A method of presenting content to a subject based on eye position measurements includes presenting the subject with content. While presenting the content to the subject, one or more of the subject's eye positions is measured. The method includes continuously performing the operations of: generating an attention metric using the one or more measured eye positions; based on the attention metric, determining an attention state of the subject; and determining a trajectory of the one or more eye positions. In accordance with detecting a change in the attention state of the subject, the presentation of the content is modified based on the trajectory of the one or more eye positions so as to present different content than if the attention state of the subject had remained the not attending state.