Blindsight and Betting: An Experiment by Persaud, McLeod and Cowey


Blindsight is a strange brain/mind condition that philosophers like to discuss in the context of discussions about consciousness.  People with blindsight have a problem with their visual cortex, and as a result are “blind” in an area of their visual field, what is called a scotoma.   Why do I put the word “blind” in quotation marks?  It is because these blindsighted people claim that they don’t see any stimulus in a certain area of their visual field, and there is no reason to believe that they are fabricating, but when asked to guess as to whether a stimulus is present or about specific features of the stimulus, such as whether it is an ‘X’ or an ‘O’, they do considerably better than chance.  These blindsighted individuals still seem to have some sort of awareness – call it “sight” – in the area in which they are blind.   The condition is therefore called “blindsight”.  The cartoon above nicely illustrates the condition.

Some philosophers say that blindsighted people lack a certain type of consciousness, sometimes called phenomenal consciousness, of the objects presented to their visual fields.  These philosophers say things like there is “nothing it is like for these people to see the objects” or ‘the objects don’t appear any way to them”.  Some philosophers have suggested that non-human animals are like blindsighted people in that they are in some sense aware of what’s going on in their environments, but they aren’t phenomenally conscious of these events.

Phenomenal consciousness – the way things appear -is what some philosophers, believe makes the mind-body problem so difficult to solve (see e.g. Thomas Nagel or Colin McGinn or David Chalmers or John Searle).  In short, the mind-body problem is the problem of understanding how conscious mental states are related to the body, specifically the brain and central nervous system.  These philosophers wonder about  questions such as these:  How does phenomenal consciousness, something that is subjective, arise from the brain, something that can be understood objectively?  Why does brain state X give rise to phenomenal conscious state Y, as opposed to some other phenomenally conscious state or no phenomenal consciousness at all?

Perhaps in another post I’ll explain how different philosophers try to answer these philosophical questions.  But in this post I want to briefly discuss an experiment done with a blindsighted person at the University of Oxford.   This experiment was conducted by Navindra Persaud, Peter McLeod and Alan Cowey, and I first read about a synopsis of it by Kaspar Mossman in the journal Scientific American Mind.

These researchers took a blindsighted person known as GY and asked him to guess about an object placed in his scotoma and then after the guess GY was asked to place a wager, either $1 or half that amount, on his guess.  If his guess was correct, the money that he wagered would be added to his winnings.  However, if his guess was incorrect, the money he wagered would be subtracted from his winnings.

The experimenters were giving GY an incentive to guess correctly because they wanted to see if GY was conscious of his performance

Although GY guessed correctly about 70% of the time, he chose a high wager only about 50% of the time.

This surprising result (one would expect the percentages to be roughly the same) raises the question as to why there is a disconnect between cognitive performance (guessing) and placing a wager.  The researchers’ answer is that betting is a special type of decision, one that requires some type of consciousness of one’s performance.

I don’t really understand this answer.  Does GY know that his ability to guess is better than 50%.  If so, then why doesn’t he make the higher wager each time?  If he doesn’t know that he has this better than average guessing ability, an ability which suggests that he is conscious of the stimulus at some level of consciousness, then why wouldn’t he trust his hunches?  Saying that wagering involves a special decision process doesn’t answer this for me.

To be fair to the researchers, I think I’ll need to read the actual study, and then I’ll get back to you with my thoughts.

Leave a Reply

Your email address will not be published. Required fields are marked *