At present, the psychological process and neural correlates of visual spatial attention is still not clear, and the role of visual spatial attention in information processing is still to be clarified. The "zoom-lens" theory about spatial attention put forward by Eriksen et al holds that the visual attention is a system with limited resources. It can be directed to a certain spatial region, and increasing the spatialattention region can enlarge the distribution area of attention resources.
The even-related potentials (ERPs) and behavioral experiments were carried out using a "cue-target" paradigm precued by the different spatial regions in the young and old people. The goal of the present experiment is to the study neural basis of different scales of regions as well as different conditions of interference on visual spatial attention. The behavioral data and electrophysiological results on the early dynamic mechanisms of visual attention were as the following:
(1) The faster for the reaction time, the larger in the amplitude of early ERP component P1 and N1, and the smaller with the cue scale. This suggests that "zoom-lens effect" took place at the early stage of information processing. The P 1 and P2 effect separated, means the cue effect enhanced, and the additional computation was needed. The left and right sphere of P2 effect separated, which indicated the left hemisphere predominated in the attention processing under cue.
(2) Under the condition of fixed cue region, the location of targets did not significantly affect the early ERP component of the P1 and N1. That is, the early visual cortical activities represented by the P1 and N1 were not regulated by the target location.
(3) Interference enlarged the amplitude of the posterior P1，the anterior N 1 and prolonged the latency of the anterior P2; the effects of endogenous interference were also manifested by the obvious inhibition of P2 amplitude in the medline area and the right hemisphere. The affection of the interior interference on the target discrimination was bigger than of the interior interference.
(4) The scales effects of ERP under semantic cue and region cue had different forms;compared with that in region cue, target stimulation in semantic cue could lead to the increase of posterior Pl, the decrease of N1 and the increase of P2. Region cue could make target discrimination faster; what's more, with exterior interference, the speed superiority in target stimulation discrimination on region cue was much more outstanding.
(5) The change in the relative position between interference stimulation and target stimulation could have significant effect on target discrimination, and there was early ERP component effect, which indicated the scale effect of attention on interference stimulation, and exterior interference and interior interference had their different features. In case of interior interference, the nearer the interference to the target, the larger the posterior P 1 amplitude and the smaller the posterior N 1 amplitude; while in case of exterior interference, the nearer the interference to the target, the longer the reaction time, the smaller the anterior N1 amplitude and the larger the anterior P2 amplitude;
(6) Aging could lead to the decrease in the function of visual spatial attention (voluntary and involuntary); The earliest stage of visual analysis was affected by aging, which originated from the obvious increase of posterior P1 in extrastriate cortical areas; Aging resulted in the dysfunction of prefrontal areas in visual spatial attention----the obvious inhibition of anterior P2 and the instability in its wave. Under interior interference, aging had more effect on the early element of ERP which was consistent with "complexity effect" of aging.
In conclusion, different attention scale, different interference condition and the different effects of aging on anterior N1 and P2 proved the important role of prefrontal area in visual spatial attention, which further developed the "Where Pathway”Theory. The results of the interference-free experiments in the research could support the "zoom-lens”theory in spatial attention which was put forward by Eriksen et al, but the interference mechanisms of visual spatial attention were a beneficial supplement for "zoom-lens”theory.