Eye Movements, Pupillometry, and Cognitive Processes

Moving our eyes is one of the most frequent behavioural activities that we engage in during our waking hours. Indeed, we typically move our eyes three to four times per second throughout much of our day. We even move our eyes while we sleep (although a discussion of this topic is beyond the scope of this chapter), and on occasion we keep moving our eyes during cognitive processing tasks even if the mind wanders somewhere else. Because of the tight connection between the behaviour of the eyes and activity in the brain, where we look and how long we look are good online measures of the various cognitive activities in which we engage when we perform a task. In this chapter, we review the basic properties of eye movements and how they relate to ongoing cognitive processing. In particular, we focus on eye movements during reading, scene perception, visual search and we briefly discuss pupillometry. In reading, scene perception, and visual search, we continually make eye movements called saccades. Between the saccades, when static images are being processed, our eyes are relatively still in what are called fixations. It is during these fixations that we encode new information from the visual stimulus that we are processing. During saccades, cognitive processing continues in some tasks (e.g., lexical processing), whereas in others (such as mental rotation) research suggests there is a suspension of processing (Irwin, 1998)