What are the neural correlates of conscious visual awareness? Tackling this question requires contrasting neural correlates of stimulus processing culminating in visual awareness with neural correlates of stimulus processing unaccompanied by awareness. To contrast these two neural states, one must be able to erase an otherwise visible stimulus from awareness. This paper describes and critiques visual phenomena involving dissociation of physical stimulation and conscious awareness: degraded stimulation, visual masking, visual crowding, bistable figures, binocular rivalry, motion-induced blindness, inattentional blindness, change blindness (...) and attentional blink. While no single strategy stands above the others, those producing changing visual awareness despite invariant physical stimulation are clearly preferable. (shrink)

People with grapheme-color synesthesia perceive specific colors when viewing different letters or numbers. Previous studies have suggested that synesthetic color experience can be bistable when induced by an ambiguous character. However, the exact relationship between processes underlying the identity of an alphanumeric character and the experience of the induced synesthetic color has not been examined. In the present study, we explored this by focusing on the temporal relation of inducer identification and color emergence using inducers whose identity could be rendered (...) ambiguous upon rotation of the characters. Specifically, achromatic alphabetic letters and digits were presented at varying angles to 9 grapheme-color synesthetes. Results showed that grapheme identification and synesthetically perceived grapheme color covary with the orientation of the test stimulus and that synesthetes were slower naming the experienced color than identifying the character, particularly at intermediate angles where ambiguity was greatest. (shrink)

Colour synaesthesia is the mental experience involving a strong association between specific colours and specific auditory stimuli, such as words, or achromatic visual stimuli, such as numerals or letters. In the contemporary literature on colour synaesthesia, the majority view treats the phenomenon as one arising from some of the same neural events mediating colour perception triggered by genuinely coloured objects; this view that synaesthesia is perceptually based, however, is not universally endorsed. What strategies have been utilized to evaluate the perceptual (...) reality of colour synaesthesia, and what is the evidence produced by those strategies? This chapter tackles those questions within the context of colour graphemic synaesthesia, the most widely studied form of synaesthesia. We divide the research strategies into those employing behavioral measures to assess whether synaesthetia influences performance on tasks known to be sensitive stimulus colour and those employing indirect measures that use physiological responses as proxies for colour perception. Our chapter concludes that there is sufficient justification for the belief in the perceptual reality of colour grapheme synaesthesia. At the same time, we applaud those who remain disbelievers, for their skepticism has underscored the logical issues surrounding research on this question. (shrink)