The strange case of an American woman suffering from a rare form of tunnel vision has presented scientists with a unique opportunity to understand more about how the brain percieves things.
The unnamed woman is suffering from simultanagnosia, a rare brain condition that causes people to see only one object at a time - a fruit bowl, a chair, a lamp, a door, - but not the room as a whole.
In this particular case, the woman's brain was otherwise healthy and normal, which means scientists from the University of Missourigot a chance to look at the effects of simultanagnosia more closely, and independently of the diseases that often accompany it, such as Alzheimer's.
What they found could give us clues about how our brain processes incoming information, and how it decides what to ignore and what to become conscious of, Helen Thomson explains for BBC Future.
The woman in question was first called in for a neurological exam after a short illness, and showed signs of classic simultanagnosia, because she was unable to see all of the individual elements in a picture at the same time.
"In theory if we showed her the picture many times, she might be able to describe the entire scene individually, but could never put it together, she never saw it as a whole," one of the doctors who examined her, Joel Shenker, told the BBC.
But the woman had been leading an otherwise normal life, which led the researchers to suspect her brain was actually taking in everything and filtering out most of the information before it reached her consciousness.
Next, Shenker presented his patient with a variation of the Stroop test, where words for the names of colours are shown in different colours. Participants in such tests can usually name the colours faster when both the ink and text match up.
In this case, the twist was that Shenker made up larger letters out of lots of smaller ones (assembled in the shape of the larger letter). Perhaps unsurprisingly, the woman being studied could only see the smaller letters - not the bigger letters the smaller characters formed.
But, bizarrely enough, her reaction times in identifying colours were linked to the larger letters.
So was her brain somehow seeing the larger letters without really seeing them? We don't know for sure - the woman didn't come back for follow-up tests, and didn't seem to understand what all the fuss was about.
Even so, Shenker has a hypothesis he calls the 'cocktail party effect'. While we generally tune out of the babble in a room at a party, once someone says your name, your ears prick up, at which point it's possible to realise that you were taking in details of other conversations in the room, even if you weren't aware of it.
According to Shenker, that could be another example of a filtered system of consciousness. "Your brain is taking care of a lot of stuff that you might eventually want to become aware of," the told the BBC.
"The fact that [the woman] had no problems going about her life illustrates the extent to which your brain can process things unconsciously, without you ever needing to become aware of them. I've never encountered a better example of that concept."
The research has been published in Neurocase.