Activation of a memory node in SOP theory. (A) When the stimulus is presented, the node goes into A!, decays to A2, and then becomes inactive again. (B) Activation of the node actually depends on the proportion of elements within the node that individually go from A1, to A2, and then inactive. Some elements decay more quickly than others; activation of the node really reflects the proportion of elements in A! or A2 at any given time. Reprinted from (Bouton, 2007). Copyright 2007 by Sinauer Aoociates, Inc. Reprinted by permission.