Purpose: To test the importance of geometric information (splay angle, splay rate; Beall Loomis, Perception, 25: 481-494, 1996) and optical flow information provided by road surface texture in steering accuracy. Methods: Subjects drove along a simulated one-lane road using a force-feedback steering wheel. The road was defined by either (a) one continuous white line on a black background, (b) two continuous white lines as kerbs, or (c) two lines and road surface texture. Turns in the road appeared in random order. The subjects drove with constant velocity of 16.9 m/s (60.8 km/h). Lateral deviation from the center line, velocity and frequency content of the steering maneuvers served as performance indices. Results: Most subjects reported finding the task easier under condition (b) than under condition (a). Despite their impression the data suggested different, counter-intuitive results. Under condition (a) subjects performed more accurately (p < 0.01) than under condition (b), and steering on a textured road (c) appeared to be more accurate (p < 0.05) than on a road with no surface texture (a). Conclusions: The difference between conditions (a) and (b) may be due to the fact that apparent lateral shifts of the road markings (splay angle) decrease with the distance from the road's center line. Our results support the view that optical flow obtained from road texture (c) enhances steering performance. Currently we are testing increasing realism by shifting this paradigm to a 180 deg projection screen
