1991'3, p.17
Kataeva A. A. , Obuhova T. I. , Strebeleva E. A.
Concerning the genesis of thinking development in preschoolers

Comparative study of normal, deaf and mentally retarded children shows that visual-active thinking evolves when certain level of perception, object activity and speech, leading to substitution function emergence is obtained. Visual-active thinking though developing early enough is neither initial, nor the most primitive form of thinking. It appears on the basis of visual-image-bearing thinking and of elements of logical one. So, all the fundamental forms of thinking interrelation is confirmed.