In order to investigate the relative effectiveness of specific media attributes on student performance on criterion tests, a comparison was made of the effectiveness of two levels of stimulus explicitness in visuals in facilitating student achievement on criterion tests of knowledge, comprehension, and total understanding. Subjects were 171 students possessing two different levels of entering behavior. The two-way ANOVA procedure was used to investigate the existence of interaction between entering behavior and level of stimulus explicitness. Results indicated that a significant relationship existed between entering behavior and performance on post-criterion tests; no relationship existed between stimulus explicitness and achievement on the criterion tests; and insignificant interactions were found to exist between entering behavior and instructional treatment. This study was designed to evaluate the predictability of Salomon's theory of stimulus explicitness, which attempts to present an understanding of how the use of media affects learning. Seven references are listed. (Author/LMM)