Specific impairments in visual processing following lesion side in hemianopic patients.
BACKGROUND
Following unilateral damage of the primary visual cortex one of the most common visual field defects observed is Homonymous Hemianopia (HH), a loss of vision of the contralesional hemifield in each eye. The ipsilesional ("intact") part of the central visual field is often used to compensate for difficulties encountered in the peripheral hemianopic visual field. However, the quality of vision within the central visual field is not well-known.


METHODS
To better describe and understand visual processing in hemianopia, two tasks were conducted with 25 healthy controls, six left hemianopes, and five right hemianopes. Filtered (in high, above 6 cycles/degree, or low, below 4 cycles/degree, spatial frequencies - HSF and LSF, respectively) and unfiltered natural scene images (5° of visual angle) were briefly presented (100 msec) centrally on a computer screen. Participants were required either to respond when a natural scene was presented (yes/no detection task) or to indicate if the stimulus was a city or a highway (categorization task).


RESULTS
The three groups showed similar accuracy levels but significant differences were observed in response times. More precisely, left hemianopes were impaired both in the detection and in the categorization tasks whereas right hemianopes were only impaired in the categorization task. However, the three groups had similar responses to spatial frequencies: HSF were processed more slowly than LSF.


CONCLUSIONS
Overall these results suggest that central vision is not intact in hemianopia. Lesion side selectively affects reaction times (RTs) in the detection and the categorization tasks, but does not seem to determine a specific deficit in spatial frequency processing.
Cavézian
Céline
C
Laboratoire de Psychologie et NeuroCognition, CNRS, UMR 5105, UPMF, Grenoble, France.
Gaudry
Isabelle
I
Perez
Céline
C
Coubard
Olivier
O
Doucet
Gaëlle
G
Peyrin
Carole
C
Marendaz
Christian
C
Obadia
Mickaël
M
Gout
Olivier
O
Chokron
Sylvie
S
D000368:Aged; D001930:Brain Injuries / Q000150:complications* / Q000503:physiopathology; D016022:Case-Control Studies; D005260:Female; D007839:Functional Laterality; D006423:Hemianopsia / Q000209:etiology / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009483:Neuropsychological Tests; D010775:Photic Stimulation / Q000379:methods; D011930:Reaction Time; D014785:Vision, Ocular; D014794:Visual Fields; D014796:Visual Perception