Nonconscious perception and information-processing in a visual reaction time task using a backward masking paradigm

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This research project examined the nature of information processing underlying perception without awareness and motor responses. We conducted several experiments using reaction time (RT) tasks (1) with double-stimulus presentations (i.e., a preceding/prime and the following/target simuli) to cause either metacontrast or backward-masking and (2) using finger-lift and aiming movements as responses to imperative stimuli. In the metacontrast experiment we manipulated SOAs (stimulus onset asynchrony) to be either 40ms (40ms-SOA), in which the sensation of a preceding stimulus was completely masked by the following stimulus, or much longer time (threshold-SOA) which resulted in the preceding stimulus being nearly masked. Results showed that RTs and awareness of the preceding stimuli were altered in a different way to each other for the 40ms- and threshold-SOAs. This suggests that information processing for motor responses may independently occur in parallel with information processing causin … More g awareness of perception. We also conducted a somatosensory backward-masking experiment, manipulating the intensity of preceding stimulus so as to set sensory sensitivity to stimuli at either a threshold level, 1.2 times and 2 of the threshold. RTs and the awareness of perception altered independently to each other for the stimulus intensities, indicating the same findings as those in the metacontrast experiment. In the experiment using finger-lift and aiming tasks we manipulated the size, luminance contrast, and location of visual stimuli. Differences in RTs calculated by subtracting RTs for the finger-lift from those for aiming tasks altered as a function of presentation loci alone. This suggests that motor response is directly correlated to the perception of spatial rather than physical nature of presented stimuli. Collectively, these findings of this research project suggest that information processing for motor response does not occur on the basis of the awareness of perceived stimuli and that both types of information processing underlying the production of motor response and awareness of perception may well be activated in parallel. Although we measured EEG throughout these experiments, the EEG data could not result in effective explanations of nonconscious perception and motor responses. These issues should be further examined in the future research projects. Less