Abstract
An input consisting of one or four sine waves was tracked by 12 Naval ratings. Their view behind and ahead was varied systematically in different trials. A post-view was found to help only when the more complex input was tracked without preview, the condition in which prediction was most difficult. Preview had its greatest effect when it allowed the subject to see the next reversal before ho had reached the previous one, so that he could aim directly at each reversal in turn. It reduced all sources of error, more so with the loss predictable complex input than with the simple input. The complex input produced higher scores on most of the measures of error.