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Unformatted text preview: l. experiments The Libet experiment
brainpotential…………….. voluntary will ……… voluntary action
550 ms At time 0, a brain potential can be recorded (readiness potential).
Only 350 ms later, we are aware we want to perform a certain
Another 200 ms later, the voluntary action is initiated. Libet: brain activity begins before willed judgement
A brain potential is measured before willed judgement:
a readiness potential (Bereitschaftspotenzial) As causes necessarily precede effects, conscious intention cannot
be the cause of the neural processes that lead to action. Libet, neuropsychologist, 1970, California The Libet et al. experiments “Die freie Wille ist eine Illusion“
Some neurobiological challenges Are we are puppets on a string? (Crevits) 13 The Crevits et al. ‘zombie* experiments’ The Freudian concepts Light stim. When a target has moved during a saccade (the subject being
blind in that time),
he adjusts the trajectory without consciously having seen the
*A zombie: a hypothetical human being without consciousness ATTENTION
CONSCIOUS CONSCIOUS INATTENTION Unconsciousness
a condition of information inaccessibility
where bottom-up activation is insufficient to become aware
potentially conscious, but not now because of lack of attention (topdown) SUBLIMINAL Consciousness
Trends in Cognitive Sciences, 2006, 10, 204-211 14 Subliminal visual stimuli evoke a strong activation in extrastriate visual cortex, but their
intensity quickly decrease in higher visual areas
Only conscious stimuli trigger a late surge of activation in a global prefronto-parietal
PLoS Biology, 2007, 5, 10, e260, 2408-23
2006, 10, 204-11 Proposed distinction between subliminal, preconscious, and conscious processing defined by
bottomup stimulus strength (vertical axis) and top-down attention (horizontal axis).
Shades of color: the amount of activation in local areas.
Small arrows: the interactions among them...
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- Spring '10