Blindsight: A Case of Nonconscious Sensation

Blindsight is the curious neurological syndrome where someone is capable of “seeing” to a limited extent but claims to have no subjective experience of seeing. They could, for example, post cards into slits at the right orientation while verbally reporting they have no idea what the orientation is. Such patients have led cognitive scientists to talk about there being two different visual streams in the brain: the ventral “what” stream and the dorsal “where/how” stream. In blindsight patients, the hypothesis was that they had a functioning “where/how” stream but their “what” stream was damaged. The idea then was that only the “what” stream is conscious, and this explained why the blindsight patients lacked visual phenomenology.

But some philosophers have disputed the idea that the dorsal stream is nonconscious. These people have argued that just because someone can’t report or have access to phenomenology that doesn’t mean there is no phenomenology. So now there is a big debate about whether and to what extent the “where/how” stream is conscious.

In order to determine whether the “where/how” stream is conscious, we need to first define what we mean by consciousness. Most philosophers like to define it in terms of what-it-is-likeness, which is more or less synonymous with “awareness”. I like to define consciousness more precisely because the term “awareness” is one of the most vague and least helpful words in the vocabulary of philosophers. Does a moth have “awareness” of a light? Sure, but should we therefore think the moth is conscious? That doesn’t follow. I prefer to follow Julian Jaynes in defining consciousness narrowly as a kind of introspective power. To get an idea of what introspection means close your eyes and imagine yourself sitting in a chair 50 years in the future. Such mental time travel is one of the functions of what I am calling consciousness. It allows you to reflect on what you have done or might do. Its content is varied, ranging from visual, auditory, gustatory, haptic, emotional, bodily, and linguistic content. It allows you to have an inner monologue. On how I define it, consciousness is a kind of reflective/introspective/metacognitive/higher-order monitoring system that takes as its content other brain representations.

But if we thought this kind of reflective consciousness was the generator of “phenomenology” then we would have to think that a great deal of nonhuman animals had no phenomenology. This is a bad result, so we should not conflate reflective consciousness with what-it-is-likeness. Now, in the case of the blindsight patient, what should we say? On my account, we should say that the patients lack reflective consciousness but there is still something-it-is-like to have an operational “what/how” stream. Thus, we can distinguish nonconscious sensation from conscious sensation. The blindsight patients has nonconscious visual sensations in virtue of having an operational “what/how” stream that can accurately discriminate visual information so as to aid motor planning, but lacks “conscious visual sensations”. In virtue of being tied into higher-order monitoring systems that has access to linguistic contents and global workspaces, consciousness is responsible for reportability. So only conscious sensations can be reported on, explaining why the blindsight patients claim to have no visual experience. We can now clarify that they don’t lack nonconscious experience but conscious experience. Since conscious experience is by definition introspectable, we can now clarify the way in which their phenomenology is changed when blindsight sights lose the ability to introspect on their visual stream. So blindsight patients have nonconscious sensation, but lack conscious sensations, which are reportable by definition. They maintain the ability to respond intelligently to the world, but lack the ability to be metacognitively aware of what’s going on in their visual experience.


1 Comment

Filed under Consciousness, Philosophy, Psychology

One response to “Blindsight: A Case of Nonconscious Sensation

  1. This is the first time I hear about blindsight. Seems fascinating, but I’m not sure I understand it right. If you would throw a basketball at them, would they react as if they’re seeing it, or would it just hit their head out of the blue?

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