What's Your Source: Evaluating the Effects of Context in Episodic Memory for Objects in Natural Scenes

What’s Your Source: Evaluating the Effects of Context in Episodic Memory for Objects in Natural Scenes Pernille Hemmer (pernille.hemmer@rutgers.edu) 1 Kimele Persaud (kimele.persaud@rutgers.edu) 1 Rachel Venaglia (venaglir@lafayette.edu) 2 Joseph DeAngelis (joseph.deangelis@rutgers.edu) 1 Department of Psychology, Rutgers University 1 Department of Psychology, Lafayette College 2 Abstract It is well known that the context of a scene can have a strong effect on the identification of objects in the scene (e.g., Biederman, 1972). However, it is unclear what role global versus local context plays on episodic memory for objects. We present results from a series of experiments that evaluate the degree to which the global and local context contributes to memory performance: partial scene context, where global context was partially removed, no-spatial scene context, where the local spatial relationships among objects was distorted, and random context, where the associative relationship among objects was altered. Study time was also manipulated. We compare the findings to memory performance for objects in natural scenes (Hemmer & Steyvers, 2009; Steyvers & Hemmer, 2012). Results show that background context of a scene is important for initial scene interpretation. In addition, associative and spatial context is important for the retention of a larger number of objects in memory. Keywords: Context; Episodic Memory; Prior Knowledge; Natural scenes; Objects in scenes. Introduction The context of a natural scene can be defined as the structure and permanence (i.e. stable over time) of relationships among the background and objects in an environment consistent with the real world. The context of a natural scene has important implications for a variety of cognitive tasks including: how we visually search a scene, how we categorize objects in a scene, scene perception, memory for objects in a scene, attention, etc. However, the functional components of context that influence these areas of cognition are not yet fully understood. The context of natural scenes is thought to be both globally and locally structured (Galleguillos & Belongie, 2010; Torralba, 2003). The global context (also known as scene centered context) refers to the overall configuration of a scene. Global context is responsible for the unification of objects and the background (see Figure 1a for an example of a scene with global context preserved and partially removed) and supports quick high-level semantic interpretation of a scene (Potter, Staub, Rado, & O’Connor, 2002; Torralba, 2003). It also affords individuals the ability to make predictions about objects that prototypically accompany the scene type (Galleguillos & Belongie, 2010). Similarly, local context (a.k.a. object centered context) refers to the relations among objects in the entire scene, or in a particular region of a scene. Local context is derived from the associative and spatial arrangements of the scene objects. These associative and spatial relationships enhance scene perception and aid object recognition (Biederman, 1972; Biederman et al., 1982; Galleguillos & Belongie, 2010; Palmer, 1975; Torralba, 2003). Take for example the ambiguous object in Figure 1b (left panel). The intrinsic properties of this object make confident object recognition quite difficult. However, when that same ambiguous object is placed next to another object (i.e., the trashcan in the next panel), object recognition occurs more readily. The spatial relationship among objects in a scene also contributes to object recognition. Figure 1c (left panel) demonstrates an ambiguous object placed above a table, which leads one to conclude that the object is a table cloth. However, in Figure 1c (middle panel), that same object is placed below the table and now one may conclude that it is an area rug. In Figure 1c (right panel), the same object is placed above a bed and now appears to be a blanket. Taken together, the context of a scene is comprised of the global level, which unifies the objects and the background of the scene, and the local level which determines the associative and spatial relationships of objects. Although a great deal of research suggests that global and local features of scene context facilitates object identification, object categorization, and scene perception, it remains unclear how these components of context influence long-term episodic memory for objects in scenes. In this study, we employ novel stimuli, in which we systematically remove both global and local contextual features from simulated natural scenes, to measure their influences on memory. The contribution of this study is that it bridges the influence of scene context effects on object perception, object categorization, and computer vision to long term episodic memory. Previous research of scene context effects has either employed short term or working memory in an effort to understand scene perception (Biederman, 1972; Hollingworth & Henderson, 1998) or failed to demarcate the influence of global and local components of context (Hemmer & Steyvers, 2009; Steyvers & Hemmer, 2012). We extend the work of Hemmer and Steyvers (2009) which measured long-term episodic memory for objects in full context natural scenes (figure 1a, left panel) in an effort to investigate the influence of the functional units of natural scene context on episodic memory. We outline the methodology in their study as it serves as a basis of