According to a linguistic survey report, people often confuse the pronunciation of /hi/ with that of /si/ in the dialect of Tokyo and the Tohoku region of Japan. A team of researchers at Toyohashi University of Technology and the National Institute for Japanese Language and Linguistics (NINJAL) found that the confusion resulted from the articulation of the tongue varying in the transverse direction while the tongue tip is positioned at the same place of articulation. The study was published online in the Journal of the Acoustical Society of America on April 7, 2021.