Donny’s mother has just poured two glasses of orange juice, one for Donny and one for his sister. After they are poured, Donny becomes very upset that he got less juice than his sister. Their mother points out that while Donny’s glass is short, it is also wider, and thus both children have the same amount. Donny continues to protest, arguing that his juice is shorter, thus he has less juice. Piaget would explain Donny’s behavior as being the result of_________.