Igor Utochkin¹ (), Edward Vogel¹; ¹University of Chicago

Previous research investigated the neural dynamics of memory search using electrophysiological markers of old-new recognition and working-memory load (Rugg, 2007; Williams et al., 2024). All those studies involved situations when only one test item, either old or new, was present per trial. However, in many cases, observers deal with several simultaneously presented items and have to decide which are familiar or novel; this is often termed a hybrid visual and memory search or forced-choice memory test. Here, we present a method to reveal ERP markers of hybrid search. In each block of our experiment, participants studied 20 visual objects. At the test, participants were bilaterally shown two objects, old and new. We manipulated search instructions across blocks, asking participants to localize either the old or the new object. The bilateral presentation allowed us to analyze ERP signals from the old and new items as the differences between lateralized ERP’s. We found two lateralized ERP effects. First, we found a sustained negative activity in the posterior electrodes contralateral to the location of the old item regardless of search instruction. It resembles an established ERP component known as contralateral delay activity (CDA) (Vogel & Machizawa, 2004) associated with encoding and active storage of information in working memory. It may indicate that familiar items get prioritized access into working memory. We label this effect r-CDA (retrieval-CDA). Second, we found a frontal negativity contralateral to the new item when participants looked for those items. The onset latency of this frontal effect was later than the r-CDA, which can suggest a specific novelty-related signal following the initial familiarity check developing only if novelty is relevant. The dissociation between these two ERP markers can indicate an essential separation between two components or pathways used by recognition memory to evaluate the familiarity and novelty of multiple objects.

Acknowledgements: Project funding: ONR N00014-22-1-2123