Information processing for motor control under non-coscious perception using ERP

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This study examined the nature of information processing underlying perception without awareness and motor responses, conducting several experiments using simple reaction time (RT) tasks with a backward masking paradigm, in which a prime and mask stimuli were presented with a short SOA. To examine behavioral aspects we measured (1) the awareness of perception of the prime stimulus in a two-forced-choice task, (2) reaction times as motor responses to the imperative stimulus set (prime and mask), and (3) Event-related potentials (ERP), lateralized readiness potentials (LRPs), which were calculated on the basis of averaged EEG waves.Results of experiments showed that simple reaction times were correlated with the latency of S-LRPs (i. e., the time from the stimulus onset to the initiation of motor processes), whereas the latency of R-LRPs (i. e., the processing time for motor preparation processes) was not correlated with simple reaction times. This suggested that the prime stimulus facilitated the stages of motor information processing earlier than conditions without prime stimulus. Awareness of perception of the prime stimulus was absent for backward masking conditions in which the prime stimulus was masked by the mask stimulus. The results that the latency of S-LRPs other than R-LRPs for the prime-masked conditions was correlated with simple reaction times suggested that non-consciously perceived prime stimulus facilitated motor responses, resulting in short reaction times. ERPs also showed that P100 appeared clearly whereas P300 did not appear for the prime-masked conditions, indicating that the prime stimulus was processed at early stages of visual information processing but not at cognitive stages. Such sensory inputs from the masked prime stimulus may facilitate directly the stages of motor information, bypassing the stages of explicit, cognitive information processing of the prime stimulus.