Figure 2. Sequence and timing of events.

Liquid-crystal goggles occluded vision for 2s (interval T1) at the start of each trial, while the movable handhold moved to and stopped at one of four possible locations. Vision was then allowed for 2s (T2) and subjects were instructed to look at the handhold during this viewing period. Vision was then occluded again, for a recall-delay interval of 0s, 2s, 5s or 10s (T3) prior to perturbation-onset, and continued to be occluded for 2s after PO (T4), i.e. until the end of trial. For trials with recall delays of 5s or 10s, subjects performed either a spatial-memory task, a non-spatial-memory task or no secondary task during the recall-delay interval (T3).