Instrumentation to track observers’ gaze has been in use for over a century [e.g., Delabarrer, 1898], resulting in a rich literature on the descriptive statistics of dynamics and behaviors of the oculomotor system. Early methods relied on mechanical connections to the eye and/or sometimes painful methods of restraining natural movements of the head. Later systems incorporated still or motion film and analog systems. The experiments were necessarily limited to the reduced laboratory environments, with stationary observers’ eye movements monitored over trial durations typically limited from milliseconds to a few seconds. Low-level metrics such as the distributions of fixation duration, saccade size and direction, etc. were likely influenced by the rigid constraints imposed by early (and some current) instrumentation necessary to track gaze.

Investigators have developed custom instrumentation to extend oculomotor experiments into the real world, pioneered by Land and colleagues [1994, 1999, 2000]. Video cameras and electronics have been reduced in bulk and power consumption to the extent that real-time, wearable head and eyetrackers are practical, so it is now possible to monitor the eye and head movement behavior of observers in a wide range of tasks [Land & Hayhoe, 2001, Pelz & colleagues, 2000, 2001a,b, 2004a,b].

Some of the basic findings from laboratory-based experiments extend into natural behavior, but experiments have also revealed sophisticated strategies that were not seen simplified tasks under reduced laboratory conditions.