It should be noted that clinical definitions of acuity are based on controlled tests conducted under ideal viewing conditions—bold black letters on a pure white background near percent contrast , good illumination, no distracting symbols, and no time pressure. By comparison, the letters and numbers on U. As a result, direct extrapolation from acuity testing to feature recognition on bills is likely to underestimate the number of people who will experience difficulty.
Visual-field size refers to the range of visual directions, centered on the line of sight, over which a standardized test target can be detected. Field loss results from damage to portions of the retina, resulting in blind regions in the visual field. The various scenarios shown in Figure illustrate the effects of different types of visual-field loss and are discussed in detail below.
Age-related macular degeneration AMD afflicts many older people and is the leading cause of low vision. Because vision is lost in the high-resolution central portion of the visual field, afflicted individuals must rely on sight in their low-resolution peripheral vision. Figure shows the same photo of New York City's Metropolitan Opera House a number of times—once in sharp focus Figure a and then as it would be seen with various types of visual impairment figures b through e.
Figure b shows the picture with the central field completely blocked, illustrating a severe case of age-related macular degeneration. Typically, reading is impaired, and individuals afflicted with this degeneration require large letters high magnification to read. Some diseases, such as advanced glaucoma or retinitis pigmentosa, can result in the loss of almost all peripheral vision. Only a small island of central vision remains tunnel vision. Figure c illustrates vision with this type of impairment.
Individuals with this form of low vision may have fairly high acuity, but they experience great difficulty in mobility walking or driving , and they have problems in visual search tasks e. Other diseases, such as diabetic retinopathy, can result in patchy vision with losses in a number of areas within the visual field, as illustrated in Figure d. Since it is impossible to accurately portray what vision loss is like for a person with low vision, the illustrations in these figures are meant only to demonstrate the types of vision loss that might occur with various diseases and impairments.
However, it should be remembered that the scotomatous blind areas in these simulations would move with the eye, so, for example, a person with age-related macular degeneration will always have a centrally located blind spot when viewing different areas of the picture. In addition to low acuity and reduced field, a third kind of visual deficit, intensively studied in recent years, is reduced contrast sensitivity see illustration in Figure e.
Figure demonstrates the effects of this type of visual impairment; imagine reading text printed with contrasts of 60 percent "he made plans" , 30 percent "to go camping" , 13 percent "and hiking in" , and 6. Many types of eye disease, such as cataract, can cause a reduction in retinal-image contrast or a loss of sensitivity to contrast by retinal neurons.
The consequence is an effective reduction in the contrast difference between light and dark areas of images. People with normal vision have a substantial tolerance to contrast reduction for many visual tasks. In the case of reading, print contrast can be quite low down to 10 percent before there is much effect on reading speed Legge et al. For many people with low vision, however, and for those with normal aging vision, there is much less tolerance to poor contrast. For such people, even rather small reductions in print contrast can adversely affect reading Rubin and Legge, Two aspects of contrast are relevant to currency design.
Contrast polarity specifies whether the letters are light and the background dark, or vice versa. The contrast polarity of. For some people with low vision especially those with ocular light scatter due to cataracts , acuity and reading performance are better for the light-on-dark polarity, which is a property of present U. More important than polarity is the overall contrast level. Under conditions of poor visibility especially low lighting and long viewing distance , the suboptimal contrast will also take its toll on recognition by normally sighted people.
In addition to the 3. Estimates of the number of Americans with mild forms of visual impairment, referred to here as visually impaired, extend to nearly 9 million Benson and Marano, When viewing conditions are bad often the case for poorly lit indoor settings or at night , the portion of the population likely to have difficulty identifying U.
Under poor lighting conditions, the visual acuity of persons with "normal" vision is compromised, while the visual capabilities of those with mild visual impairments due to disease or the natural cause of aging are further reduced.
Even in the absence of disease, aging eyes are particularly disadvantaged in recognition tasks in poor illumination. For example, the reduced pupil size of an average year-old. This diminished light is then diffused and scattered by opacities in the optical media which increase with age before it reaches the retina, which is likely to be reduced in its ability to detect low contrast features.
The net result is a severe reduction in visual performance under adverse lighting conditions for older people. The committee notes also that special difficulties are encountered by individuals with multiple disabilities.
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New currency features relying on sound would not be accessible to people who are both hearing and visually disabled, for example, the 10, individuals with Usher syndrome in the United States RPFFB, Also, individuals with decreased tactile sensitivity accompanying visual impairment e. It is important to note that normally sighted Americans would clearly benefit in ease of use, especially in conditions of adverse visibility, from most features intended for use by visually disabled people.
Some who are working for the full integration of blind people in American society have expressed opposition to certain special features such as obvious "braille" markings , for fear that these markings would be a ubiquitous signal that special accommodations are required for blind people Maurer, The committee evaluated prospective features with respect to their ability to enhance the recognition of the currency by all users.
The currency identification needs of our target population can be conveniently divided into commercial and daily-living categories.
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A commercial need for currency identification arises for those who are engaged in any kind of retail or other trade in which ability to identify currency is a necessary part of the job. Lack of suitable banknote identification features raises obstacles to employment in such jobs. Daily activities include using currency in many situations, such as purchasing groceries and using public transportation.
Significant experience and insight comes from visually disabled workers who operate cafeterias or vending stands, usually in government-owned buildings, under the Randolph Sheppard Act Business Enterprises Program. Such workers must accept bills rapidly and give out accurate change as a routine part of the job. A blind cashier cannot independently identify bills in a transaction and must rely on the customer. Visually disabled people face problems in identifying U.
For blind individuals, the overwhelming need is for denomination without dependence on a sighted person. For people with low vision, needs vary according to the nature. There are anecdotal stories that some blind people are able to denominate U. Although some people who are "legally blind" have sufficient vision to identify bills, the committee was unable to substantiate through literature search or interaction with representatives of associations of blind people any such claims for people who are blind.
An older person with macular degeneration may have relatively little difficulty in identifying bills at a well lit checkout counter but may be unable to identify bills in a dimly lit restaurant or in a taxi at night. Although denomination of banknotes is the committee's primary focus, it is frequently useful to know the orientation of a bill. Specific orientation of bills is required by some money-changing machines and for stacking purposes by banks.
A currency feature that conveys bill orientation would be useful for such purposes. In both commercial and daily-living situations, successful currency transactions require rapid and accurate denomination of banknotes without the need for lengthy inspection or thought.
To achieve this goal, specification of new or enhanced features should not be aimed at minimal levels of recognition performance i. For example, research on reading has shown that letter sizes should be three to five times larger than acuity values in order to achieve comfortable and rapid reading Legge, Similar consideration should be applied to currency identification features.
This chapter has focused on the difficulties encountered by visually disabled people in currency identification. The design of new visual, tactile, or other features for banknote identification should take into consideration perceptual limitations on discrimination and absolute judgment that limit performance by everyone.
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Discrimination refers to the perceptual ability to compare two physical magnitudes e. The smallest difference that can be reliably discriminated is called the difference threshold. For perceptual discrimination on many physical dimensions, the difference threshold is constant or nearly constant in percentage terms across the range of that dimension.
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This constancy is termed Weber's Law, and is expressed as:. Several examples are shown in Table As an example, according to this table, two weights can be discriminated if they differ by more than 4. The discrimination of length by the sense of touch alone is a very complicated experimental problem because of the variety of sensory inputs a human being uses when trying to identify an object by touch.
It is not clear that this simple form of Weber's law is applicable to the task of distinguishing length by the sense of touch. Some possible features for coding currency denomination, such as size or roughness, can be analyzed in terms of their difference thresholds. In designing a code:. Inherent in discrimination is a comparison between two stimuli. In the case of banknote identification, the comparison may be between two bills based on size, weight, etc.
A second kind of perceptual judgment, called absolute judgment, may be more important to currency identification. Absolute judgment refers to the ability to identify any one of N distinct values along a physical dimension. For example, imagine having N different weights, or N light intensifies, or N loudness levels of a given tone, etc. A human subject has to learn to attach labels to these stimuli so they can be identified when presented on their own. The Weber fraction in these cases decreases as the stimulus magnitude increases, indicating that more subtle changes in visual contrast or tone loudness are distinguishable at higher absolute stimulus magnitude.
He showed that when N is 4 or less, people tend to be accurate in absolute judgment. When N rises to about 7 plus or minus 2 , people begin to make errors. There is some variation across stimulus dimensions.
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The key point is that if banknotes are coded as six points along a single physical dimension such as length, roughness, thickness , people are likely to make some errors in absolute judgment when a single cue is present. That is, if presented with a single bill with no measuring gauge or other bill for comparison , some errors are likely to be made. Recognizing that humans are limited to sets of less than seven in their ability to make absolute judgments is a case for limiting the number of denominations of banknotes in general circulation to no more than the present six, and even fewer would be preferable.
In the context of currency identification, this means that accuracy in identification of six denominations is likely to be improved if two dimensions are used for coding e. This likelihood was confirmed in a demonstration experiment conducted by the committee, which is briefly described in Chapter 4 in connection with the size feature. To summarize the research into discrimination and absolute judgment: 1 Data on perceptual discrimination can provide lower bounds on the step sizes for coding denomination along a physical dimension.
Many visually disabled people must trust others to inform them about the denomination of bills received. Touch-typing should become an automatic skill like changing the gears on a car. Early identification and intervention 33 With good keyboarding skills a child can handle the secretarial aspects of projects and coursework efficiently. In practice this will often make the work easier for him to do.
It will be legible, neater and often of a higher standard. Being able to choose a larger font and different font styles also helps. A font no smaller than 12 point should be used.
Some individuals prefer Arial and younger users like Comic Sans because it looks more like cursive writing. A survey conducted on line Smythe, reported that of 6, voters 28 per cent prefer white, 22 per cent blue and 19 per cent prefer cream backgrounds and 50 per cent preferred Arial font. When the physical slog of writing by hand is removed and the confidence and comfort of the spellchecker provided, often reluctant and restricted writers blossom and their ideas and opinions then flow onto the page.
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