视网膜离心率影响空间注意梯度分布

Retinal Eccentricity Affects Visual Spatial Attention Gradient

采用同步判断(Simultaneous judgment,SJ)的研究范式探讨空间注意梯度是否受到视网膜离心率的影响。实验中给被试呈现两个目标刺激,调节它们的呈现距离和间隔时间,让被试进行不限时的同步判断,计算出各种距离上的主观等同点(Point of Subjective Simultaneous,PSS)变化情况。实验中对比了注视点和注意点重合与分离的两种状态。其中注视点和注意点分离的状态是指使用反向掩蔽后的线索刺激将注意点内隐地引导到外周。通过控制似动等影响因素,发现在注意点和注视点分离的状态下存在距离效应--也就是随着距离的增长主观等同点变化越大,但是在重合的状态下则没有。结果表明分离状态下存在传统意义上的注意梯度效应,而重合时,注意易化梯度受到一个抑制梯度的影响。这说明,注意梯度分布受到视网膜离心率的影响,而影响方式符合注意点为中心的易化梯度场和注视点为中心的抑制梯度场的双梯度场理论。

The distribution of spatial attention in visual field has been one of the most interesting topics in visual studies. However to date it remains controversial due to different paradigms used and many confounding factors involved. One such factor, the retinal eccentricity, can potentially spatial attention but has been largely overlook in previous reports. In the current study we aimed to investigate whether and how retinal eccentricity affects gradient distribution of visual spatial attention using Scharlau’s paradigm. In Experiment 1, the participants were presented with two target stimuli with different stimulus onset asynchrony （SOA）, and were asked to make untimed simultaneous judgment （SJ）. Two target stimuli were separated at 6.4° or 3.2° distribution of retina. In addition, two conditions were set for the fixation point and attentional point, including an overlapping condition where two points overlapped and a separate condition where the attentional point was covertly pulled away from the fixation point by a peripheral exogenous cue. To avoid occurrence of response bias, the cue was backward-masked by the following target. The points of subjective simultaneous （PSS） across each conditions and distances were compared. The results showed that only PSS in the separate condition with long distances apartment between two points was significantly different with 0 ms. In order to prevent apparent movement which might confound the results of Experiment 1, the two target stimuli were assigned different topological structures in the Experiment 2, which confirmed that there was no significant difference of the subjective brightness between two stimuli. A follow-up study Experiment 3 replicated the procedure of Experiment 1 with the following modifications： the two target stimuli were topologically different; the contrast degree was reduced; and four dots were converged to the center cross before each trial to ensure the subjects focused their attentions on the center. The result showed that a distance effect was found only under the overlapping condition but not the separate condition, indicating that the gradient distribution of visual spatial attention was affected by retinal eccentricity. To sum up, the present study demonstrates that retinal eccentricity affects the gradient distribution of visual attention. Current findings also provide further evidences to support the ＂two attentional gradients theory＂ which argues for an inhibition gradient centered at the fixation point and an excitation gradient centered at the cued location in the visual field.