The works of Tod Williams, FAIA, and Billie Tsien beg to be touched. Walk up to their Neurosciences Institute in La Jolla, Calif., and you find yourself running a hand over the low-slung building’s long concrete walls, which have been softened by heavy sandblasting to expose their blue-green aggregate. Or go inside their addition to the Phoenix Art Museum and compare the smoothness of a grand limestone stair with that of its cast-in-place concrete mate. The architects bring out the timeless qualities of materials such as stone, concrete, steel, glass, and wood, and they experiment with newer ones such as Homasote, plastic laminates, and resins. Theirs is a tactile architecture.