Abstract
Previous research has shown that prism adaptation (prism adaptation) can ameliorate several symptoms of spatial neglect after right-hemisphere damage. But the mechanisms behind this remain unclear. Recently we reported that prisms may increase leftward awareness for neglect in a task using chimeric visual objects, despite apparently not affecting awareness in a task using chimeric emotional faces (Sarri et al., 2006). Here we explored potential reasons for this apparent discrepancy in outcome, by testing further whether the lack of a prism effect on the chimeric face task task could be explained by: i) the specific category of stimuli used (faces as opposed to objects); ii) the affective nature of the stimuli; and/or iii) the particular task implemented, with the chimeric face task requiring forced-choice judgements of lateral ‘preference’ between pairs of identical, but left/right mirror-reversed chimeric face tasks (as opposed to identification for the chimeric object task). We replicated our previous pattern of no impact of prisms on the emotional chimeric face task here in a new series of patients, while also similarly finding no beneficial impact on another lateral ‘preference’ measure that used non-face non-emotional stimuli, namely greyscale gradients. By contrast, we found the usual beneficial impact of prism adaptation (prism adaptation) on some conventional measures of neglect, and improvements for at least some patients in a different face task, requiring explicit discrimination of the chimeric or non-chimeric nature of face stimuli. The new findings indicate that prism therapy does not alter spatial biases in neglect as revealed by ‘lateral preference tasks’ that have no right or wrong answer (requiring forced-choice judgements on left/right mirror-reversed stimuli), regardless of whether these employ face or non-face stimuli. But our data also show that prism therapy can beneficially modulate some aspects of visual awareness in spatial neglect not only for objects, but also for face stimuli, in some cases.
Highlights
Spatial neglect is a frequent multi-component syndrome following stroke, with the deficits including losses of awareness, orientation and exploration towards the contralesional side of space, which typically cannot be attributed to primary sensory or motor deficits
Our previous work (Sarri et al, 2006) had reported that while prism therapy may apparently have no effect on neglect patients’ awareness for the contralesional side of chimeric face tasks, when measured by forced-choice spatial preference judgements of emotional expression, it can significantly increase awareness for the left side of chimeric nonface objects
The lack of any prism impact on the face expression lateral preference task contrasted with the clear and significant prism impact on openloop pointing, and with the beneficial impact on subjective straight-ahead and line bisection, for which neglect in our patients was clearly reduced by the prism intervention
Summary
Spatial neglect is a frequent multi-component syndrome following stroke, with the deficits including losses of awareness, orientation and exploration towards the contralesional side of space, which typically cannot be attributed to primary sensory or motor deficits. Neglect patients may fail to acknowledge the existence of contralesional stimuli, and may even neglect contralesional parts of their own body or of mental representations (Mesulam, 1999; Karnath et al, 2002; Driver et al, 2004). Recent efforts to rehabilitate neglect include a promising approach involving adaptation to rightward optical displacement induced by prisms (e.g., Rossetti et al, 1998). The procedure involves a short exposure period (typically lasting only w5–10 min) to a prismatic optical shift of 10–15 to the right, combined with a concurrent visuomotor task (usually pointing to visual targets in free vision, while wearing the prisms). Subsequent testing takes place after the prisms have been removed
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