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Vision
Published in Anne McLaughlin, Richard Pak, Designing Displays for Older Adults, 2020
Acuity is the sharpness with which a person perceives a visual image. It is a measure of the resolving power of vision, or the ability to see fine detail. Acuity is what is measured with the Snellen eye chart (which may be familiar from the optometrist’s office) and is expressed in terms of two numbers (e.g., 20/10). Figure 2.2 illustrates the Snellen chart. The observer stands 20 feet from the chart and reads as far down as possible. The Snellen acuity score represents the farthest that one can read down the chart. The 20/20 level is what a “standard” person (that is, with “normal” acuity) can read from 20 feet away, but healthy, young eyes often exceed this standard level. The denominator gets smaller to indicate better than normal vision. For example, a person with 20/15 vision indicates that what a normal person can see at 15 feet, that person can see from 20 feet away. Similarly, the denominator gets larger to indicate worse than normal acuity. If a person has a score of 20/200, that person can only see at 20 feet what most people can see at 200 – quite bad vision! A person whose best optically corrected acuity is worse than 20/200 is considered legally blind in the United States. When acuity is low, fine detail and hard edges, what is known as high-frequency information, become harder to see.
Perceptual Impairments
Published in Julie A. Jacko, The Human–Computer Interaction Handbook, 2012
Julie A. Jacko, V. Kathlene Leonard, Molly A. McClellan, Ingrid U. Scott
Visual acuity is the most common measure of central visual function and refers to the smallest object resolvable by the eye at a given distance. It is defined as the reciprocal of the smallest object size that can be recognized. Visual acuity is expressed as a fraction in which the numerator is the distance at which the patient recognizes the object and the denominator is the distance at which a standard eye recognizes the object. For instance, a visual acuity of 20/60 means that the patient needs an object three times larger or three times closer than a standard eye requires. The traditional visual acuity chart presents symbols of decreasing size with fixed high contrast. The visual acuity chart used most often in the clinical setting is the Snellen acuity chart, which is comprised of certain letters of the alphabet; the size of the letters are constant on a given line of the eye chart, and decrease in size the lower the line on the chart. In accurate Snellen notation, the numerator indicates the test distance and the denominator indicates the letter size seen by the patient.
The role of peripheral vision in vertical road sign identification and discrimination
Published in Ergonomics, 2018
Marco Costa, Leonardo Bonetti, Valeria Vignali, Claudio Lantieri, Andrea Simone
The sample was composed by 24 participants, 10 males and 14 females. Mean age was 21 (±1.02). All participants had a normal vision and none wore glasses or contact lenses, since this prevented the eye-movement recording. The participants were undergraduate students of the University of Bologna. All participants had a category B driving license with a mean driving experience of 2.75 (±1.33) years. Participants passed the minimum Italian driver’s licensing criteria for binocular visual acuity (at least 20/20 - 0 LogMAR overall, with not less of 2 missing diopters in the weaker eye) (Italian Highway Code 1992). Left and right eye visual acuity was assessed by a Monoyer Eye Chart at 3 m distance. The values on a decimal scale obtained by the Monoyer Chart were converted to LogMAR units. Mean visual acuity for left and right eyes was 0.05 (±0.18) LogMAR. Participants were given a full explanation of the experimental protocol, and an informed consent was obtained, with the option to withdraw from the study at any time. The research has been approved by the Ethics Committees of the University of Bologna.
Dark mode vogue: Do light-on-dark displays have measurable benefits to users?
Published in Ergonomics, 2022
Before the experimental tasks, participants were tested for normal visual acuity using a Snellen eye chart. The chart was placed on the wall and participants performed the test 10 feet from the chat. Participants also performed a simple ocular dominance test to determine their dominant eye using the thumb test (Heiting 2000). In this test, participants were asked to extend one arm in front of them and place their thumb on a target. Then, participants were asked to close one eye at a time. The eye that keeps the thumb directly in front of the target while the other eye is closed is the dominant eye.
Effect of correlated colour temperature and illuminance levels on user’s visual perception under LED lighting in Taiwan
Published in Ergonomics, 2020
Wei-Cheng Chao, Li-Ying Hong, Min-Chih Hsieh, Eric Min-Yang Wang, Chi-Chin Yang, Li-Chi Su
Prior to the visual perception experiment, all the participants underwent vision tests to assess their visual acuity, colour vision, and colour discrimination to ensure that they satisfied the vision requirements; the tests were conducted using the Tumbling E Eye Chart, Ishihara Colour Test, and Farnsworth–Munsell 100-Hue Test in that order. All the participants gave their informed consent before participating in the formal experiment.