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History and Theoretical Background

Studies of eye movement have a long history. In the nineteenth century, Emile Javal (reported by Huey 1908) discovered that eyes do not move continuously along text, as previously assumed, but instead make short, rapid movements, intermingled with short stops. These discoveries were confirmed with eye-tracking technology in subsequent eye-tracking studies (for a review, see Rayner 1978, 1998). The short rapid movements and short stops are now known as saccades (i.e., continuous, rapid movement of eye gazes between fixations with a velocity of 500 degrees or more) and fixations (i.e., a relatively motionless gaze that lasts 200-300 ms, in which visual attention is aimed at a specific area of a visual display; Rayner 1998), and they remain the most widely used terms to describe eye movements.

Early technologies for tracking the location of eye fixations were quite invasive, involving direct mechanical contact with the cornea. The first nonintrusive eye tracker, using beams of light reflected on the eye and then recorded on film, was used by Guy Thomas Buswell (1920) to study reading and picture viewing; Hartridge and Thompson (1948) then invented the first head-mounted eye tracker. A wide range of eye-trackers now exist, though they mainly represent three categories: invasive, such as a special contact lens with embedded sensors (used in medicine diagnosis and studies of the physiology of eye movements); EOG electrodes placed near the eyes to register variations in the electric field (sensitive to even miniature saccades and capable of working without a light and with eyes closed, as widely used in studies on sleep); and optical eye-trackers, which reflect light, typically infrared, in the eye and measure it with a video camera or some specially designed optical sensor. The latter category are neither invasive nor expensive and thus are used most frequently. Moreover, they can support quantitative, not just qualitative, studies. Therefore, we focus specifically on optical eye-tracking studies.

These studies, including those in marketing, have flourished not only due to technological developments but also because of the great advances in psychological theories that link eye-tracking data with cognitive processes (e.g., Jacob and Karn 2003). In their strong eye-mind hypothesis, Just and Carpenter (1976a, 1976b) claim that no appreciable lag occurs between what a person fixates on and what he or she processes, so when a person looks at a word or object, he or she also cognitively processes that word or object for exactly as long as the recorded fixation. Thus gaze direction can be linked to the focus of attention, which provides a mechanism to filter information received by an organism (Deutsch and Deutsch 1963; Posner and Peterson 1990; Treisman 1964). This hypothesis has been questioned, though modern research has proven systematically that shifts of attention without eye movement is possible (Posner 1980), and as soon as attention moves to a new position, the eyes follow if they can (Hoffmann 1998). The questions that remain then are, What conditions or features evoke attentional shifts to specific locations, and what is the nature of the emotional and motivational processes behind visual attention?

 


Date: 2016-01-14; view: 724


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