Eye movement in language reading

The study of eye movement in language reading stretches back almost a thousand years. Until the late 19th century, it was characterised by a reliance on naked-eye observation of eye movement, in the absence of technology. From the late 19th to the mid-20th centuries, investigators used early tracking technologies to assist their observation, in a research climate that emphasised the measurement of human behaviour and skill for educational ends. Much basic knowledge about eye movement was obtained during this period. Since the mid-20th century, there have been three major changes: the development of noninvasive eye-movement tracking equipment; the introduction of computer technology to enhance the power of this equipment to pick up, record and process the huge volume of data that eye movement generates; and the emergence of cognitive psychology as a theoretical and methodological framework within which reading processes are examined.

Cognitive psychology, infrared tracking and computer technology
Eye trackers bounce near infra-red light off the interior of the eyeball, and monitor the reflection on the eye to determine gaze location.

With this technique, the exact position of fixation on screen is determinable.