Spatial attention has been related to overt movements of eyes, body, head and etc. but the relationship between movement and attention has been entirely unclear. A number of theories governing the degree of dependence of the attentional systems to eye movements have been postulated along the years. The common system says that attention movements are fixed to the movement of the eyes.
However, the behavioral evidence suggests that attention can be shifted with the eyes fixed, this findings and together with results showing enhancement of evoked potentials (Eason, Harter & White, 1969; Von Vorrhis & Hillyard, 1977) and the firing rates of single cells (Bushnell, et. al. , 1978), have eliminated the idea that attention and eye movements are identical systems. The efference theory (Wurtz & Mohler, 1976) proposed that attention shifts were programs for the movement of the eyes.
Klein (1979) said “when attention to a particular location is desired , the observer prepares to make an eye movement to that location; the oculomotor readiness, via as yet unknown feedforward pathways , has the effect of enhancing processing in or from sensory pathways dealing with information from the target location”. In his experiments, Klein (1979) found that there are clearly conditions under which one gets no relationship between spatial attention shifts and eye movement latencies. Functional relation theory (Remington, 1978) found that under simpler testing conditions like those conducted by Klein (1979), a relationship between eye movement and spatial attention is present.
He found that there is a strong tendency for attention to shift to the target position for an eye movement prior to the eye leaving the fixation point. He also found that just before and after the stimulus presentation that detection was high at both the peripheral targets. In general, the results suggest that the relationship between eye movements and attention is not as close as either a complete dependence or efference view.
Klein’s findings that eye movements does not influence latencies of shifts of attention and Posner’s results showing that attention movements is in the opposite direction to eye movement programs, debunk the popular notion that attention can be measured through overt bodily movements. Nevertheless, the two orienting systems are not completely independent; it has been observed that attention can focus on the target prior to an eye movement even when detection signals are more probable for fixation.
Posner (1980) concluded that eye movements have a functional relationship with the spatial attentional system. It seems that eye movements are programmed by an initial movement of attention to the new eye position well before the eyes actually begin to move. This presupposes the idea that even without moving, we are already using our attention system to process the target object. Further, Remington (1978) compared peripheral and central cues for eye movements in order to determine their relationship to shifts of attention.
When he used a peripheral cue he found improved sensitivity in the vicinity of peripheral target after the cue and well before eye movement. When a central arrow was used to cue movement, there was no evidence of any change in sensitivity in the direction of the target until after the eye movement began. Thus, eye movement is not a reliable measure of attention shifts and in the same way overt attention cannot reliably demonstrate the mechanisms of attention, hence we turn our attention to covert attention.
Posner (1980) emphasized that the study of spatial attention should focus on covert attention for it gives a better picture of how attentional systems work than overt attention which can be subjected to external influences. Overt attention is manifested through external movements and more often than not the person is aware of that behavior, hence results on overt attention may be due to various factors not related to attention.
In studying covert spatial attention, Posner (1980) said that it is important to keep in mind the functions of orienting, detecting and the distinction between external and central control. Orienting is the ability of the individual to shift attention around the visual field; detecting is when the individual becomes conscious of the stimuli, external and central control identifies the process by which the individual is attending to the stimuli and overt and covert attention is the ways in which the individual process the stimuli.
Thus, even before attention is directed to a target, the individual can orient his/her sensory receptors to focus on the stimuli, and when the attention has been oriented, the individual can now detect the stimulus and depending on the context with which the stimulus is presented may attend to the stimuli exogenously or endogenously. Based on Posner’s influential work, it can be deduced that the study of covert attention is more important and scientifically worthwhile than overt attention, hence the number of models used to explain and study covert attention.