Cartesian dualism is derived from the thinking of Rene Descartes, who believed that the brain is merely the seat of the mind. The latter was seen as a disembodied non-material entity, interacting with the former via the pineal gland, now known to be a small endocrinal gland linked to sexual development. However, most current theories seek to explain the mind in purely material terms. Historically these theories divided into two types, horizontal and vertical.
Horizontal theories refer to mental processes as if they are interactions between non-domain specific faculties such as memory, imagination, judgement, and perception. By contrast, vertical theories assert mental faculties are differentiated on the basis of domain specificity, are genetically determined, are associated with distinct neurological structures, and are computationally autonomous. This view has its origins in the 19th century phrenology movement founded by Franz Joseph Gall, who claimed that the individual mental faculties were associated with specific physical areas of the brain.
While this early view of modularity has long since been discarded, the theory was revived by Jerry Fodor in his 1983 work The Modularity of Mind. This theory abandons the notion of the “modular hardware” physically located in particular areas of the brain and draws on the work of Noam Chomsky in linguistics.
According to Fodor, the mind has two parts – input systems and cognition or central systems. The input systems are a series of discreet modules with dedicated architectures that govern sight, hearing, touch, etc. Language is also regarded as an input system. However the cognitive or central system has no architecture at all – this is where “thought”, “imagination” and “problem solving” happen and “intelligence” resides.
Each input system is based on independent brain processes and they are quite different from each other, reflecting their different purposes. These systems are localized in specific areas of the brain. The input systems are mandatory, if for example somebody sits behind you on the bus and spends the entire journey gassing away on their mobile, you cannot switch off the hearing module. However this has the advantage of saving time that would otherwise spent on decision-making.
As per the “vertical” view of mental architecture, Fodor believes that the input systems are “encapsulated”, i.e. they do not have direct access to the information being acquired by other input systems. What one is experiencing at a given time in one sensory modality does not any of the others – you cannot, for example, “see” sounds. [One problem for this view is the condition known as synaesthesia where sensory modalities apparently do interact and people can indeed see or taste sounds, etc. Well-known synaesthetes include David Hockney, Wassily Kandinsky and Vladimir Nabokov. The condition was evidently known to the French Romantic poets Arthur Rimbaud and Charles Baudelaire, who both described it in their work.]
A second feature of the input modules is that they only have limited information from the central systems. Fodor cites a number of optical illusions such as the Muller-Lyre arrows, which continue to apparently differ in length even when one is fully aware that this is not the case. The input modules are essentially “dumb” systems that act independently of the cognitive system and each other. To sum up, they are encapsulated, mandatory, fast-operating and hard-wired. Perception is innate, i.e. hard wired into the mind at birth.
The central cognitive systems are very different to the “dumb” input systems. According to Fodor, they are “smart”, they operate slowly, are unencapsulated and domain-neutral, i.e. they cannot be related to specific areas of the brain.
The Fodorian view is that evolution has given the modern human mind the best of both worlds: input modules that can enable swift, unthinking reactions in situations of danger (predators, etc) or opportunity (prey, etc) on one hand; and a slower central cognitive system, to be used when there is time for quiet contemplation, integrating information of many types and from many sources.
(This article was originally published on my blog http://www.christopherseddon.com on 27 April 2009)