Illusory Conjunction

An illusory conjunction is an error of visual perception in which features belonging to two different objects seen at the same time, such as their color and shape, are wrongly combined into the perception of a single object that never actually existed, for example mistakenly perceiving a small green triangle when the actual stimuli were a small green circle and a differently colored triangle. Anne Treisman, working with Schmidt, demonstrated the effect experimentally by briefly displaying, for around two hundred milliseconds, numerals and colored geometric shapes and finding that participants frequently reported the wrong color paired with the wrong shape. The effect provides central evidence for Treisman's feature integration theory, which holds that basic visual features such as color, shape and orientation are initially registered separately across the visual field and must be actively bound together through focused spatial attention; when attention is limited, whether by a very brief exposure or by having to divide attention elsewhere, features from nearby objects can be wrongly combined. Illusory conjunctions become more likely when the objects involved share similar features or are positioned close together in the visual field.