Categorical perception of relative orientation in visual object recognition

(T)he purpose of the present investigation was to determine whether the ori entation between an object's parts is coded categorically for object recogn ition and physical discrimination. In three experiments, line drawings of n ovel objects in which the relative orientation of object parts varied by st eps of 30 degrees were used. Participants performed either an object recogn ition task, in which they had to determine whether two objects were compose d of the same set of parts, or a physical discrimination task, in which the y had to determine whether two objects were physically identical. For objec t recognition, participants found it more difficult to compare the 0 degree s and 30 degrees versions and the 90 degrees and 60 degrees versions of an object than to compare the 30 degrees and 60 degrees versions, but only at an extended interstimulus interval (ISI). Categorical coding was also found in the physical discrimination task. These results suggest that relative o rientation is coded categorically for both object recognition and physical discrimination, although metric information appears to be coded as well, es pecially at brief ISIs.