Mechanisms of selective attention exert a powerful influence on visual perception. We examined whether attentional selection is necessary for generation of the vivid colours experienced by individuals with grapheme-colour synaesthesia. Twelve synaesthetes and matched controls viewed rapid serial displays of nonsense characters within which were embedded an oriented grating (T1) and a letter-prime (T2), forming a modified attentional blink (AB) task. At the end of the stream a coloured probe appeared that was either congruent or incongruent with the synaesthetic colour (...) elicited by the letter-prime. When the prime was attended, synaesthetes showed a reliable effect of prime-probe congruency. In contrast, when the prime appeared at 350 ms following T1 (during the AB), the congruency effect was eliminated. Our findings suggest that focused attention is crucial for inducing letters to elicit colours in synaesthesia. © 2009 Elsevier B.V. All rights reserved. (shrink)

Mechanisms of attention play a crucial role in filtering sensory inputs from the external world, allowing information to be prioritised for goal directed behaviour. To what extent might these same capacity-limited processes influence grapheme-colour synaesthesia, in which letters, numbers or words evoke concurrent experiences of colour? Asking synaesthetes themselves whether attention seems important in their experiences has provided a range of answers. On the one hand, for some synaesthetes, diverting attention can diminish the quality of their synaesthetic colours. On the (...) other, there are suggestions that synaesthetic experiences can themselves alter the manner in which attention is allocated to sensory stimuli in the environment. Here, we review a range of empirical investigations that have examined the role of attention in grapheme-colour synaesthesia. A particular focus of these studies has been the extent to which an inducing stimulus - such as an achromatic letter or digit - must be attended or consciously perceived to trigger a concurrent synaesthetic experience. In most cases, limiting attention or masking inducers tends to reduce or eliminate behavioural evidence of synaesthetic experiences. We also discuss how synaesthesia might improve performance in visual search tasks through post-attentive processes such as grouping, or by facilitating decision-making processes. (shrink)