Unlike in clinical blindsight patients, unconscious processing of chromatic information depends on early visual cortex in healthy humans.
BACKGROUND
Large amount of data concerning the neural mechanisms that mediate unconscious vision come from cortically blind patients who can process stimuli presented in their blind visual field. How well the findings generalize to neurologically healthy humans remains open.


OBJECTIVE
Using transcranial magnetic stimulation (TMS), we studied whether chromatic processing depends on the early visual cortex in healthy participants.


METHODS
We employed a phenomenon called the redundant target effect (RTE): simple reaction times to two stimuli are faster than to one stimulus, even when one of the stimuli is presented outside consciousness.


RESULTS
The RTE produced by chromatically defined stimuli disappeared when the contralateral stimulus of two bilateral stimuli was suppressed from consciousness.


CONCLUSIONS
In contrast to studies on blindsight patients, the results imply that the early visual cortex is necessary for the processing of chromatic information in neurologically healthy humans.
Department of Psychology, University of Turku, FI-20014 Turku, Finland; Centre for Cognitive Neuroscience, University of Turku, FI-20014 Turku, Finland. Electronic address: hmrail@utu.fi.
Henry
H
Railo
Department of Psychology, University of Turku, FI-20014 Turku, Finland.
Eki
E
Andersson
Division of Clinical Neurosciences, University of Turku and Turku University Hospital, FI-20521 Turku, Finland; Turku PET Centre, University of Turku and Turku University Hospital, FI-20521 Turku, Finland.
Valtteri
V
Kaasinen
Centre for Cognitive Neuroscience, University of Turku, FI-20014 Turku, Finland.
Teemu
T
Laine
Department of Psychology, University of Turku, FI-20014 Turku, Finland; Centre for Cognitive Neuroscience, University of Turku, FI-20014 Turku, Finland.
Mika
M
Koivisto
D000328:Adult; D003243:Consciousness; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D008297:Male; D010465:Perception; D010775:Photic Stimulation / Q000379:methods*; D011930:Reaction Time; D050781:Transcranial Magnetic Stimulation / Q000379:methods*; D014474:Unconsciousness; D014785:Vision, Ocular; D014793:Visual Cortex / Q000502:physiology*; D014794:Visual Fields; D014796:Visual Perception / Q000502:physiology*; D055815:Young Adult
Blindsight; Color; Redundant target effect; TMS; Unconscious processing; V1