Monday, December 28, 2009

Blindsight: Evidence that we don't have souls!

From time immemorial, philosophers have professed that we are supremely conscious beings, distinguished from other animals by the possession of a flickering soul. Religious thinkers especially believe that unlike lesser species, humans are dichotomous creatures - part material and part spiritual. There are many different versions of this view (commonly referred to as mind-body dualism), each designed to explain how corporeal matter and transcendent soul interact so harmoniously in the living human being. Some versions have proven more compelling than others, but regardless of the particularities of mind-body dualism, the theory possesses many alluring features. Dualism grants us rationality, supremacy, and best of all, immortality - souls are eternal and persist even after we’ve “sloughed of this mortal coil.”

But the most alluring theories aren’t always the most convincing. Today, psychologists and neuroscientists have abandoned dualism in favor of monism – the idea that the mind is ultimately the same thing as the body.  There are no souls, according to contemporary scientists, just an abundance of neural networks that collectively give rise to our thoughts and actions. Material monism is elegant because it eradicates the need to account for how two antithetical entities – body and spirit – interact. The ultimate goal of neuroscience is to link every aspect of consciousness and behavior to the brain and, as a result, render obsolete all reference to the soul.

Some compelling evidence against the notion that we have souls comes from the frontiers of neuropsychology, with a curious syndrome called “blindsight.” Blindsight is a strange phenomenon - a veritable paradox. Surely, there can be no such thing as blind sight! How could an individual see and be blind at the same time?

Remarkably, such a phenomenon does exist. In fact, it is the rule (not the exception) in patients who are cortically blind. This form of blindness occurs when there is tissue damage to the visual center of the brain - the primary visual cortex, or “v1” as it is called by most scientists. Cortically blind individuals still have good eyes (the input device that transmits light signals to the brain), but v1 (the central visual processor and output device) is defective and cannot produce what we experience as normal vision.
For at least a century, doctors knew about cortical blindness (the kind of blindnes that resuls from brain damage). But it wasn’t until 1974 that they discovered that some visual function survives the trauma. At the time, the discovery transformed the way scientists understood vision and generated much speculation about the nature of consciousness.

Why consciousness?

Blindsight tells us something about consciousness because the syndrome revealed that cortically blind patients are not really blind; they are just unaware of what they see.

The first case of blindsight occurred with a patient (referred to as D.B.), who endured damage to the right portion of v1. As the doctors expected, D.B. became blind in the left half of his visual field, which corresponds to the brain tissue that was lost. Yet despite not being able to see anything in his blind field, D.B. could detect the precise location of objects that were presented there.

D.B. could also detect whether an image in his blind field was an X or an O and whether a line was oriented horizontally or vertically. Strangely, while D.B. was detecting the location, shape, and orientation of these stimuli, he insisted that he was guessing and that he could not see the images. 

When blindsight was first reported, the phenomenon was so strange that many researchers did not believe it. But there have since been many reports on many different patients with blindsight, each study refining our understanding of the syndrome. Since its initial discovery, many alternative explanations have been ruled out including the idea that D.B. was malingering or that somehow light from his blind field was spilling over into his intact visual field, enabling him to sense what was there.

Today, it is understood that blindsight is not a degraded form of vision that may be improved with a magnifying glass. Rather, it appears to be a different kind of vision altogether – one that does not rely on v1 or conscious experience. In blindsight, cortically blind patients retain some form of visual function, without the ability to consciously perceive. Thus, damage to v1 does not wipe out vision; it just reduces it to the kind of unconscious vision you would find in other species (like reptiles). *

Blindsight represents what neurologists call a “dissociation,” which occurs when a given function can be broken down into two or more distinct sub-functions, each traced to distinct pathways in the brain. When a dissociation exists, damage to one pathway disrupts only one aspect of function while the other is preserved.

Blindsight reveals that vision is comprised of multiple sub-functions, mediated by at least two distinct pathways in the brain. One pathway projects from our eyes to v1 and is responsible for conscious perception. This circuitry allows us to build a mental representation of the visual scene within our field of view. But there is also a second pathway, which projects from our eyes to the motor cortex and allows us to reflexively react to visual stimuli unconsciously. When a ball suddenly flies in your direction, you flinch even before you consciously perceive it. This ability to respond to visual stimuli without conscious perception is what makes blindsight possible.

D.B. could tell you where an object was located without consciously seeing it, because the pathway responsible for such unconscious visual processing remains intact in D.B.’s brain.

What is most compelling about blindsight is not that we can see without perceiving, but rather that damage to corporal matter (v1) disrupts conscious experience.

Blindsight is now one of many dissociation syndromes that slap us with this uncomfortable realization: the content of our minds is reducible to the mechanical circuitry of our brains. It is becoming increasingly evident that human beings are a single physical apparatus, rather than a two-part being. The tale of humans as both a mortal machine and an eternal spirit is yet another piece of fantasy fiction, in which dichotomous creatures (from mermaid to centaur) abound unfettered by the shackles of scientific discovery. 

*For economical considerations, the science here is superficial and unsubstantiated. But I’d be more than willing to provide greater detail if you so desire. 


  1. This comment has been removed by the author.

  2. Fascinating stuff. Although. The argumentation jumps a few steps from blindsight to monism, perhaps because its just a "test?" In any event just a quick remark: I can't speak for other religions but the bible's description of the 'soul' is very ambiguous and doesn't necessarily indicate an intrinsic dualism. The faculties of what we commonly refer to as the soul can also be conceived or described as the very extraordinary faculties invested in the average human brain; some of which lead us to question the purpose of existence, to seek deeper meaning and reach out for the infinite.
    Spirit and matter are simply categories we use to make some sense out of the mysteriousness of life. They are words that point to certain realities we experience like day and night hot and cold happy and sad etc. Our appreciation for these realities relates to how thoroughly we understand these words and the concepts behind them. Upon reflection we see that despite our reflexive binary perception, all opposites form a part of the vast, insanely complex yet totally unified natural order.

    -Shmuel Shimon

  3. I appreciate the feedback Shmuel!
    I sort of agree with you. The claim that we have no souls is a bit radical. I'm not suggesting that we don't have minds, or personalities, or spiritual experiences - just that it all amounts to material phenomena.
    Whether or not the bible is clear about the soul, other religious sources disambiguate the issue. You can hardly get through Chassidic texts (the Tanya in particular comes to mind) withought an analysis of the dichotomy between our physical bodies and transcendent souls. I think you'd be hard-pressed to find a Rabbi or priest that does not endorse the view that our souls survive death. This is the kind of dualism that I am challenging.
    You're right! Blindsight does not tell the whole story. But it is a sample of the kind of evidence that exists against the notion of Dualism that, i belive, figures prominantly in religious circles.

  4. ...the "test" was literally just a test of how this commenting thing works.