[8] Another influential idea came from Posner and Petersen in 1990, who theorized that the orienting of attention could be organized into three distinct stages.
[10][page needed] Within the human eye only a small part, the fovea, is able to bring objects into sharp focus.
However, it is this high visual acuity that is needed to perform actions such as reading words or recognizing facial features, for example.
[11][12][13][14] However, it is important to keep in mind that attention is also able to shift covertly to objects, locations, or even thoughts while the eyes remain fixated.
Additionally, previous research has shown support for covert attention shifts being associated with activity in the parietal lobe.
[17] Although, after reviewing Posner's research, it may seem logical to conclude that covert and overt attention shifts utilize different neural mechanisms, other more recent studies have shown more overlap than not.
Utilizing functional magnetic resonance imaging (fMRI) technology, Corbetta et al., found that overt and covert attention shift tasks showed activation within the same areas, namely, the frontal, parietal and temporal lobes.
[17] Nobre et al. also sought to determine whether covert and overt attention shifts revealed activation in the same brain areas.
Results showed overlap in activated areas for overt and covert attention shifts, mainly in the parietal and frontal lobes.
[19] Beauchamp et al. more recently attempted to reproduce these same results by performing a study utilizing the same task for both conditions, as well as across multiple shift rates.
This larger activation evident with overt attention shifts was attributed to the added involvement of eye movements.
[2] Corbetta and Shulman, who are proponents of the belief that separate neural systems exist for endogenous and exogenous control, conducted a meta-analysis of multiple studies showing brain activation due to either of the two attentional processes.
The endogenous mechanisms are thought to integrate previous knowledge, expectations and goals to voluntarily decide where to shift attention.
Rosen et al.'s study found a fair amount of overlap between endogenous and exogenous shifts of attention.
The anterior attentional system is involved in detecting salient stimuli and preparing motor responses.