Prof Ed Awh (University of Chicago)

Title: Content-independent pointers mediate storage in working memory

Abstract:

Although past neural studies of working memory (WM) have focused on stimulus-specific activity that tracks the stored feature values, a separate line of evidence has revealed neural signals that track the number of items in WM, independent of the contents of those items. Thus, a common neural signature of WM load has been identified for highly distinct visual features, and even across visual and auditory sensory modalities. Our working hypothesis is that these content-independent load signals reflect the operation of spatiotemporal “pointers” that enable the binding of stored items to the surrounding event context, a process that is critical for precise access online memories despite high levels of proactive interference. This hypothesis predicts that pointer deployment is a key limiting factor for WM capacity. To test this prediction, we applied representational similarity analysis (RSA) to EEG data to determine the number of pointers deployed across set sizes that ranged from 1 to 8 items. We observed a “neural load” function that rises with increasing numbers of stored items, while controlling for differences in sensory energy and spatial attention. Critically, this function differed sharply as a function of individual differences in WM capacity. Subjects with higher capacity showed a monotonic rise in the number of pointers deployed that leveled off at higher set sizes. By contrast, low capacity subjects showed an initial rise followed by a sharp decline in the number of pointers deployed at higher set sizes. This empirical pattern dovetails with past behavioral and neural studies that have documented increased costs for low capacity observers as the number of memoranda exceeds capacity. We conclude that content-independent indexing is a core component of individual differences in WM ability.

Bio:

I’m a cognitive neuroscientist who received a doctoral degree from the University of Michigan, training with Drs. John Jonides and Edward Smith. I then spent 2 years at UC San Diego, working with Dr. Hal Pashler, and Dr. Steve Hillyard. I took my first professor position at the University of Oregon in 1999, where I spent 16 years and developed a close collaboration with Dr. Ed Vogel. In 2015, Vogel and I both took positions at the University of Chicago where I still reside. My core research interests focus on working memory and attention, with an eye towards the intertwined nature of these constructs. I’ve been very interested in the sharp capacity limits that characterize working memory performance, and we have recently proposed that those limits may relate to limits on content-independent operations that serve to bind item representations to the observer’s current context. My talk will focus on the evidence supporting this broad hypothesis.