On one hand, such a limitation could reflect an etiologically important functional restriction reflected by the trajectory of the high-risk young men. On the other hand, the inverse correlation of intercept with slope might reflect a psychophysiological floor effect consistent with the law of initial values (Raykov, 1995; Wilder, 1967). If the difference between target and nontarget P300 amplitude is largely a function of the extent to which relevant neural systems are engaged rather than different systems being activated, this floor does not appear to have been met for the target P300 amplitude of the high-risk men during the age range examined. The difference between target and nontarget P300 (M = 10.78 µV) was significant and sizable for this group relative to the differences in target amplitude from age 17 to age 24 (M = 3.72 µV). It is unlikely that the trajectory of P300 development observed in these young men merely reflects an artifact of having a low initial intercept.
