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Abstract

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.