Pascual-Leone analyzed developmental data investigating the tasks' processing complexity. He assessed complexity by modeling the number of essential operators, relations, or schemes that children must simultaneously hold in mind to produce performance. In 1963, he inferred with his analyses that there is a maximum mental demand that each child's age group can cope with – the characteristic mental (M-) power of each developmental stage-level. Only when the growth of mental power in a child is equal to or larger than the task's mental demand, can the child reliably solve a task. Today this information is well recognized; but in the nineteen seventies and eighties the idea was controversial. Pascual-Leone was the first to claim, via his task analyses, that the true organismic stages were in fact the sub-stages of Piaget. Recently Arsalidou, Pascual-Leone, Johnson, Morris, and Taylor have produced data suggesting that these levels of functioning may be expressed in adults by incrementation of brain activity in the executive (prefrontal lobes, etc.) network.
