Detection of symmetry and perceptual organization: the way a lock-and-key process works

We studied the speed with which observers could detect symmetry in drawings that incorporated symmetric contours--related by reflection or translation--within single objects or across different objects. We asked observers to perform a speeded decision whether pairs of contours are the same, i.e., related by reflection or by translation, or different. When the contours belong to a single object, observers are faster to see the relation between contours when they are related by reflection than by translation. When the contours belong to different objects, observers are faster to see the relation between the contours when they are related by translation than by reflection. We tested whether this advantage of translation is due to a lock-and-key process. We first tested our hypothesis by manipulating the correspondence of the features, so as to make matching more difficult. This change did not produce the predicted pattern of results. We performed a second manipulation to change the appearance of the objects: we increased the prägnanz of the objects by changing the type of lines used to connect the contours. Results indicate that perceptual organization can alter detectability of symmetry.