Analog Shape Transformations in Basic Level Categorization?

It has been shown that basic level categorization performance deteriorates systematically with increasing shape transformation between two sequentially presented objects, providing evidence for an image-based model of categorization. Furthermore, categorization latencies were shown to be sequentially additive, which suggests that categorization relies on analog compensation processes, i.e. on processes which traverse intermediate points on the transformational path between category representation and perceived stimulus (Graf, doctoral dissertation, Wissenschaftlicher Verlag Berlin, 2002). Using a dierent experimental paradigm, we tried to nd converging evidence that categorization is based on analog shape transformations. Category members from common object categories were produced by morphing between two objects from the same basic level category. Subjects were rst familiarized with all category members. In the experiment, three objects were presented sequentially and subjects were required to decide whether all three belonged to the same category. The third object was a morph whose shape was either in between the rst and the second object (INTER), the same as the second object, or morphed beyond the second object (EXTRA). A signicant main eect of condition was found. Reaction times for the INTER condition were faster then for the EXTRA condition. Thus, categorization decisions were faster when the third object was located on the assumed path of transformation between the rst two objects. Since all objects were familiar, the advantage for the INTER condition seems to result from a previous activation of intermediate shapes in the categorization process, suggesting analog shape transformations in categorization. Other image-based accounts seem less appropriate, but cannot be excluded at present