Spatial attentional bias in normal people: Object or viewer-centered

When bisecting radial lines, normal subjects often have a distal bias. To help in explaining this systematic bias, it has been proposed that normal people have an attentional bias to the top of the lines (object centered hypothesis) or toward stimuli falling in the lower portion of the retina (retinotopic hypotheses) or to distal peripersonal space (body centered hypotheses). The primary aim of this study is to test these hypotheses by having normal subjects bisect radial lines, placed in a clockwise distribution in the transverse plane, below eye level. Our results demonstrate that the perception of the midpoint progressively changes as a function of the body centered orientation of the lines, with subjects demonstrating a progressively greater distal bias as they approached the midsagittal plane or radial condition. These findings provide support for the postulate that distal bias on radial lines bisections is body centered.