Foundations Of Cognitive Science


EPIC (for executive-process interactive control) (Meyer & Kieras, 1997a, 1997b), is an example of a modern production system that includes sensing and acting.  EPIC simulates the performance of  multiple tasks, and can produce the psychological refractory period (PRP).  When two tasks can be performed at the same time, the stimulus onset asynchrony (SOA) between the tasks is the length of time from the start of the first task the start of the second task.  When SOAs are long, the time taken by a subject to make a response is roughly the same for both tasks.  However, for SOAs of half a second or less, it takes a longer time to perform the second task than it does to perform the first.  This increase in response time for short SOAs is the PRP.

EPIC is an advanced production system.  One of its key properties is that productions in EPIC can act in parallel.  That is, at any time cycle in EPIC processing, all productions that have matched their conditions in working memory will act to alter working memory.  This is important; when multiple tasks are modeled there will be two different sets of productions in action, one for each task.  EPIC also includes sensory processors, such as virtual eyes, and motor processors, because actions can constrain task performance.  For example, EPIC uses single motor processor to control two “virtual hands”.  This results in interference   between two tasks that involve making responses with different hands.

While EPIC (Meyer & Kieras, 1997a, 1997b) explicitly incorporates sensing, acting, and thinking, it does so in a fashion that still exemplifies the classical sandwich (Dawson, Dupuis & Wilson, 2010).  In EPIC, sensing transduces properties of the external world into symbols to be added to working memory.  Working memory provides symbolic expressions that guide the actions of motor processors.  Thus working memory centralizes the “thinking” that maps sensations onto actions.  There are no direct connections between sensing and acting that bypass working memory.  EPIC is an example of sense-think-act processing.


  1. Dawson, M. R. W., Dupuis, B., & Wilson, M. (2010). From Bricks To Brains: The Embodied Cognitive Science Of LEGO Robots. Edmonton, AB: Athabasca University Press.
  2. Meyer, D. E., & Kieras, D. E. (1997a). A computational theory of executive cognitive processes and multiple-task performance .2. Accounts of psychological refractory-period phenomena. Psychological Review, 104(4), 749-791.
  3. Meyer, D. E., & Kieras, D. E. (1997). A computational theory of executive cognitive processes and multiple-task performance .1. Basic mechanisms. Psychological Review, 104(1), 3-65.

(Added September 2010)