The Japanese journal of neuropsychology

Full Text of this Article
in Japanese PDF (501K)

ArticleTitle	The evaluation of the cerebral dyschromatopsia using image-processing and psychophysics
Language	J
AuthorList	Shinichi Koyama¹⁾²⁾, Machiko Kezuka³⁾, Haruo Hibino²⁾, Hiroyuki Tomimitsu³⁾, Mitsuru Kawamura¹⁾⁴⁾
Affiliation	1) Showa University School of Medicine 2) Chiba University, Department of Engineering 3) Aoyama Hospital 4) CREST, JST
Publication	Japanese Journal of Neuropsychology: 23 (2), 132-138, 2007
Received	Apr 20, 2006
Accepted	Jun 28, 2006
Abstract	The color perception in two patients with bilateral occipital damages was evaluated by means of our newly developed technique combining image-processing and psychophysics. Cerebral dyschromatopsia has been evaluated by color discrimination tasks such as Farnsworth-Maunsell 100 Hue test and Panel D-15. However, those tasks would not tell us how the visual scenes would appear to the patients. We first simulated the patients' perception using image-processing software. The patients simulated their perception by adjusting color balance (cyan vs. red, magenta vs. green, and yellow vs. blue) in digital images. After that, we psychophysically evaluated the patients' color perception by measuring the duration of color afterimages. The patients and four age-matched normal controls viewed a color square for 10 seconds and a white screen immediately after disappearance of the color square. The color of the square was red, green, yellow, or blue. The background color was white. The subjects recorded the duration of the color afterimage by pressing a button when they started seeing the afterimage and when the afterimage disappeared. The results of the image-processing task and the color afterimage task were consistent. The pictures simulated by the patients were tinted in yellow and brown, suggesting that the patients would perceive blue abnormally weakly. The results of the color-afterimage task also indicated the patients' weak response to blue: in the patients, the duration of the afterimage of yellow was shorter than the afterimages of the other colors whereas the duration of the afterimage of blue was longer than the afterimages of the other colors. In the normal control, the durations of the afterimages were similar between colors. The results suggest that the neural mechanisms for blue, which should be active after adaptation to yellow, were weakened by the brain damage. On the other hand, the balance between the neural mechanisms for red and green was relatively preserved. The neural mechanism for the perception of blue may be vulnerable to the brain damage because its retinal input is sparse. The evaluation of cerebral dyschromatopsia using image-processing and psychophysics would be useful because the new method enables us to evaluate color-perception deficits quantitatively. In addition, the method enables the patient and the other people to share the patient's visual experiences.
Keywords	cerebral dyschromatopsia, ventral occipital cortex, color afterimage, image processing, psychophysics