Abstract: LAI is the effect that the objects could not be easily differentiated when they are close in the tasks of visual search. This is because of visual competition that objects would compete for the same receptive fields to be represented. Most previous studies on LAI used the behavioral measurements (e.g., response time) and failed to indicate whether it happens during the process of visual search or later process such as decision making. As suggested by Steelman-Allen, McCarley & Mount (2009), processing of visual information involved a rapid feedforward from the lower level to higher level in the neural architecture (completed within 150 ms, allowing for a coarse object recognition), which was followed by the reentrant processing that information was re-processed from the higher to lower levels to deal with the detail. As a more natural and on-line measurement, eye-tracking techniques could reflect the dynamic processes of LAI and thus enable researchers to get a better understanding of the mechanism underlying this effect. In two eye tracking experiments, this study examined the LAI effects with a 2-target search task, in which 2 non-circle targets were displayed with 10 circles (irrelevant stimuli). The distance between the two targets varied at 30°/90°/150° and subjects were required to determine whether 2 targets were the same or not. In Experiment 1, stimuli were presented for 70ms and the results showed a strong LAI effect. Specifically, compared to the 90° and 150°coniditon, subjects made longer response time, longer total fixation duration, more fixations, lower accuracy rate, and higher saccade average velocity when the two targets were at 30° distance. Stimuli presentation duration was increased to 1500 ms in Experiment 2 to examine whether LAI occurs during visual search or later processes. If LAI effect occurred in the visual search processes, longer presentation duration should help to reduce this effect; on the other hand, if LAI occurred in later process, Experiment 2 should generate stronger LAI effects than Experiment 1. In addition to the similar LAI effects to Experiment 1, Experiment 2 showed that saccade average velocity and saccade amplitude decreased, and total saccade duration increased with a closer distance between the targets. More important, Experiment 2 generated stronger LAI effects than Experiment 1 as indicated by a 2×3 ANOVA between the two experiments in response time. A similar analysis on saccade duration also indicated that subjects in Experiment 2 spent more time on searching. The eye movement results disclosed subjects’ strategies that how they distributed attention among multiple objects under visual competition of various levels. The major conclusions are as follows: (1) when targets were close, subjects needed more fixations and longer fixation duration to accomplish the tasks, (2) when the targets were displayed for a longer time, subjects were encouraged to conduct more searching to cope with the interference, and (3) The LAI-related competition occurred in the process of decision making, instead of the process of searching and recognizing targets. Moreover, the current study indicated the advantage of using the eye tracking paradigm in exploring LAI effect as the traditional paradigm (e.g., response time) failed to reflect the dynamic processes.

Key words: localized attentional interference, attention resource, fixation, saccade

摘要： 采用眼动追踪范式，本研究通过两个实验探讨局部注意干扰效应（LAI）的注意分配特点和机制。实验一采用搜索时间有限的范式，目标呈现70毫秒后消失，在行为和眼动指标上均发现LAI效应：当两个目标距离较近时，反应时增加，正确率降低，总注视时长增长、注视点增加和眼跳速度加快。实验二增加目标呈现时间至1500毫秒以鼓励搜索，产生了比实验一更强烈的LAI效应，且眼跳速度的模式也有不同，说明增加搜索时间并不利于减轻LAI，从而推断LAI的竞争发生在判断阶段，而非搜索和识别目标阶段。

关键词: 局部注意干扰, 注意资源, 注视, 眼跳