Event-related potentials during encoding: Comparing unitization to relational processing

Context details are typically encoded into episodic memory via arbitrary associations to the relevant item, known as relational binding. Subsequent retrieval of those context details is primarily supported by recollection. Research suggests that context retrieval can rely on familiarity if the context details are “unitized” and thereby encoded as features of the item itself in a single new representation. With most investigations into unitization focusing on the contributions of familiarity and recollection during retrieval, little is known about unitization during encoding. In an effort to begin understanding unitization as an encoding process, we used event-related potentials to monitor brain activity while participants were instructed to encode words with color information using relational association or unitization. Results showed that unitization-based encoding elicited significantly more negative potentials in the left parietal region than relational encoding during presentation of the second segment of strategically-specific sentences. This difference continued through presentation of the third sentence segment, becoming less lateralized, and ended before the final two segments were presented. During the mental imagery period, unitization-based encoding elicited significantly more positive potentials than relational encoding in the first 200 ms centrally and from 400 through 1000 ms in left fronto-temporal and parieto-occipital regions. Our findings indicate that unitization and relational processing diverged at approximately the time that the context item was presented in the relational condition. During mental imagery, unitization diverged from relational processing immediately, suggesting that unitization affected the nature of the item representation, and possibly the brain regions involved, during memory encoding.