Unconsciously Guided Behavior With a Bias-Free Measurement of Consciousness

Abstract

\n Many researchers believe that unconscious, invisible stimuli can guide behaviour, but convincing evidence for this phenomenon is lacking. The controversy results from the difficulty of defining and measuring consciousness in an unbiased way. We utilized a bias-free 2-interval forced-choice (2IFC) paradigm to study whether orientation or color of unconscious, masked stimuli can guide behaviour. Each trial consisted of two intervals, only one of which contained the target stimulus. The observers were forced to discriminate the orientation or color of the stimulus in each interval, and in the end of the trial they made a 2IFC decision on which one of the intervals the stimulus was present. We focused on the trials in which the 2IFC decision was made incorrectly, suggesting unconsciousness of the presence of the target. In masked trials both orientation and color was discriminated with higher accuracy than expected by chance. Control trials showed that the participants followed the instructions and performed at ceiling in the 2IFC task, indicating that the specific non-perceptual cognitive requirements of the 2IFC task cannot explain the incorrect 2IFC decisions. The present results provide strong evidence for unconsciously guided behaviour. Further studies should examine the constraints of this phenomenon with the unbiased procedure.