The Otter and the Cleaver: Exploring the neural underpinnings of unitization using the Gestalt principle of proximity

Associative memory requires the binding of multiple objects into a single representation in memory. As such it is viewed as harder and more resource demanding than item memory. One means of facilitating associative memory is through the process of unitization. Previous work has suggested that, once unitized, discrete stimuli are processed as a single ensemble. The present study aims to test whether the grouping principle of proximity enhances associative memory by creating unitized representations of item pairs that resemble how single items are processed in memory in younger and older adults. To examine the neural basis of perceptual unitization, young and older participants encoded unrelated object pairs either proximally arranged (unitized condition) or distally arranged (associative condition) as well as single objects. Behaviorally, results showed enhanced memory for proximally organized object pairs compared to distally organized object pairs across both younger and older adults. Examination of neural pattern similarity across conditions suggested that while regions critical to associative memory largely processed the proximal object pairs more similarly to the distal object pairs, clusters of neural activity throughout the cortex did show greater similarity of neural patterns across proximal pairs and single objects during both encoding and retrieval. Results suggest that the simple act of configural placement is enough to initiate unitized-based encoding and maintain that representation at retrieval. Age differences emerged during retrieval suggesting that older adults have more difficulty maintaining unique memory representations.