PARALLEL SEARCH FOR A CONJUNCTION OF CONTRAST POLARITY AND SHAPE

When a target object embedded in an array of other objects can be dist inguished along a single feature dimension (e.g. color or shape), it c an be detected in parallel. When a target object is defined by a conju nction of stimulus features, at least some serial search is required, indicating that the visual system is less efficient in conducting a pa rallel search over two stimulus dimensions simultaneously. Some except ions to this finding have been reported. The present results suggest a nother exception: search for a conjunction of contrast polarity and sh ape can be conducted in parallel while the same conjunction consisting of color and shape requires some serial search. The neurophysiologica l implications are discussed.