University of Alberta Dictionary of Cognitive Science: Modularity

Jerry Fodor (1983) is the strongest proponent of a modular theory of cognition. Fodor argues that certain psychological processes are self contained--or modular. This is in contrast to "New look" or Modern Cognitivist positions which hold that nearly all psychological processes are interconnected, and freely exchange information.

Fodor proposes a three tiered cognitive system. The first level of the system, the transducer level, transforms environmental signals into a form that can be used by the cognizing organism. The second level, the input systems level, performs basic recognition and description functions. In Fodor's model input systems are modular. The third level of the system, higher level cognitive functions, performs complex operations on the output of the input systems. An example of a higher level process is analogous thinking.

Fodor holds that input systems are modular and that higher level cognitive processes are nonmodular. This means that all of the information necessary for performing their tasks of recognition and description is contained within the input systems. For example, object perception might be modular, in which case the object perception module need not reference language modules, or music modules, or mathematics modules in order to perform its operations. In contrast, higher level processes have access to all information contained within the cognitive system when performing a given operation. Fodor provides the example of scientific reasoning (a higher level cognitive process). Potentially, when solving a scientific problem, the scientist can reference any knowledge that he or she has about the world to help in solving this problem. As such, if necessary, knowledge about botany can be referenced in order to understand problems in mathematics.

Modular systems have the following properties:

They are domain specific--they operate on, and have a computational architecture that is unique to certain stimuli.
Their operation is mandatory, or they are cognitively impenetrable--beliefs cannot affect the operations of modules, we cannot help seeing, or hearing the world in a certain way.
Modules are fast--modular processes are among the fastest psychological processes,this is because modules are self-contained and need not spend time referencing information outside of the module to complete their tasks.
Modules are informationally encapsulated--they need not reference any other psycholgical systems in order to perform their operations.
Modules have shallow outputs--the output of modules is very basic, more complex representations follow after higher level computation.

References:

Fodor, J.A. (1983). The modularity of mind. Cambridge, MA: MIT Press.
Fodor, J.A. (1985). Precis on The Modularity of Mind. Behavioral and Brain Sciences, 8, 1-42.