You might have heard the saying, “seeing is believing.” For many people, vision is one of the most relied upon senses for day-to-day life, learning, and ascertaining truth. Did the magician really make a rabbit disappear into a hat? Can your friend scarf down a whole cake in under ten minutes, like they claim? Is that new gaming console truly selling for less than 100 dollars this week? For these unbelievable or surprising slews of events, beliefs, and assumptions, we often conclude: “I’ll have to see it to believe it.” While in most cases, this adage is foolproof, there are notable exceptions to the rule. An examination of the rare neurological condition Anton syndrome reveals that we can’t always believe everything we “see.”

Vision is, by far, the most researched sensory modality and, arguably, the sense that human society relies upon the most [1]. Regrettably, there are many ways the sense of sight can be lost and ways that loss of sight can affect how we perceive the world. Anton syndrome is a form of visual anosognosia – the denial of weakness or impairment [2,3]. In visual anosognosia, patients cannot realize they have lost their vision. They will go to lengths to confabulate, or unconsciously generate, false memories and explanations to supplement their denial of visual loss [4,5]. As a result, loss of sight in Anton syndrome may initially seem to have little effect on a patient.

Anton syndrome commonly occurs from cerebrovascular damage in the occipital lobe, or visual cortex [5]. Different causes include strokes that affect the bilateral arteries on both sides of the occipital lobe, head trauma, multiple sclerosis, and genetics [5]. Our ability to see depends upon visual pathways in the front (anterior) part of the brain and the back (posterior) visual cortical areas [Figure 1, 5]. The anterior components are usually unaffected in cases of Anton syndrome, but bilateral damage to the occipital lobes renders the brain unable to process information that comes from functional anterior pathways – rendering patients completely blind [5].

On an almost opposite note (think “seeing is disbelieving”), cortical blindness allows the phenomenon of “blindsight” to develop. Patients with blindsight can detect, localize, and respond to visual stimuli without technically seeing them (because their visual processing areas in the occipital cortices are damaged) [6]. The distinction between detecting visual stimuli and seeing the stimuli is a fine but important one. Patients with blindsight can still demonstrate reflexive responses to light like blinking or tracking a stimulus with their eyes [6]. However, these patients will deny having seen the stimulus in spite of having reacted to it [6]. Similarly, a patient with blindsight can successfully navigate a hallway cluttered with obstacles, but will not acknowledge there are obstacles in their way [7]. To explain these demonstrations, it’s hypothesized that the intact anterior visual pathway components have direct connections to motor brain areas that do not require feedback or interaction with the damaged posterior pathway leading to the occipital visual cortex. Another more likely hypothesis is that parts of the visual cortex remain intact, not enough for perception but sufficing for reflexive and suboptimal interpretation of visual information. Blindsight has been frequently observed in case reports of patients with Anton syndrome [3.5,8].

In one case report, a stroke patient who developed Anton syndrome had completely lost her vision, but insisted that she could still see [5]. Her vision loss was evident when she walked into objects and felt around her tray for utensils when she tried to eat [5]. When asked about the appearance of a doctor’s tie, she answered quickly, but incorrectly. The continuous denial of vision loss and made up answers exemplify confabulation as a result of visual anosognosia [5].
In another report, a patient who developed visual hallucinations in addition to complete blindness demonstrated additional examples of anosognosia [3]. Unaware of his blindness, he would confabulate that he “was old, stupid and weak,” trapped in a dark place that needed light. He acted on assumptions of his settings, believing he was outdoors, when he was not, and demanding to go home [3].

One possible explanation for the patients’ confabulations is that the damage to visual pathways disconnects them from other still-functioning parts of the brain, such as speech-language centers [5]. Another hypothesis poses the possibility that disrupted visual pathways send false signals to the rest of the brain and convince other processing centers to come up with an explanation [5]. The result of unusual absence or false supplementation of visual information manifests in the form of the creative answers the patients in the case reports deliver. For these patients, believing takes over seeing.

Anton syndrome represents only one of the many ways loss of vision reveals to us what “seeing” truly is – how our brains perceive and process visual information, as opposed to directly perceiving visual stimuli at face value. Furthermore, it is a reminder of the importance of all modules and connections in the brain. Even though only the visual cortex is damaged, the information from the anterior visual pathways are blocked from the rest of the brain, stunting other functioning areas responsible for speech and language. Losing the ability to see cripples these patients’ abilities to reason and even believe their loss. From the cases of Anton syndrome, we learn that seeing doesn’t always equal believing, and sometimes, believing can even replace seeing.

References

1. Hutmacher, F. (2019). Why Is There So Much More Research on Vision Than on Any Other Sensory Modality?. Front. Psychol., vol. 10:2246. https://doi.org/10.3389/fpsyg.2019.02246
2. Cutting, J. (1978). Study of anosognosia. J. Neurol. Neurosurg. Psychiatry, vol. 41:548–555. https://doi.org/10.1136/jnnp.41.6.548
3. Marková, I.S. & Berrios, G.E. (2014). “The construction of anosognosia: History and implications.” Cortex, vol. 61:9–17. https://doi.org/10.1016/j.cortex.2014.09.011
4. M Das, J., & Naqvi, I.A. (2021). Anton Syndrome. In StatPearls. StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK538155/
5. Maddula, M., Lutton, S., & Keegan, B. (2009). “Anton’s syndrome due to cerebrovascular disease: a case report.” J. Med. Case Reports, vol. 3:9028. https://doi.org/10.4076/1752-1947-3-9028
6. Cowey, A. (2010). The blindsight saga. Exp. Brain. Res., vol. 200:3–24. https://doi.org/10.1007/s00221-009-1914-2
7. Abbott, A. (2008). Blind man walking. Nature. https://doi.org/10.1038/news.2008.1328
8. Solcà, M., Guggisberg, A.G., Schnider, A., & Leemann, B. (2015). Facial Blindsight. Front. Hum. Neurosci., vol. 9:522. https://doi.org/10.3389/fnhum.2015.00522