Psihologija (Feb 2009)
PRIMING OF OBJECT CATEGORIZATION WITHIN AND ACROSS LEVELS OF SPECIFICITY
Abstract
Identification of objects can occur at different levels of specificity. Dependingon task and context, an object can be classified at the superordinate level (as ananimal), at the basic level (a bird) or at the subordinate level (a sparrow). Whatare the interactions between these representational levels and do they rely onthe same sequential processes that lead to successful object identification? Inthis electroencephalogram study, a task-switching paradigm (covert naming orliving/non-living judgment) was used. Images of objects were repeated eitherwithin the same task, or with a switch from a covert naming task to a livingor non-living judgment and vice versa. While covert naming accesses entrylevel(basic or subordinate), living/non-living judgments rely on superordinateclassification. Our beha-vioural results demonstrated clear priming effectswithin both tasks. However, asymmetries were found when task-switching hadoccurred, with facilitation for covert naming but not for categorization. Wealso found lower accuracy and early-starting and persistent enhancements ofevent-related potentials (ERPs) for covert naming, indicating that this task wasmore difficult and involved more intense perceptual and semantic processing.Perceptual priming was marked by consistent reductions of the ERP componentL1 for repeated presentations, both with and without task switching. Additionalrepetition effects were found in early event-related activity between 150-190 ms(N1) when a repeated image had been named at initial presentation. We conclude that differences in N1 indicate task-related changes in the identification processitself. Such enhancements for covert naming again emerge in a later timewindow associated with depth of semantic processing. Meanwhile, L1 reflectsmodulations due to implicit memory of objects. In conclusion, evidence wasfound for representational overlap; changes in ERP markers started early andrevealed cross-task priming at the level of object structure analysis and moreintense perceptual and semantic processing for covert naming.
