Shankaran Ramaswamy

Ability of the D-15 panel tests and HRR pseudoisochromatic plates to predict performance in naming VDT colors

Color codes in VDT displays often contain sets of colors that are confusing to individuals with color-vision deficiencies. The purpose of this study is to determine whether individuals with color-vision deficiencies (color defectives) can perform as well as individuals without color-vision deficiencies (color normals) on a colored VDT display used in the railway industry and to determine whether clinical color-vision tests can predict their performance. Of the 52 color defectives, 58% failed the VDT test. The kappa coefficients of agreement for the Farnsworth D-15, Adams desaturated D-15, and Richmond 3rd Edition HRR PIC diagnostic plates were significantly greater than chance. In particular, the D-15 tests have a high probability of predicting who fails the practical test. However, all three tests had an unacceptably high false-negative rate (9.5-35%); so that a practical test is still needed.

Repeatability indices for the Farnsworth D-15 test.

The repeatability of the D-15 color-vision test is considered to be excellent. However, this conclusion is based on a subject pool which contained a large percentage of color-normals. This type of sampling could bias the repeatability results because color-normals rarely fail the test. Furthermore, color-normals usually do not perform the D-15 in the clinical setting. To establish the repeatability of the D-15 for a relevant clinical population, we examined the D-15 results from two different sessions for 116 subjects who had a congenital red-green color-vision defect. The kappa coefficient for intersession agreement indicated that approximately 84% of the subjects obtained the same pass/fail results at both sessions. The type of defect was repeatable on approximately 80% of the subjects. Although the repeatability of the D-15 for color-defective subjects was good, it was lower than the near-perfect agreement reported previously. The coefficients of repeatability for the crossings show that if a person makes less than five crossings then the test should be administered again in order to ensure that the test result is repeatable.

Repeatability indices for the Adams D-15 test for colour-normal and colour-defective adults.

Purpose: The Adarns desaturated D‐15 test was administered to individuals with normal colour vision or with congenital red‐green colour vision defects to establish the repeatability of the test.

Does dichromatic color simulation predict color identification error rates

Purpose. Several algorithms are available to transform colored digital images into simulated dichromatic color perception. These algorithms can be very illustrative of the problems dichromats experience in discriminating colors. The purpose of this study was to determine whether one type of transformation could provide a quantitative account of error rates in identifying colors displayed on a computer monitor. Methods. The experimental task required observers to identify the color of small rectangles displayed on a computer monitor within a black background. There were eight colors. The number of errors for each color was recorded. Four deuteranopes and five protanopes participated. Color differences were calculated using normal trichromatic and dichromatic values. The dichromatic color differences were calculated using the procedure developed by Brettel et al. [J Opt Soc Am (A) 1997;14:2647–55]. Results. The relationship between error rates and color differences calculated in either color space was fit by an exponential decay function. However, the fit provided by the dichromatic color differences was no better than that using color differences calculated in trichromatic color space and both regressions could only account for approximately 30% of the variance in the data. Conclusions. Correlations between the error rates in identifying colors for dichromats and color differences were low-to-moderate whether the color differences were based on normal trichromatic color space or a dichromatic transformation. This finding suggests that it may be sufficient to calculate the color difference only in color-normal space to determine whether the colors will be confused by a person with a congenital color vision defect. Although computer algorithms are useful in illustrating color discrimination problems experienced by dichromats, they may not offer any advantage over typical trichromatic color spaces in predicting performance in color identification. The lack of any advantage may be due to how dichromats use brightness information to identify colors.

The effect of test distance on the CN lantern results

The purpose of this study is to determine how the viewing distance affects the pass/fail results of the CN Lantern (CNLan). The CNLan is a color vision test designed for the railway industry. It presents 15 triplets of colored lights that could be any combination of red, green and yellow. The test was viewed from 4.6 m and 2.3 m. Sixty-seven color-defectives participated in the first part of the study. Sixty-six percent of the subjects repeated the experiment 10 days later. There was a significant (P < 0.05) decrease in the mean number of errors from 7.6 to 4.3 as the distance decreased. There was also a corresponding increase in the percentage of subjects who passed from 9.0% at 4.6 m to 20.9% at the 2.3 m viewing distance. None of the subjects who passed at the longer distance failed at the shorter distance. The replication results were statistically identical to the first session (P > 0.05). Decreasing the CNLan viewing distance by 50% does decrease the number of errors and increase the pass rate. This indicates that some color-defectives could work in the railway yards where the sighting distances for the signal lights are shorter than on the main track.

Do color-deficient observers take longer to complete a color-related task?

Purpose. Previous research has shown that observers with congenital red-green color vision deficiencies (color-deficient) have longer reaction and response times in making color-related judgments compared with individuals with normal color vision (color-normals). The objectives of this study were to determine how much longer color-deficient observers take to complete a visual display terminal (VDT) based color naming test without imposed time constraints, whether there was any correlation between error rate and time to complete the task, to determine the effect of familiarity on the time to complete the task, and whether the completion times were correlated with the anomaloscope or Farnsworth D-15. Methods. The VDT task requires individuals to identify colors used to code information in a railway dispatcher display. The test typically takes 8 to 10 min to complete. Eighty-one color-normals and 41 color-deficient observers participated. The total number of errors and time to complete the test were recorded. There were two sessions separated by ∼2 weeks. The color-deficient group was divided into those that passed the test and those that failed. Pass/fail criteria for the color naming test was established based on the number and types of color-normal errors. Results. The time to complete the task for the color-deficient group who passed was 14% longer than color-normals. Color-deficient observers who failed took 29% longer than color-normals. Mean times to complete the task at the second session were significantly faster (18%) for all three groups with the reduction in time approximately equal across the groups. There was no significant correlation between the number of errors and time to complete or the clinical tests and completion times for any of the three groups. Conclusions. In general, color-deficient observers required more time to the complete the color identification test than color-normals. Although color-deficient observers who failed the VDT test took the longest, there was no correlation between time and the number of errors for any of the subject groups.

Color vision and fatigue: an incidental finding.

INTRODUCTION Because there is little information available as to how fatigue and color vision interact, we present some incidental findings on how a protanope and a color-normal perform on several color vision tests after 1 night of sleep deprivation. CASE REPORT A series of clinically and occupationally based color vision tests were administered to a protanope and a color-normal subject after they had stayed awake all night and after a regular nights sleep. There was essentially no change in their performance on the clinical color vision tests; however, both did worse on the occupationally based color vision tests after 1 night of sleep deprivation. The color-normal made numerous errors in identifying colors displayed on a video display terminal, whereas the protanope had a large increase in errors on the CN Lantern Test. Both subjects passed these respective tests after a regular nights sleep. CONCLUSIONS The primary reason for color-normals poor performance on the video display terminal test was probably due to a decrement in his visuo-motor control rather than a loss in color discrimination. In contrast, the protanopes poor performance on the lantern test was probably due to the additive effects of the inherent limitations of his visual system and fatigue.