Schedule of Events | Symposia

The big item theory: A high-resolution fMRI investigation into unitization using pattern similarity analysis

Poster Session C - Sunday, March 30, 2025, 5:00 – 7:00 pm EDT, Back Bay Ballroom/Republic Ballroom

Catherine Carpenter¹ (cmc84@psu.edu), Alexa Becker¹, Amy Overman², Nancy Dennis¹; ¹The Pennsylvania State University, ²Xavier University

Unitization has traditionally been defined as the process by which two or more discrete items (typically words or objects) are processed in memory, such that they are perceived as a single ensemble (or unit). Evidence for the item theory of unitization comes from behavioral and neuroimaging evidence that shows a reliance on familiarity processing and the recruitment of item-based neural resources, such as perirhinal cortex. Yet, because a single item condition has not been utilized in this past work as a point of comparison, a true test of the item theory has not been undertaken. The current study tests the item account of unitization by investigating whether unitized words (in the form of compound words) are processed more similarly to single words than to unrelated word pairs. Challenging a strict account of the item theory, the results show that unitized information is represented more similarly to unrelated associations (unrelated word pairs) than to single items, during both encoding and retrieval. Specifically, greater neural pattern similarity between compound words and unrelated word pairs was found across the associative memory network, including hippocampal subfields such as the perirhinal cortex, CA1 and DG/CA3, as well as the inferior frontal gyrus, and regions in the parietal lobe. The results suggest that unitization, even in its strongest form, may not operate through item-like processing and may represent an intermediate level of processing between associative and item level representations.

Topic Area: LONG-TERM MEMORY: Episodic