Another influential experiment was performed by Helmholtz (2005 [1924]: §29), who practiced reaching to targets while wearing prisms that displaced the retinal image 16–18° to the left. The initial tendency was to reach too far in the direction of lateral displacement. After a number of trials, however, reaching gradually regained its former level of accuracy. Helmholtz made two additional discoveries. First, there was an intermanual transfer effect: visuomotor adaptation to prisms extended to his non-exposed hand. Second, immediately after removing the prisms from his eyes, errors were made in the opposite direction, i.e., when reaching for a target, Helmholtz now moved his hand too far to the right. This negative after-effect is now standardly used as a measure of adaptation to lateral displacement.