Level-repetition effects in hierarchical stimulus processing: timing and location of cortical activity

The specific mechanisms that underlie repetition priming effects are only partly understood. We examined the timing and extent of brain activity in response to level-repeated and level-shifted conditions during hierarchical stimulus processing. A response cost in behavioral reaction times was evident for level-shifted compared to level-repeated conditions. Larger event-related potentials amplitudes for level-shifted conditions were evident over occipital scalp regions for an early component peaking at 132 ms post-stimulus onset. A negative potential over posterior temporal electrodes that peaked at 204 ms showed asymmetries in amplitudes that were consistent with lateralized differences in global and local level processing. A positive potential peaking at 290 ms also showed differences between level-repeated and level-shifted conditions over left parietal and left posterior temporal scalp regions. The study demonstrates cortical activity related to repetition priming for both local and global level targets. Early sensory ("P1") and later cortical processing can be affected by the need to shift attention across hierarchical levels. The results support the existence of multiple processes underlying level-repetition effects.