Nurit Gronau¹, Makaela Nartker², Sharon Yakim^1,3, Igor Utochkin⁴, Jeremy Wolfe^5,6; ¹The Open University of Israel, Israel, ²University of Texas at Austin, USA, ³The Hebrew University, Israel, ⁴University of Chicago, USA, ⁵Brigham and Women’s Hospital, ⁶Harvard Medical School, USA

In many everyday situations, we search our visual surroundings for one of many types of possible targets held in memory, a process known as hybrid search (e.g., searching for items on a shopping list). In some cases, only a portion of the memorized list is relevant to a specific visual context, so restricting the memory search to the relevant subset would be beneficial (e.g. there’s no need to search for carrots in the dairy section). Previous research has shown that participants often fail to "partition" memory into distinct, useful subsets on a trial-by-trial basis. However, given the known role of semantic content in long-term memory organization, we hypothesized that clearly semantically-defined subsets could facilitate flexible memory partitioning in dynamic hybrid search situations. Experiment 1 revealed that, indeed, semantic characteristics (i.e., object category), but not perceptual features (e.g., arbitrary color), can serve as a strong basis for flexible memory partitioning. Experiments 2 and 3 further demonstrated that this memory partitioning is cost-free and independent of the nature of surrounding visual distractors (i.e., whether the distractors are categorically homogeneous or heterogeneous). These findings demonstrate that confining memory search to a relevant subset of items can be highly effective when the subsets are defined by clear semantic categories. The results underscore the importance of conceptual information in the organization of activated long-term memory (aLTM) – the portion of LTM relevant to the current task - and to aLTM’s role in enabling flexible, trial-by-trial memory selection. Additionally, our findings highlight the relationship between visual search and memory search: Despite the activation of multiple sets or categories that could interfere with each other at the attentional (visual search) level, category-based memory partitioning seems to remain relatively immune to interference from other categories during this type of memory search.

Acknowledgements: Israeli Science Foundation (ISF) grant 1622/15 (to NG) and by the National Institutes of Health (NIH) grant EY017001 (to JMW).