r An Introduction to Human Factors Engineering Second Edition Christopher D. Wickens University of Illinois at Champaign-Urbana John Lee University of Iowa Viii Uu University of Michigan Sallie Gordon Becker Becker & Associates, Palo Alto, California Upper Saddle River, New Jersey 07458Library of Congress Cataloging-in-Publication Data Wickens, Christopher D. An introduction to human factors engineering I Christopher D. Wickens, Sallie E. Gordon, Yili Liu.-2nd ed. p.cm. Includes bibliographical references and index. ISBN 0-13-183736-2 1. Human engineering. 1. Gordon, Sallie E. II. Liu, Yili III. Title. 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Ltd Pearson Education, Upper Saddle River, New Jersey 1098765 0-13-183736-2Chapter Visual T he 50-year-old traveler, arriving in an unfa-miliar city on a dark, rainy night, is picking up a rental car. The rental agency bus driver points to "the red sedan over there" and drives off, but in the dim light of the parking lot, our traveler cannot easily tell which car is red and which is brown. He climbs into the wrong car, realizes his mistake, and settles at last in the correct vehi-cle. He pulls out a city map to figure out the way to his destination, but in the dim illumination of the dome light, the printed street npmes on the map are just a haze of black. Giving up on the map, he remains confident that he will see the appropri-ate sign age to Route 60 that will direct him toward his destination, so he starts the motor to pull out of the lot. The streaming rain forces him to search for the wiper switch, but the switch is hard to find because the dark printed labels cannot be read against the gray color of the interior. A little fumbling, however, and the wipers are on, and he emerges from the lot onto the highway. The rapid traffic closing behind him and bright glare of headlights in his rearview mirror force him to accelerate to an uncomfortably rapid speed. He cannot read the first sign to his right as he speeds by. Did that sign say Route 60 or Route 66? He drives on, assuming that the turnoff will be announced again; he peers ahead, watching for the sign. Suddenly, there it is on the left side of the highway, not the right where he had expected it, and he passes it before he can change lanes. Frustrated, he turns on the dome light to glance at the map again, but in the fraction of a second his head is down, the sound of gravel on the undercarriage signals that his car has slid off the highway. As he drives along the berm, waiting to pull back on the road, he fails to see the huge pothole that unkindly brings his car to an abrupt halt. Our unfortunate traveler is in a situation that is far from unique. Night driving in unfamiliar locations is one of the more hazardous endeavors that humans un-dertake (Evans, 1991), especially as they become older (see Chapter 17). The 6162 Chapter 4: Visual Sensory Systems reasons the dangers are so great relate to the pronounced limits of the visual sen-sory system. Many of these limits reside within the peripheral features of the eyeball itself and the neural pathways that send messages of visual information to the brain. Others relate more directly to brain processing and to many of the percep-tual processes we discuss in Chapter 6. In this chapter we discuss the nature of light stimulus and the eyeball anatomy as it processes this light. We then discuss several of the important characteristics of human visual performance as it is affected by this interaction between characteristics of the stimulus and the human perceiver. THE STIMULUS: LIGHT Essentially all visual stimuli that the human can perceive may be described as a wave of electromagnetic energy. The wave can be represented as a point along the visual spectrum. As shown in Figure 4.1a, this point has a wavelength, typi-cally expressed in nanometers along the horizontal axis, and an amplitUde on the vertical axis. The wavelength determines the hue of the stimulus that is per-ceived, and the amplitude determines its brightness. As the figure shows, the range of wavelengths typically visible to the eye runs from short wavelengths of around 400 nm (typically observed as blue-violet) to long wavelengths of around 700 nm (typically observed as red). In fact, the eye rarely encounters "pure" wavelengths. On the one hand, mixtures of different wavelengths often CD 1. 'a 1 :::J :I:: a. E c 00 0f::-0 S:-0 \3-'1) 4,0 <?-0 400 WAVELENGTH 700 (nanometers) Visual Spectrum (a) FIGURE 4.18 (a) The visible spectrum of electromagnetic energy (light). Very short (ultraviolet) and very long (infrared) wavelengths falling just outside of this spectrum are shown. Monochromatic (black, gray, white) hues are not shown because these are generated by the combinations of wavelengths.