Information Processing System Assumptions

The material below is taken from Newell, A. & Simon, H. Human Problem Solving. Englewood Cliffs, NJ: Prentice Hall, 1972. It represents the general statement of the set of assumptions that they have made about the human information processing system. Note that this set of assumptions is consistent with their statement of the Physical Symbol System Hypothesis. However, it is a special case of this hypothesis that is more specific since it is intended to characterize the architecture that supports human intelligence.

Definition of an IPS (Information Processing System)

1. There is a set of elements, called symbols.
2. A symbol structure consists of a set of tokens (equivalently, instances or occurrences) of symbols connected by a set of relations.
3. A memory is a component of an IPS capable of storing and retaining symbol structures.
4. An information process is a process that has symbol structures for (some of) its inputs or outputs.
5. A processor is a component of an IPS consisting of:
   • a (fixed) set of elementary information processes (eip's);
   • a short-term memory (STM) that holds the input and output symbol structures of the eip's;
   • an interpreter that determines the sequence of eip's to be executed by the IPS as a function of the symbol structures in STM.
6. A symbol structure designates (Equivalently, references or points to) an object if there exist information processes that admit the symbol structure as input and either:
   • affect the object; or
   • produce as output, symbol structures that depend on the object.
7. A symbol structure is a program if (a) the object it designates is an information process and (b) the interpreter, if given the program, can execute the designated process. (literally this should read, "if given an input that designates the program.")
8. A symbol is primitive if its designation (or its creation) is fixed by the elementary information processes or by the external environment of the IPS.

The term object is used to encompass at least three sorts of things:

1. symbol structures stored in one or another of the IPS's memories, which are often usefully classified into (a) data structures, and (b) programs.
2. processes that the IPS is capable of executing;
3. an external environment of sensible (readable) stimuli. Reading consists in creating in memory internal symbol structures that designate external stimuli; writing is the inverse operation of creating responses in the external environment that are designated by internal symbol structures.

Note: the relation between a designating symbol and the object it points to can have any degree of directness or indirectness.

Symbols and Symbol Structures

Symbol tokens are patterns that can be compared by the IPS and judged equal or different. A class of all tokens that are judged to be identical is called a symbol type. Thus, tokens of the same symbol type differ from each other only in being distinct occurrences or instances.

Symbol structures are built up from symbol tokens and relations.

Five General Propositions

1. Humans when engaged in problem solving in tasks such as solving cryptarithmetic problems, proving theorems, playing chess, ..., are representable as information processing systems.
2. This representation can be carried to great detail with fidelity in any specific instance of person and task.
3. Substantial subject differences exist among programs, which are not simply parametric variations but involve differences of structure and content.
4. Substantial task differences exist among programs, which are also not simply parametric variations but involve differences of structure and content.
5. The task environment (plus the intelligence of the problem solver) determines to a large extent the behavior of the problem solver, independently of the detailed internal structure of his information processing system.

Four propositions that shape the theory of human information processing:

1. A few and only a few, gross characteristics of the human IPS are invariant over task and problem solver.
2. These characteristics are sufficient to determine that a task environment is represented (in the IPS) as a problem space, and that problem solving takes place in a problem space.
3. The structure of the task environment determines the possible structures of the problem space.
4. The structure of the problem space determines the possible programs that can be used for problem solving.

Additional Characteristics of the IPS that seem to be invariant over problem solver and task:

1. Size, access characteristics, and read and write times for the various memories of the Human IPS.
2. Serial character of the information processing and the rate at which elementary information processes can be performed.
3. Program organization is production-like and goal-like in character.