What causes specificity of practice in a manual aiming movement: Vision dominance or transformation errors?

The withdrawal of vision of the arm during a manual aiming task has been fo und to result in a large increase in aiming error, regardless of the amount of practice in normal vision before its withdrawal. In the present study, the authors investigated whether the increase in error reflects the dominat ion of visual afferent information over the movement representation develop ed during practice to the detriment of other sources of afferent informatio n or whether it reflects only transformation errors of the location of the target from an allocentric to an egocentric frame of reference. Participant s (N = 40) performed aiming movements with their dominant or nondominant ar m in a full-vision or target-only condition. The results of the present exp eriment supported both of those hypotheses, The data indicated that practic e does not eliminate the need for visual information for optimizing movemen t accuracy and that learning is specific to the source or sources of affere nt information more likely to ensure optimal accuracy during practice. In a ddition, the results indicated that movement planning in an allocentric fra me of reference might require simultaneous vision of the arm and the target . Finally, practice in a target-only condition, with knowledge of results, was found to improve recoding of the target in an egocentric frame of refer ence.