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Abstract

It is assumed that the location of the edges of the road in the field of view provide the principal visual cues for driver's steering control. However, we have shown that when the optic-flow field of the environment is perturbed by superimposing a second (irrelevant) optic-flow field simulating drifting snow across the street, the drivers exhibit systematic changes in steering. Specifically, they tend to steer in a direction opposite the visual motion of the irrelevant flow field (Chatziastros et al, 2000 Perception 29 Supplement, 118). In a new series of experiments, we investigated the interdependence of gaze direction and head orientation with this steering behaviour. In a driving simulation, the position within a straight lane had to be controlled, while drifting snow created a second focus of expansion at ±30° horizontally. A cross correlation between gaze direction and steering wheel movements shows that gaze preceded the steering movement by 0.5 s. Systematic changes in horizontal head and gaze orientation occurred mainly during the first 6 s after the onset of lateral snow drift, but not during later periods, although the lateral deviation on the road persisted. We conclude that eye and head position are associated with the early phase of the steering response, and that other factors have to be considered to account for the maintenance of an offset position. These findings are discussed in terms of induced motion and shifts in heading direction and apparent straight-ahead.