Impaired orientation processing in hemispatial neglect.

Patients with hemispatial neglect show deficits in size perception. We investigated how this effect would be modulated by a change in object orientation. Seven right-hemisphere-lesioned patients, with and without neglect, and a control group, were asked to indicate which one of two bilaterally presented lines was longer, shorter or the same. Depending on the participant's response, the length was increased or decreased in a staircase-like procedure. Line orientation was varied over separate blocks. All neglect patients judged a line on the left as shorter, predominantly for horizontal lines and lines rotated by 30 degrees. Moreover, the magnitude of the distortion effect varied considerably between patients from as little as 2% objective underestimation to as much as 20%.