Performance on the Farnsworth-Munsell 100-Hue Test Is Significantly Related to Nonverbal IQ

The Farnsworth-Munsell 100-Hue test (FM100) is a standardized measure of chromatic discrimination, based on colored cap-sorting, which has been widely used in both adults and children. Its dependence on seriation ability raises questions as to its universal suitability and accuracy in assessing purely sensory discrimination. This study investigates how general intellectual ability relates to performance on both the FM100 and a new computer-based chromatic discrimination threshold test, across different age groups in both typical and atypical development.

Participants were divided into two main age groups, children (6-15 years) and young adults (16-25 years), with each group further subdivided into typically developing (TD; three groups; TD 6-7 years, TD 8-9 years, TD Adult) individuals and atypically developing individuals, all but one carrying a diagnosis of Autism Spectrum Disorders (ASD; two groups; atypically developing [ATY] child 7-15 years, ASD Adult). General intelligence was measured using the Wechsler Abbreviated Intelligence Scale and Wechsler Intelligence Scale for Children. All participants completed the FM100. Both child groups also completed a computer-based chromatic discrimination threshold test, which assessed discrimination along cone-opponent ("red-green," "blue-yellow") and luminance cardinal axes using a controlled staircase procedure.

Farnsworth-Munsell 100-Hue test performance was better in adults than in children. Furthermore, performance significantly positively correlated with nonverbal intelligence quotient (NVIQ) for all child groups and the young adult ASD group. The slope of this relationship was steeper for the ASD than TD groups. Performance on the chromatic discrimination threshold test was not significantly related to any IQ measure. Regression models reveal that chromatic discrimination threshold, although a significant predictor of FM100 performance when used alone, is a weaker predictor than NVIQ used alone or in combination.

The results indicate that FM100 performance is not purely a measure of color discrimination but instead also reflects general nonverbal ability. Other measures of chromatic discrimination ability are therefore required for its accurate assessment, particularly in early or atypical development.