Estimation of Human Workload from the Auditory Steady-State Response Recorded via a Wearable Electroencephalography System during Walking

Figures

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  Figure 1. Wearable electroencephalography (EEG) system and experimental setup. (A) Portable EEG device (Polymate Mini AP108) and dry electrodes. (B) Custom-designed headgear. (C) Experimental setup.

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  Figure 2. Experimental procedure. Participants performed an N-back task with visual stimuli “1” and “2”. The auditory stimuli had a carrier frequency of 500 Hz and 40 Hz amplitude modulation.

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  Figure 3. Data analysis. The continuous EEG data were divided into 3000 ms epochs based on triggers that occurred every second. Subsequently, each epoch was subjected to Fourier analysis to calculate the frequency response. Finally, we calculated the 40 Hz phase-locking index (PLI) from the frequency response.

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  Figure 4. Behavioral results. (A) Accuracy for button pressing during each task. (B) Reaction time. We observed significant differences in both behavioral measures between the no-load (NL) and N-back tasks. Error bars indicate the 95% confidence limits of the mean.

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  Figure 5. PLI vs. frequency. The grand-averaged PLI vs. frequency measured at the anterior, fronto-central and occipital electrodes. The shaded areas indicate the standard error.

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  Figure 6. Change in fronto-central PLI according to experimental block. We observed significant differences in the auditory steady-state response (ASSR) between the first and second block.

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  Figure 7. PLI results. The PLIs measured at the (A) anterior, (B) fronto-central and (C) occipital electrodes of the participants and the grand averaged value. We observed significant differences in the ASSR between the NL and 2-back task at the anterior, and between each tasks at the fronto-central electrodes. Error bars indicate the 95% confidence limits of the mean. The hatched bars indicate the PLI value that was below a threshold value of random variations tested using the Rayleigh test.

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  Figure 8. Correlation of reaction times and fronto-central PLIs for each participant.