Latent response time analysis of students on an electronic version of the Force and Motion Conceptual Evaluation (FMCE) provides information on student reading patterns and the role of mental models in student reasoning.  Regression analysis looked at the dependence of response times on characteristics of questions, such as amount of text and inclusion of graphs. Results indicate that students generally read through the question text and instructions when first presented, but do not systematically read through answer choices and graphs. Comparison of average response times between pre- and post-instructional assessment found a drop in response times when students used Newtonian ideas but no change for responses using the main alternative concept.  The average response time for students who answered using a mix of Newtonian and alternative concepts was not different from those using primarily one or the other; questions rarely activated both concepts at the same time.