The present study examined a common category effect that has been reported
in the literature: the tendency for estimates of individual stimuli to be b
iased toward the central value of the presented set of stimuli. Both encodi
ng and reconstruction accounts of this central-tendency effect are consider
ed. Plain vertical lines and vertical lines embedded in the Muller-Lyer ill
usion were estimated while still in view or from memory. Although bias due
to the Muller-Lyer illusion remained constant across the two conditions, bi
as due to the contest set (category) occurred only when stimuli were estima
ted from memory at a later stage of processing than the Muller-Lyer effect
and offer support for a reconstruction account of category effects on stimu
lus estimation.