A significant main effect of visibility showed that the angles of tilt were generally smaller without
visual feedback. Hence, the physically correct angles were underestimated more without visual feedback.
This can be explained by the fact that the glass diameter was not discriminated, so the thin
glasses were tilted to the same angle as the wide glasses even though in fact the thin glasses should
have been tilted much farther. The 7-year-olds tilted all glasses on average farther than the adult participants
and, therefore, underestimated the tilting angles less than adults. This is further discussed in
the following section.