A stimulus-centered reading disorder for words and numbers: Is it neglect dyslexia?

Abstract

A single case, RCG, showing a unilateral reading disorder without unilateral spatial neglect was studied. The disorder was characterized by substitutions of the initial (left) letters of words, nonwords and Arabic numbers, independently of egocentered spatial coordinates. MRI showed a bilateral lesion with the involvement of the splenium. Although, within the framework of the visual word recognition model proposed by Caramazza and Hillis (1990), RCG disorder could be defined as a stimulus-centered neglect dyslexia, we discuss the hypothesis of a dissociation in neural correlates and mechanisms between the syndrome of unilateral spatial neglect and such a unilateral reading disorder.

Acknowledgments

We are particularly grateful to Cristina Burani and Roberto Cubelli for the many useful suggestions they made and for their comments on earlier versions of this manuscript. A sincere vote of thanks is due to RCG for participating in the study.

Notes

*refers to pathological scores

In all cases, even in reading triplets of letters, the patient's reading errors involved the first letter on the left.

The Line cancellation (Albert, 1973) test is made of a sheet of paper where 21 black lines, oriented and located in random order, are printed. The subject's task was to mark all the lines. The scores were the numbers of omissions in the left- (range = 0–11) and right- (range = 0–10) sides of the sheet. Normal subjects perform this task without errors. In the Letter cancellation test (Diller and Weinberg, 1977) the subject is presented with six lines of letters and is required to mark all the ‘H’. The scores were the numbers of omissions on the left- (range = 0–53) and right- (range = 0–51) sides of the sheet. The maximum number of omission errors for normal subjects is four, and two is the maximum difference between errors on the two sides of the sheet (Vallar et al., 1994).

It is made of 40 stimuli, each made out of printed illusory configuration: two identical black curves, shifted one in reference to the other, are seen of different lengths. The figures are horizontally oriented, can be of four different sizes, two different directions of the illusory effect (left and right), and two directions of curving (up and down). The subject's task was to judge which of the curved lines was longer. The score was the number of responses not showing the illusory effect (‘unexpected’), arising from the left (range = 0–20), and right (range = 0–20) sides of the stimulus. Patients with right brain damage and left neglect make errors only on stimuli with a left-sided illusory effect.

The subject is required to mark the midpoint of three lines: one shifted on the right side of the sheet, one aligned with the center and the third shifted on the left side.

It is made out of pre-bisected horizontal lines. Two sets of stimuli were presented. In one set the subject's task was to identify which of the two segments composing the line was the longer/shorter (motor Landmark); in the other set the two segments were of different colors and the subject had to name the color of the longer/shorter segment (verbal Landmark). For the scoring see Capitani et al. (2000).

Istituto di Linguistica Computazionale, CNR, Pisa, Corpus di Italiano contemporaneo, Unpublished manuscript, 1989.