This thesis asks what happens when two rare conditions, autism and synaesthesia, co-occur within the same individual. I focus on two outcomes of this co-occurrence in particular. Firstly, I investigate how the combination of autism and synaesthesia might result in the development of prodigious talents and skills (e.g. maths, art, music skills etc.) - otherwise known as savant syndrome. Secondly, I investigate how this same combination can result in a very different unique outcome altogether known as objectum sexuality, which involves the development of sexual or romantic feelings towards inanimate objects (e.g. a bridge). Through five experimental studies, I show that these two vastly different outcomes (savant syndrome and objectum sexuality) can develop based on the precise nature of the interaction between traits and behaviours related to both autism and synaesthesia. Chapters 2, 3, and 4 together confirm the existence of a link between autism, synaesthesia, and savant syndrome as well as showing for the first time how a behavioural and psychological profile within autism predisposes autistic individuals to talent. In Chapter 5, I develop a new type of test designed to objectively measure sequence-personality synaesthesia (a type of synaesthesia involving the projection of personality traits and genders onto inanimate objects). This test is then utilised in Chapter 6 to show that autism and sequence personality synaesthesia are linked to the development of objectum sexuality. Overall, this thesis shows that when autism and synaesthesia co-occur within the same individual the chances of developing yet rarer outcomes is increased.