The challenge of spoken language systems: research directions for the nineties. - Ronald A. Cole; Lynette Hirschman; Les E. Atlas; Mary E. Beckman; Alan Biermann; Marcia A. Bush; Mark Clements; Jordan Cohen; Oscar Garcia; Brian A. Hanson; Hynek Hermansky; Steve Levinson; et al. (IEEE Trans. Speech Audio Process., 1995)