁹	– Stroke patients with hemiparesis ( $n = 6$ ; $57 \pm 6$ )	1. Quiet standing	1. N/A (arbitrary unit)
	– Healthy controls ( $n = 6$ , $53 \pm 11$ )	2. Middle 20 s	2. HPF at 0.03 Hz
	• Walking with weight support vs. walking without weight support	3. $4 \times$ ; 30 s	3. Linear interpolation; baseline correction; averaging
		4. 30 s between trials	4. OxyHb
		4. 30 s between trials	5. Last 20 s of task phase
Nieuwhof et al.⁸¹	– Parkinson patients ( $n = 14$ ; $71.2 \pm 5.4$ )	1. Quiet standing	1. Constant value (6.0)
	• DTW (with different tasks)	2. Last 5 s of standing	2. LPF at 0.1 Hz; visual inspected
		3. $5 \times$ ; 40 s	3. Baseline correction; averaging
		4. 20 s between trials / 1 to 2 min between blocks	4. OxyHb and deoxyHb
		4. 20 s between trials / 1 to 2 min between blocks	5. Entire task phase
Osofundiya et al.⁸⁷	– Obese old adults ( $n = 10$ ; $80.6 \pm 6.79$ )	1. Quiet standing	1. Constant value (6.0)
	– nonobese old adults ( $n = 10$ ; $80.6 \pm 7.50$ )	2. 10 s	2. Not reported
	• Quiet sitting vs. NW vs. precision walking vs. DTW	3. $8 \times$ a 30 s	3. Baseline correction; averaging
		4. 10 s between trials	4. OxyHb and HbT
		4. 10 s between trials	5. Entire task phase
Saitou et al.⁷⁸	– Hemiplegic stroke patients ( $n = 44$ ; $66 \pm 9.3$ )	1. Quiet standing	1. Constant value (5.9)
	• Different tasks (e.g., calculation, pulley, we only consider walking vs. baseline)	2. 5 min	2. Not reported
		3. $1 \times$ ; 5 min	3. Averaging
		4. 5 min	4. OxyHb; CBV; COV
		4. 5 min	5. Entire task phase
Suzuki et al.⁶²	– Healthy, young adults ( $n = 9$ ; $28.1 \pm 7.4$ , 22 to 46)	1. Quiet standing	1. N/A (arbitrary unit)
	• Walking at different speeds	2. First 13 s	2. HPF at 0.03 Hz
		3. $3 \times$ ; 90 s	3. Linear interpolation; baseline correction; averaging
		4. 30 s between trials	4. Oxy- and deoxyHb; regional cortical activation ratio (oxy Hb of the specific channel divided by oxyHb of all 42 channels multiplied by 100)
		4. 30 s between trials	5. 13.5 s in task phase
Suzuki et al.⁶⁷	– Healthy, young adults ( $n = 7$ ; $31.3 \pm 4.8$ , 24 to 45)	1. Quiet standing	1. Not relevant (arbitrary unit)
	• Walking with vs. without verbal preadvice	2. 10 s before walking	2. HPF at 0.03 Hz
		3. $4 \times$ ; 40 s	3. Baseline normalization; averaging
		4. 10 to 25 s between trials (randomized order)	4. Oxy- and deoxyHb
		4. 10 to 25 s between trials (randomized order)	5. First 10 s of task phase
Takeuchi et al.⁸⁹	– Young healthy adults ( $n = 16$ ; $25.9 \pm 4.4$ , 20 to 33)	1. Walking	1. Constant value (no details reported)
	– Healthy older adults ( $n = 15$ ; $71.7 \pm 3.3$ , 65 to 78)	2. 30 s	2. Spike rejection (artifact with more than 3 SD); 5 s moving average; bandpass filter (LPF at 0.5 Hz; HPF at 0.01 Hz)
	• Walking vs. walking with smartphone	3. $15 \times$ ; 10 s	3. Baseline normalization; averaging
		4. No rest	4. OxyHb
		4. No rest	5. Entire task phase
Takakura et al.⁹⁶	– Healthy young adults ( $n = 11$ ; $33.4 \pm 7.4$ )	1. Quiet standing	1. Constant value (1.0)
	• SOT conditions	2. 20 s before task	2. Bandpass Fourier filter (0.01 to 0.1 Hz)
		3. $3 \times$ ; 20 s	3. Averaging
		4. Few minutes after $3$ trials	4. OxyHb
		4. Few minutes after $3$ trials	5. Entire task phase
Verghese et al.⁸³	– Older adults ( $n = 166$ ; $75 \pm 6.1$ )	1. Quiet standing	1. Constant value (6.0)
	– NW vs. DTW vs. standing	2. 10 s (counting silently forward in steps of 1)	2. LPF at 0.14 Hz; noisy channels excluded (dark current condition or saturation); visual inspected
		3. $3 \times$ walking loops (= $6 \times$ straight walks a 14 ft.) / standing for 30 s)	3. Baseline normalization; averaging
		4. “Short break” reported	4. OxyHb
		4. “Short break” reported	5. Entire task phase
Wang et al.¹⁰⁴	– Healthy young adults ( $n = 22$ ; $24.4 \pm 1.6$ )	1. Sitting (eyes closed)	1. Age-dependent constant value (WL: $760 nm = 5.91$ ; WL: $850 = 5.40$ )
	– Healthy older adults ( $n = 39$ ; $70.5 \pm 7.7$ )	2. 20 min	2. Bandpass filter (0.005 to 2 HZ)
	• Standing connectivity differences healthy young and healthy old adults	3. $1 \times$ ; 10 min	3. Wavelet phase coherence analysis
		4. No rest	4. OxyHb
		4. No rest	5. Entire task time

Abbreviations: deoxyHb, deoxygenated hemoglobin; DTS, dual-task standing; DTW, dual-task walking; ft., feet; HC, healthy controls; HPF, high-pass filter; HRF, hemodynamic response function; LPF, low-pass filter; MDL, minimum description length; MRI, magnetic resonance imaging; N/A, not applicable; NW, normal walking; NGA, neurological gait abnormalities; oxyHb, oxygenated hemoglobin; PCA, principal component analysis; RAW, robot assisted walking; SOT, sensory organization test; ST, stepping; TOI, tissue oxygenation index; and vs., versus.