Figure 2
Continuous wavelet transform of time series in different tasks: (Left) usual-walking, (Right) walking+S7. The raw time courses of the task were analyzed in the frequency domain to express the oxygenation response in terms of intensity (concentration of HbO2 levels) and timing (slow or rapid response in HbO2 levels). An inclination towards more oxygenation (represented by warmer colors) was observed around 20-30 frequency seconds in usual-walking, suggesting low frequencies (relatively slow change) in HbO2 signal as compared to quiet standing. In contrast, during walking+S7, a stronger and more rapid oxygenation pattern (represented by warm colors) appears earlier (12-20 frequency seconds), reflecting a quick and intense increase in oxygenation.