A method of presenting content to a subject based on eye position measurements is provided. The method 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 further includes continuously performing the operations of generating a variability metric using the one or more measured eye positions and comparing the variability metric with a predetermined baseline to determine an attention state of the subject. Upon detection of a change in the attention state, the presentation of the content is modified.