From blindsight to sight: cognitive rehabilitation of visual field defects.
OBJECTIVE
Traditionally, post-chiasmatic lesions were believed to result in complete and permanent visual loss in the topographically related areas of the visual field. However, a number of studies with monkeys, and later with humans, have demonstrated spared implicit visual functioning, referred to as 'blindsight'. The present study assessed whether training this phenomenon would induce an objective restoration of conscious vision in the blind field of hemianopic patients.


METHODS
For a period of 22 weeks nine patients with unilateral occipital damage participated in several forced-choice visual tasks known to elicit blindsight: pointing to visual targets, letter recognition, visual comparison between the two hemifields, target localization, and letter identification. Before and after rehabilitation, patients were submitted to a behavioral pre- and post-test, including visual detection and letter identification as well as to automated perimetry visual field testing (Humphrey Automated 24-2 Full Threshold).


RESULTS
An objective improvement was found in the behavioral tasks for all patients at the post-test stage as well as an objective enlargement of the contralesional visual field for all except one of the nine patients. An overall decrease is seen in the number of undetected points (out of 30) on automated perimetry visual field testing after rehabilitation (F (1, 16)=22.57; p<0.001) for both eyes (Right Eye, RE: T=0; z=2.52; p<0.05; Left Eye, LE: T=0, z=2.37; p<0.05) regardless of lesion side.


CONCLUSIONS
The results suggest that explicit (conscious) visual detection can be restored in the blind visual field by using implicit (unconscious) visual capacities. Results are discussed regarding visual field defect rehabilitation, blindsight, attention, and brain plasticity hypotheses.
Chokron
Sylvie
S
Laboratoire de Psychologie et NeuroCognition, CNRS, UMR5105, UPMF, Grenoble, France. chokron@ext.jussieu.fr
Perez
Celine
C
Obadia
Michaël
M
Gaudry
Isabelle
I
Laloum
Laurent
L
Gout
Olivier
O
D000328:Adult; D000368:Aged; D000704:Analysis of Variance; D015928:Cognitive Behavioral Therapy / Q000379:methods*; D005260:Female; D007839:Functional Laterality; D006423:Hemianopsia / Q000473:pathology / Q000534:rehabilitation*; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008875:Middle Aged; D020127:Recovery of Function / Q000502:physiology*; D014787:Vision Tests; D014793:Visual Cortex / Q000473:pathology; D058609:Visual Field Tests / Q000379:methods; D014794:Visual Fields / Q000502:physiology*