Abstract
Working memory (WM) is a key executive function for operating aircraft, especially when pilots have to recall series of air traffic control instructions. There is a need to implement tools to monitor WM as its limitation may jeopardize flight safety. An innovative way to address this issue is to adopt a Neuroergonomics approach that merges knowledge and methods from Human Factors, System Engineering, and Neuroscience. A challenge of great importance for Neuroergonomics is to implement efficient brain imaging techniques to measure the brain at work and to design Brain Computer Interfaces (BCI). We used functional near infrared spectroscopy as it has been already successfully tested to measure WM capacity in complex environment with air traffic controllers (ATC), pilots, or unmanned vehicle operators. However, the extraction of relevant features from the raw signal in ecological environment is still a critical issue due to the complexity of implementing real-time signal processing techniques without a priori knowledge. We proposed to implement the Kalman filtering approach, a signal processing technique that is efficient when the dynamics of the signal can be modeled. We based our approach on the Boynton model of hemodynamic response. We conducted a first experiment with nine participants involving a basic WM task to estimate the noise covariances of the Kalman filter. We then conducted a more ecological experiment in our flight simulator with 18 pilots who interacted with ATC instructions (two levels of difficulty). The data was processed with the same Kalman filter settings implemented in the first experiment. This filter was benchmarked with a classical pass-band IIR filter and a Moving Average Convergence Divergence (MACD) filter. Statistical analysis revealed that the Kalman filter was the most efficient to separate the two levels of load, by increasing the observed effect size in prefrontal areas involved in WM. In addition, the use of a Kalman filter increased the performance of the classification of WM levels based on brain signal. The results suggest that Kalman filter is a suitable approach for real-time improvement of near infrared spectroscopy signal in ecological situations and the development of BCI.
Highlights
The development of passive Brain Computer Interfaces (BCI) is a key topic of research in Neuroergonomics
The results show that the use of Moving Average Convergence Divergence (MACD) elicits a better statistical effect size than the classical Infinite Impulse Response (IIR) filter
The effect of trial difficulty on the level of HbO2 measured over the prefrontal cortex is shown on Figure 8. We observe that both the MACD and Kalman filter over classical IIR
Summary
The development of passive Brain Computer Interfaces (BCI) is a key topic of research in Neuroergonomics. In the field of BCI design to enhance user performance, there is a growing interest for functional near infrared spectroscopy (fNIRS) based BCI (Coyle et al, 2004; Derosière et al, 2014; Strait et al, 2014) This brain imaging device uses near infrared light absorption properties to estimate local variations of cortical hemodynamics. The extraction of the relevant activity from brain signals requires complex techniques (van Erp et al, 2012), and most efficient ones often rely on long calibration times [e.g., in subspace artifact removal techniques (von Bünau et al, 2009), adaptive filtering (Zheng et al, 2002)] The complexity of these methods limits their applicability for Neuroergonomics purpose, as the signal has to be useable in real-time
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