Kaneko and Howard (1997) reported that the horizontal dimension of the integration area for vertical-size disparity information defining perceived surface slant is about 20 degrees. We examined the vertical dimensions of this integration area to extend this finding. We measured perceived slant of surfaces defined by vertical-size disparity modulations to determine the spatial properties of vertical-size disparity processing. The stimuli were random-dot stereograms containing a sinusoidal modulation of vertical-size disparity along horizontal and vertical axes. Subjects indicated local surface slant by adjusting the angle of a manual rod. The results show that vertical-size disparity modulation along a vertical axis, as well as a horizontal axis, produces a modulation of perceived slant, and that local slant depends on the vertical-size disparity within a local area. Therefore, the integration area for vertical-size disparity infomation defining surface slant has a vertical limit, as well as a horizontal limit. We conclude that vertical-size disparity information is not necessarily integrated over the entire visual field.

This study examined characteristics of Chinese character identification of young and old subjects and age effects in a visual-search task. Five college students (19-24 years) and eight old subjects (65-70 years) participated in a Chinese character visual-search task that required choosing a target among 12 stimuli. Characters were manipulated by varying the complexity (5, 10, 15, or 20 strokes) and the font size (18, 26, 36, or 48 point). Stimuli were presented for five kinds of duration (0.5, 0.78, 1, 2, or 3 s) in young subjects and only one (3 s) in old subjects. Performance accuracy and response speed decreased as functions of the complexity of characters and of the size. Age differences increased as a function of the complexity in performance accuracy, but were constant in response speed.