Neuropsychologia 40 (2002) 718–729 Ameliorating neglect with prism adaptation: visuo-manual and visuo-verbal measures Alessandro Farnè a,d,∗ , Yves Rossetti b , Silvia Toniolo c , Elisabetta Làdavas a a Dipartimento Psicologia, Università di Bologna, Viale Berti Pichat 5, 40127 Bologna, Italy b Espace et Action INSERM Unité 534, Bron, France c San Giacomo Hospital, Ponte dell’Olio, Italy d I Fraticini Hospital, Firenze, Italy Received 31 May 2001; accepted 5 September 2001 Abstract Previous studies have shown that adaptation to rightward displacing prisms improves performance of neglect patients on visuo-manual (VM) tasks such as line cancellation, figure copying, and line bisection [Nature 395 (1998) 166]. The present study further evaluated the effect of prism adaptation (PA) on neglect symptoms by investigating: (a) the range of beneficial effects on common visuo-spatial deficits as well as less frequent phenomena like neglect dyslexia; (b) the duration of improvement following a single exposure to the right optical deviation; (c) the extent to which visuo-spatial performance can be comparatively ameliorated in VM tasks and visuo-verbal (VV) tasks (i.e. involving or not the adapted arm, respectively) and (d) the presence and duration of the manual visuo-motor bias induced by the prismatic adaptation (i.e. the after-effect). We investigated these issues in a group of neglect patients with right hemispheric damage who were also affected by neglect dyslexia. Following a single, brief prismatic adaptation the results showed that (a) several visuo-spatial abilities, including accuracy in reading single words and non-words, considerably improved, (b) the amelioration was long-lasting, continuing for at least 24 h, (c) the presence, amount, and duration of neglect amelioration was not limited to VM tasks, but extended to VV tasks and (d) the presence and duration of the after-effect induced by prismatic adaptation remarkably paralleled the presence and duration of the improvement of neglect symptoms. These findings clearly demonstrate that beneficial effects induced by a single PA are very long-lasting and spread over a wide range of visuo-spatial deficits, independent of the type of response required. In addition, our results strongly suggest that the process of adaptation, as revealed by the presence of a visuo-motor after-effect, might be essential for establishing amelioration. In light of its characteristics, the prismatic adaptation technique should be a priority tool for the rehabilitation of the multifaceted hemispatial neglect syndrome. © 2002 Elsevier Science Ltd. All rights reserved. Keywords: Hemispatial neglect; Prism adaptation; Manual pointing; After-effect; Neglect dyslexia; Manual and verbal response 1. Introduction Hemispatial neglect is defined as the patient’s failure to report, respond to, or orient toward novel and/or meaning- ful stimuli presented to the side opposite the brain lesion [21]. This condition is frequently found in right brain dam- aged (RBD) patients, often in association with contralesional hemiplegia or hemiparesis [5,50]. In addition to inducing many functional debilitating effects on everyday life, left visuo-spatial neglect has been shown to be responsible for poor functional recovery and reduced ability to benefit from treatment of impaired motor functions [11,17,19,27,38]. For these reasons, many attempts have been made in the past 15 years to rehabilitate hemispatial neglect, which ∗ Corresponding author. Tel.: +39-51-2091347; fax: +39-51-243086. E-mail address: farne@psibo.unibo.it (A. Farn` e). has lead to a variety of different approaches [29,33,40,47]. More recently, researchers have paid particular attention to physiological manoeuvres that induce a strong amelioration to many pathological aspects of the neglect syndrome (for review, see [56,65]). These manoeuvres consist of tem- porarily manipulating some spatial aspect of the sensory input to overcome the contralesional visuo-spatial deficit in neglect patients. Furthermore, neglect can be improved by several sensory manipulations, such as caloric vestibu- lar stimulation [7,25,64], neck muscles [26] or plantar [46] vibration, transcutaneous [66] or optokinetic stimu- lation [32,41], active/passive limb proprioceptive stimu- lation [14,18,28,49,52] or non-spatial manipulations such as arousal increase [51]. However, in all such cases, the effects of a single application of these sensory manip- ulations were usually very transient, lasting only a few minutes. 0028-3932/02/$ – see front matter © 2002 Elsevier Science Ltd. All rights reserved. PII:S0028-3932(01)00186-5