Sensitivity to Differences in the Extent of Neck-Retraction and -Rotation Movements Made with and without Vision

19 subjects (10 men, 9 women) ages 19 to 30 years (M = 23.2, SD = 3.3) volunteered to participate in a study to investigate the just-noticeable-difference in movement extent for neck retraction and neck rotation. Testing was carried out with stopped movements, conducted according to the method of constant stimuli, and repeated both with and without vision in a comfortable seated position. Sensitivity was greatest for neck-retraction movements, which had lower just-noticeable-difference than either left or right rotation movements. Having full vision available gave no significant advantage in any direction when discriminating between different extents of midrange head movements.