Out of mind, out of sight: The blind man who can 'see' obstacles

Experiments on a blind man who can ‘see’ to avoid obstacles could have huge implications for the visually impaired

In a darkened room, a blind man walks along a white line in the shape of a large ellipse.

He is taking part in an experiment which I have been invited to watch, at the University of Geneva in Switzerland. At one point, the scientist running the experiment, Beatrice de Gelder, asks me to stand on the white line, in the man’s path. I mustn’t move or make a sound. When he is about a metre away, he comes to a halt and asks: “Is somebody there?”

TN, as the blind man is known, suffered a stroke in 2003 which destroyed an area at the back of his brain that processes visual information: the primary visual cortex. The stroke affected only one hemisphere of his brain. What places TN in a category of his own, at least as far as the annals of science are concerned, is that about a month later he suffered a second stroke which wiped out the primary visual cortex on the other side of his brain. Suddenly, though his eyes were healthy, he became blind.

TN’s blindness is unusual, however, because he can still see in some situations, although he is unaware that he does so – a phenomenon known as blindsight. The most striking demonstration of this came two years ago, when de Gelder, a neuropsychologist at Tilburg University in the Netherlands and Harvard Medical School in the US, and neuropsychologist Alan Pegna of Geneva University and others, asked him to walk down a corridor which they had arranged like an obstacle course, having littered it with tripods, filing trays and boxes. He navigated his way successfully through the obstacles, though he said he saw none of them.

It’s well-known that hearing can become more acute in blind people, so to exclude the possibility that TN was relying on sound cues to negotiate his way through the obstacles the researchers asked him to repeat the experiment wearing earplugs. His performance didn’t change. “So it’s not auditory information that’s helping him,” says Pegna. “On the other hand, when we blindfolded him, he started bumping into the obstacles.”

Pegna first tested TN in 2004, and at that time he identified another visual skill that had been partially preserved in him: the ability to recognise facial expressions of emotion. When TN was asked to look at a series of angry, happy and fearful faces, and to guess what expression was being displayed, he guessed correctly more often than he would have had he been responding at random.

The effect wasn’t as dramatic as in some blindsight patients whose primary visual cortex has been damaged on one side of the brain only, and to whom faces have been presented in the blind half of their visual fields – some of whom responded correctly 90 per cent of the time. TN’s success rate was closer to 60 per cent. Nevertheless, he seemed to have retained some ability to detect emotional expressions without being consciously aware of them. And when the researchers put him in a brain scanner and watched how his brain responded, they found that one of his amygdalae – a pair of brain structures known to be sensitive to emotion – became significantly more active when he was looking at emotional expressions than when he was looking at neutral ones.

Pegna and de Gelder would like to know what brain pathways TN is using to see. The mechanics of vision are complex and still not well-understood, but scientists know that the main fibre tract leaving the retina at the back of the eye passes via a structure called the lateral geniculate nucleus (LGN) to reach the primary visual cortex, or V1 – the area that is damaged in TN. V1 is responsible for the earliest and most basic processing of visual information. It essentially parses the visual scene according to colour, form and motion, sending the results to other visual areas of the brain’s cortex for more higher-order processing.

TN’s case raises two possibilities. The first is that fibres leaving the LGN don’t just project to V1, but that some go directly to the other visual areas without first passing through V1. There is now good evidence, for example, that the LGN has a direct connection to an area called V5, which is involved in processing movement, and which is probably intact in TN.

In 1993, visual scientist John Barbur of London’s City University, and colleagues, used brain imaging to show that V5 still responded to input from the retina in a patient with damage to V1 who was able to detect moving visual stimuli. And this year, researchers at the US National Institute of Mental Health in Bethesda, Maryland, led by Michael Schmid, showed a similar effect in V1-damaged macaque monkeys. Schmid’s team also showed that when the LGN was damaged in addition to V1, the V5 response was abolished, and the monkeys could not detect visual stimuli in tests.

De Gelder suspects that TN’s ability to detect obstacles might arise from optic flow effects as he moves towards them. It’s a hypothesis she has yet to prove, but it is telling, she says, that his performance on the obstacle course deteriorates when he wears goggles that block his peripheral vision. Optic flow is exemplified by the opening sequence of the film Star Trek, in which stars moving past the starship Enterprise give viewers the impression they are moving into the screen, and the effect is most-pronounced at the periphery of the visual field.

The other possibility is that TN is making use of a separate visual pathway altogether. This second pathway bypasses the LGN and is mediated instead by a structure in the brainstem called the superior colliculus. The brainstem is the oldest part of the brain, evolutionarily speaking, and this pathway is not accessible to consciousness. This month, TN was back in Geneva for more tests. Though the scientists haven’t yet found any hard evidence of regeneration or reorganisation in his brain since his strokes, his condition seems to have improved. Larry Weiskrantz, an emeritus professor of psychology at Oxford University, has identified two subtypes of blindsight: type 1, in which patients perceive nothing at all, and type 2, in which they have an impression of seeing something, but cannot say what it is.

“TN seems to have shifted from type 1 to type 2,” says Pegna. He now complains of visual hallucinations, for example. De Gelder says that in healthy people, the streams of information that makeupvision – the perception of colour, motion and form – are integrated into one seamless visual percept, and that this integration may be performed with the help of consciousness. Because TN is not conscious of what he sees, he may have lost that coherent quality of his perceptual experience, while retaining some or all of the separate components of it.

Last month, when I had the opportunity to watch him, TN negotiated obstacle courses more efficiently than he did two years ago, though he still wasn’t comfortable relying on his subconscious skills, asking for someone’s arm when he left the testing situation. And he remained unable to identify the obstacles. When, in de Gelder’s experiment that had him follow a white line on the floor, I replaced a wooden stick as the obstacle, he still asked: “Is someone there?”

When it came to detecting facial emotion, his slight recovery seemed, counter-intuitively, to have impaired his performance. Though his amygdalae responded as before in brain scans, his rate of successful identification of the facial expressions he was looking at was now no higher than 50 per cent, which is the same as getting it right by chance. Pegna thinks he may have been trying to interpret those vague impressions that he has. In other words, conscious processes may have been interfering with his subconscious seeing.

Ultimately, the researchers’ goal is to understand how the normal brain sees. The subconscious visual pathway is present in all of us, for example, but do healthy people use it? Is it normally suppressed by the conscious pathway, or does it constantly feed into and influence our conscious visual experience, perhaps by directing our attention to, and so amplifying the signal from, relevant aspects of the visual scene? For the moment these questions have no answers, but with the continued cooperation of TN and other visually impaired patients, Pegna and de Gelder hope it won’t be long before they do.

Sport
Brazilian fans watch the match for third place between Brazil and Netherlands
world cup 2014Brazil 0 Netherlands 3: Dutch pile on the misery in third place playoff
Sport
Robin van Persie hands his third-place medal to a supporter
Van Persie gives bronze medal to eccentric fan moments after being handed it by Blatter
Arts and Entertainment
TV The follow-up documentary that has got locals worried
Arts and Entertainment
'Deep Breath' is Peter Capaldi's first full-length adventure as the twelfth Doctor
TVFirst episode of new series has ended up on the internet
PROMOTED VIDEO
News
Ian Thorpe had Rio 2016 in his sights
people
Arts and Entertainment
Original Netflix series such as Orange Is The New Black are to benefit from a 'substantial' increase in investment
TVHoax announcement had caused outrage
Life and Style
Swimsuit, £245, by Agent Provocateur
fashion

Diving in at the deep end is no excuse for shirking the style stakes

News
Monkey business: Serkis is the king of the non-human character performance
peopleFirst Gollum, then King Kong - now the actor is swinging through trees in Dawn of the Planet of the Apes
Arts and Entertainment
Blackman: Landscape of children’s literature does not reflect the cultural diversity of young people
booksMalorie Blackman appeals for a better ethnic mix of authors and characters and the illustrator Quentin Blake comes to the rescue
News
One Direction star Harry Styles who says he has no plans to follow his pal Cara Delevingne down the catwalk.
peopleManagement confirms rumours singer is going it alone are false
Voices
Mrs Brown's Boy: D'Movie has been a huge commercial success
voicesWhen it comes to national stereotyping, the Irish know it can pay to play up to outsiders' expectations, says DJ Taylor
Arts and Entertainment
Curtain calls: Madani Younis
theatreMadani Younis wants the neighbourhood to follow his work as closely as his audiences do
News
ebookA unique anthology of reporting and analysis of a crucial period of history
Life and Style
Douglas McMaster says the food industry is ‘traumatised’
food + drinkSilo in Brighton will have just six staple dishes on the menu every day, including one meat option, one fish, one vegan, and one 'wild card'
Sport
Mario Balotelli, Divock Origi, Loic Remy, Wilfried Bony and Karim Benzema
transfersBony, Benzema and the other transfer targets
Life and Style
Once a month, waistline watcher Suran steps into a 3D body scanner that maps his body shape and records measurements with pinpoint accuracy
techFrom heart rates to happiness, there is little this fast-growing, self-tracking community won't monitor
News
Soft power: Matthew Barzun
peopleThe US Ambassador to London, Matthew Barzun, holds 'jeans and beer' gigs at his official residence. He says it's all part of the job
Sport
Joe Root and James Anderson celebrate their record-beaking partnership
cricketEngland's last-wicket stand against India rewrites the history books
Independent
Travel Shop
the manor
Up to 70% off luxury travel
on city breaks Find out more
santorini
Up to 70% off luxury travel
on chic beach resorts Find out more
sardina foodie
Up to 70% off luxury travel
on country retreats Find out more
Have you tried new the Independent Digital Edition apps?
Independent Dating
and  

By clicking 'Search' you
are agreeing to our
Terms of Use.

iJobs Job Widget
iJobs General

Information Security Manager (ISO 27001, Accreditation, ITIL)

£70000 per annum: Harrington Starr: Information Security Manager (ISO 27001, A...

C# Developer (HTML5, JavaScript, ASP.NET, Mathematics, Entity)

£30000 - £45000 per annum + Benefits + Bonus: Harrington Starr: C# Developer (...

C# Integration Developer (.NET, Tibco EMS, SQL 2008/2012, XML)

£60000 - £80000 per annum + Benefits + Bonus: Harrington Starr: C# Integration...

Biztalk - outstanding opportunity

£75000 - £85000 per annum + ex bens: Deerfoot IT Resources Limited: Biztalk Te...

Day In a Page

Iraq crisis: How Saudi Arabia helped Isis take over the north of the country

How Saudi Arabia helped Isis take over northern Iraq

A speech by an ex-MI6 boss hints at a plan going back over a decade. In some areas, being Shia is akin to being a Jew in Nazi Germany, says Patrick Cockburn
The evolution of Andy Serkis: First Gollum, then King Kong - now the actor is swinging through the trees in Dawn of the Planet of the Apes

The evolution of Andy Serkis

First Gollum, then King Kong - now the actor is swinging through the trees in Dawn of the Planet of the Apes
You thought 'Benefits Street' was controversial: Follow-up documentary 'Immigrant Street' has got locals worried

You thought 'Benefits Street' was controversial...

Follow-up documentary 'Immigrant Street' has got locals worried
Refugee children from Central America let down by Washington's high ideals

Refugee children let down by Washington's high ideals

Democrats and Republicans refuse to set aside their differences to cope with the influx of desperate Central Americas, says Rupert Cornwell
Children's books are too white, says Laureate

Children's books are too white, says Laureate

Malorie Blackman appeals for a better ethnic mix of authors and characters and the illustrator Quentin Blake comes to the rescue
Blackest is the new black: Scientists have developed a material so dark that you can't see it...

Blackest is the new black

Scientists have developed a material so dark that you can't see it...
Matthew Barzun: America's diplomatic dude

Matthew Barzun: America's diplomatic dude

The US Ambassador to London holds 'jeans and beer' gigs at his official residence – it's all part of the job, he tells Chris Green
Meet the Quantified Selfers: From heart rates to happiness, there is little this fast-growing, self-tracking community won't monitor

Meet the 'Quantified Selfers'

From heart rates to happiness, there is little this fast-growing, self-tracking community won't monitor
Madani Younis: Five-star reviews are just the opening act for British theatre's first non-white artistic director

Five-star reviews are just the opening act for British theatre's first non-white artistic director

Madani Younis wants the neighbourhood to follow his work as closely as his audiences do
Mrs Brown and her boys: are they having a laugh?

Mrs Brown and her boys: are they having a laugh?

When it comes to national stereotyping, the Irish – among others – know it can pay to play up to outsiders' expectations, says DJ Taylor
Gavin Maxwell's bitter legacy: Was the otter man the wildlife champion he appeared to be?

Otter man Gavin Maxwell's bitter legacy

The aristocrat's eccentric devotion to his pets inspired a generation. But our greatest living nature writer believes his legacy has been quite toxic
Joanna Rowsell: The World Champion cyclist on breaking her collarbone, shattering her teeth - and dealing with alopecia

Joanna Rowsell: 'I wear my wig to look normal'

The World Champion cyclist on breaking her collarbone, shattering her teeth - and dealing with alopecia
Bill Granger recipes: Our chef gives raw ingredients a lift with his quick marinades

Bill Granger's quick and delicious marinades

Our chef's marinades are great for weekend barbecuing, but are also a delicious way of injecting flavour into, and breaking the monotony of, weekday meals
Germany vs Argentina World Cup 2014 preview: Why Brazilians don't love their neighbours Argentina any more

Anyone but Argentina – why Brazilians don’t love their neighbours any more

The hosts will be supporting Germany in today's World Cup final, reports Alex Bellos
The Open 2014: Time again to ask that major question - can Lee Westwood win at last?

The Open 2014

Time again to ask that major question - can Lee Westwood win at last?