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Title: The effects of prism adaptation on unilateral spatial neglect
Author: Fisher, Zoe
Awarding Body: Swansea University
Current Institution: Swansea University
Date of Award: 2009
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This thesis concerns the syndrome of visual unilateral spatial neglect (USN). Pisella and Mattingley (2004) argue that two of the core deficits associated with USN, the ipsilesional reaction time (RT) bias (thought to reflect the ipsilesional attention bias) and the ipsilesional detection bias, may have distinct neural substrates and thus may dissociate. In the research reported in this thesis, the 'dissociation hypothesis' was explored in a single patient (JH). JH was impaired at detecting contralesional targets on the visual search task in near space but her far space contralesional target detection was comparable with a healthy control group. However, despite showing 'normal' target detection in far space her far space RTs were significantly slower to detect contralesional targets relative to ipsilesional targets. In fact her RT data was comparable with the far space RT data of 6 patients with USN and was significantly different that that of 10 healthy control participants. This data suggests that the ipsilesional RT and the ipsilesional detection bias can dissociate and may be underpinned by distinct neural processes. The patient was then given PA training. Overall, the analysis showed that the ipsilesional detection bias was ameliorated after PA but the ipsilesional RT gradient remained unchanged. A group study was carried out to explore whether PA ameliorated both the ipsilesional detection bias and the ipsilesional RT bias, (due to the limitations of the case study approach). As research has already shown that PA improves contralesional target detection (Rossetti et al., 1998; Frassinetti et al., 2002) the experiments asked whether increased target detection after PA is accompanied by a normalisation of the ipsilesional RT bias on a visual search task, as would be predicted if PA ameliorated USN by facilitating a redistribution of spatial attention (Rode, 2003; and Pisella, 1999). The findings showed that increased contralesional target detection was not accompanied by a normalisation of the ipsilesional RT gradient. This suggests that a) the ipsilesional detection and the ipsilesional RT bias are not intrinsically related and b) that PA does not facilitate a redistribution of spatial attention. It was argued that PA improves target detection by ameliorating the remapping deficit associated with PA (Pisella and Mattingley, 2004) without ameliorating the ipsilesional attentional bias. It was argued in the rationale section of this thesis that the conventional PA procedure described by Rossetti (1998) is a far space based procedure as patients adapt to the prismatic shift by pointing to objects in far space (beyond arm's reach). However, die patients in Rossetti's (1998) study, and subsequent studies by others, were asked to perform tasks that evaluated the effects of PA only in near space. The findings of Rossetti (1998) and others showed that 'far PA training' ameliorated left USN performance in near space, thereby suggesting that a common underlying mechanism involved in both near and far space processing is ameliorated by PA. A candidate for this mechanism may be the oculomotor system since research has shown that it may be involved in die detection of objects in both far and near space (Previc, 1995). Further, the oculomotor system has been implicated as being involved in the amelioration of USN after PA training (Serino et al., 2007). If it is the case that a mechanism common to processing of both near and far space is ameliorated by PA training, then near space training should also ameliorate USN of far space. On the other hand, there are indications in the literature that the oculomotor system is involved in processing of near and far space to different degrees, being more directly involved in processing of far than near space (Berti and Rizzolatti, 2002) There is also evidence that near and far space are processed by different neural circuits (Rizzolatti et al., 1987, 1985 and 2002). It is conceivable, therefore, that a PA training method based on processing of near space information would have a greater effect on neglect for near space than for far space. A 'near space' training procedure was therefore devised to explore this issue. Specifically, the experiments reported in Chapter 7 asked whether a 'near PA' procedure, which attempted to activate near/reaching circuits (in addition to the oculomotor system), would ameliorate USN in near and far space but to a greater degree in near space. The findings showed that 'near PA' significantly increased contralesional target detection in both near and far space with no enhanced benefit in near space. It was evident when carrying out die group study described above that not all patients benefited from PA training. The group data was re-analysed at a single case level and the findings showed that of the 9 patients who were given PA training only 6 showed a subsequent reduction in symptoms of USN. All of the patients who responded to PA showed error reduction and after effect. Of the patients who did not respond to PA, none showed error reduction and two showed an after effect It was concluded that error reduction and not after effect is the critical predictor of amelioration of USN symptoms after PA. A final longitudinal study explored how long the effects of PA lasted in three patients with USN who responded to PA training. The findings showed that the beneficial effects of PA were maintained for at least two years in one patient but two patients who initially benefited initially from PA lost their training gains over time.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available