tech report available

[Michael C. Mozer]

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        On the Interaction of Selective Attention and Lexical Knowledge:
  		   A Connectionist Account of Neglect Dyslexia

		         Mike Mozer & Marlene Behrmann
			    Tech Report CU-CS-441-89


          Neglect dyslexia, a reading impairment acquired as a  consequence
     of  brain  injury,  is  traditionally  interpreted as a disturbance of
     selective attention.  Patients with neglect dyslexia  may  ignore  the
     left  side  of an open book, the beginning words of a line of text, or
     the beginning letters of a single word.  These patients provide a rich
     but  sometimes  contradictory  source  of  data regarding the locus of
     attentional selectivity.  We have reconsidered the patient data within
     the  framework  of an existing connectionist model of word recognition
     and spatial attention.  We show that the  effects  of  damage  to  the
     model  resemble  the reading impairments observed in neglect dyslexia.
     In  simulation  experiments,  we  account  for  a  broad  spectrum  of
     behaviours including the following: (1) when two noncontiguous stimuli
     are presented simultaneously, the contralesional stimulus is neglected
     (extinction);  (2) explicit instructions to the patient can reduce the
     severity of neglect; (3) stimulus position in the visual field affects
     reading performance; (4) words are read much better than pronounceable
     nonwords; (5) the nature of error responses depends on  the  morphemic
     composition of the stimulus; and (6) extinction interacts with lexical
     knowledge (if two words are presented that form a compound, e.g.,  COW
     and  BOY,  the patient is more likely to report both than in a control
     condition, e.g., SUN and FLY).  The convergence of findings  from  the
     neuropsychological  research  and  the  computational  modelling sheds
     light on the role of  attention  in  normal  visuospatial  processing,
     supporting  a hybrid view of attentional selection that has properties
     of both early and late selection.


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