One blue colour channel or two?

Contrary to the general belief that the yellow – blue mechanism has lower spatial resolution than the red – green mechanism, it has been recently claimed that both mechanisms have similar spatial sensitivity (McKeefry et al, 2001 Vision Research 41 245 – 255). Studying high-spatial-frequency tritanopia (a colour illusion based on spatio-chromatic interactions in human vision), we found strong evidence for the existence of two blue mechanisms--with low and high spatial-frequency resolution. If confirmed, this may resolve the apparent paradox concerning spatial resolution of the yellow – blue mechanism.