The cognitive mechanisms underlying question generation are not yet well understood. Recently, the Obstacle-Goal model has been proposed. This model assimilates comprehension to a problem-solving cognitive process: the obstacles in the way to the intended goal originate the questions asked. A direct prediction from this model is the relationship between the distribution of types of questions asked, and the kinds of mental representations subjects elaborate to understand the provided information. Up to now, this prediction has been partially validated, and only textual information has been used to this purpose. In the present paper an empirical two-phase study is developed to validate the above prediction in a more reliable way, using non-textual information: the operation of experimental devices. Results support the prediction of the model with enough statistical power.