Milner and Goodale (1995, 2006) propose a model of vision that makes a distinction between ‘vision for perception’ and ‘vision for action’. Regarding hemispatial neglect, they, somewhat contentiously, hypothesize that this disorder is better explained by damage to a high-level representational structure that receives input from the ventral visual stream, but not from the dorsal-stream. Consequently, they postulate that neglect patients should code spatial parameters for action veridically. Another strong claim of the model is that the dorsal stream’s control of action is designed for dealing with target stimuli in the ‘here and now’, yet when time is allowed to pass and a reaction has to be made on the basis of a visual memory, the ventral stream is required for successful performance. One prediction from this is that neglect patients should be able to perform immediate actions, but should present specific impairments when the action is delayed. In Part I of this thesis the pattern of spared and impaired visuomotor abilities in patients with neglect, as specifically predicted by the perception and action model (Milner & Goodale, 1995, 2006), was investigated. In Chapter 1, the performance of patients with and without neglect after right hemisphere stroke was compared with that of age-matched controls. Participants were asked to point either directly towards targets or halfway between two stimuli (gap bisection), both with and without visual feedback during movement. No neglect-specific impairment was found in timing, accuracy or reach trajectory measures in either pointing or gap bisection. In Chapter 2, I tested whether neglect patients would be unimpaired in immediate pointing, yet show inaccurate pointing in a condition where a delay is interposed between the presentation of the stimulus and the response signal. Similarly to Chapter 1, it was found that neglect patients showed no accuracy impairments when asked to perform an immediate action. Conversely, when pointing towards remembered leftward locations they presented specific accuracy deficits that correlated with neglect severity. Moreover, an initial voxel-based lesion-symptom analysis further revealed that these deficits were associated with damage to occipito-temporal areas which were also mostly damaged in the neglect group.Furthermore, training of grasping the centre of rods (visuomotor feedback training) has been shown to improve neglect (Robertson, Nico & Hood, 1997; Harvey et al., 2003). It is postulated that by using the spared visuomotor abilities in these patients it is possible to ‘bootstrap’ their perceptual deficits through some ‘dorsal-to-ventral recalibration’. Hence, in Part II the immediate and long-term effects of visuomotor feedback training were explored on neglect conventional measures, as well as in daily life tasks. I found that this technique improves neglect symptoms and crucially that these improvements were long lasting, as they were present even after 4-months post-training. Importantly, I also show that the training effects generalize to the patient’s daily lives at follow-up. These findings are very encouraging for the rehabilitation of neglect as this condition has been shown to be the best single predictor of poor recovery after stroke and very difficult to treat.
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