Fuzzy laterality index for examining the language dominance using near-infrared spectroscopy

Near-infrared spectroscopy (NIRS) is a recently developed method, which can be used to investigate the human brain function with noninvasive, high time resolution and high portability. It has been applied to the assessment of language dominance by Watanabe et al. (1998); however, it has a risk that some of the measurement points took include other brain activities occurred in the motor area. This paper improves the method by introducing fuzzy logic. Fuzzy logic is used to giving fuzzy degrees belonging to the speech, motor and other areas for each of the measurement point. Using the obtained fuzzy degrees, we redefine the laterality index as the fuzzy mean of the laterality indexes for all the paired measurement points.