Change Detection
Ronald A. Rensink, Departments of Psychology and Computer Science, University of British Columbia, Vancouver BC, Canada.

In E. Bruce Goldstein (ed). Encyclopedia of Perception. (pp. xx). Thousand Oaks CA: Sage Publications. 2009   [pdf]


Change detection is the noticing of change in the world around us. For example, when driving in traffic, the vehicles around us constantly change their position, and sometimes their speed and direction as well. In order to avoid collisions, we must notice any such changes and respond to them. More generally, the ability to detect change is important for coping with everyday life; humans (and most animals) are consequently very good at it. However, our knowledge of how changes are detected remains incomplete. The progress that has recently been made owes its existence to two related developments: (i) a realization of some of the confusions and assumptions built into our previous ideas about change, and (ii) new methodologies that allow it to be more effectively isolated and studied.

An important step is to clarify the meaning of the terms themselves. As used here, "change detection" is restricted to the noticing of a change (i.e., the observer seeing that a change exists) via the use of vision. This can include the related abilities of identifying the change (i.e., seeing what it is), as well as localizing it (i.e., seeing where it is), although these abilities likely involve somewhat different mechanisms.

An adequate understanding of change detection has been difficult to achieve. Part of this is due to the nature of change itself. Although the concept of change appears simple, attempts to formalize it have shown otherwise. For example, change requires that some aspect of an object remain constant while another aspect does not, a situation that has not been completely resolved by present-day philosophers. Furthermore, our intuitions about change detection are often highly inaccurate. For example, we generally believe that we could easily detect any change in front of us provided that its size is sufficiently large. But we can be amazingly "blind" to such changes, failing to detect them even when they are large, repeatedly made, and are expected. Such change blindness is a phenomenon strikingly at odds with our intuitions about how change detection should work. However, such counterintuitive results have taught us much about what change detection is and how it works.

BBack to The Need for Attention to See Change.