The effect of slant on visuomotor localization

Visuomotor localization in the presence of slant was measured. Five subjects pointed at the center LED of an array of five LEDs viewed monocularly. Pointing was open-loop. The LEDs were separated by 1.5, 3.0, or 4.5 cm. The array was rotated about a vertical axis coincident with the center LED to slant the array from -50 degrees to +50 degrees. LED separation had no effect. A small linear relationship was found between errors in localization and slant (slope = -0.02). The errors were as expected if the perceived straight ahead was in the direction of the normal to the surface, but these errors were so small as to be functionally insignificant. It is concluded that extraretinal eye position information dominates over slant for visuomotor localization.