Dissociation in Optokinetic Stimulation Sensitivity between Omission and Substitution Reading Errors in Neglect Dyslexia

Abstract

Although omission and substitution errors in neglect dyslexia (ND) patients have always been considered as different manifestations of the same acquired reading disorder, recently, we proposed a new dual mechanism model. While omissions are related to the exploratory disorder which characterizes unilateral spatial neglect (USN), substitutions are due to a perceptual integration mechanism. A consequence of this hypothesis is that specific training for omission-type ND patients would aim at restoring the oculo-motor scanning and should not improve reading in substitution-type ND. With this aim we administered an optokinetic stimulation (OKS) to two brain-damaged patients with both USN and ND, MA and EP, who showed ND mainly characterized by omissions and substitutions, respectively. MA also showed an impairment in oculo-motor behavior with a non-reading task, while EP did not. The two patients presented a dissociation with respect to their sensitivity to OKS, so that, as expected, MA was positively affected, while EP was not. Our results confirm a dissociation between the two mechanisms underlying omission and substitution reading errors in ND patients. Moreover, they suggest that such a dissociation could possibly be extended to the effectiveness of rehabilitative procedures, and that patients who mainly omit contralesional-sided letters would benefit from OKS.

What role for prism adaptation in the rehabilitation of pure neglect dyslexia?

“…Previous studies have shown that specific neglect dyslexia reading patterns predict the success of a targeted intervention. For example, Daini et al (2013) found that optokinetic stimulation only affected omission errors, and only in one out of two patients. Such observations may serve as the starting point for larger case studies with the ultimate goal to identify individualized and targeted interventions for specific impairments.…”

“…Most previous intervention studies targeted neglect defined as deficit of spatial attention and exploration (Kerkhoff & Schenk, 2012), but did not specifically measure improvements in single-word reading (see Daini et al, 2013;and Reinhart, Schindler, & Kerkhoff, 2011; for an exception using optokinetic stimulation). However, several studies used reading measures to evaluate the effect of different interventions on neglect symptoms.…”

Adaptive Cueing Treatment of Neglect in Stroke Patients Leads to Improvements in Activities of Daily Living: A Randomized Controlled, Crossover Trial

“…As reported in previous studies, sensory and cognitive therapies may have a differential impact on different neglect symptoms. 13,23 Gossmann et al 6 combined prism adaptation with a motor task. The patients improved on a test measuring egocentric symptoms, whereas there was no effect on allocentric symptoms.…”

Acquired spatial dyslexia

“…They also found that omission errors were pathognomonic of ND. For Daini et al [8], omissions might be related to an exploratory deficit, and substitutions to a deficit of perceptual integration. Omissions at the level of the word [8] or the text [9] are specifically reduced by optokinetic stimulation, which improves oculomotor behaviour.…”

“…For Daini et al [8], omissions might be related to an exploratory deficit, and substitutions to a deficit of perceptual integration. Omissions at the level of the word [8] or the text [9] are specifically reduced by optokinetic stimulation, which improves oculomotor behaviour. However, Primativo et al [10] showed that neglect errors in reading are identical when words are tachistoscopically presented, preventing saccades, or in an unlimited presentation duration, allowing saccades.…”