Mason was appointed to the faculty at Columbia University in 1987.[1] She co-directs the Neurobiology and Behaviour program and the National Institutes of Health Vision Sciences training program.[7] Mason studies the role of transcriptional regulators and guidance mechanisms in the mammalian visual system.[8] In particular, she studies the retinal ganglion cell, which connects the eye to the thalamus, which act as sensory relay stations.[9] Half of the retinal ganglion cells send information to one side of the thalamus, whereas the other half send information to the other side. Mason studies how these axons know whether or not to cross over the optical chiasm.[9] To understand how this happens, Mason used a camera lucida to trace out the axons at the root of retinal ganglion cells.[10] Mason focussed on the tips of the axons, and found that most extend across the same side of their brains as where they start.[10] Mason identified that when one type of retinal ganglion cell reaches this chiasm, molecules bind to receptors that prevent them from crossing over, whereas the other type does not.[9]