From phenomena to models

Abstract

Over the past ten years there has been a dramatic expansion in the number of empirical studies concerned with the phenomena of neglect: for instance, there has been research into the systematic, directional errors made by neglect patients in line bisection, the omissions made in line cancellation tasks, the misidentifications in reading and object identification tasks, the errors made in copying and drawing from memory, the denial of neglect (anosognosia), and so forth. This work, whilst welcome, has led to a burgeoning amount of empirical detail that needs to be digested by any researcher coming into the field. In addition, much of the work has suggested that, within the general syndrome of neglect, patients can differ quite strikingly from one another. There are now well-documented dissociations between (for example) patients whose neglect is dependent on visual feedback and those whose neglect is dependent on kineasthetic feedback concerning the position of the limb in space (e.g. Tegnér & Levander, 1991), between neglect in cancellation tasks and anosagnosia (Bisiach, Perani, Vallar, & Berti, 1986), between neglect for peripersonal but not for extrapersonal space (Halligan & Marshall, 1991). This fractionation of symptoms underlines the important point that neglect is not a unitary disorder. A number of functionally different problems exist within (in the most general terms) the systems mapping between sensory input and motor output. And, though these problems are all characterised by being “spatial”, the “space” involved seems to vary according to the task and even the nature of the stimuli (see below). A major task for researchers is to document the nature of the different “spaces” that seem to be affected within particular patients.