Using neuroimaging to measure mental representations: Finding color-opponent neurons in visual cortex

To date, most neuroimaging studies have tried to localize large regions in the brain that are responsible for specific behaviors or mental operations. Psychological theory, however, is more concerned with the nature of mental functions than with the locations of their neural substrates. This article reviews work that moves beyond functional anatomy to measure how color is represented by neurons in visual cortex. The general approach has three basic steps: First, the areas under investigation are localized in the brain. Second, responses of these areas are measured to sets of systematically varying stimuli, designed to uncover the nature of cortial representations. Third, the neuroimaging data are compared with behavioral data measured with the same stimuli. Results obtained using this approach support the hypothesis that primary visual cortex contains color-opponent neurons that support perception.