“A hallucination is a perception in the absence of external stimulus that has qualities of real perception” (Wikipedia, retrieved April 2020). Not unlike using a different tool or perspective through which to derive information enfolded in a visual scene, studying the anomalous nature of hallucinations can similarly provide insight into how human perception and cognition work. Neurologist Oliver Sacks spent many years closely observing his patients and how they lived with their various neurological afflictions, a number of whom experienced hallucinations. His approach was one of complete immersion, fostered by a driving curiosity and compassion: He wanted to live in their shoes. This level of engagement led to helping many of them see what had been initially diagnosed as a deficit worthy of nothing but social shame, as rather a unique and extraordinary ability.

In patients with Charles Bonnet syndrome, the onset of blindness through macular degeneration can lead to the sudden and unpredictable appearance of visual hallucinations. From a neurological perspective, Sacks believed this form of hallucination was caused by damage to the perceptual system resulting in a misfiring or miscommunication between the lower order region of the visual cortext, the fusiform gyrus, associated with recognition, and the higher order region of the inferotemporal cortex, believed to be associated with emotion and memory. Under normal circumstances this latter area is said to attenuate or dampen the lower order region’s activity. Hallucinations originating in this manner manifest as completely unrecognizable people or cartoon-like faces with exaggerated eyes and mouths. Random visual apparitions that have sometimes led the unfortunate souls experiencing them to believe they were losing their minds, and despite being completely sane, wind up feeling ashamed of their experiences.

According to Sacks, in patients with Charles Bonnet syndrome, the numerous pieces and figments of perceptual information that litter their lower cortical regions can materialize inexplicably and unexpectedly in awareness as hallucinations, free from the apparent filtering of the inferotemporal cortex. The mind confabulates an image from such fragments, believed to be parts of the subconscious recipes for memory and imagination. Under ordinary circumstances, could these be the visual recognition impressions referred to by Manzotti in his Spread Mind theory of consciousness which, as a form of template, are used to match live sensory experience?

Hallucinations may more broadly be related to hyper-stimulated brain activity and behaviour on the manic-seizure side of things, such as that associated with Tourette’s syndrome. In such scenarios, the lower order regions of the brain appear to operate in a way that the higher processing levels and sense gates simply cannot keep up with. Sacks himself experienced visual hallucinations, similar to Charles Bonnet syndrome, but of a geometric variety that accompany a slightly different diagnosis. Interestingly, in his hallucinations he recognized what he felt were simple archetypical designs, described as similar to motifs from prehistoric cave paintings.