Multiple states of working memory: A new era of fractionation?
Several models that explain working memory as “activated long-term memory” (e.g., Cowan, Oberauer) posit multiple states of activation, including, variously, a capacity-limited focus of attention, a region of direct access, and a broader pool of temporarily activated representations. This symposium will consider these models in light of recent theoretical and empirical advances in three literatures: attention; visual perception; and cognitive neuroscience. Synthesizing across these developments will raise several questions: What is the psychological and physiological reality, indeed, the utility, of categorical distinctions between iconic vs. short-term vs. working vs. long-term memory? How far can we push the overlap of the constructs of attention and working memory? Does the concept of ‘activation’ mean different things in a psychological vs. a computational vs. a physiological context? Answers to these questions will move us toward a coherent model of working memory that can accommodate and withstand further pressure toward functional fractionation.
Bradley R. Postle; Departments of Psychology and Psychiatry, University of Wisconsin-Madison
Feature memory and the guidance of attention
Chris Olivers; Cognitive Psychology, VU University Amsterdam
Many models of visual search assume that targets are prioritized on the basis of their match to a visual working memory representation. Experiments by myself and others converge on the idea that maintaining a visual feature in working memory can be, but is not always, sufficient for inducing an attentional bias towards that object. Nor is visual working memory necessary for such feature-based biases to occur: More implicit, episodic memories, as well as long-term feature associations induce very similar biases. Taken together, the evidence suggests that working memory tries to be as lazy as possible by specifying just the minimal task requirements, and letting the visual details be filled in on a "need-to-know" basis, either by the stimulus or by other memory systems. Only when a new attentional template is recruited is visual working memory involved, but this takes time, effort, and appears subject to a single item capacity limit.
Handing off attentional templates from working memory to long-term memory
Geoffrey F. Woodman; Vanderbilt Vision Research Center, Center for Cognitive and Integrative Neuroscience, Vanderbilt University
Theories of attention propose that target representations are stored in working memory to bias attention mechanisms to find critical targets in cluttered scenes. However, theories of learning and automaticity suggest that working memory should only serve this function of controlling processing early in practice. Using electrophysiological methods, our research shows that when humans search complex visual scenes, a representation of the target is maintained in visual working memory, provided the identity of the searched-for item changes frequently across trials. However, when the target identity is stable across trials we can watch these working memory ‘attentional templates’ handed off to long-term memory. This talk concludes by discussing new questions we are addressing using these methods. Specifically, I will discuss recent work that determines how reward changes the source of the memory representations that control attention and whether we share these mechanisms of attentional control with other primates.
Delay-period activity reflects the internal focus of attention, not short-term storage
Jarrod A. Lewis-Peacock; Department of Psychology and Neuroscience Institute, Princeton University
It is widely assumed that the short-term retention of information is accomplished via an active trace. Thus, although models differ about the capacity of the internal “focus of attention” (e.g., 1 item (McElree, Oberauer) vs. a few (e.g., Cowan)), there is general agreement that it represents a subset of a broader pool of “activated” long-term memory representations. We present multivariate pattern analyses of fMRI and EEG data that generally support this framework, but challenge important details. First, our data indicate that two items can be held in the focus simultaneously. Perhaps more surprisingly, they also indicate that the active neural signature of an item that is removed from the focus drops quickly to baseline (NOT to an intermediate state), even though its neural signature can be just as quickly reactivated if it is needed later in the trial. Thus, short-term memory outside the focus of attention may not require activation.
A neurally informed taxonomy of visual short-term memory
Ilja Sligte; Cognitive Neuroscience Group, University of Amsterdam
At the psychological level, visual short-term memory (VSTM) can be dissociated into iconic memory (brief, high-capacity) and visual working memory (sustained, limited-capacity). In addition, our recent work provides overwhelming evidence for an in-between stage with high capacity and long lifetime (Sligte, Scholte, & Lamme, 2008). While this new fragile VSTM stage can be dissociated from iconic memory and working memory, one can question the use of a taxonomy that fractionates VSTM into increasingly smaller subparts. Here, I propose a neural framework that brings everything together. By assuming that the contents of VSTM are continually refreshed by loops of brain activity, the behavioral characteristics of iconic memory, fragile VSTM, and working memory are natural consequences of the architecture of the system. As higher brain areas have increasingly complex tuning characteristics and larger receptive field sizes, the depth of neural processing will then determine capacity, duration, and fragility of individual VSTM traces.