Spatial neglect (neglect), a common, disabling condition following stroke, predicts poor rehabilitation outcome. Contemporary theories of neglect, predicated on spatial representations through which attention and movement are directed, cannot explain a number of recent empirical findings.Treatment may be of limited benefit because the theories are incomplete. Research in this proposal will investigate a new concept in neglect and apply this concept in treatment. The investigators want to broaden the framework of neglect theory. They propose that some aspects of neglect behavior reflect altered representations of space, whereas others reflect altered representations of stimulus intensity. The hypothesis of this proposal is that representations of stimulus intensity are derived in accordance with the Power-Law in psychophysics. The Power-Law describes a quantitative relationship between the physical intensity of a stimulus and its perceived intensity, and it applies across sensory modalities. It is predicated on the concept of ratio scaling -- equal ratios of stimulus intensity produce equal ratios of perceived intensity. Ratio scaling is operationalized in this proposal through use of power functions. The investigators' preliminary work shows that empirical constraints on neglect theory can be explained by a theory that combines the concepts of spatial representations with representation of stimulus intensity.
Aim 1 is to extend the investigators preliminary work by examining ratio scaling in 8 perceptual continua.
Aim 2 is to compare ratio scaling among patients with and without neglect following unilateral ischemic strokes of the left and right hemispheres and non-patient controls.
Aim 3 is to compare patients with neglect trained vs. those untrained in ratio scaling on outcomes related to neglect and activities of daily living. Maintenance of treatment benefits over time will be assessed. Results will either support or modify the investigators' central hypothesis. The investigators anticipate this proposal's studies will lead to a comprehensive theory of neglect and a comprehensive interpretation of the Power-Law. They will advance understanding of the multi-faceted nature of mental representation and the cortical contributions to ratio scaling. The investigators anticipate Aim 3 will yield a treatment approach that can be widely applied in rehabilitation and can improve performance on real-life tasks in real-life settings.
