Color naming deficits and attention-deficit/hyperactivity disorder: A retinal dopaminergic hypothesis

BACKGROUND: Individuals with Attention-Deficit/Hyperactive Disorder (ADHD) have unexplained difficulties on tasks requiring speeded processing of colored stimuli. Color vision mechanisms, particularly short-wavelength (blue-yellow) pathways, are highly sensitive to various diseases, toxins and drugs that alter dopaminergic neurotransmission. Thus, slow color processing might reflect subtle impairments in the perceptual encoding stage of stimulus color, which arise from hypodopaminergic functioning. PRESENTATION OF HYPOTHESES: 1) Color perception of blue-yellow (but not red-green) stimuli is impaired in ADHD as a result of deficient retinal dopamine; 2) Impairments in the blue-yellow color mechanism in ADHD contribute to poor performance on speeded color naming tasks that include a substantial proportion of blue-yellow stimuli; and 3) Methylphenidate increases central dopamine and is also believed to increase retinal dopamine, thereby normalizing blue-yellow color perception, which in turn improves performance on the speeded color naming tasks. TESTING THE HYPOTHESIS: Requires three approaches, including:1) direct assessment of color perception in individuals with ADHD to determine whether blue-yellow color perception is selectively impaired; 2) determination of relationship between performance on neuropsychological tasks requiring speeded color processing and color perception; and 3) randomized, controlled pharmacological intervention with stimulant medication to examine the effects of enhancing central dopamine on color perception and task performance IMPLICATIONS OF HYPOTHESIS: If substantiated, the findings of color perception problems would necessitate a re-consideration of current neuropsychological models of attention-deficit/hyperactivity disorder, guide psycho-education, academic instruction, and require consideration of stimulus color in many of the widely used neuropsychological tests.