  The application of psychophysiologicy in human-computer interaction is a
growing field with significant potential for future smart personalised systems.
Working in this emerging field requires comprehension of an array of
physiological signals and analysis techniques.
  Eye tracking is a widely used method for tracking user attention with gaze
location, but also provides information on the internal cognitive and
contextual state, intention, and the locus of the user's visual attention in
interactive settings through a number of eye and eyelid movement related
parameters. This paper presents a short review on the application of eye
tracking in human-computer interaction.
  This paper aims to serve as a primer for the novice, enabling rapid
familiarisation with the latest core concepts. We put special emphasis on
everyday human-computer interface applications to distinguish from the more
common clinical or sports uses of psychophysiology.
  This paper is an extract from a comprehensive review of the entire field of
ambulatory psychophysiology, including 12 similar chapters, plus application
guidelines and systematic review. Thus any citation should be made using the
following reference:
  B. Cowley, M. Filetti, K. Lukander, J. Torniainen, A. Henelius, L. Ahonen, O.
Barral, I. Kosunen, T. Valtonen, M. Huotilainen, N. Ravaja, G. Jacucci. The
Psychophysiology Primer: a guide to methods and a broad review with a focus on
human-computer interaction. Foundations and Trends in Human-Computer
Interaction, vol. 9, no. 3-4, pp. 150--307, 2016.
