SSVEP as a no-report paradigm to capture phenomenal experience of complex visual images

The goals of this study were (1) to develop a novel type of no-report paradigm capable of capturing people9s phenomenal experience when they see complex images, and (2) to explore the extent to which such images can be processed in the absence of consciousness. To this end, we took advantage of a powerful technique derived from electroencephalography: the steady state visual evoked potentials (SSVEP) technique. We used faces embedded in sequences of non-face stimuli, which we manipulated the contrast of so as to create subliminal and supraliminal conditions. Our results are twofold. On the one hand, they indicate that the SSVEP response, which signalled the ability of the brain to categorize faces, was strongly reduced, but nevertheless maintained, when participants reported being unable to see the stimuli. In this condition, the response was confined to early visual stages, whereas it propagated through the ventral stream in conditions in which image contrast increased. On the other hand, the method appears as useful to consider as a novel instance of a no-report paradigm because it requires no overt behavioural response and because its outputs (signal magnitude and scalp topography) predict people9s self-reported phenomenal experience.