Information Processing Theory 49 



drive shaft that the motor has) drives) is on)) osciUates)) operate 

 the said rocker arm." 



Tiie preceding examples, tiien, represent four approaches to the 

 same general type of observation. I have called them mentalistic, 

 statistical, information theoretical, and information processing 

 theoretical. The latter consists of postulating" some sort of mechan- 

 istic decision procedure; the operation of the mechanism is then 

 examined and compared with human behavior. Assumptions are 

 stated as processes; the method of deduction is not analytic. For 

 processes more complex than that in the Yngve example, the de- 

 duction often takes the foim of specifying the processes for a digital 

 computer, the running of which then provides the predictions. 



There are yet several points of this discussion which deserve 

 more elaboration. First, why go to all the trouble and expense to 

 build and instruct this device when we might do better to hire a 

 mathematician, whose services are certainly cheaper, to solve the 

 problem analytically? This is certainly a good suggestion, and 

 many people who have resorted to simulation might better have 

 resorted to mathematics. But the systems which are of major 

 interest to the psychologist and biologist have the property of 

 being complex. Mathematics, although it has earned its place of 

 respect in science, is not a completely developed discipline. The 

 task of writing equations for the human system is far too difficult. 

 Some attempts have been made to describe mathematically cer- 

 tain learning processes, for example. Bush and Mostellar (19), 

 Estes (20); but it has been necessary to limit the complexity of 

 the equations in the interest of getting them solved. Learning 

 processes have pretty well resisted linear descriptions. It is, how- 

 ever, possible to define in computer terms systems which cannot 

 be defined in normal mathematical notation; and if the system 

 can be defined as a computer program, a computer can simulate 

 the behavior of the system. It is important to realize that writing 

 a program is analogous to writing an equation, and running the 

 program is analogous to solving the equation. It is then clear 

 what I meant when I said that the program is a theory: it is a 

 theory in the same sense that a mathematical equation is a theory — 

 it makes some well-defined assumptions and makes some predic- 

 tions which are rigorously deduced from these assumptions. 



