Four experiments were carried out to examine the effects of item imagery and detrimental effects of Peterson-type (Peterson and Peterson, 1959) intervening tasks on PA performance as well as on associative directionality. The results showed facilitative effects of item imagery and detrimental effects of intervening tasks on R-S as well as S-R learning. Furthermore, those effects had interacted with reduced percentage occurence of stimulus or response members. The result was supposed to be relevant to Schultz (1965)'s remarks that detrimental erects of reduced % ORM had adversely affected both item discrimination and association, while detrimental effects of reduced % OSM had adversely affected association.