7–3–1 NTT 3–1 Graduate School of Information Science and Technology, The University of Tokyo, 7–3–1 Hongo, Bunkyo-ku, Tokyo, Japan NTT Communication Science Laboratories, Nippon Telegraph and Tele- phone Corporation, 3–1 Morinosato Wakamiya, Atsugi, Kanagawa, Japan E-mail: kameoka@hil.t.u-tokyo.ac.jp, kameoka.hirokazu@lab.ntt.co.jp (multivariate analysis) (dimension- ality reduction) (signal decom