The task of driving involves paying attention to multiple factors such as: direction, speed, other vehicles, traffic signals, detours, etc., a series of elements in which vision plays a fundamental role.

In this article we will try to give you a "technical" explanation of how the visual perception processes the information coming from outside to calculate the direction of the vehicle, both on a straight line and in a curve.

Vision to drive on a straight

If we drive on a straight road, the tracks that guide us or guide us, are the lateral and central lines and the vanishing point of the sides of the road when we look straight ahead.

It is about keeping the vehicle at a constant distance between the center line that separates the two directions of the road and the lateral line. Still circulating in our lane, if we move slightly to one side or the other, getting closer to the central line or the lateral one, the vision of the references varies, as we see in the following figure, taken from an English article and therefore where you drive on the left.

Circulating under normal conditions in (a), within the limits of the lane in (b) and (c) and, in a course parallel to the median line but offset from the center of the lane.

It is admitted that the references that we use regarding what happens in front of us, reaches a limit of 30-50 meters, beyond the data that appear on the scene are less significant.

The speed of driving, that is to say, the dynamism that the driving supposes, will be given by the speed of approach of the objects that are ahead and by how we perceive the central dashed line, if we still see it as discontinuous or it has already become a continuous line, which indicates that we exceed 90 Km / h.

These are clues that we use unconsciously while driving, just as the angle that forms our line of sight with the vanishing point of the road, is what is known as "visual information flow" (Warren and Hannon, 1988) .

Driving on a curve

In this case we do not have a vanishing point as a reference, we are guided by the direction of the median line, the distance to the median and lateral lines of the road, 25º and 50º respectively, and the tangent that describes the curve, as shown shown in the figure.

The driver must take a reference point, P, generally between 3 and 10 meters, and mentally calculate the angle θ between that point and the current direction, H. We do the calculation according to the formula:

1 / r = (2 sin θ) / D

As driving is dynamic, the flow of visual information is again essential to calculate the speed and readjust the angle θ in a continuous way.

It is evident that the situation will be very different depending on the radius of the curve, whether it is constant or variable.

• Stable radio curve: It is easy to set the angle θ and keep it throughout the curve travel
• Variable radius curve: We must calculate the angulation at all times. In these cases, a continuous adjustment must be made based on the tangent to the curve, starting from the driver's eyes, θA, and the distance to the side of the curve, θB (see figure). 

It seems that the tangent line would be fixed with the taint or regions for maculae, and the lateral line, with the retina peripheral

In driving the eyes are aligned with the head, so that before a curve, we move the head but not the eyes, we look for the tangent with the head and only in cases of very sharp curves, such as when turning a corner in driving urban, we combine both movements, we move the head about 50º and ampWe make the total angle, up to 90º, with the movement of the eyes.

One of the least studied aspects, but which seems to be of significant importance in the drawing of a curve, is the centrifugal force that is exerted on the head and the stimulus that is generated in the semicircular canals of the ear. These effects help us calculate the speed and radius of the curve. This fact is precisely one of the weak points of the driving simulators that were intended to be used for the practices of those who learn to drive or even for professional drivers. Not having the signal from the ear canals distorts the reality of driving, reducing the effectiveness of the simulators, which is why they have stayed to know a circuit or just for fun, although we know that there are important brands that are already trying to incorporate the centrifugal force was missing.