认知与发展心理学研究室知识库

    由于物体恒常性的存在，物体的大小变化通常不会被认知为物体本身大小的变化，而会被认知为与观察者之间的距离变化。相比于远离的物体，生物体必须快速地注意到靠近的物体(如天敌、竞争者等)并及时做出反应，才能得以生存。因此，从进化的角度来看，视觉通道物体的扩张运动相比于收缩运动具有更为重要的生存意义。以往的许多研究证明，生物对扩张刺激具有更强的知觉敏感性和认知偏好，称为扩张优先性。
    以往大多数研究中使用的刺激是实心的图形，变化的过程中伴随着物理面积的变化，因此无法排除刺激的物理面积变化对实验结果的影响。本研究尝试采用主观轮廓图形，控制了物理面积保持不变，通过改变主观轮廓图形四角之间的距离，改变被试知觉到的刺激的大小。
    研究1包括3个实验，根据刺激扩张收缩时的物理面积变化程度，分别选择主观轮廓方形、边框方形、实心方形作为实验材料，要求被试完成一个动态的视觉搜索任务:即判断在扩张的刺激中是否有收缩的刺激，或者是在收缩的刺激中是否有扩张的刺激。研究发现主观轮廓和实心方形具有相似的扩张优先性:相对于在扩张的干扰子中搜索收缩的目标，被试能更准确、更快地在收缩的干扰子中搜索到扩张的目标。而边框的扩张优先性较弱，仅反映在正确率指标上。研究1发现，控制物理面积保持恒定的主观轮廓刺激可以产生类似于实心方形的扩张优先性，证明知觉到的和真实的扩张具有相似的优先性，且扩张优先性的强度与物理面积变化程度无关。
    研究2探讨研究1发现的搜索不对性是否受到主观轮廓强度、大小和聚集扩散运动的影响。实验4使用经典的Kanizsa Pacman主观轮廓图形重复实验1，发现更强的扩张优先性效应。实验_5要求被试完成静态视觉搜索任务，发现大的主观轮廓具有搜索优先性:在较小的主观轮廓中搜索较大的主观轮廓的正确率较高，反应时较短，可能主观轮廓的静态大小对扩张优先性具有重要贡献;实验6通过改变主观轮廓四个角的朝向，破坏主观轮廓知觉，发现四角的聚集和扩散运动不具有搜索不对称性，排除了扩散优先性在实验1中的影响。研究2证明在实验1中，被试确实将主观轮廓诱导物正确分组并知觉为一个整体，同时这个整体具有扩张优先效应。
    研究3探究研究1发现的边框的扩张优先性弱于主观轮廓和实心方形的原因，通过加入点状背景，改变刺激的通透性，探究其对于扩张优先性的影响。实验7减弱边框刺激的通透性，发现其扩张优先性强度增强;实验8加强主观轮廓刺激的通透性，发现其扩张优先性强度减弱;实验9加强边框刺激的通透性，发现其扩张优先性强度减弱。研究3证明，刺激通透性的强弱对扩张优先性有重要的影响作用:刺激越倾向于一个不通透的平面，其扩张优先性越强;刺激越倾向于一个通透的轮廓，其扩张优先性越弱。
    研究发现，物理面积保持恒定的主观轮廓刺激可以产生类似于实心方形的扩张优先性。扩张优先效应与刺激通透性有关，刺激越通透，扩张优先效应的强度越弱。本研究也说明了对于主观轮廓，视觉系统除了表征其轮廓信息之外，还将其内部表征为不通透的平面。

    Because of object constancy, the change of the size of an object usually means the change of the distance between the object and the observer. Comparing to receding objects, looming objects (such as predators, competitors, etc.) must be perceived and responded in priority. From the evolutionary perspective, expanding signals should be more important than contracting signals in survival for organisms. Consistent with this view, previous researches have demonstrated that organisms are more sensitive and show a cognitive bias to expanding signals, which is defined as expanding priority.
    However, most stimuli used in previous studies were solid objects. When solid objects expand, their areas also expand, thus we can't exclude the influence of physical area change. As a result, in this thesis we used subjective contours as experimental stimuli whose physical areas keep constant even when they expand. We manipulated the distance between the four inducers of the subjective contour to change the perceived size of the stimulus.
    Study 1 contained 3 experiments, which used subjective squares, normal squares and solid squares as experimental stimuli respectively. Subjects were asked to complete a dynamic visual searching task, in which they should judge whether there was a expanding stimulus in several contracting stimuli, or whether there was a contracting stimulus in several expanding stimuli. Similar search asymmetry were found for subjective squares and solid squares. That is, subjects can find out an expanding target in contracting distractors more accurately and quickly, compared to searching for a contracting target in expanding distractors. However, the expanding priority of square contour was weaker, which only appears in accuracy, not in reaction time. This study found that subjective contours whose physical areas keep constant can generate similar expanding priority as solid objects. The results suggested that perceived and real expanding had the same priority and the degree of physical area change had nothing to do with the intensity of expanding priority.
    Study 2 explored whether the search asymmetry found in research 1 can be influenced by the type of inducers, the size of subjective contours or motion of inducers per se. In experiment 4, classic Kanizsa Pacman subjective contours were used as experimental stimuli. The results demonstrated stronger expanding priority than experiment 1，indicating that stronger inducers can lead to stronger expanding priority. In experiment 5, subjects were required to complete a static search task. Results showed that subjects were able to find out a bigger target in smaller distractors more accurately and quickly, compared to searching for a smaller target in bigger distractors. In experiment 6, we found that the search asymmetry disappeared when the subject contours were impaired by changing the orientations of four inducers, indicating that the motion of the inducers per se cannot lead to expanding priority, which ruled out the possibility of aggregating priority. It can be proved that the inducers were grouped correctly and perceived as a whole which can produce expanding priority.
    In Study 1 we found the expanding priority of square contours was weaker than that of subjective squares and solid squares. We argue that the solidness of the expanding stimuli might play an important role. In Study 3, we try to manipulate the solidness of the experimental stimuli by using a background of dot texture. In experiment 7, we reduced the solidness of border stimuli, finding the expanding priority enhanced. In experiment 8 and 9, we found weaker expanding priority effects when solidness were decreased. Research 3 proved that thesolidness of stimuli could influence expanding priority. If the stimulus is more like a solid surface, the expanding priority is stronger. If the stimulus is more like a penetrable contour, the expanding priority is weaker.
    In this thesis, we found that subjective contours whose physical areas keep constant could generate similar expanding priority effect as solid objects did. The solidness of the expanding stimuli plays an important role. More solid the expanding stimuli are, stronger expanding priority effect could be observed. Furthermore, it seemed that subjective contours were not only represented as merely contours but also represented as solid-like surfaces.