Do you hear my mother walking downstairs?为什么用该walking?

Do you hear my mother walking downstairs?为什么用该walking?

因为该句用了hear这个感官动词.
hear有两种搭配,分别是hear to do 和hear doing.
hear doing强调此人正在做某事,强调动作.
虽然有do,但是因为有hear,所以应为walking.