“Campbell (1979) has shown how the learning theory developed in the tight research group surrounding Kenneth Spence was less powerful than the learning theory developed within the much looser group surrounding Edward Tolman. These differences are explained in part by the relative ease people in Tolman's group had evaluating and changing ideas without regard for the effect of these changes on their reputations and the relative difficulty people in Spence's group had when they tried to do the same thing.”