Despite the general consensus that synaesthesia emerges at an early developmental stage and is only rarely acquired during adulthood, the transient induction of synaesthesia with chemical agents has been frequently reported in research on different psychoactive substances. Nevertheless, these effects remain poorly understood and have not been systematically incorporated. Here we review the know...

Savant syndrome is a condition where prodigious talent co-occurs with developmental difficulties such as autism spectrum conditions (ASC). To better understand savant skills, we previously proposed a link with synaesthesia: that savant syndrome may arise in ASC individuals who also happen to have synaesthesia. A second, unrelated claim is that people with autism may have higher rates of synaest...

Synaesthesia denotes a condition of remarkable individual differences in experience characterized by specific additional experiences in response to normal sensory input. Synaesthesia seems to (i) run in families which suggests a genetic component, (ii) is associated with marked structural and functional neural differences, and (iii) is usually reported to exist from early childhood. Hence, syna...

This paper is an author response to two commentaries on 'Defining Synaesthesia' (Simner, 2012) by David M. Eagleman ('Synesthesia in its protean guises', 2012), and Roi Cohen Kadosh and Devin B. Terhune ('Redefining synaesthesia?', 2012). Together with these authors, I seek to more closely examine existing criteria on which definitions of synaesthesia have been based. In particular, I focus on ...

The last few years have seen the publication of a number of studies by researchers claiming to have induced "synaesthesia," "pseudo-synaesthesia," or "synaesthesia-like" phenomena in non-synaesthetic participants. Although the intention of these studies has been to try and shed light on the way in which synaesthesia might have been acquired in developmental synaesthestes, we argue that they may...

The healthy ‘special case’ in neuropsychology! Synaesthesia (Galton, 1883) is a condition in which a particular stimulus (e.g., seeing the letter R) evokes a particular additional sensation (e.g., a deep purple colour). Synaesthesia is automatic in the sense that the cross-sensations are fast and seemingly effortless, and highly consistent as the same associations persist from early childhood. ...

Synaesthesia (one sense triggering another) has recently become amenable to scientific investigation. Recent findings are reviewed. Maurer's developmental theory of synaesthesia is then discussed. The theory states that all human neonates have synaesthesia, but that by about 4 months of age the senses have become modularized to the extent that we no longer have synaesthesia. Possible ways of te...

In this chapter we review research examining the induction of synaesthesia with training, posthypnotic suggestion, and pharmacological agents in non-synaesthetes. Each of these methods has been shown to produce different aspects of synaesthesia, but none have produced experiences that have been corroborated using neuroimaging assays. Nevertheless, the close parallels between induced and congeni...

Synaesthesia is a rare phenomenon in which stimulation in one modality (e.g., audition) evokes a secondary percept not associated with the first (e.g., colour). Prior work has suggested links between synaesthesia and other neurodevelopmental conditions that are linked to altered social perception abilities. With this in mind, here we sought to examine social perception abilities in grapheme-col...

In synaesthesia one type of stimulation evokes the sensation of another, such as when hearing a sound produces photisms--that is, mental percepts of colours. In the past, the idiosyncrasy of this phenomenon, as well as the natural mistrust of scientists towards the subjective, consigned synaesthesia to the periphery of scientific interest. However, the landscape has changed radically in the las...