The human brain is a sneaky little organ. It is constantly carrying out processes relevant for both perception and function without letting you know a thing.
In the 1930s Sigmund Freud popularized the notion of the conscious versus the unconscious mind. According to Freud the conscious mind consists of all the mental processes within our awareness. The unconscious mind on the other hand, houses all sorts of things that we have no conscious awareness of.
Freud’s work on the unconscious mind was primarily based on patient analysis and personal insights and, as such, had no true empirical foundation. Flashing forward to the technological and methodological advances of contemporary neuroscience however and much evidence has been produced revealing silent workings of unconscious processing.
Just one example of the unconscious mind at work is seen in cases of blindsight. Blindsight refers to the capacity of certain blind individuals to accurately guess the identity, movement and location of visual stimuli even though they cannot consciously see anything at all.
One hypothesis regarding a physiological basis of this phenomenon has been gleaned through studies of the brain’s visual system. The visual system of the human brain has two main pathways; the retinocortical pathway* which tracts from the retina to the cortex, and the retinotectal pathway*, tracking from the retina to the tectum.
*(for the sake of clarity the retinocortical pathway will remain in red font and the retinotectal pathway in green)
The retinotectal visual pathway was the first to develop in phylogenetic history and is primarily responsible for controlling eye movements and orienting our attention to sudden movements in the periphery of our visual field. The retinocortical visual pathway developed later on in evolution and is responsible for conscious perception of the visual world. The primary visual cortex is the area of the cortex that begins processing visual information retrieved through the retinocortical visual pathway. It is this area of the brain that is damaged in individuals with blindsight.
To reiterate, though consciously completely blind, blindsighted individuals have been found to respond better than chance to visual stimuli presented in their visual field. For instance, studies have shown that such individuals when pressed to locate the position of a flashed light or the movement of an object can do so reasonably accurately. Other studies have shown such individuals can even discriminate between facial expressions of emotion.
One supported hypothesis for this unconscious awareness is that the retained retinotectal visual pathway, which still receives visual input, is guiding the movements of the blindsighted. Another idea is that the lateral geniculate nucleus (LGN), which forms an earlier part of the retinocortical visual pathway, is responsible for these aspects of visual processing before the information reaches intact primary visual cortex. If this were the case the LGN may continue to carry out these functions in brains of blindsighted individuals.
Whether or not the retinotectal pathway, the LGN or another as yet unidentified structure is guiding the perceptions of the blindsighted, their intact perceptual awareness clearly indicates that there are many processes occurring within our heads, which the brain slyly keeps to itself.
To return to Freud’s model, the material housed in the unconscious mind was also conceptualised as having an important and powerful influence on human behaviour. Extrapolating to cases of blindsight, unconscious processes in the visual system of the brain may help blindsighted individuals navigate their world or avoid obstacles.
So not only does unconscious mental processing occur on a regular basis within the brain, but these processes may be meaningful for our behaviour, driving our seemingly conscious decisions or dictating what we focus our attention on.
With all that in mind, next time you find your eyes wandering out a window, glancing at an attractive stranger or fixating on a snickers bar, stop yourself, and then ask yourself; was that me? Or was that brain?