Foveal vision

The GIE Standard Observer. The CIE standard observer is a set of curves giving the tristimulus responses of an imaginary observer representing an average population for three primary colors arbitrarily chosen for convenience. The 1931 CIE standard observer was deterrnined for 2° foveal vision, while the later 1964 CIE supplementary standard observer appHes to a 10° vision a subscript 10 is usually used for the latter. The curves for both are given in Eigure 7 and the differences between the two observers can be seen in Table 2. The standard observers were defined in such a way that of the three primary responses x(X),jy(X), and X), the value ofjy(X) corresponds to the spectral photopic luminous efficiency, ie, to the perceived overall lightness of an object. 

Fig. 7.1. The useful visual field and peripheral vision. The entire visual field covers 180-90° to either side. High-resolution foveal vision extends about 2.5° to either side for a total useful visual field of about 5°. Peripheral vision operates outside this region...

Figure 7.4 shows a typical scanning pattern of a mammographer searching a breast image. Each dot represents a fixation or where the eye directs foveal vision. The lines represent saccades or the jumps that the eyes make between fixations and reflect the order in which the fixations were generated. 

Rods are long and thin, and are more concentrated towards the periphery of the retina. As seen in Fig. 5.2, the maximum density is at 25° eccentricity, and decreases towards the outer edges of the retina. Rods only have one type of photopigment and can therefore only detect differences in luminance (i.e. these see only in monochrome). During night-time, when illumination is low and the iris wide open, the rods are used for vision (called scotopic vision). Peripheral vision in a dark environment is much better than foveal vision due to the low distribution-density of rods in the central part of the human eye. However, rods are about two-and-a-half times more sensitive than cones (Fig. 5.3, after data published by ) szechy and Stiles, 1982, p. 256). They do not contribute to photopic vision because of over-exposure when illumination is high (a process called bleaching). 

Test-object illuminance, contrast between the test object and its background, time of viewing, and other factors greatly affect visual-acuity measurements. Up to a visual distance of about 20-ft (6-m) acuity is partially a function of distance, because of changes in shape of the eye lens in focusing. Beyond 20 ft it remains relatively constant. Visual acuity is highest for foveal vision, dropping off rapidly for retinal areas outside the fovea. 

The direction of our visual gaze is a most important tool for understanding attention. This is because we gather most of our visual information during the fixations, and because to resolve details we need foveal vision. This is even imbedded in our language in the figure of speech "look here" when we want to direct a person s attention to a specific object. Thus, our visual system becomes a critical mechanism in selecting objects for attention. The selection process is reflected in the eye movements and the objects on which we fixate. 

Keywords Foveal vision Peripheral vison Optical flow Combined fields of view Ergonomics Safety Commercial vehicles Camera monitor system Mirror replacement... 

The examples show that the two types of vision serve different purposes. With foveal vision, perception is focused onto one point In humans, this point is often the object that is actively perceived, or the object on which we concentrate. This is not the case with peripheral vision Perception in the periphery is normally of a subconscious nature. Both types of vision may he regarded— to the extent that any comparison between the two could be usefiil— as equally important. Without foveal vision, it would be impossible to identify an object or, for example, read a book. Without peripheral vision, humans would be virtually blind and unable to orient themselves in 3-D space [16]. The properties of foveal and peripheral vision are collated in the Table 1. 

Human perception utilizes the advantages of both types of vision. Unless we intentionally scout objects in the far distance, the process usually involves the peripheral detection of objects and then the identification of these objects with foveal vision. One thing to note here is that the pre-selection as to which objects we should focus on with foveal vision is made subconsciously in the periphery. The decisive factors for this pre-selection process comprise the intensify of the stimulus (the more intensive the movement/brightness of the object, the more likely it is for us to focus on it), as well as the expectation and experience of the respective person. 

The far point is extremely important for human orientation. Foveal vision is naturally often directed towards the far point (the endpoint in the direction of movement). The optical flow runs evenly towards or away from this point. 

Consequently, the currently used mirror systems entail that the surroundings have to be monitored through foveal vision (also demonstrated in [19] [20]). This, in turn, means that drivers using the current mirror systems must deliberately direct their sight to the respective rnirror in order to see the areas to the side and back of the vehicle. This is not an issue for the primary rear view mirror in the buck because it is directed into the distance (to the rear) and thus corresponds perfectly to the evolutionary purpose of foveal vision, namely the targeted localization and perception ( spotting ) of distant objects (near the far point). 

However, the peripheral detection of objects in the wide-angle mirror is unlikely and even less likely in the close proximity mirror. In wide-angle and close proximity mirrors, the driver s task, namely the reliable, random detection of objects in the vicinity (as described above in the example with the hare), which would ideally be accomplished with peripheral vision, must now be completed with foveal vision, i.e. with a conscious and time-consuming look at the respective mirror (see Fig. 6) [9]. 

Since it is only possible to focus in one viewing direction— foveal vision cannot work in a parallel fashion— the successive inspection of all individual mirrors requires a certain amount of time. The driver needs, for example, at least 2 s to check the three mirrors on the passenger side [19]. In the meanwhile, at a speed of 30 km/h, the truck has already moved about 17 m forward (by way of comparison the prescribed length for a class V field of view is currently 4.75 m, which would have been exceeded 3.5 times in this timeframe). Especially in complex trafiic simations, drivers are forced to limit themselves to the fields of view that they need... 

The decision as to which mirror should be looked at is based on the objective by nature, i.e. it is motivated by foveal vision. In studies that tracked the eyes of volunteers in real trafihc, the following has been observed and summarized ... 

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