Transfer of training from an instructional environment to a natural environment may bring about ineffective language performance by bilingual individuals. In that regard, this study was designed to demonstrate the effect of such a transition on individuals' language performance. A series of Japanese and English words were used as sample and comparisons in a matching procedure. Differential conditioning was implemented in the presence two types of contextual stimuli. After three sets of relations were established, the physical configuration of the contextual stimuli was changed to more subtle appearance, and the number of variations in the contextual stimuli was increased. Measures of percent correct and response latency were used to show the negative influence on second language performance. Percent correct responses decreased with the subtle contextual stimuli for 11 out of 14 participants, and average response latency increased with the increased number of variations in the last phase. These findings indicate that the change in environmental stimuli will be a significant participatory factor in training of second languages. (Contains 8 figures and 4 tables.)