Their main asset is that they are sensitive to motion - you can imagine that due to their width they can track a signal flashing across several bipolar cells. These two types of information, motion vs. color and form, are maintained in separate compartments all the way up the visual pathway. Any emotional response you attach to this event will be mediated by the amygdala, incidentally. Way back at the beginning of this section, there was mention of a few optic tract fibers which bypassed the LGN entirely, traveling instead to the less glamorous but equally essential midbrain. One of their targets in the midbrain is the pretectal area , which mediates the pupillary light reflex .
Light enters the retina and from there travels directly to the pretectal area.
The Edinger-Westphal nuclei, via the IIIrd nerve , control the pupillary constrictors that narrow the pupils. Knowledge of all this enables you to test the status of your patient's visual system by shining a light into each eye. There must be a problem with constriction on the right, such as IIIrd nerve damage. Here the problem must be with the right optic nerve itself, or possibly the right pretectal area.