How many neglects? Some considerations based on anatomy and information processing

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Abstract
Despite implying a unitary impairment in spatial cognition. the term “neglect” covers numerous behavioural manifestations that are themselves consequent upon damage to distinct neural systems. Aphasia, agnosia, and amnesia have long been acknowledged as heterogeneous conditions, but only recently has spatial cognition proved amenable to similar taxonomic initiatives. Unfortunately, with the advent of a nascent taxonomy, terms have emerged whose meanings have failed to remain consistent. For example, in the motor domain, “directional hypokinesia” originally characterised slowed initiation of contralesional movements (Heilman et al., 1985); subsequently it covered reduced spatial exploration in a contralesional direction (Tegnér & Levander, 1991), or even insufficiently extensive movements in the contralesional direction (Bisiach, Geminiani, Berti, & Rusconi, 1990). Conversely, the implied semantic differences between terms such as “directional motor neglect”, “hemispatial motor neglect” and “hemispatial limb hypometria” may be more apparent than real. In the absence of a precisely defined lexicon devoted to describing spatial cognition, we cannot hope to achieve a principled understanding of its disorders.