Context congruency effects in change detection: Opposing effects on detection and identification

In tasks of visual change detection, researchers have shown that objects embedded in a contextually incongruent scene tend to be detected faster than objects embedded in a contextually congruent scene. This finding is curious given that a contextually congruent scene contains a host of cues that should aid in object perception, such as which types of objects are to be expected and their probable location. We replicated this context incongruency benefit (Experiment 1), but also showed that this effect reversed to a context congruency benefit when change detection was made trivial by reducing the interstimulus interval between image presentations from a more conventional 250 ms to 0 ms (Experiment 2). Across Experiments 2 and 3, we also showed that context incongruency impeded change detection performance when the task required identification of the changing object, but aided change detection performance when the task required only localization of the changing object. These results highlight the contribution of two processes to change detection performance that are affected in opposite ways by context congruency. Whereas incongruent contexts appear to facilitate the process of detecting and localizing the object that is changing, congruent contexts appear to facilitate identification of the object that is changing.