Gaze direction and two-choice reaction time : multiple tests of a theory : a dissertation presented in partial fulfilmen of the requirements for the degree of Doctor of Philosophy in Psychology at Massey University

Abstract

That vision is the preeminent human sensory system is shown by the fact that fully 75% of the entire brain (Woltzin, 1976, cited in Morse, 1990) and 40% of the human cerebral cortex (Findlay, 1985) is either dedicated to or involved in visual processing. This preeminence is reflected in the extent of our knowledge of the sensory systems; the basic visual system is better understood than any of the other major senses. Eye movements are fundamental to understanding the visual system. The constant "trembling" of the eyes, (microsaccades), which is essential to allow the nervous system continually to "read" the retinal image, shows that eye movements are a very important feature of the visual system. This importance can be seen by the fact that their study can be traced back for over 1000 years to the Arabs (Grusser, 1986; Heller, 1988), and today comprises a very large body of empirical research and sophisticated mathematical models. Eye movements, which can be automatic or voluntary, may range in size from microsaccades to large movements that can reach the limits of mobility. One example of automatic movements is when compensating for body motion, another being the startle reflex when the eye flicks toward a sudden, novel stimulus. Voluntary movements are deliberately guided movements during, for instance, inspection, panoramic search or visual pursuit.