When information becomes easier to access as a result of having been used recently, we say it is more activated. This activation spreads between semantically related concepts. Given a word, subjects are asked to give an associated word. Text is easier to read if semantically related words are used. We've seen that speed of recall of information from long term memory depends in part on how recently that information has been activated.
Activation changes quickly over time.
Thus these are believed to be distinct processes. Figure 6.10a illustrates a typical power law curve. Practice helps a lot at first, then provides decreasing gains as you reach the limits of your performance ability. There appears to be a neural basis for this law of learning. The change in sensitivity follows a power law relationship.