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Welcome to the course Ergonomics in Automotive Design Now, we are going to discuss our 5th module that is in-vehicle and external visibility of the driver So, under this module, we will discuss four topics; first one – human field of view, second ñ driverís field of view inside vehicle and outside vehicle, third one – field of view through windshield and windows, and fourth one – field of view through mirrors; side mirrors as well as rear-view mirror Now, first, we should know; what is field of view? So, while we are discussing about human field of view So, we need to understand; that what is field of view? So, as per the definition, we can define field of view as the region or extent of the external world or space which is visible at an instant during steady fixation of gaze in one direction So, when we are looking at a particular direction, at that time, the extent of the external world which we are perceiving through our eyes, that is the field of view Now, according to Society of Automotive Engineers (SAE), J standard, J985, the extent of visual field; if we look to this figure then the; for left eye If we consider the left eye, the monocular field of view, means, only by left eye, we can see 150 degree So, starting from one side; left side, up to 90 degrees, that is the mid-line, straight forward line, and across the nose, we can see another 60 degree So, this side 90 degree, and so, first portion, this is 90 degree and after that another 60 degree So, total 150 degree, this is the monocular field of view for left eye Similarly, for the right eye, from the side-line, we can see up to 90 degree on the same side; right side and across the nose, we can see another 60 degree So, total 150 degree So, this is the monocular field of view for the left eye, and this is a monocular field of view for right eye Then, the overlapping area So, this middle portion, this is the overlapping zone So, the size of the overlapping zone, that is the binocular field of view, that is 120 degree So, whereas, monocular field of view for both the eyes is about 150 degree, but the binocular field of view 120 degree Now, so, one aspect is monocular field of view while we are visualizing the external world by either left eye or right eye While we are looking the external world; the common zone for both eyes; right and left that is called binocular field of view The third area; that is the ambinocular field of view, that is actually the sum of field of view, for the both eyes So, both for left eye and right eye; total how much area we can see, that is the; from this point to up to this much, means, 180 degree; where there is only by the left eye, only by the right eye; at the same time both left eye and right eye So, monocular field of view, binocular field of view and then again monocular field of view for the right eye So, this total zone is defined as the ambinocular field of view Now, binocular field of view; vertically if we consider, then it is 50 to 55 degree upward and 60 to 70 degree downward So, downward field of view is more Binocular field of view; as defined by the Henson (1993), it is 60 degree vertically, 25 degree up and 35 degree down Now, if we see the perspective view of binocular field of view, earlier what we were discussing, that was the horizontal field of view, but if we consider both; horizontal field of view as well as vertical field of view, then how much is the binocular field of view? So, if we look at this image So, this is the left eye, and this is the right eye For left eye; this is the monocular field of view for the left eye Similarly, for the right eye; this is the monocular field of view, then the middle portion, this common zone, that is called binocular field of view for the both eyes

So, what is the comfortable viewing distance? Comfortable viewing distance is approximately 50 centimeters, while the character height or the font size is 3 to 4.3 millimeter Centre for Disease Control, USA in 2000, prescribed that comfortable viewing distance ranges between 46 centimeter to 76 centimeter away from the eyes for visual display unit workstation Now, we are moving to the human field of view; the visible spectrum of electromagnetic radiation From this image, we can see electromagnetic spectrum Out of this, only this zone, that is starting from 380 nanometer to 760 nanometers, within this range of electromagnetic radiation human can see object So, human eye is sensitive within this electromagnetic wavelength So, that is 380 to 760 Now, to understand human field of view, it is very important to understand the anatomy of eye, different parts of the eye, that how light enters inside the eye and image is formed So, for that purpose, now, we are going to discuss about the anatomy of eye So, if we take the cross-section of eyeball, then what we can see? There are mainly three layers So, the innermost layer, you can see in yellow color, here, that is the retina Next, there is another layer called choroid, then the third layer is the Sclera So, when we see from the outside, that white portion of the eye, that is actually the Sclera Now, from the front portion, the outermost layer of the eye, which is visible from the outside, that portion is actually, this is that one, so, that is called Cornea So, first one is the cornea, after that there is another, this is, this zone is called Pupil So, how Pupil is formed? There are actually Iris muscles; two types of Iris muscles are there So, one is a radially arranged and another is concentrically arranged So, Iris muscles, at the centre of the, this Iris muscle arrangement, there is a hole, that hole is called Pupil So, this Pupil is actually, the diameter of the Pupil is maintained by the muscle tone of the Iris muscles So, while the radial Iris muscles constrict, then the diameter of the Pupil increases, whereas, concentric Iris muscles contract, then the diameter of the Pupil reduces So, behind the Pupil, there is a Lens and Lens is actually suspended through suspensory ligament and attached with this ciliary body So, ciliary body and ciliary ligaments actually hold the, this is the Lens So, from the outside So, first portion is the Cornea, then there is a chamber; liquid field chamber, that liquid is called aqueous humor; after that there is a hole, that hole is called Pupil, then there is the Lens, and after the Lens, there is another chamber, that chamber is filled of jelly like material that is called vitreous humor So, outside chamber, that is filled with aqueous humor and inside chamber is filled with vitreous humor Now, when light rays enter from the outside, then it actually passes through; first, cornea, then enters to the Pupil, then from Pupil, it enters through the Lens, and then vitreous humor and ultimately falls on the Retina And while the light rays is falling on the Retina, then there is some electrochemical changes, then it leads to electrical potential and that information goes to brain and perception about the image happens So, on the Retina, there are different types of photoreceptor cell, generally, two types of photoreceptor cells are; these are called rod cells and cone cells We will discuss in subsequent slides Now, as I mentioned, the earlier slide So, from any object, say for example, one object is presented, its top portion is ëaí and bottom portion is ëbí So, from that object, light rays enter through the Cornea, then passes through the Pupil, then through the Lens, and ultimately falls on the Retina, and on the Retina inverted image is formed So, ëaí was up and ëbí was down; here ëb dashí and ëa dashí So, it is one inverted image is for me So, light rays enter and passing through different segments, and ultimately falling on the Retina and in the Retina, there is photoreceptor cells, where the photoreceptor cells, there is generation of electrical potential and that impulse transmitted towards the brain And now, important aspect is this zone The point on the Retina, towards the nasal side, with the nasal, towards the, at which

blood vessels and nerve fibers pass by, is called Blind spot No image formation occurs in this particular zone So, we are going back to the earlier image So, this particular area, this area is called Blind spot because the nerve fibers and blood vessels are passing by through this area, and there is no photoreceptor cells As there is no photoreceptor cells, so, there is, for example, if light rays comes like this, and falls on this particular area, then there is no formation of image because there is lack of photoreceptor cells So, that is mentioned here So, what is Blind spot? So, Blind spot is the point or is the area on the Retina, where there is no rod and cone cells and the through that particular area blood vessels and nerve fibers are passing by and that area is mentioned as Blind spot Now, there are various intrinsic muscle inside the eye Apart from that, there are extrinsic muscles, which actually regulates the eye movement So, if we look at these two images So, eye have different types of movements So, one is abduction, another is adduction So, adduction and abduction, means, this, towards lateral side or medial side; these type of lateral or medial movement of the eye happens with the help of medial rectus and lateral rectus muscles On the other hand, up-down movement of eye, that is the elevation and depression, it happens by, with the help of these two muscles So, one is called superior rectus, and another is inferior rectus So, superior and inferior rectus, here it is also mentioned; superior or inferior rectus, when superior or inferior rectus muscles contract, then what happens? The eye moves upward and downward On the other hand, rotation of eye happens, when there is the constriction or contraction of superior oblique muscle as well as inferior oblique muscle Superior or inferior oblique muscle is attached with the eyeball in such a way, when this muscles contract, then eye actually rotate So, understanding of the eye movement is also important for understanding the human field of view as well as in this automobile design, the driverís field of view The Cornea, the humours, as we mentioned, the first chamber, the first outside chamber, where this liquid is filled, called aqueous humor So, this portion, the Cornea, the humours and the Lens are the main refractive apparatus of the eye So, these are the main refractive apparatus The refractive power of the eye is measured in terms of diopters, this is the unit of the refraction capability of the eyes The eye has a single lens of 17 millimeter in front of the retina It has refractive power of 59 diopter So, the eye have total refractive power of 59 diopters About 48 diopters of the eyes, total refractive power is due to the cornea So, only due to the cornea, the refractive power of the eye is 48 diopters rather than the lens because the outside air, its refractive index is 1, then the corneaís refractive index 1.38 So, there is huge change in the refractive index between these two mediums; air and the cornea So, at this point, maximum refraction occurs So, that is why, the total refractive power of the eye that is 59 diopters; out of this 48 diopters refraction happens only due to cornea So, in this image various parts of the eye and their refractive index are mentioned Now, due to the refract; variation in the refractive capabilities of the eyes, there different scenario or different situations happen, like, if the eye condition is normal so, that is called normal or emmetropic eye, where parallel light rays focused sharply on the retina So, while parallel light rays are coming and entering through the cornea, then pupil, then lens and ultimately it is falling on the retina, so exactly properly, it is falling on the retina So, this type of; if it is properly happening; that parallel light rays are coming, and it is ultimately projected on the retina, then that type of our eye is called normal or emmetropic eye Next, category is the hypermetropic eye or farsightedness; in this case what happens? Parallel light rays enter inside the eye but form the image or focused behind the retina So, this is the retinal surface, it is forming the image behind the retina So, this type of situation is called hypermetropia; another condition, we call it myopia and the eye is called myopic eye; it is also known as nearsightedness When parallel light rays are focused at a point, some distance, in front of the retina So, this is the retina surface but actually the parallel light rays are focused to some

extent forward of the retinal surface So, this type of phenomena is called myopia and that eye is called myopic eye Now, for this type of condition; how it can be corrected? So, for that purpose, different types of lens are used So, one; we can correct this type of hypermetropic eye with the use of convex lens While we are using convex lens, then convex lens direct the parallel light rays in such a way, so, that it can form the image on the retinal surface On the other hand, in case of myopic eye; what is happening? The image is actually forming in front of the retinal surface So, in that case, if we use concave lens; earlier case it was convex lens; now, if we use concave lens, then what is happening? That parallel light rays actually focusing on this retinal surface So, this type of hypermetropic eye or myopic eye can be corrected with the help of different types of lenses Now, we will discuss about the accommodation; what is the accommodation for eye? The lens can change its refractive power So, lens has the capability; it can change the refractive power; how? By changing its shape or the focal length The lens can change its refractive power by changing the focal length; enabling light from both distant object as well as from the nearer object; it can focus sharply on the retina; this process is known as accommodation So, lens has the capability to change its focal length and focusing the light rays; either parallel light rays or divergent light rays, it can focus in such a way, so, that the image is formed on the retinal surface or the light is properly focused on the retinal surface and particularly in the foveal area, while eye movement is happening Now, in this accommodation process; how lens actually reacts? So, while divergent light rays are coming from the near object So, this type of lights are coming, then how is the lens shape? Lens is in spherical shape, at that time lens is spherical Due to spherical shape, that divergent light is refracted more and falling on the retinal surface On the other hand, while parallel light rays are coming from the object at longer distance, then lens changes it is shape to a flatter one; flat shape Then, the light rays are focused on the retinal surface So, in this way, lens can change its shape and helps in focusing the light rays on the retinal surface So, an eye with normal accommodation capability can focus on object located at a long distance, that is far away or infinity to objects as close as 90 millimeters; means, 9 centimeters So, far distance; we can see infinity distance On the other hand, as the near distance, we can see as close as 90 millimeter or 9 centimeter Now, on the retina, there are different types of photoreceptor cells; one is rod cell; another is cone cell So, this is the schematic representation of rod and cone cells Based on the intensity of light, the activity of rod and cone cells changes So, during daylight, while the or bright light condition, that is called photopic vision, mainly cone cells become active On the other hand, while there is low level of illumination, during night, then that type of vision is called scotopic vision and that vision is actually perceived by rod cells So, for photopic vision or daylight vision or bright light vision it is actually done by cone cells On the other hand, night vision or dim light vision happens using rod cells, that is called scotopic vision But in between, there is, during dusk or dawn, when there is relatively low illumination level, then we call that vision is mesopic vision and that during mesopic vision; both cone cells as well as rod cell participate In our eye, on the retina, there are about 125 million rod cells scattered across the different parts of the retina, except foveal region, that foveal region is the specific region on the retina, so, that is very important because, there is the; again, we are going back to this image So, if we look at this particular image, then this area; little bit depressed area on the retinal surface which is on the visual axis So, when light rays enter this visual axis, actually light comes on this particular depressed area on the retinal surface This point is called fovea centralis or foveal zone, where there is maximum number of or

most densely packed cone cells and this is most clear vision or visual clarity is possible in this area, that is called foveal area Now, about 70 million cones are densely packed in foveal region So, the densities 140,000 cones per millimeter square Now, fovea with greater temporal and spatial resolution due to its cone cells; acquire information faster than in the peripheral parts of the visual field So, as in the foveal region, cone cells are densely packed So, it has the greatest temporal and spatial resolution, and it has the capability to process the visual information faster Now, if we consider the visual acuity; but first, we should know, what is Visual acuity? For a fixed gaze angle and a focus distance, visual acuity is defined as the angular separation between two just perceivable points So, while we are looking at a particular point or fixing our eyes at a particular focal distance, then visual acuity is defined as the angular separation between two just perceivable points, as defined by Stenstrom (1964) Now, in details, if we try to understand; what is visual acuity? So, as we mentioned; the foveal region with cone cell it has the maximum visual acuity So, now, if this is, if you consider So, this is the distance from the fovea So, this is the center point; these 0 degrees, it is a foveal region From the foveal region, if we move towards the periphery, that is the, towards temporal retina, means, and another is the nasal retina; either towards nasal side or towards the temporal side If we move, with the increase of the angle; view cone angle; what is happening? The density of the cone cells at the foveal region; 0 degree, this is the straightforward line or that is the visual axis So, around that visual axis, near the 0 degree, the concentration or density of the cone cell is the maximum So, at this point density is the maximum As it was; we mentioned earlier, 140,000 cone cells per millimeter square region After that, drastically, the density of the cone cells reduces towards the periphery but in case of rod cells, the density is maximum, in this zone There is no rod cells at the foveal area but after that, the density of the rod cells gradually increases and it is maximum in the area of 20 to 30 degree and then gradually it reduces towards the periphery And towards that nasal retina, what is happening? The density of the rod cells increases and there is no, as we mentioned, in the blind spot region, there is no rod cells or cone cells; after that, again the density increases, increasing and gradually it is reducing So, the density of the cone cells is maximum at the 0 degree or 1 to 2 degree of the foveal area So, at the fovea; 1 to 2 degree within this zone the concentration or density of the cone cell is maximum, and there is no rod cells Then, from that centre point if we move towards the periphery; in both the direction, the density of the cone cells reduces but in case of rod cell; what is happening? The density is maximum within the area of 20 degree, from the center point of fovea So, both the sides; 20 to 30 degree; the density of the rod cell is maximum, then it gradually reduces So, due to this type of distribution of rod and cone cells, visual acuity also differs So, visual acuity is maximum within this zone, in this image, it is shown field of view eccentricity from the fovea So, if we consider, this is a foveal region; from the fovea if we go two degree both sides; within this region, the visual acuity is the maximum So, visual acuity within the 2-degree angle of fovea, it is maximum, that is 1; visual acuity Then, from 2 degree to 20 degree; within this zone, the visual acuity, where there is also; there is concentration of rod cells are increasing and that is the maximum, within this zone, as we mentioned So, that region, it has the visual acuity of 0.3 After that, from 25 to 45 or beyond that, it is drastically reducing, it is 0.1 So, maximum visual acuity is possible in the center point of the fovea, and gradually,

it is reducing towards the periphery So, visual acuity; maximum at the fovea centralis, and then reducing gradually, as I mentioned So, 0.3 from 2 to 20-degree angle and from; after that, it is only 0.1 Now, if an image on the retina is perfectly stationary, means, if eye is not moving for over a second, then what happens? The image gradually fades away, as mentioned by Yarbus (1967) So, for that purpose, human eyes always move little bit and rapid fixation happens This small size rapid fixation is actually; we call it dwell or fixate on a visual detail for about 200 to 300 milliseconds So, always, while we are fixing at a particular point, but our eyes gradually moves, and makes very small fixations, which is known as dwells for the duration of 200 to 300 millisecond and then eyes move a very rapidly; microsaccades happens So, this type of dwell movement for the duration of 200 to 300 millisecond actually helps in refreshing the visual image, otherwise that image will be faded away Movement speed of the eye between fixation is very fast So, from one point to another point, when eye is; eye fixation is happening, then eye movement happens at a very fast speed So, from about 200 degree per second for 5-degree eye movement When, there is requirement of 5-degree eye movement, then, eye movement speed is 200 degree per second On the other hand, when there is movement of 20-degree eye movement, then eye movement speed is 450 degree per second About 5 to 20-degree eye movement take place within the time frame of 20 to 70 millisecond So, for 5-degree eye movement, have, it takes time 40 millisecond; on the other hand, 20 degree eye movement takes the time 70 millisecond Now, on the retina, as we mentioned, in the foveal area, there is the maximum density of cone cells, there are different types of cone cells, that cone cells helps in colour vision and the sensitivity of the cone cells for different wavelengths of lights are also different So, there are mainly three types of cone cells So, one is; red sensitive cone cells, another is green sensitive cone cells, another is blue sensitive cone cells So, colour vision characteristics and colour perceptions are related to relative sensitivities of these cones of different wavelengths of light If we look at this image So, from starting from 400 nanometer to 700 nanometers, within these wavelengths, there are different areas, where blue cones are got activated; similarly, this is for green cones and similarly, for, this is for red cones So, there, this is the sensitive zone for the blue cone; similarly, for green cones the wavelengths is also different; it is sensitive within this zone, from this point to this point, and for red cones, this is from, the wavelengths varies from this point to this point, and peak sensitivity at this points, and this dotted line showing the wavelength sensitivity for rod cells Now, Grandjean (1988) mentioned three types of human field of view; one is distinct or foveal field This foveal field is the viewing angle of 1-degree foveal area, while the human being is fixing their eyes at a particular point So, there a, that line connecting from the eye to that particular point, that is the line of sight or line of gaze, around that 1- degree foveal area is actually very good for visibility and where very distinct vision is possible, that is called distinct or foveal field So, here it is shown, say, if this is the eye So, this 1-degree angle is actually very sensitive for the vision So, that area is called distinct or foveal field, then from 2 degree to 40 degree, within this view cone, this is called middle or central field of view So, there is, that is also good for visibility but not as good as distinct or foveal field After that, if it is beyond 40 degree, that is called outer or peripheral field So, beyond 40- degree eccentricity angle from the visual axis, this zone is called outer or peripheral field, where visibility or visual acuity is relatively less, only the objects which have some movement is perceived by eye Now, colour perception in the field of view In our field of view, the whole field of view is not equally sensitive for all the colors

The size of the visual field varies on the color, it is largest for yellow and blue and smallest for the green So, if this is the center point, means, this is the foveal; fovea, if we move; left-right or up and down, then with the changes in degree, the, so, this is the location of blind spot So, within the view field, the viewing zone for different colours or sensitivity to different colours within the, our view field, is different So, these are the different area, it is shown So, this area is actually sensitive for red colour, then this one is for green, it is almost 15 degree up-down and so, this is actually shown for the right eye; in case of right eye, so, this is the green sensitivity zone for view field Similarly, this is for red, similarly, this is for blue and these dotted lines showing the yellow sensitive zone So, within the view field, all the points or all the areas is not equally sensitive for different types of color Now, for a driverís license, in most of the states in United States, what are the criteria, we are discussing The minimum visual field requirements; a person with two functional eyes; the field of view – 140 degree horizontal should be there, for getting the license A person with one functional eye; field a view – horizontal should be 105 degree The minimum visual field requirement – uncorrected far visual acuity score of 20 by 40 to qualify for an unrestricted license On the other hand, for restricted license – corrected far visual acuity, corrected far visual acuity is 20 by 50, then that person can qualify for restricted license So, this type of, based on the field of view and visual acuity license are actually issued in United States Now, after discussing various aspects of human field of view or driverís field of view, now, we are moving to a field of view of the driverís; inside and outside of the vehicle Target of the automobile designer is to provide 360-degree field of view to the drivers seated on the driving seat, means, both direct and indirect view, it should be almost 360 degree So, the driver can see all around and can ride the car safely Driverís direct field of view and driverís indirect field of view; driverís direct field of view happens through forward-view, through the windshield Then looking back, through rear-window; side views through the side-windows So, by neck movement as well as eye movement, so, driver can directly visualize the external world through the windshield side-view mirror, side windows and back-side windows Apart from this direct view, there is also indirect views So, for indirect views, the driver can use inside mirror or rear-view mirror, then outside mirror for side-view and using different types of display screen, with the help of camera So, both direct and indirect view field is possible So, while we are discussing about the view field, then in that view field, there is also visual obstruction or obscuration due to presence of different vehicle components or other objects So, visual obstruction or obscuration in the driverís field of view happens by vehicle structure and components such as A pillar, B pillar, C pillar or different types of mirrors particularly rear-view; inside rear-view mirror, side-view mirrors, then instrument panels may also create visual obscuration Steering wheel rim, the upper portion of the steering wheel rim, then hood, then lower edges of the window opening, that is the belt line, and headrest of the backseats So, all these vehicle components may create the obscuration in the view field Now, if we look at this image, assume this is a vehicle under consideration, that is the subject vehicle and this is the position of the driver and around that vehicle, there are other vehicles in right-side and left-side lanes So, this is the vehicle R1 and R2, on the right lane Similarly, this is the L1 and L2, another two vehicles on the left lane and this is a vehicle which is following the ëSí vehicle or subject vehicle So, this is located just behind the subject vehicle Now, how is the visibility of the driver? So, driver at this driving seat, he or she can see direct field through the windshield So, this is the direct field of view through the windshield; forward view

Similarly, this is the area, direct field of view through right-side window; right-side front window Similarly, this is the zone for the direct view through left-side window Now, this portion, while the drivers looking at the side mirror, then he or she can also see directly 70 degree right peripheral field So, during looking at the side-view mirror, then there is also direct visibility of the outside, through the windows, that is actually mentioned as 70-degree peripheral field So, this peripheral field, it is also present on the left-side So, while driver is looking at the left-side side-view mirror, then directly he can see this area, through the side view mirror So, this is mentioned as the peripheral field So, it is also 70 degree So, direct forward-view, this is direct side-view, at the same time, this is direct peripheral view; this is direct peripheral view Apart from this using different types of mirrors; side-view mirror and rear-view mirror So, using this right-side side-view mirror, drivers can see this area By the help of right-side mirror, he can see, this zone Using the rear-view mirror, inside rear-view mirror, this zone is visible to the driver So, inside mirror field; this is the left mirror field, and this is the right mirror field So, if we see, so, ultimately almost 360-degree area is visible for the driver Only some portion is obscured by A pillar, B pillar or C pillar So, in this way, by direct visibility or indirect visibility, through different types of mirrors, actually helps the driver to visualize almost 360 degree around that driver during driving So, due to this type of visibility, here you can see, either at least some part of the vehicle is visible to the, suppose R1, this much, this part is visible to the driver Similarly, for L1, this part is visible, through the, whole portion is actually visible through the peripheral field of view So, using peripheral field of view, driver can see L1, similarly, using the peripheral field of view as well as the side-view mirror, he can see, that, these two portion of the R1, R2; it is visible through a rear mirror view field, this vehicle is visible using this inside mirror field and vehicle L2, it is actually visible through the left mirror field So, this is during day condition but in the night condition also; either the headlamp of the following vehicle or the vehicles on the side lanes, otherwise at least the side indicator lamp, the indicator lamp on this side, it is also visible So, due to this type of mirror arrangement; in the day daytime as well as in the night time, at least some part of the vehicle or the vehicle light are visible to the driver, and accordingly he can navigate his vehicle in relation to other vehicles Now, driverís field of view is influenced by various factors; one factor is the characteristics of the driver So, drivers eye location is very important; where drivers eye is positioned? So, it is actually depending on the driverís anthropometry, then accordingly seat adjustment So, drivers eye location has been defined by SAE J standard 941, by the eye ellipse So, eye ellipse, we discussed in our earlier modules, what is eye ellipse So, from the eyellipse we can understand, that how much will be the visibility by the driver Then, visual capability of the driver; visual acuity, accommodation capability, visual contrast threshold So, these factors also affecting the visibility or driverís field of view So, visual acuity gradually reduces with the age, for the older driver due to cataract and other problems there also loss of visual activity On the other hand, with the age, accommodation capability of the lens also reduces, then eye and neck movement is also important for maintaining the field of view Then information processing capabilities of the driver, that is also affecting, then, age of the driver; as we mentioned; with the age visual capability of the driver changes and accordingly it affects the driverís field of view