Spatial and linguistic encoding of orthographic material. Evidence from neglect patients in line bisection tasks

In line bisection tasks, right-brain damaged patients with unilateral spatial neglect (USN) exhibit a rightward deviation with respect to the objective midpoint of the stimulus, while in neurologically unimpaired participants a reversed bias (“pseudoneglect”) has been consistently reported. In a study with healthy subjects, Arduino et al. (2010) suggested the existence of partially independent mechanisms involved in word and line bisection, not only linguistic but also visuo-perceptual. Furthermore, both lexical and syntactic factors are shown to modulate the reading performance in patients with neglect dyslexia (Rusconi et al., 2004; Cubelli & Beschin, 2005; Friedmann et al., 2011). A series of studies involving USN patients were conducted in order to investigate the spatial and linguistic encoding of orthographic material through a bisection task. In Study I, right-brain damaged patients with USN, right-brain damaged patients without USN, and matched controls were asked to manually bisect words (5-10-13 letters) and lines of comparable length (Exp. 1), and words with final sequences differing on the prediction made concerning how the word should have been read (stressed on the penultimate or antepenultimate syllable; Exp. 2). Study II required the bisection of words and lines of different lengths, radially oriented. In Study III, patients were asked to bisect affirmative and interrogative sentences varying on the syntactic structure, compared to letter strings and lines (Exp. 1), and sentences in which lexical and syntactic alterations were introduced (Exp.2). Data from Study I demonstrated that most USN patients show a rightward deviation similar for words and lines, with the bias increasing with stimulus length. However, in individual patients USN can affect the bisection of lines and orthographic material with various degrees of severity, demonstrating that at least partially independent mechanisms interact during bisection (Arduino et al., 2010). Furthermore, the ortho-phonological information contained in the final part of a word could act as a cue, modulating the bisection error in patients and healthy subjects. In Study II, radial words are re-oriented during bisection, reaching their canonical orientation. Finally, the linguistic nature of the stimulus induces facilitation in USN patients, who show a reduced error deviation in case of sentences with respect to letter strings and lines (Study III), even when lexical and syntactic alterations were introduced. In conclusion, visuo-perceptual and linguistic information (both lexical and possibly syntactic) modulates the allocation of attention in word and sentence bisection.