Enhancing Classification Performance of Functional Near-Infrared Spectroscopy- Brain-Computer Interface Using Adaptive Estimation of General Linear Model Coefficients

Abstract

In this paper, a novel methodology for enhanced classification of functional near-infrared spectroscopy (fNIRS) signals utilizable in a two-class [motor imagery (MI) and rest; mental rotation (MR) and rest] brain-computer interface (BCI) is presented. First, fNIRS signals corresponding to MI and MR are acquired from the motor and prefrontal cortex, respectively, afterward, filtered to remove physiological noises. Then, the signals are modeled using the general linear model, the coefficients of which are adaptively estimated using the least squares technique. Subsequently, multiple feature combinations of estimated coefficients were used for classification. The best classification accuracies achieved for five subjects, for MI versus rest are 79.5, 83.7, 82.6, 81.4, and 84.1% whereas those for MR versus rest are 85.5, 85.2, 87.8, 83.7, and 84.8%, respectively, using support vector machine. These results are compared with the best classification accuracies obtained using the conventional hemodynamic response. By means of the proposed methodology, the average classification accuracy obtained was significantly higher (p < 0.05). These results serve to demonstrate the feasibility of developing a high-classification-performance fNIRS-BCI.

Keywords: adaptive estimation; brain–computer interface; functional near-infrared spectroscopy; general linear model; least squares estimation; support vector machine.

Figure 1

Optode placement and channel location. (A) 12-channel with 4 detectors and 5 emitters on the left motor cortex and (B) 12-channel with 8 detectors and 3 emitters on the prefrontal cortex of brain region.

Figure 2

Δc_HbO(t) signals and their corresponding adaptively estimated β values for subject 5.

Figure 3

Schematic of (A) proposed and (B) conventional methodology.