Sophia Brous and Carlos Soto, performance artists, will each share works in progress with the public on Saturday at the Watermill Center. Ms. Brous, an Australian performer who will be in residence at the center in January, will be gathering material from 11 a.m. to 3 p.m. for “Lullaby Movement,” a project exploring lullaby rituals from around the world that she is developing with David Coulter and Leo Abrahams, British musicians.