There is an interesting, though not kind, experiment by Held and Hein in 1963. Two kittens were put into a mini carousel, one walked while the other was in a cradle and could not walk. Wherever the walking cat walked, the cradled cat was passively moved to the same degree in the same environment. Though they both had exactly the same visual stimulation, only the one that walked developed visual intelligence. Well functioning motor functions, in both bipedals and quadripedals, may be vital to the development of many kinds of intelligence.