1. A system for use in an assessment of an attentional deficit, comprising: a user interaction subsystem connectable to a display for presenting a test image to a subject as part of the assessment; a camera for obtaining a camera image indicative of a geometric relation between the head of the subject and the display during the assessment; an analysis subsystem for analyzing the camera image to determine a deviation in the geometric relation between the head of the subject and the display from a reference geometric relation; and a data interface for outputting deviation data indicative of the deviation to enable compensating for the deviation in the assessment.