To date, research to date on personal response systems (clickers) has focused on external issues pertaining to the implementation of this technology or broadly measured student learning gains rather than investigating differences in the responses themselves. Multimedia learning makes use of both words and pictures, and research from cognitive psychology suggests that using both words and illustrations improves student learning. This study analyzed student response data from 561 students taking an introductory earth science course to determine whether including an illustration in a clicker question resulted in a higher percentage of correct responses than questions that did not include a corresponding illustration. Questions on topics pertaining to the solid earth were categorized as "illustrated" questions if they contained a picture, or graph and "text-only" if the question only contained text. For each type of question, we calculated the percentage of correct responses for each student and compared the results to student ACT-reading, math, and science scores. A within-groups, repeated measures analysis of covariance with instructor as the covariate yielded no significant differences between the percentage of correct responses to either the text-only or the illustrated questions. Similar non-significant differences were obtained when students were grouped into quartiles according to their ACT-reading, -math, and -science scores. These results suggest that the way in which a conceptest question is written does not affect student responses and supports the claim that conceptest questions are a valid formative assessment tool.