The definition of module has caused confusion and dispute. In J.A. Fodor's views, modules can be found in peripheral and low-level visual processing, but not in central processing. Later, he narrowed the two essential features to domain-specificity and information encapsulation. According to Frankenhuis and Ploeger, domain-specificity means that "a given cognitive mechanism accepts, or is specialized to operate on, only a specific class of information". Information encapsulation means that information processing in the module cannot be affected by information in the rest of the brain. One example is that the effects of an optical illusion, created by low-level processes, persist despite high-level processing caused by conscious awareness of the illusion itself.
