关键词: 局部注意干扰, 注意资源, 注视, 眼跳

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