Estimation of the direction of arm force by using NIRS signals

In this study, we tried to discriminate the direction of arm force from hemoglobin concentration changes measured by near-infrared spectroscopy (NIRS). A self-organizing map (SOM) was used to classify the force direction information obtained from the NIRS signals. In a human subject experiment, the subjects were required to perform isometric arm movements in four directions. We investigated the feature quantities extracted from the time series data of the NIRS signals during the movement task. The feature vectors were used as the input vectors to the SOM. We tried to estimate the arm force direction by using a simple method based on the clusters given by the SOM. The results confirm that the direction of force is discriminable from the NIRS signal. In spite of the simple classification approach, the discrimination test yielded an average discrimination rate of 87.5 % for two directions. The experiment results suggest that NIRS signal must contain information related to the force directions.