Modularity

While there has historically been variation in the use of the term, in some communities "modularity" has come to refer to the extent to which a mechanism is functionally specialized (Barrett and Kurzban 2006).It was introduced into broad use within cognitive science by Fodor (1983), who concluded that while some systems in the mind (e.g., sensory systems) were modular, according to his use of the term, others were not. This conclusion rested on the idea that the ties, which Fodor associated with modularity depended on how many properties, which Fodor associated with modularity (e.g., automaticity, fast operation), the system in question had.
     In current use, the issue is less about how many of the properties that Fodor associated with modularity a given system possess, and more of a guide for investigation. Present conceptions of modularity focus attention on the empirical question how modular, or functionally specialized, a putative mechanism is. This approach follows the suggestion that modularity was not an all-or-none property, but a property that a computational system can have to a greater or lesser degree (Fodor 1983).
     To take one example from a well-understood model, consider the visual system. The front end of the visual system consists of photoreceptors, which are sensitive to the presence of light, and fire depending on the wavelength of light that hits them. Their function is to detect light and send information about its presence downstream to the visual system, more generally, is specialized as well, designed to use incoming light, as well as knowledge in the rest of the brain, to construct an image of the outside world, which can then be used to identify objects, plan motion, and so forth.
     A potentially important feature of modular systems is that they can be "walled off" from other systems. (Fodor used the term "informationally encapsulated" to refer to this property.) To return to the example of the visual system, consider the Miller-Lyer optical illusion (Figure 8.1), to which many, but not all, people are susceptible (for further details, see Henrich et al. 2010). If one disregards the arrowheads or fins at the end of these lines, are the lines the same length or is one longer?