The multiplicity of neglect phenomena

Abstract

Neglect for the extrapersonal space is not a disorder of seeing, hearing, or moving but one of looking, detecting, listening, and exploring. It is said to be present when the impact of sensory events upon conscious (explicit) behaviours displays a spatially-addressed bias that cannot be attributed entirely to elementary sensory-motor deficits such as weakness, clumsiness, or poor acuity. In clinical practice. the more dramatic manifestations of neglect occur within the left side of the extrapersonal space in patients with right hemisphere damage. The distribution of left neglect can display retinocentric, cephalocentric, or somatocentric coordinates and can shift from one coordinate to another in the same individual, usually gravitating towards the coordinates that maximise the extent of neglect. On occasion, an allocentric, object-centred component can also emerge, so that the patient neglects not only the left hemispace but also the left side of sensory events in the right hemispace. Neglect can be multimodal or unimodal. It can encompass the extrapersonal, peripersonal, or personal spaces. It can be elicited by a large number of tasks, including lime bisection, target detection, bilateral simultaneous stimulation, clock drawing, and reading. The severity of deficits may vary considerably from one task to another. Neglected sensory events do not influence overt, declarative responses but may exert an implicit influence on behaviour even when the patient denies conscious awareness of the stimulus.