Our ability to detect change between real-world scenes is rich in information about how we represent the visual world. Of particular recent interest has been the information also available from change detection failures, cases in which observers are seemingly "blind" to the occurrence of a change (Rensink, 2002;. Whereas correct change detection judgments imply a successful representation and comparison of the objects undergoing change, systematic failures to detect change may indicate weaknesses or holes in a representational structure.In the present study, I use behavioral and imageprocessing techniques to explore the representational constraints revealed by a change detection task. I will first discuss three forms of representational limitation likely to affect change detection behavior, loosely characterized as memory-, attention-, and similarity-based constraints. I will argue that renewed attention should be paid especially to the visual similarity relationships between the objects undergoing change. Second, I will explore the theoretical implications that these various forms of constraint have for capacity-limited models of change detection, arguing that higher level processes or parameters should be assumed only after similarity-based constraints have been found inadequate for explaining the observed data. Third, I will report a behavioral experiment demonstrating a similarity-based constraint, one involving an effect of orientation and categorical similarity on change detection. Last, I will outline an imagebased representational substrate capable of capturing these effects of visual similarity on real-world change detection performance. This f inal contribution of the study is particularly important in that a simple technique is described that can be used to quantify the visual similarity relationships between pre-and postchange patterns regardless of their featural complexity. Moreover, this technique is framed in terms of a computational model. Despite the prominent use of realistic stimuli in the change detection literature, no computationally explicit model has been demonstrated to work for real-world changes. The present work is intended to help bridge this gap between change detection theory and the stimuli commonly used to investigate this behavior.
Sources of Representational Constraint in a Change Detection TaskThe representational weaknesses revealed by change detection failure are described most often in terms of memory and attentional constraints. Memory-based detection failures will result if the objects undergoing change are not represented in an enduring form (Grimes, 1996;O'Regan, 1992), or if a coherent representation of the prechange object does not exist at the time of the postchange comparison (Rensink, 2000a). Memory might also constrain performance if the number of objects in the prechange scene exceeds a capacity limit imposed by working memory (but see Rensink, 2000b), or if the build-up I thank George McConkie and Gary Wolverton for the stimulus presentation environment used in...