Human locognosic acuity on the arm varies with explicit and implicit manipulations of attention: implications for interpreting elevated tactile acuity on an amputation stump

In Experiment 1, normal subjects' ability to localize tactile stimuli (loco gnosia) delivered to the upper arm was significantly higher when they were instructed explicitly to direct their attention selectively to that segment than when they were instructed explicitly to distribute their attention ac ross the whole arm. This elevation of acuity was eliminated when subjects' attentional resources were divided by superimposition of an effortful, seco ndary task during stimulation. In Experiment 2, in the absence of explicit attentional instruction, subjects' locognosic acuity on one of three arm se gments was significantly higher when stimulation of that segment was 2.5 ti mes more probable than that of stimulation of the other two segments. We su rmise that the attentional mechanisms responsible for such modulations of l ocognosic acuity in normal subjects may contribute to the elevated sensory acuity observed on the stumps of amputees. (C) 2001 Elsevier Science Irelan d Ltd. All rights reserved.