We tried to measure visual extinction level of patients with brain damage using contrast threshold of luminance grating. A grating stimulus was presented unilaterally either in the extinction visual field (contralateral to the lesion) or in the normal visual field (ipsilateral to the lesion), or bilaterally in bothvisual fields. In the bilateral presentation condition, contrast threshold was measured only for grating stimuli presented in the extinction visual field. In Experiment I, two patients with right brain damage were tested and showed a complete extinction in the bilateral presentation condition: the patients could not detect a stimulus in the extinction field even when it was presented in the maximum contrast of the apparatus. In Experiment 2, four new patients with right brain damage were tested in the bilateral presentation condition with stimuli of three contrast levels in the normal field. The results indicated that extinction level could be measured as a change of contrast threshold of luminance gratings. It was also suggested that the extinction rate increased along with the intensity of stimuli presented in the normal field.
