OVERLAPPING STAGE MODELS AND REACTION-TIME ADDITIVITY - EFFECTS OF THE ACTIVATION EQUATION

Many experimental factors have been found to affect mean reaction time (RT) additively in factorial experiments. What sorts of RT models are compatible with this fact? Sternberg (1969) showed that serial, discr ete-stage models are consistent with additivity, and as a result addit ivity has sometimes been regarded as evidence in favor of such models. However, McClelland (1979) showed that an alternative ''cascade'' mod el, which violates crucial assumptions of discrete-stage models, also predicts RT additivity in many cases. This article examines various mo dified versions of the cascade model, and shows that mean RT additivit y arises from many overlapping stage models, including some with thres holds, information quantization, and nonlinear activation transformati ons. This suggests that other aspects of the data besides mean RT addi tivity should be examined to distinguish between serial and overlappin g stage models.