“…T h e first, C,, is presented at time t after a warning signal, and the second, 'c2, F 2 ) , the RT to X2. It has been found that RTc2) is minimal when I is large, that this minimum is maintained as I is reduced down to some value, I $ , and that for I < I%, RTc2) is greater than the minimum (Craik, 1948;Hick, 1948; Vince, 1948). The period of length I, is called the Psychological Refractory Period.…”