Abstract
Purpose: The previous study has shown that two moving lines shown in vertically arranged apertures in combination with a positively-oriented line in the upper aperture and a negatively-oriented line in the lower aperture (“<“ shape) tend to be integrated more than those in the reverse combination (“>” shape) when they move rightward (ARVO2000). The present study tries to examine the determinant of this result. Methods: Lines oriented 15 and −15 deg, 30 and −30 deg, 45 and −45 deg, 60 and −60 deg, or 75 and −75 deg, were presented in pairs, in a combination of either “<” shape or “>” shape, and two 90 deg lines were used as a control condition. Eccentricity, that is, the distance between the fixation point in the center of the display and the center of the two apertures, was varied either horizontally or vertically. The lines moved horizontally rightward or leftward. Subjects reported whether the two motions cohered or not. Results: (1) Perceived coherence depended on the spatial configuration of line orientation. Performance declined from 100% for 90 deg lines to 0% for 15 and −15 deg lines, and considerably degraded at 30 and −30 deg lines. (2) The lines presented in peripheral vision were integrated more than those presented in fovea. (3) Not the shape of the two lines, but the combination of local directions affected coherence. (4) Perceived coherence was higher when the lines in “<” shape moved rightward rather than leftward, and when the lines in “>” shape moved leftward rather than rightward. These results show that converging motions cohere more than diverging motions. Conclusions: The direction combination effect turned out to be the determinant in the line combination effect, and whether local motions are converging or diverging plays an important role in motion integration.