Effekte maskierter visueller Stimuli auf die Ausführung von konkurrierenden motorischen Reaktionen und kognitiven Aufgaben

Abstract

The masked priming paradigm is an often used method to investigate to what extent unconscious information can affect human behavior. In masked priming a poorly visible prime is followed by a relevant stimulus that serves as mask reducing the visibility of the prime. It could be shown that the prime affects the motor response to the following consciously perceived masking stimulus. Faster responses are observed when prime and mask indicate the same motor response compared to different motor responses (target priming). In priming of mental operations prime and mask are not associated with a motor response but with one of two tasks that have to be performed with a subsequent target stimulus. Again faster responses are observed when prime and mask indicate the same task. Importantly, the capacity of the prime to influence behavior is independent of its visibility. These effects have already been shown in a number of experiments. The aim of the present work was to understand the mechanism underlying priming effects and to investigate the question whether the effects of unconscious stimuli are generated by a common mechanism. Using behavioral experiments and functional magnetic resonance imaging the levels of stimulus processing and the brain structures that might be involved in the origin of priming effects were examined. In Experiments 1 3 target priming effects were investigated with the PRP paradigm. The results suggest that primes influence the perceptual analysis of the following mask and the selection of the appropriate motor response. This was confirmed by an fMRI experiment (Experiment 5) where priming effects in visual areas (BA 17, 18) and brain areas that might be involved in the control and selection of the correct motor response (supplementary motor area, anterior cingular cortex, dorsolateral prefrontal cortex, intraparietal sulcus) were found. Furthermore results suggest that primes activate the associated motor response in primary motor cortex. In experiments 4b and 6 priming of mental operations was investigated with the PRP paradigm. Results point to a priming effect in the visual system (BA 17, 18) and suggest that primes activate the associated task set (medial frontal superior gyrus, intraparietal sulcus, precuneus, inferior parietal lobule). However only weak evidence was found for priming effects in task specific brain areas. In both priming paradigms results suggest that primes affect early perceptual and response or task selection processes. Furthermore only weak evidence was found for priming effects in motor and task specific brain areas. Therefore it is assumed that effects of masked stimuli are controlled by a similar mechanism.