Abstract
Purpose: :
Prediction of real-world performance from clinical tests is a perennial challenge but essential for optimal safety and welfare in cue-limited settings, individuals with vision deficiencies, and in the expanding elderly population. Our purpose is to determine if a threshold clinical color test of cone contrast sensitivity (cone contrast test; CCT) predicts reaction time on a suprathreshold color discrimination task.
Methods: :
The computer-based CCT presents a series of red, green and violet letters visible only to L, M or S cones in decreasing steps of cone contrast to determine L, M and S cone letter recognition thresholds. The color reaction time task (CRTT) presents 35 aircraft symbols identical in shape, size (1 deg), and luminance (14 cd/m2) but different in color (5 symbols in each of 7 saturated colors: red, green, blue, orange, yellow, purple, grey). On each trial the 35 colored aircraft symbols appear in a random distribution on the black CRT display and on command (e.g., "eliminate red"), the subject uses the computer mouse cursor to "mouse-over and click" each designated symbol (on this trial "red") until all five are deleted (proper alignment of cursor and depressing the mouse deletes the symbol). The total time required to complete each 5-symbol trial and error rate are tabulated by the program. Each subsequent trial commences with a random distribution of all 35 symbols and the program continues until all 7 colors are tested. The threshold CCT and suprathreshold CRTT were conducted on 18 hereditary color vision deficient subjects (CVD; confirmed by PIP and anomaloscope tests) and on 8 color vision normals (CVN).
Results: :
In CVN mean reaction time for each color was 5 sec (range 4 to 7 sec) and mean total reaction time for all 7 colors was 35 sec (range 29 to 42 sec). No CVNs made any errors on the reaction time task. Mean CCT scores in CVN, averaged across L, M and S cone CCTs, predicted total color reaction time (r2= 0.76, p<0.005). In CVD mean reaction time was 10 sec (range 4 to 59 sec) and mean total reaction time was 71 sec (range 37 to 124 sec). CVD mean reaction time and error rate were highest for yellow (15 sec, 14 errors) and orange (14 sec, 33 errors). The CCT identified type and severity of CVD and predicted reaction time for yellow symbols (r2= 0.42, p<0.005) but prediction did reach significance for other colors.
Conclusions: :
The threshold CCT is predictive of reaction time on a suprathreshold color task applicable to real-world color discrimination demands. Prediction is stronger in CVN than CVD presumably due to higher variability and error rate in CVD subjects on color discrimination tasks.
Keywords: color vision • contrast sensitivity • color appearance/constancy