Reflections on synaesthesia, perception, and cognition

In this paper, we reflect on three long-standing problems: The relationship between the physical worlds and the perceived world, accounting for individual differences in the way in which we perceive the world around us, and the problem of understanding other minds. We begin by examining the relationship between synaesthesia and hallucinations, as well as between hallucinations and normal perception, attempting to show in both cases that the phenomena in question may share more in common than previously assumed. We consider the plausibility of a functional analysis of synaesthesia and examine the mechanisms of the different types of ordinary and extraordinary perceptions. We propose that synaesthesia-like mechanisms may underlie a range of perceptual phenomena and cognitive functions and demonstrate the usefulness of such an approach given the ubiquity of synaesthesia-like mental processes in human cognition.