PERCEPTION 



163I 



It is already clear, however, that there are different 

 aspects of spatial organization in man that are 

 rather selectively affected by different brain lesions. 

 Such a picture then does not agree with the simple 

 and traditional view of a unitary change in spatial 

 orientation, for example the so-called 'visuo-spatial 

 agnosia' [cf. Nielsen (362)], which should follow 

 lesions in a restricted area such as the posterior parietal 

 lobe. There are at least three fairly distinct forms of 

 spatial disturbance that can be ascribed, provisionally, 

 to occipital, frontal and parietal involvement. 



DISTORTIONS IN THE TRIDIMENSIONAL STRUCTURE OF 



visual space. After acute lesions of occipital (or 

 occipitoparietal or occipitotemporal) regions, visual 

 space may be deformed in a systematic fashion so 

 that objects seen in an affected (homonymous) 

 half-field or quadrant are consistently mislocalized 

 (31, 32, 469). Most frequently, objects are seen too 

 far ('teleopsia') and conjointly as too small ('microp- 

 sia') compared with their appearance in less affected 

 regions of the field. The disturbance can be demon- 

 strated with variations of the three-needle experiment 

 (31); in the stereoscope, there are difficulties with 

 binocular fusion and distortion-, akin to those pro- 

 duced in normal subjects wearing aniseikonic lenses 

 (6). sl The disorder is found in the absence of any 

 demonstrable impairment of cerebellar function, 

 postural sensations or (peripheral) vestibular re- 

 activity. The syndrome max persist for months after 

 acute occipital lobe lesions, but is rarely found several 

 years after injury (469). However, at these later 

 stages the distortions may appear transiently during 

 paroxysmal changes in visual function ('visual tits' 1, 

 in which the EEG shows focal alterations. Curiously, 

 these paroxysmal visuospatial disorders are sig- 

 nificantly more frequent with lesions of the posterior 

 lobe substance in the right (rather than left) hemi- 

 sphere. 



In rare instances, extreme disarticulation of visual 

 space may occur during a fit (469), or a migraine 

 attack (41) in which there is optic allesthesia; objects 

 seen instead of appearing in their appropriate places 

 in the visual field seem to lie elsewhere, e.g. in the 



21 None of the studies here reviewed describe the peculiar 

 syndrome of 'loss of depth' reported by Sir Gordon Holmes 

 1218) as an occasional consequence of occipitoparietal lesion. 

 Complete 'flattening' of the visual scene is difficult to conceive, 

 perhaps the patients in question experienced diminished rather 

 than absent depth. The issue cannot be decided as long as there 

 air no experimental studies of space perception in such in- 

 stances. 



opposite half-field, sometimes with 180 inversion in 

 a diagonally opposite quadrant. Similar forms of 

 allesthesia can be encountered in the somatosensorv 

 sphere with lesions at various levels [see Critchley 

 (95) for review]. 



ABNORMALITY OF VISUOPOSTURAL INTERACTION. A 



more subtle, but equally intriguing alteration can 

 be found after lesions of the anterior lobe substance. 

 Men with penetrating gunshot wounds of the frontal 

 lobes (right, left or both) tend to show an exaggerated 

 compensatory error in setting a luminous line to the 

 vertical when their head and body are tilted (Aubert 

 task) [see Bender & Jung (27) and Teuber & Mishkin 

 (478)^. The effect is an enhancement of the 'normal 

 error' (E-phenomenon) described above; it may also 

 exist for auditorv sruinys, but data are incomplete 

 on this point. Xor do we know the minimal effective 

 lesion. In studies of acute brain injury or disease. 

 Bender & Jung (-'71 showed that the exaggerated 

 errors occurred with frontal and frontoparietal lesions. 

 Abnormal errors appeared not only when the patients 

 were tilted, but when thev were upright, the luminous 

 line was then set with a constant inclination away 

 In mi the affected lobe. These errors in the upright 

 position, hist described bv Goldstein (161), ap- 

 parentlv disappear gradually, since they are not 

 found in the late stages after anterior brain lesions 

 (47K1 where body tilts are needed to uncover the 

 abnormal interaction between visual localization and 

 posture. Figure 25 summarizes a series of experiments 

 employing Aubert's task and several variations and 

 revealing the rather surprising specificity of the 

 symptom. 25 



'SPATIAL DISORIENTATION' VI 1F.R PARIETAL LESIONS. 



The most obvious forms of difficulty with spatial 

 relations are those seen in parietal lobe involvement 



B Further analyses of changes in the Aubert phenomenon 

 alter' cerebral lesions 1771 have shown that settings of the 

 vertical 1 with body tilted) can reveal two kinds of change: the 

 specific one viz the exaggerated overcorrection after frontal 

 lesions) and a nonspecific one If one extracts the so-called 

 starting-position effects see footnote 20), one tinds that groups 

 of patients with brain injury in any lobe, and regardless of 

 presence or absence of particular sensory or motor symptoms, 

 manifest significantly larger starting-position effects than do 

 matched controls. These enhanced starting-position effects 

 are also found in children with brain damage tested on the 

 auditory analogue of the task 1 Rudel, Teuber & Liebert, 

 manuscript in preparation). By contrast, these children do not 

 show the specific effect (found in adults with frontal lesion I 

 until they reach early adolescence. 



