Eye Movements, Eye Blinks, and Behavior
The process of measuring eye movements in different environmental contexts is called electroculography (EOG). The EOG technique is concerned with measuring changes in electrical potential that occur when the eyes move. Eye movements enable the visual system to acquire information by scanning relevant aspects of the environment. Object recognition, discrimination, and other information intake by the visual system is accomplished mostly through unconscious scanning eye movements. The major part of processing the new information takes place when the eyes make brief pauses. The EOG has been useful in a wide range of applications from the rapid eye movements measured in sleep studies to the recording of visual fixations during perception, visual search, the experience of illusions and in psychopathology. Studies of reading, eye movements during real and simulated car driving, radar scanning, and reading instrument dials under vibrating conditions have been some of the practical tasks examined with eye movement recordings.
Eye blinks are easily recorded with EOG procedures and are particularly useful in studies of eyelid conditioning as a control for possible eyeblink contamination in EEG research, and as measures of fatigue, lapses in attention, and stress. There are also the periodic eye blinks that occur throughout the waking day that serve to moisten the eyeball. Still another type of eyeblink is that which occurs to a sudden loud stimulus, considered to be a component of the startle reflex. The startle eyeblink is largely muscular and is related to activity in the muscles that close the lids of the eye. Research on the eyeblink component of startle has revealed interesting findings that have implications for both attentional and emotional processes. The sections to follow include information about the anatomy and physiology of the system that controls movements of the eye, how these movements are measured and how psychologists have related them to behavioral phenomena.
Eye movements are controlled by cortical and subcortical systems in conjunction with cranial nerves and sets of eye muscles attached to the outside of each eyeball. The cerebral areas involved in eye fixations are the occipital and frontal cortices. Innervation of the eye muscles is by the third (oculomotor), fourth (trochlear), and sixth (abducens) cranial nerves. They influence movements of three separate pairs of eye muscles: the superior and inferior rectus, the lateral and medial rectus, and the superior and inferior obliques (see Fig. 11.1). The superior and inferior recti contract to move the eyes up or down. The lateral and medial recti allow