Daniel J. Simons - US grants

This project investigates the visual representations of objects and scenes people construct as they view the world. Although conscious experience suggests that we form a detailed representation of what we are looking at, recent findings that observers often fail to detect large changes to scenes from one view to the next (change blindness) have been interpreted as evidence we don't represent our visual surroundings in much detail. This project examines an alternative hypothesis: Although observers cannot consciously detect changes to the visual details of complex scenes, these details are nevertheless represented. The experiments test this hypothesis by examining the nature of visual representations when change detection fails. Two procedural innovations are used in the studies. First, stimuli will be motion pictures rather than static scenes, to allow assessment of scene representation in a context closer to the real-world experiences of observers. Second, eye movements will be monitored during change detection. Eye movements should provide a more sensitive measure of scene representation, and will allow the role of attention in formation of scene representations to be examined. These methods will be used to investigate whether failures of change detection imply the lack of a representation or simply the inaccessibility of a representation to awareness. The results should add to our understanding of how the visual environment is represented from one view to the next, and how the representations contribute to our perception and awareness of a stable visual world.

People often do not notice large changes to displays ranging from simple arrays of novel objects to complex, naturalistic motion pictures. For example, observers sometimes fail to notice when the central actor in a motion picture is replaced by a different person during a cut to a different camera view. Yet, the mechanisms underlying such change detection failures, or "change blindness," are not well understood. The primary goal of this proposal is to investigate the way in which our representations of the visual world influence our ability (or inability) to detect changes when viewers intentionally search for a change and when they do not anticipate a change. Experimental tasks will be used both in and out of the laboratory thereby including conditions in which the representation of visual scenes is tested under more ecologically valid viewing conditions. Variables will include the magnitude of the change, the initial viewing time, the delay between the original and changed display, and the complexity of the scene. Another series of experiments will use both intentional and incidental tasks to explore the detection of categorical changes to in simple arrays of objects, photographs of natural scenes, and motion pictures. A third series of experiments explores the possibility that we may form implicit or even explicit traces of changed objects even when we are unaware of the change itself. These experiments investigate whether failures of change detection imply the lack of a representation or simply the inaccessibility of a representation to awareness. Previous work on change blindness has assumed that the failure to detect a change implies the absence of a representation. This inference has led to the conclusion that people retain little information about their visual world from one view to the next. The studies in this proposal will explore the possibility that we represent more of our visual world than the existence of change blindness might imply. By using both intentional and incidental tasks with displays ranging from simple arrays of objects to complex, dynamic scenes, these experiments will allow a more complete description of the nature of our visual representations from one view to the next and of visual short-term memory in general.

DESCRIPTION (provided by applicant): The issue of attention capture is of fundamental importance to understanding what we perceive and how we react when confronted with a salient, but previously unattended object or event. Two distinct, and almost entirely separate, literatures have examined this issue. One has measured implicit attention capture the effects of an unattended stimulus on performance of a primary task. Implicit capture studies determine whether attention capture has occurred by measuring whether or not the presence of a stimulus disrupts (or facilitates) performance on an attention-demanding primary task. Such studies address only the behavioral consequences of an irrelevant stimulus and do not systematically explore whether or not observers are aware of the capturing stimulus. The other literature measures explicit attention capture - the conscious awareness of a previously unanticipated stimulus. Both approaches are crucial to a complete understanding of capture in the laboratory and in the real world. However, in isolation, each literature has neglected critical aspects of capture. The proposed experiments use attention tasks developed in prior work on attention capture as well as several new paradigms in order to identify the factors that influence the explicit noticing of unexpected objects as well as subtle effects of irrelevant or unexpected events on behavior. In so doing, they address a number of open issues in both literatures. The studies focus on three main questions: (1) what role do expectations play in capture? (2) how does the nature of the critical object or event contribute to capture? and (3) how does engagement in a primary task contribute to capture? By varying the nature of the critical, unattended event, these studies will explore how capture is influenced by the behavioral relevance of the new object. Moreover, by varying the nature of the primary task and the degree of engagement required of subjects, these studies provide a more accurate picture of how attention capture operates in demanding and dynamic situations. Ideally, these studies will help to generalize results from simplified visual search tasks to more complex, real-world perception, thereby leading to a better understanding of the detection of important, but unexpected objects. By integrating approaches from both the implicit and explicit capture literatures, these studies may contribute to an improved understanding of both normal and damaged attentional processing (e.g., as in people with attention deficit disorder).