Abstract
Opponent and vector models are important, yet incomplete foundations for color theory; they dictate how to compute hue, saturation and brightness, but offer few clues to their neural correlates. Here we derive hue, saturation and brightness from nonlinear dynamic interactions between cortical broadband and narrowband-wavelength selective mechanisms. HUE: Hue opponency can be modeled as a competitive (winner-take-all) interaction between cortical narrowband wavelength selective mechanisms; e.g., blueness-labeled neurons compete with yellowness-labeled neurons for the right to fire, and opponency resides in the fact that only one wins out. This competition opponency reproduces psychophysical opponency and also models some otherwise intractable color behaviors (e.g., Billock et al., JOSA A, 2001). SATURATION & BRIGHTNESS: Another nonlinear dynamic interaction (widely employed in circadian and binding models) is neural synchronization. Coupled neural oscillators can synchronize at a compromise frequency (which lies above or between the uncoupled frequencies). The behavior of the coupled system depends on the nature of the coupling (e.g., excitatory or inhibitory, mutual or asymmetric) and on system nonlinearities. We coupled neural oscillators driven by narrowband hue and broadband luminance mechanisms and identified coupling conditions and nonlinearities that lead to vector-like summation, such as that used in modeling brightness, and to power law functions of signal ratios, such as that used to model chromatic saturation. Competition and coupled oscillators are used extensively in other neural modeling; it is natural to apply them to color theory. Similarly, it is natural to apply binding-like models to saturation and brightness, which are combinations of chromatic and achromatic information. The exciting aspect of these models is that hue, saturation and brightness are emergent properties of physiologically plausible interactions between known cell populations.