9/26 HMC

About Henry and Rogers' experiment(1960) and Kilapp and Erwin (1976), see Figure 3.9(p. 54). Where the "600 ms " effect comes from? My point is, if RT is positive related to complexity, as mentioned by Henry and Rogers. And it also has a positive relation to MT(duration), then duration time should be insreased as long as RT increased, and without limitation (linear). How can we explain the relation between RT and duration presented in figure 3.9? especially when the response durations were below 600ms?