位置和轨迹信息在短暂消失目标复原过程中的作用

The Role of Location and Trajectory Information in the Recovery of Moving Objects

研究发现在多目标追踪任务中，即使视野中的所有物体同时消失长达几百毫秒，被试也能成功地完成追踪任务。Horowitz等（2006）认为这种能力主要是依靠把刺激消失时的目标信息保存在一种离线存储（off-line memory）记忆当中。这样，当刺激再现时，被试就可以把当前画面与存储的内容进行比较来区分目标和非目标。本研究的目的在于探讨目标位置、运动轨迹等信息在目标复原过程中的作用。结果发现：(1) 目标再现位置与消失位置相同时，被试的成绩最好，这说明在目标复原过程中利用了基于位置匹配的策略。(2)当目标再现位置与其消失前的运动方向一致或位于其消失前的运动轨迹上时，成绩较对照条件（目标再现于运动轨迹的法线方向）要好，这说明被试能够利用目标运动的轨迹和方向等信息。（3）当追踪的目标数量增加时，目标运动轨迹和方向等信息在复原过程中的相对作用下降，且被试只能利用1~2个目标的轨迹和运动方向信息。

In Multiple Object Tracking task， participants can successfully track 4-5 targets even though all the stimuli (typically， 8 objects) disappeared for several hundred milliseconds during the tracking time. One theory by Horowitz， (other authors) states that the relevant information of targets was stored into a so-called off-line memory when the stimuli disappeared. The successful tracking of re-appeared targets is then based on the comparison between the information obtained from the present display and the information that was stored. According to my knowledge， there are few studies to investigate what information was stored. The goal of the present study was to tap into this question by examining the effect of target location and trajectory on the target tracking.Eighteen undergraduates in Beijing Normal University participated in this study. They were 18-24 years old. They all reported to have normal or correct-to-normal vision and normal color perception. Two dependent variables， Target Number and Re-appearance Position were manipulated in a within-subject design (see details in the second part of the paper).The experimental procedure was controlled by Multiple Object Tracking program (developed in the lab). Participants pressed one of the two keys to judge the presented stimuli as target or non-target. Response accuracy was recorded by computer. The principle analysis was 4×5 analysis of variances (ANOVAs).The results showed a significant main effect of Target Number. Accuracy decreased with the increase of target number. The main effect of Re-appearance Position was also significant. The targets re-appeared in the same location as where it disappeared were easier to track than the targets in the different location were. No significant interaction between Target Number and Target Location was observed.The findings of the present study indicated that at least three types of information (target location， target trajectory， and target number) were encoded into the off-line memory. The re-appearance of the stimuli serves as a strong cue to retrieve the stored information. Targets were distinguished from the distractors based on this information then they were successfully tracked after they are re-presented. Furthermore， this information only can be retrieved efficiently when there are less than 2 targets. With the increase of target number， the effects of target location and trajectory became smaller. Further research should be focused on how the target number interacts with target location and trajectory