Question

____ is a relatively early form of animation which uses clay sculptures that are moved and photographed in tiny increments.

Answer 1

I think it may be Stop Motion. Stop motion is a fairly early form of animation. You take a photo, then move the object/sculpture to a different position etc. Then take continuous photos with the sculpture/object in a different environment or position. It's very time consuming though.
Hope this helps!

Answer 2

claymation is a relatively early form of animation