Visual attention and objects: New tests of two-object cost

Baylis and Driver (1993) proposed that the positions of object parts are coded relative to the position of the object they belong to and that parts of different objects are not directly coded relative to each other. This theory predicts that it is easier to judge a difference in height of parts belonging to a single object (one-object condition) than of parts belonging to two objects (two-object condition). This two-object cost has been reported in several articles (Baylis, 1994; Baylis & Driver, 1993, 1995). However, in all these experiments, the method that was used favored the one-object condition. In the present experiments we obtained, for the first time, evidence for the existence of two-object cost without such a bias.