Neglect "Around the Clock": Dissociating Number and Spatial Neglect in Right Brain Damage

This chapter examines the link between number and the spatial biases observed in spatial neglect. Right-brain-damaged patients affected by left unilateral neglect are characterized by a pathological attentional bias to the right side of space. This left-sided deficit encompasses eye and head deviations, visual, somatosensory and auditory sensory processing, action initiation and realization, and mental representations. The spatial cueing effect arising in the external space coordinates was present irrespective of the emphasis in the instructions either concerning fingers or side of space. Neglect patient populations manifested a clear-cut double dissociation. Some of the patients displayed very severe neglect on the bisection of visual lines and normal performance for the bisection of number intervals. The increasing rightward error displayed by D participants in the bisection of large 7-unit intervals located to the "left" side of decades offers another example of the apparent similarity between bisection behavior in visual and number space. Another point that needs careful consideration when one discusses the associations and dissociations between numerical and spatial coding that can be observed in the healthy brain is whether the influence of numerical cues on spatial processing is as strong as the reciprocal influence of spatial cues on number processing.