DATA SET 11: Mike Land's Urban Driving Data SetEXPERIMENT DESCRIPTION
Fig 1: Map of Lewes High Street, showing the route taken in the driving clip. From Google Maps.
Fig 2: Record showing driver gaze distribution during two phases of the drive up the High Street: steering through dense traffic (left, gaze is on the oncoming car) and when stationary at traffic lights (right, gaze is on a pedestrian on the left). When driving almost all fixations are on objects on the roadway; when stationary almost all are off-road. N, near-side off-road; P, parked vehicles on near-side; C, car in front; R, on or above open roadway; T, oncoming traffic; O, off-side off road. Grey lines are edges of roadway (kerbs). Each ‘look’ at a particular region usually involves more than one fixation.
Steering round the kind of right-angle corner we encounter in cities is a rather different task from following the curves of a country road. It is a well-rehearsed, rather stereotyped task, with the amount the steering wheel has to be turned varying little from one corner to another. The following account is based on a study of three drivers each negotiating eight suburban right-angle corners. Each turn proceeds in two distinct phases, which we can call orientational and compensatory phases. In the orientational phase gaze is directed into the bend by 50º or more relative to the car, with most of the rotation performed by the neck (head/car in Fig. 3 b&c); meanwhile the eyes fixate various positions around the bend. Once the car turn has begun the neck reverses its direction of rotation (seconds 53 and 9 in the two examples in Fig. 3), and the head starts to come into line with the car. However, it continues to rotate in space for a while, carried by the continued rotation of the car. This is the compensatory phase, so-called because the head rotation counteracts to a large degree the rotation of the car. As can be seen in Fig. 4 the car-in-space and head-in-car rotations are almost (but not quite) equal and opposite during this phase. This strongly suggests that the head is being stabilized by a feedback mechanism in which the vestibular system measures the residual head-in-space rotation, and converts it into a neck rotation command that counteracts the head-in-space rotation (Land, 2004). There is a known reflex, the vestibulo-collic reflex, which operates in just this manner. At about the same time as the neck reverses its direction of rotation, gaze shifts from the entrance to the bend to more distant regions of the road.
Fig 3: Records of two drivers turning the same left-hand urban corner (near-side in UK). The principal feature of both records is the orientation of the head, which rotates into the bend during the first 3 s so that it leads the car’s heading by as much as 70º. Thereafter as the car continues to turn, the neck rotates the head back into line with the car at a speed that is almost equal and opposite to the rate of rotation of the car itself. The effect of this compensatory rotation is that the head direction in space stays nearly constant, rotating by a further 20º as the car rotates through 70º. The effect of this manoeuvre is that gaze is directed to the exit of the bend almost as soon as turning has begun, and remains there throughout the turn. The driver is thus in a position to anticipate potential hazards several seconds ahead. Plain line shows the eye in head angle.
What is critical in getting this manoeuvre right is the timing of the steering action, both when entering and exiting from the corner. Using the view provided by the eye-tracker, it was possible to examine what timing cues were available in the half-second or so before the driver began to steer into and out of the bend. The changes in the appearance of the road-edge (kerb) seemed to be the only cues to provide useful timing information, and which also correlated reliably with the initiation of the steering action (Fig. 4a). In a left hand turn (nearside in the UK) the tangent point slips leftward as the corner approaches (angle α), and steering starts when a reaches between 30º and 40º (Fig. 4b and c left). The cue for straightening up at the exit of the bend seems to be rotation of the nearside kerb in the visual field (angle β). Just before the end of the bend the kerb angle rotates through the vertical in the driver’s view, with α going from acute to obtuse (Fig. 4b and c right). The change of steering direction occurred when this angle reached between 140 and 150º, about half a second after the kerb passes through the vertical in the visual field. Although these may not be the only features involved, there was little else in the drivers’ field of view that was both conspicuous and reliable. Turning right (offside in the UK) is a little more difficult as there are the added problems of crossing a traffic stream and lining up with the far kerb. However, similar cues are also available for this manoeuvre.
Fig. 4: Cues for the timing of steering action when negotiating a right angle corner. (a) Average car rotation profile and steering wheel rotation for three drivers negotiating four left-hand (nearside) corners. (b) In the driver’s visual field the most conspicuous cue for starting the turn into the corner is the increasing lateral position of the tangent point (angle α). At the exit from the turn the vertical rotation of the near-side kerb (angle β) provides a timing cue for reversing the steering wheel direction. (c) Values of α and β at the time that the steering wheel began to be turned left and right, respectively (see (a)). The vertical bars show the standard deviation of the initiation points for all 12 corners. The arrows on the ordinate show the mean values of α and β. Dotted lines on right-hand graph show the time at which the driver’s view of the kerb passes through the vertical.
SCANPATH (EYE-TRACKER) DATA