Synaesthesia: an Essay in Philosophical Psychology
We are sometimes led to a different picture of things when something unexpected occurs which needs explaining. The aim of this thesis is to examine a series of related issues in the philosophy of mind in the light of the unusual condition known to psychologists as ‘synaesthesia’. Although the emphasis will be on the philosophical issues a view of synaesthesia itself will also emerge. Synaesthesia is a distinct type of cross-modal association: stimulation of one sensory modality automatically triggers an additional phenomenal character of experience associated with a second sensory modality in the absence of any direct stimulation of the second modality. Chapter 1 introduces synaesthesia to a philosophical audience by outlining the early history of synaesthesia studies, by summarising contemporary research and by indicating areas of philosophical interest to be considered in the rest of the thesis. Chapter 2 uses synaesthesia to examine one important philosophical model of the mind, Fodor’s modularity hypothesis, and, in turn, investigates the nature of synaesthesia in the light of that model. Fodor claims that cognitive modules can be thought of as belonging to a psychological natural kind in virtue of their possession of most or all of nine specified properties. The most common form of synaesthesia possesses Fodor’s nine specified properties of modularity, and hence it should be understood in terms of an extra cognitive module, and thus as belonging to the abovementioned psychological natural kind. Many psychologists believe that synaesthesia involves a breakdown in modularity. A breakdown in modularity would also explain the apparent presence of the nine specified properties in synaesthesia. I discuss the two concepts of function which underlie the respective theories, defending the breakdown thesis, arguing, in any case, that properties deriving from evolutionary history should also be used to decide between the two theses and thus ultimately membership of a psychological natural kind such as Fodor suggests. The argument is then used to respond to two challenges to the notion of a psychological natural kind. Chapter 3 focuses on the phenomenal character of synaesthetic experience. Externalists about the phenomenal character of experience tend to argue that the character of perceptual experience is to be explained either by the properties objects present to percipients, or by the properties objects are represented by percipients as having. Some internalists argue that there is a need to postulate hrther properties of the individual - in other words, qualia - to account for the individuation of the character of perceptual experience. The existence of additional phenomenal characters of experience in synaesthesia, which cannot directly be explained by reference to features of objects, suggests the existence of extra qualia and thus the presence of qualia in normal perception. The aim of this chapter is to meet the challenge presented by synaesthesia and the extra quaZia argument, and contrariwise, use synaesthesia as a way of fbrther clarifjmg the merits of the respective externalist positions. In the previous chapters the locution of ‘coloured hearing’ will have been adopted. Occasionally the process underlying synaesthesia is described as one of ‘hearing colours’. Chapter 4 rejects the latter usage. In so doing it focuses on the place of synaesthesia vis-a-vis normal perceptual processes. Considerations from previous chapters are further developed in order to shed light both on the metaphysical individuation of perceptual modalities and on how we know the distinctive perceptual modalities. Given the actual content of our concepts of perceptual modalities, it is argued that the actual world is one in which even synaesthetes are unable to hear colours. Consideration is given as to whether there is a possible world in which people could hear colours. The justification of the usage of ‘coloured-hearing’ then leads to a discussion of the relative importance of the individuating conditions of modes of perception. The thesis focuses largely on coloured hearing. What merits the preceding considerations have might be supported if they can be generalised. Chapter 5 goes a small way in that direction.