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Traffic signal color recognition is a problem for both protan and deutan color-vision deficients.

Article Excerpt
INTRODUCTION

Approximately 8% of males and 0.5% of females in the population have congenital red-green color-deficient vision. There is little true color blindness (~0.0005%; Pokorny, Smith, Verriest, & Pinckers, 1979). These people have reduced ability to discriminate redness-greenness throughout the full gamut of colors. Most significantly, from a safety point of view, the problem includes the red, orange, yellow, and yellow-green parts of the visible spectrum.

Red-green color-vision deficiencies are subdivided into a number of categories (after von Kries, 1899):

People with dichromasy lack one of the three normal receptors. As a consequence, their ability to discriminate colors is two- rather than three-dimensional. The two forms are protanopia and deuteranopia, lacking the long-wavelength ("red") receptor or the middle-wavelength ("green") receptor; respectively. Their ability to discriminate a red, yellow, and yellow green signal code on the basis of color is absent, and they must rely on the usual brightness hierarchy that yellow is brighter than yellow green, which is brighter than red. The use of a bluish green rather than yellowish green signal solves this problem for them. In addition, in protanopia, red signals are seen as substantially darker and are less alerting. A red traffic signal as seen in protanopia has approximately 25% the luminous intensity as it has for a color normal (Dain & King-Smith, 1981). Protanopia and deuteranopia each constitute about 1% of males.

People with anomalous trichromasy have one receptor altered as compared with a color normal. As a consequence, their ability to discriminate colors is reduced rather than absent in the third dimension. The two forms are participants and 49 color-vision deficient participants, divided into 25 deutans and 24 protans selected according to the criteria shown in Table 1. All participants had binocular visual acuity of 6/6 or better, but to achieve this 11 participants wore (untinted) ophthalmic corrections.

The experimental setup is shown in Figure 1. The participant viewed a fixation target placed in the center of a computer monitor at a distance of 4 m. Simulated single-aspect traffic signals were briefly displayed at small angles to either side of the direction of fixation. The participant's task was to identify the color as quickly as possible. The single light presentation was adopted because the positional clues in a laboratory-based three-aspect lantern would be consistent and significant. In the real driving task the positional clue is not always available.

[FIGURE 1 OMITTED]

The two lights were located 5[degrees] away from the participant's line of sight (10[degrees] apart). The angular subtense of the lights was equivalent to that of a 200-mm traffic signal lantern at a distance of 100 m (2 mrad or 6.9 arcmin). This is the standard Australian practice as detailed by Fisher and Cole (1974) and AS/NZS2144:2002 (Standards Australia International, 2002). The same specifications appear in CIE publications (CIE, 1977, 1980). The lights were created using 20-W, 12-V tungsten halogen globes with appropriate filters to provide the appropriate traffic signal chromaticity coordinates specified in AS/NZS 2144:2002, and the intensity was controlled using neutral density filters. The chromaticity coordinates shown in Figure 2 were calculated according to CIE (1986). The lights were turned on for a maximum duration of 5 s. Rise time to full intensity was approximately 200 ms.

[FIGURE 2 OMITTED]

The backgrounds to these lights were black backboards scaled in accord with the backgrounds around normal traffic lights (Fisher & Cole, 1974; Standards Australia International, 2002). Between the two lights was a computer monitor. Around the monitor and the black backboards was a white matte board. Two fluorescent light tubes illuminated this so that it provided a luminance of 300 cd/[m.sup.2] for the participant. The participant was shielded from a view of the light tubes. Traffic signals may operate over a range of intensity levels. The...