IN SEARCH OF BIASED EGOCENTRIC REFERENCE FRAMES IN NEGLECT

The present study was aimed at assessing, by means of visual as well a s proprioceptive-kinaesthetic straight-ahead tasks, the possible causa l role of the ipsilesional deviation of the egocentric reference frame in determining neglect syndrome. The hypothesis. originally proposed by Ventre et al. [3], that an alteration of the representation of body -centred space can be a cause of asymmetrical spatial behaviour in hum ans has been recently revived by Karnath and co-workers [24]. The resu lts of the present study seem to challenge the view that a systematic ipsilesional displacement of the egocentric reference is the crucial m echanism responsible for unilateral visual neglect. Under visual condi tions, in which patients were required to stop a moving spot as it cro ssed their perceived midline, the ipsilesional deviation of the egocen tric reference frame was dependent upon the direction of visual scanni ng. Right to left visual scanning direction produced a rightward displ acement of the egocentric reference. In contrast, left to right visual scanning direction allowed neglect patients to correctly locate their perceived egocentre with an accuracy which did not differ from contro ls. The notion that the effect of a deviation of the egocentric refere nce frame is actually dependent on a bias in the visual scanning orien ting response was also confirmed in the proprioceptive straight-ahead pointing tasks, in which the patients were blindfolded and therefore n o visual information was available. In these conditions, in which pati ents were required to judge the subjective midline by using head, trun k and shoulder co-ordinate systems, the displacement of the subjective egocentric midline was not present. (C) 1998 Elsevier Science Ltd. Al l rights reserved.