Selective and delay adaptation of human saccades.

The consistently triggered step back of a target during primary saccades of a human subject induced a gradual change in gain, the ratio of the saccade amplitude to the target eccentricity. After a few hundred trials, subjects were able to foveate the displaced target in a single saccade. Presentation of a displaced target showed that human memory guided saccades have gain adaptation just like the well-established adaptation of visually guided saccades. Examining the transfer of adaptation between the memory guided saccade and two other types of visually guided saccades showed that each saccade transferred a 10-25% adapted gain change to the other saccades. However, any pair of the three saccades acquired different gains by adaptation in the same horizontal direction simultaneously, hence each saccade had adaptive capability independent of the others. Adaptation took place even when the appearance of a displaced target was delayed by 400-600 ms from the end of a primary saccade. These findings have important implications about the adaptation, particularly the location and temporal property of the adaptive mechanism in saccade generation.