LINE BISECTION IN HEMIANOPIA

The effect of hemianopia on line bisection is not known. To study this , manual line bisection in 30 patients with unilateral cerebral hemisp heric lesions was examined. The mean bisection point in a group of eig ht patients with left hemineglect was biased rightward (ipsilaterally) , as expected. Among the remaining 22 patients, eight had right hemian opic visual defects, eight had left hemianopic visual defects, and six had normal visual fields. Both groups of patients with contralateral visual field defects had mean bisection points biased contralaterally, compared with 68 normal subjects. This bias was less than the ipsilat eral (opposite) bias of patients with hemineglect. Contralateral bisec tion bias was more evident in those whose field defect involved the ma cular region. No bias was seen in patients with neither field defects nor hemineglect. The contralateral bias in hemianopia may represent ei ther non-veridical spatial representation within a visual hemifield or a consequence of the strategic adaptation of attention into contralat eral hemispace after hemianopia.