The case of the missing visual details: Occlusion and long-term visual memory.

Abstract

To investigate the critical information in long-term visual memory representations of objects, we used occlusion to emphasize one type of information or another. By occluding one solid side of the object (e.g., top 50%) or by occluding 50% of the object with stripes (like a picket fence), we emphasized visible information about the object, processing the visible details in the former and the object's overall form in the latter. On a token discrimination test, surprisingly, memory for solid or stripe occluded objects at either encoding (Experiment 1) or test (Experiment 2) was the same.In contrast, when occluded objects matched at encoding and test (Experiment 3) or when the occlusion shifted, revealing the entire object piecemeal (Experiment 4), memory was better for solid compared to stripe occluded objects, indicating that objects are represented differently in long-term visual memory. Critically, we also found that when the task emphasized remembering exactly what was shown, memory performance in the more detailed solid occlusion condition exceeded that in the stripe condition (Experiment 5). However, when the task emphasized the whole object form, memory was better in the stripe condition (Experiment 6) than in the solid condition. We argue that long-term visual memory can represent objects flexibly, and task demands can interact with visual information, allowing the viewer to cope with changing real-world visual environments.Keywords: Long-Term Visual Memory; Occlusion; Object Memory; Picture Representation 3 OCCLUSION AND LONG-TERM VISUAL MEMORY When viewing a complex scene, such as a street scene, many objects will be partially visible from a single point of view. Researchers who have explored the impact of occlusion on object perception have primarily focused on the ability of observers to perceive complete objects behind an occluding element (amodal completion; e.g., Kellman & Shipley, 1992;Murray, Sekuler, & Bennett, 2001;Palmer, Kellman, & Shipley, 2006;Rensink & Enns, 1998;Sekuler & Palmer, 1992).In other words, consistent with Gestalt principles, people appear to fill in the missing components when looking at an object. Although there may be questions regarding the ability to use amodal completion in guiding attention (Wolfe, Reijnen, Horowitz, Pedersini, Pinto, & Hulleman, 2011), it is clear that individuals can identify an object even if it extends behind another object. The ability to identify occluded objects and potentially "fill in" the missing components indicates that people can easily deal with this real-world viewing problem in real-time. We explored if these abilities had consequences for the representations of objects in long-term visual memory.The question of how occluded objects are represented may appear to be trivial given that they are so easily dealt with in everyday life, but how one represents an occluded object could be informative regarding the limitations and flexibility of long-term visual memory representations.Objects are stored in long-term visual memory with a gre...