The purpose of the study reported in this paper was to examine the effect of visuals possessing different amounts of realistic detail and the effects of integrating covert and overt rehearsal strategies into visually complemented prose instruction. A total of 128 university students participated in the study, which involved a prose text on the human heart in two versions--one complemented with simple line drawings and the other with detailed drawings. After each instructional frame, students were asked to responded covertly (mentally) or overtly (in writing) about whether the drawings in their version correctly illustrated the text. Students then completed four individual criterion tests, including drawing, identification, terminology, comprehension, and a total criterion test. Analyses indicated that significant differences in favor of the covert version of the module containing the simple line drawings existed on the terminology, comprehension and total criterion tests. In comparing the covert and overt treatments complemented by detailed line drawings, the covert treatment was significantly more effective on all criterion measures. The unexpected superiority of the covert responses may have been due to the high academic ability of the participants. When the covert versions were compared, students who received detailed line drawings achieved significantly higher scores on all criterion measures. (Contains 8 references.) (KRN)