EFFECT OF SUBTHRESHOLD TARGET STIMULI ON EVENT-RELATED POTENTIALS

Objectives: Event-related potentials (ERPs) elicited by subthreshold v isual stimuli were studied to assess the relationship between unconsci ous cognitive processing and the electrical activity of the brain. Met hods: A new method of modified visual oddball paradigm with supralimin al and subliminal stimuli was applied. prior to the experiment, the in dividual 'subjective' threshold for the conscious discrimination betwe en frequent and target stimuli was established for each subject. Supra liminal and subliminal, frequent and target visual stimuli were then a lternatively presented in random order to each subject. Results: Both the individual and the grand average ERPs revealed a typical response (P3) in the parietal region after supraliminally presented target stim uli. In subliminal conditions an analogous positive deflection in the central-parietal region was observed, which was elicited by the target stimulus, but not the frequent stimulus. Its latency could be clearly distinguished from the latency of the classical P3, the time differen ce between the two waveforms was approximately 100 ms. Results: The re sults of this study revealed the impact of unconscious processing to t arget stimuli on the configuration of event-related responses. (C) 199 8 Elsevier Science Ireland Ltd. All rights reserved.