1988'1, p.158
Ibragimov H. I.
Percertual differentiation and operational thinking in 4-8-years-old chidren

J. Piaget's experiments concerning development of the quantity retention notion have been repeated with the view to establish a wider cognitive basis of changes in perception with age. It is shown how practical and perceptual experience combined with new developments in thinking provides the ability to come to correct decisions about the observed events.