“Once her belief was sanctified by science, her sight got better and better…”
I first read about blindsight back in high school, reading an essay by Oliver Sacks and was absolutely intrigued by the thought of seeing without sight. Now there is a wonderful vignette on NPR by Lulu Miller that talks about blindsight (be sure to listen to the story on All Things Considered).
Of course we know now that there are multiple visual pathways and each one of these visual pathways mediates a different aspect or derivative of a component of vision. It turns out that vision is complex, more complex than simply carrying “visual pixels” to the brain to be mapped out topologically. After photon capture by the photoreceptors of the eye and pre-processing operations in the circuitry of the retina, information is passed to the retinal ganglion cells or the output cells of the retina. Each one of the 18-20 types of ganglion cells that project out of the retina through the optic nerve mediates different kinds of information. Aside from projections to the primary visual cortex, some ganglion cells project to the lateral geniculate nucleus, others to the superior colliculus, the pretectum, the suprachiasmatic nucleus and the hypothalamus. Each one of these projections out of the retina carries information relevant to a different feature of vision. Some of these functions help control the size of your pupil limiting the amount of light that comes into the eye. Other projections help you orient your head and eyes to the world around you while other projections still help you figure out what time of day and season it is. Most of these meta-visual functions are not conscious, but play crucial roles in how we live our everyday lives and are only revealed when things in the visual system go awry like the man Oliver Sacks described who could catch a ball despite being completely and functionally blind. Milena Channing’s experience with a stroke in her visual cortex reveals some of this unconscious aspect of seeing, ironically by causing blindness while preserving portions of the brain involved in motion detection.