Correlates of implicit semantic processing as revealed by representational similarity analysis applied to EEG

Most researchers agree that some stages of object recognition can proceed implicitly. Implicit recognition occurs when an object is automatically and unintentionally encoded and represented in the brain even though the object is irrelevant to the current task. No consensus has been reached as to what level of semantic abstraction processing can go implicitly. An informative method to explore the level of abstraction and the time courses of informational content in neural representations is representational similarity analysis (RSA). Here, we apply RSA to EEG data recorded while participants processed semantics of visually presented objects. Explicit focus on semantics was given when participants classified images of objects as manmade or natural. For implicit processing of semantics, participants judged the location of images on the screen. The category animate/inanimate as well as more concrete categories (e.g., birds, fruit, musical instruments, etc.) are processed implicitly whereas the category manmade/natural is not processed implicitly.