Prism Adaptation Changes Perceptual Awareness for Chimeric Visual Objects but Not for Chimeric Faces in Spatial Neglect after Right-hemisphere Stroke

Abstract

Prism adaptation can ameliorate some symptoms of left spatial neglect after right-hemisphere stroke. The mechanisms behind this remain unclear. Prism therapy may increase exploration towards the contralesional side, yet without improving perceptual awareness, as apparently for the left side of chimeric face stimuli (Ferber et al. 2003). However, other prism studies suggest that perceptual awareness might be improved (e.g., Maravita et al., 2003). We tested the impact of prism therapy on visual awareness for the left side of chimeric objects as well as chimeric faces, in three neglect patients. Prism therapy dramatically improved awareness for the identity of the left side of chimeric non-face objects, but had no effect on judging expressions for chimeric faces. The latter may thus be unique in showing no prism benefit.

Restoring abnormal aftereffects of prismatic adaptation through neuromodulation

“…Despite the presence of a lesion affecting the occipital cortex bilaterally, which determines a bilateral lower visual field defect, PA is not disrupted in MM, presumably because the patient still visually processes the error signal in the unimpaired upper quadrants. In line with these findings, there is evidence that both unilateral occipital damage and hemianopia do not affect the PA process, and the positive effects of prism exposure on recovery from left neglect (Frassinetti et al, 2002;Jacquin-Courtois et al, 2013;Sarri et al, 2006). The present findings are also in line with previous results from a single-case study, showing that a unilateral left cerebellar lesion does not impair the visuo-motor process of PA to a rightward visual field displacement, as indexed by a reduction of the pointing error (Pisella et al, 2005).…”

“…There is some evidence that right occipital damage reduces the extent of error correction in PA, and negatively affects neglect recovery; these negative correlations are specific for occipital damage (Serino et al, 2006;Serino et al, 2007). However, other reports have shown that both unilateral occipital damage and hemianopia neither affect the PA process, nor the PA-induced recovery of left neglect (Frassinetti et al, 2002;Jacquin-Courtois et al, 2013, for review;Sarri et al, 2006). Finally, spared PA and AEs have been described in a patient with bilateral optic ataxia, due to bilateral damage to the PPC (Pisella et al, 2004).…”

Modulation of visual attention by prismatic adaptation

“…Taken together, the evidence from these studies suggests that rightward PA affects general visuo-spatial functions attributed to the right hemisphere and improves general spatial cognition in patients with right hemispheric damage. There are, however, exceptions, which we discuss in detail in Section 5.4; rightward PA does not affect spatial bias in lateral preference tasks (Ferber et al, 2003;Sarri et al, 2011Sarri et al, , 2006, size estimation (Dijkerman et al, 2003), or visual search . Furthermore, several clinical studies reported promising, albeit not conclusive effects of rightward PA (Keane et al, 2006;Nys et al, 2008), possibly because not all types of neglect respond equally well to this treatment (Clarke et al, 2015).…”

Effectiveness of Prism Adaptation in Neglect Rehabilitation

“…Rossetti and colleagues 10 found no improvement in patients treated with neutral goggles, whereas Rosseaux and colleagues 16 found comparable improvements after treatment with both prismatic and neutral goggles. These criticisms, together with other reports showing no improvement after PA for some tasks, [17][18][19][20] or for some patients, [13][14][15] cast doubt on the specific efficacy of PA above control conditions. However, the fact that some neglect improvement can be obtained also after NP cannot be taken as an argument against the specific effectiveness of PA. During NP, patients perform a series of movements toward a visual target presented several times in the neglected hemifield.…”