OPTOKINETIC STIMULATION INFLUENCES THE DISTURBED PERCEPTION OF BODY ORIENTATION IN SPATIAL NEGLECT

The effect of optokinetic stimulation on the disturbed perception of b ody orientation in three patients with right brain damage and spatial neglect was examined. The patients were asked to direct a laser point to the position which they felt lay exactly ''straight ahead'' of thei r bodies' orientation. Without stimulation they localised the body's s agittal midplane markedly to the right of the objective orientation. T he patients' horizontal displacement of the sagittal midplane was redu ced by a movement of the surround to the left and worsened by a moveme nt to the right. The findings are consistent with those found in patie nts with spatial neglect using vestibular and neck proprioceptive stim ulation. They show that visual input, together with vestibular and nec k proprioceptive input, is used for computing a central representation of egocentric space. In spatial neglect this coordinate transformatio n works with a systematic error and deviation of the spatial reference frame to the ipsilesional side. The positive effect of optokinetic st imulation in patients with spatial neglect is interpreted with a ''cor rection'' of the neural coordinate transformation process by producing asymmetric input at the sensory organs of the contributing channels.