When two is one: a case study of spatial parsing in visual neglect.

In 'left' neglect--a frequent consequence of damage to posterior areas of the right cerebral hemisphere--the relational term 'left' immediately raises the question 'left of what?'. It is shown that on a simple copying task the answer can be 'left of the principal axis of the object or objects depicted'. Under conditions in which the stimulus material was intrinsically controlled for lateral extent and position, 'object-centred' neglect seemed to reflect some basic principles of perceptual parsing.