This article presents a constructivist model of human cognitive development during infancy. According to constructivism, the elements of mental representation-even such basic elements as the concept of physical object-are constructed afresh by each individual, rather than being innately supplied. A (partially-specified, yet-unimplemented) mechanism, the Schema Mechanism, is proposed here; this mechanism is intended to achieve a series of cognitive constructions characteristic of infants' sensorimotor-stage development, primarily as described by Piaget. In reference to Piaget's “genetic epistemology”, I call this approach genetic AI-“genetic” not in the sense of genes, but in the sense of genesis: development from the point of origin. The Schema Mechanism focuses on Piaget's concept of the activity and evolution of cognitive schemas. The schema is construed here as a context-sensitive prediction of what will follow a certain action. Schemas are used both as assertions about the world, and as elements of plans to achieve goals. A mechanism of attribution causes a schema's assertion to be extended or revised according to the observed effects of the schema's action; due to the possible relevance of conjunctions of context conditions, the attribution facility needs to be able to sort through a combinatorial explosion of hypotheses. Crucially, the mechanism constructs representations of new actions and state elements, in terms of which schemas are expressed. Included here is a sketch of the proposed Schema Mechanism, and highlights of a hypothetical scenario of the mechanism's operation. The Schema Mechanism starts with a set of sensory and motor primitives as its sole units of representation. As with the Piagetian neonate, this leads to a “solipsist” conception: the world consists of sensory impressions transformed by motor actions. My scenario suggests how the mechanism might progress from there to conceiving of objects in space-representing an object independently of how it is currently perceived, or even whether it is currently perceived. The details of this progression paralledl the Piagetian development of object conception from the first through fifth sensorimotor stage.

I propose a mechanism to model aspects of Piagetian development in infants. The mechanism combines a powerful empirical learning technique with an unusual facility for constructing novel elements of representation-- elements designating states that are not mere logical combinations of other represented states. I sketch how this mechanism might recapitulate the infant's gradual recognition that there exist physical objects that persist even when the infant does not perceive them. I also report results of a preliminary, partial implementation.

The schema mechanism is a general learning and concept-building mechanism intended to simulate aspects of Piagetian cognitive development during infancy. A computer program that implements the schema mechanism, MARCSYST I, has replicated several early milestones in the Piagetian infant’s invention of the concept of permanent object. In Piaget’s constructivist theory, an infant first represents the world only in terms of simple sensory and motor elements; initially, there is no concept of persistent, external objects-objects that exist even when not perceived. The infant must construct this concept, working backward from the perceptions that manifest external objects. This conceptual leap is first of a long series of such constructions, extending through adult-level intelligence. The schema mechanism connects to a simulated body in a microworld. The mechanism learns from its experiences by processes of induction, abstraction, and invention. A novel induction technique builds schemas, each of which asserts that a given action, in certain contexts, has particular results; contexts and results are expressed in terms of binary state elements called items. Crucially, the schema mechanism not only thus discovers relations among existing representational elements (actions and items), but also constructs new such elements. For any achievable result, the mechanism can define a new, abstract action, the action of achieving that result. Most important, the mechanism can synthesize new state elements to designate aspects of the world that the existing repertoire of representations fails to express, thus inventing new concepts. The schema mechanism builds schemas, expressing the context-dependent results of actions, by an induction technique called marginal attribution. Discovering the results of actions is complicated by the fact that a particular action typically has different effects on different occasions. Until the corresponding context conditions have been identified, a result is therefore difficult to identify as such, and vice versa. The marginal attribution facility solves this chicken-and-egg problem by identifying a relevant state transition-one which, even if it follows a given action only rarely, is even more rare in the absence of the action. Then, the mechanism searches for conditions under which the relevant result follows more reliably. The schema mechanism can define a new state element to represent the validity conditions of an unreliable schema. For example, suppose a given schema asserts that moving the hand to a certain body-relative position results in a tactile sensation. The schema mechanism defines a new state element to represent whatever unknown condition must hold for the schema to be valid; in this case, the condition is that there be a palpable object at that position. The concept of palpable objects is not built in; rather, this synthetic item itself implements the mechanism’s first approximation to that concept, thus reifying the schema’s validity conditions, treating the schema’s validity as a thing-in-itself. Having defined a new state element, the mechanism begins an open-ended process of finding the element’s verification conditions, which tell about its state.