Abstract: Individuals orient to information involving either overt movements of the head, eyes, or body, or covert shifts of attention whereby the head, eyes, or body remain stationary in their visual environment,. Overt orienting and covert orienting used to be accepted as independent systems. However, increased brain imaging studies have showed that they share the common brain functions. Both overt and covert attention can be endogenously or exogenously aroused. Endogenous attention was summoned by behavior goals or intentions of observer, whereas exogenous attention was deployed by salient information that appeared at the peripheral location of the observer’s visual field. Ever since Posner rendered this categories in early 1980’s, studies on endogenous and exogenous visual spatial attention shifts has been an important research field. A wealth of studies has revealed cue-validity effect, SOA effect and IOR effect in covert attention shifts. Yet little attention has been paid to overt attention shifts, despite that overt visual-spatial attention shift was more common in daily life. In order to better understand the relation between covert and overt attention shifts, performance of children’s overt attention shifts were examined. Similar effects in this two systems were expected because covert and overt shifts of attention are subserved by similar neural mechanisms.
Method
The cue-target paradigm was employed with a few modifications. Performances of 24 children of grade 3 and grade 6 were measured with EYELINK Ⅱ. All of the visual stimuli were presented on the white background. During the first experiment, subjects were cued by the presence of a black arrow to overtly attend to the incoming targets, and 350 ms later the target appeared at the peripheral location which may be in accordance with the cued location or not. During the second experiment, subjects were cued by the presence of a black asterisk that appeared at the peripheral location, and various intervals later the target appeared at the cued or uncued location. The task was to discriminate the color of the targets. A repeated-measured MANOVA was used to analyze the attentional effects.
Results
Children exhibited significant cue-validity effect under endogenous cue, with shorter response time in cue-valid trials than in cue-invalid trials, and with little difference between grades; they also showed significant cue-validity effect and SOA effect under exogenous cue. Children of grade 6 had the least response time at the shortest SOAs while the greater cue-validity effect appeared at a relatively longer SOAs in 3rd grade children. No IOR effect was found in any groups, although the response time was shorter under the cue-invalid conditions in children of grade 6, which did not reach the significance level.
Conclusions
These results suggested that overt attention shifts was similar with covert attention shifts for children exhibited stable cue-validity effects both in endogenous and exogenous cue conditions. The IOR effect found in covert attention shifts was absent in overt attention shifts, which indicated that overt attention shifts differed from covert attention shifts in some ways. The executing of eye movements may have contributed to this difference

Key words: cue-target paradigm, Overt Attention Shifts, cue-validity effect, SOA effect, IOR effect