Applying neuroanatomical distinctions to connectionist cognitive modelling

We show examples of how low-level, qualitative neuroanatomical hemispheric differences can give rise to detailed psychologically realistic behaviour. We illustrate this claim with examples from the cognitive modelling of unilateral visuospatial neglect and neglect dyslexia. Our models are based on two principles: the division of information processing between the two hemispheres; and the implementation of a coarse-/fine-coding distinction between the hemispheres. Line-bisection is a standard test for visuospatial neglect, in which the patient is required to mark the centre of a straight line; in neglect caused by right-hemisphere (RH) damage, bisection points tend to be displaced to the right of centre. Models of neglect have been focussed on dysfunctions following RH damage; however, patients with comparable damage to the left hemisphere (LH) typically present with a different pattern of deficits: (a) damage to the LH less often results in visuospatial neglect, or results in smaller, more variable displacements in line-bisection; (b) when damage to the LH results in neglect, recovery is generally quicker; and (c) damage to the LH often results in neglect dyslexia without more general visuospatial neglect. These asymmetries present a challenge to current models of neglect. Our models provide a principled and parsimonious account.