Following where the eyes are looking or the extent to which the pupil widens, this can be measured by means of an eye-tracker.
The Behavioural Science Lab has 3 Tobi eye trackers and 4 Eye Link 1000 EyeTrackers. The Eye-Link can provide accurate information about eye movements and pupil size up to msec. The Tobii EyeTracker is less fast (one sample every 16.7msec.), but has the advantage that it is very easy to use. The technique of Eye Tracking is widely applicable within various research fields such as clinical psychology, social psychology but is also used for market research.