Activation

When I was in the “flow” state of reading Anderson’s paper of “ACT A Simple Theory of Complex Cognition”, I could not help myself referring back to Just and Carpenter’s seminar work on capacity theory of comprehension. I am wondering perhaps there is a connection between two theories, which is the “Activation-Level”.

First of all, just a little recap of Anderson’s paper: He tries to understand the basic components and processing principles of our cognition. By studying how people write recursive programs, he claims that there are two elements: productions (procedural knowledge) and long-term chunks (declarative knowledge). Then he further explains what are “Knowledge Acquisition” and “Knowledge Deployment”.

For “Knowledge Acquisition”, it was said that long term chunks come from environment encoding, and to transform those chunks, ACT-R looks for some existing chunks for mapping; From “Knowledge Deployment”, the author answers the question: how humans select the most appropriate knowledge for a particular context. Based on a rational analysis that “knowledge is made available according to its odds of being used in a particular context, activation process implicitly performs a Bayesian inference in calculating these odds”, he elicits a basic equation, which is:

Activation_Level = Base_level + Contextual_Priming

Anderson further illustrates this equation with three domains; memory, categorization, and problem solving.  It looks to me that for those three domains, the way we see “contextual priming” slightly differs. For instance, for memory, it is the association of chunk n and chunk m; for problem-solving, it is about the effect of distance to the goal that participants set up. 

When we go back to Just and Carpenter’s paper: they “redefine” the concept of working memory by presenting a computational theory, which suggests both storage and processing are fueled by an identical property called “Activation”. More specifically, each element (e.g. word, phrase, objects from real world) carries an associated activation level. During a course of understanding, relevant chunks are activated from either a computation or long term memory; however, not all of them can enter working memory; only the one that meets certain minimum threshold value obtain the permission. As long as the total amount of activation level is within system limitation, we are good to process the information; but if the sum exceeds system limitation, we need to de-allocate some old elements. It may be not hard to get the idea if you draw a scenario in which you try to understand a difficult sentence with several clauses embedded. Some people with large working memory capacity may understand it quicker than those who own a small capacity.

You may notice that the activation level is a common thread for both works. If Anderson is right, can he help explain where the activation level from in Just and Carpenter’s theory? Just and Carpenter adopt assess working memory capacity using the "Reading-Span" task; while Anderson address his curiosity from studying people writing recursive programs, and his idea is published a few years after. I am just wondering if we swap their methodologies, are we still seeing this common thread?


Reference:

Anderson, J. R. (1996). ACT: A simple theory of complex cognition. American Psychologist, 51, 355-365.

Just, M. A., Carpenter, P.A., (1992). Capacity Theory of Comprehension: Individual Differences in Working Memory. Psychological Review, 99(1), 122-149.

(© 2012 Miaoqi Zhu)