<Li> Endogenous orienting is the voluntary movement that occurs in order for one to focus his visual attention on a goal - driven stimulus . Thus, the focus of attention of the perceiver can be manipulated by the demands of a task . A scanning saccade is triggered endogenously for the purpose of exploring the visual environment . </Li> <P> Visual search relies primarily on endogenous orienting because participants have the goal to detect the presence or absence of a specific target object in an array of other distracting objects . </P> <P> Visual orienting does not necessarily require overt movement, though . It has been shown that people can covertly (without eye movement) shift attention to peripheral stimuli . In the 1970s, it was found that the firing rate of cells in the parietal lobe of monkeys increased in response to stimuli in the receptive field when they attended to peripheral stimuli, even when no eye movements were allowed . These findings indicate that attention plays a critical role in understanding visual search . </P> <P> Subsequently, competing theories of attention have come to dominate visual search discourse . The environment contains a vast amount of information . We are limited in the amount of information we are able to process at any one time, so it is therefore necessary that we have mechanisms by which extraneous stimuli can be filtered and only relevant information attended to . In the study of attention, psychologists distinguish between preattentitive and attentional processes . Preattentive processes are evenly distributed across all input signals, forming a kind of "low - level" attention . Attentional processes are more selective and can only be applied to specific preattentive input . A large part of the current debate in visual search theory centres on selective attention and what the visual system is capable of achieving without focal attention . </P>

In a visual search we expect reaction times for recognition to be slowest for