Spatial Cue-Priming: Effects of Masked Cue Stimuli on Endogenous Visual Spatial Attention

Recent research in cognitive neuroscience has examined the relationship of consciousness and attention. On the one hand, it remains a debated topic whether attention is a necessary precondition for consciousness; on the other hand other researchers have focused on the possibility and mechanisms of attention without consciousness. Effects of unconscious stimuli on spatial attention were found in several studies but were so far restricted to peripheral cues or specific central cues which may invoke exogenous attention. Given that recent evidence suggests that unconscious stimuli have access to executive control processes, it seemed reasonable to assume that masked stimuli can affect endogenous orienting of attention as well. In the present work, masked primes were presented before visible endogenous cues in different spatial cueing tasks. These masked primes modulated speed and accuracy of responses to laterally presented visual target stimuli. This suggests that they affected endogenous orienting of attention. However, the effects of these masked primes are modulated by several factors such as perceptual similarity between prime and cue stimuli, spatial compatibility between primes and target location, validity of the visible cue stimulus, and whether the task and target parameters favor attentional selection at early or later stages of processing. Overall, results suggest different underlying mechanisms in spatial cue-priming. Large and reliable spatial cue-priming effects were found in letter discrimination tasks in which visible cues specified the target letter. In this task, priming effects on behavior seem to result in part from perceptual priming of cues and in part on later decisional processes. Direct effects of primes on attention were found in free choice task but were restricted to spatially compatible stimuli. Cue-priming effects on attention at early levels of processing seem to be mainly based on perceptual priming of cue processing. In EEG-experiments, a modulation of the visual N1 component provided further evidence for cue-priming effects on early levels of processing. In sum, results show that endogenous spatial attention can be affected by masked stimuli at different stages of target processing. However, further research is needed to clarify the mechanisms and limits of these spatial cue-priming effects