Blue Cone Signals in the Extra Striate Cortex: Explanation for Blind Sight

Abstract

Our perception of vision is largely as a result of the signals conveyed from the eye to
the brain via the retino-thalamo-cortical pathway. Visual signals within this pathway originate
from three cone photoreceptors (responsible for day vision) and one scotopic receptor, the rods.
The cones are classified according to their spectral sensitivity peaks as Long(L), Medium(M)
and Short(S) wavelength sensitive cones. Our chromatic perception is dependent upon how the
brain processes variations in the activity among these photoreceptors. Chromatic signals are
generally thought to be processed by two parallel streams, the red-green system by the parvocellular
system1,2 and the blue-yellow system by the koniocellular system.3,4 A large body of
work has already been documented to identify these streams within the retina and the main thalamic
visual nucleus, the Lateral Geniculate Nucleus (LGN). However, our knowledge about
the processing of the chromatic signal within the visual brain, particularly the pathways taken
by the blue-yellow colour signals within the brain is at its infancy.