Psychophysical influences on the validity of anomaloscopic assessments of color vision

Anomaloscopes are used in clinical and research applications involving the assessment of color vision. Output data include the matching range (MR), the midpoint, and the anomaly quotient (AQ). The latter is commonly used to compare data obtained using different instruments. However, the midpoint and AQ ultimately depend on the MR, for which there is no universal operational definition. In this study, 5 volunteers with normal color vision each completed 510 trials in a rating task with an anomaloscope employing the Moreland equation. The aim was to investigate the nature of the perceptual transition into, and out of, a metameric match. This was found to be less than abrupt, providing ample opportunity for the influence of individual response biases. Consequently, an agreed-upon definition of the MR, associated with an appropriate psychophysical technique, would facilitate the identification and tracking over time of acquired color vision deficits and would improve the validity of interstudy comparisons.