The response of the human visual system depends on a multitude of image fea
tures, such as the wavelength (colour) of the visual stimulus and its spati
al frequency content. Hence we need to take into account the spatial and ch
romatic sensitivity as well as spatio-chromatic interactions to properly ch
aracterize visual sensitivity. In this paper we report two experiments that
further characterize the spatio-chromatic sensitivity of the human visual
system for stationary stimuli, namely the detection of small visual orienta
tion differences and the detection of blur. In both cases we find that the
Visual system is equally sensitive to red-green and to black-white modulati
ons for a wide range of spatial parameters. Furthermore, the contrast depen
dence for red-green and black-white modulations is identical, suggesting th
at the same mechanism mediates both types of stimulus, Our results are in a
ccordance with the hypothesis that both tasks are mediated by the parvocell
ular as opposed to the magnocellular pathway.