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Now you see it, now you don't: what optical illusions tell us about our brains

Illusions can offer insights into how the visual system processes images.

Maurits Escher: where do the staircases lead?

The human brain is a network of about 20 billion neurons – nerve cells – linked by several trillion connections. Not to mention glial cells, which scientists used to think were inactive scaffolding, but increasingly view as an essential part of how the brain works. Our brains give us movement, language, senses, memories, consciousness and personality. We know a lot more about the brain than we used to, but it still seems far too complicated for human understanding.

Fortunately, the brain contains many small networks of neurons that carry out some specific function: vision, hearing, movement. It makes sense to tackle these simple modules first. Moreover, we have good mathematical models of nerve cell behaviour. In 1952, Alan Hodgkin and Andrew Huxley wrote down the “Hodgkin-Huxley equations” for the transmission of a nerve impulse, which won them the 1963 Nobel Prize in Medicine. We also have effective techniques for understanding small networks’ components and how they are linked.

Many of these simple networks occur in the visual system. We used to think that the eye was like a camera, taking a “snapshot” of the outside world that was stored in the brain like a photo stuck in an album. It uses a lens to focus an image on to the retina at the back of the eye, which functions a bit like a roll of film – or, in today’s digital cameras, a charge-coupled device, storing an image pixel by pixel. But we now know that when the retina sends information to the brain’s visual cortex, the similarity to a camera ends.

Although we get a strong impression that what we are seeing is “out there” in front of us, what determines that perception resides inside our own heads. The brain decomposes images into simple pieces, works out what they are, “labels” them with that information, and reassembles them. When we see three sheep and two pigs in a field, we “know” which bits are sheep, which are pigs, and how many of each there are. If you try to program a computer to do that, you quickly realise how tricky the process is. Only very recently have computers been able to distinguish between faces, let alone sheep and pigs.

Probing the brain’s detailed activity is difficult. Rapid progress is being made, but it still takes a huge effort to get reliable information. But when science cannot observe something directly, it infers it, working indirectly. An effective way to infer how something functions is to see what it does when it goes wrong. It may be hard to understand a bridge while it stays up, but you can learn a lot about strength of materials when it collapses.

The visual system can “go wrong” in several interesting ways. Hallucinogenic drugs can change how neurons behave, producing dramatic images such as spinning spirals, which originate not in the eye, but in the brain. Some images even cause the brain to misinterpret what it’s seeing without outside help. We call them optical illusions.

One of the earliest was discovered in Renaissance Italy in the 16th century. Giambattista della Porta was the middle of three surviving sons of a wealthy merchant nobleman who became secretary to the Holy Roman emperor Charles V. The father was an intellectual, and Giambattista grew up in a house in Naples that hosted innumerable mathematicians, scientists, poets and musicians. He became an outstanding polymath, with publications on secret codes (including writing on the inside of eggshells), physiology, botany, agriculture, engineering, and much else. He wrote more than 20 plays.

Della Porta was particularly interested in the science of light. He made definitive improvements to the camera obscura, a device that projects an image of the outside world into a darkened room; he claimed to have invented the telescope before Galileo, and very likely did. His De refractione optices of 1593 contained the first report of a curious optical effect. He arranged two books so that one was visible to one eye only and the other to the other eye. Instead of seeing a combination of the two images, he perceived them alternately. He discovered that he could select either image at will by consciously switching his attention. This phenomenon is known today as binocular rivalry.

Two other distinct but related effects are impossible figures and visual illusions. In rivalry, each image appears unambiguous, but the eyes are shown conflicting images. In the other two phenomena, both eyes see the same image, but in one case it doesn’t make sense, and in the other it makes sense but is ambiguous.

Impossible figures at first sight seem to be entirely normal, but depict things that cannot exist – such as Roger Shepard’s 1990 drawing of an elephant in which everything above the knees makes sense, and everything below the knees makes sense, but the two regions do not fit together correctly. The Dutch artist Maurits Escher made frequent use of this kind of visual quirk.

In 1832, the Swiss crystallographer Louis Necker invented his “Necker cube” illusion, a skeletal cube that seems to switch its orientation repeatedly. An 1892 issue of the humorous German magazine Fliegende Blätter contains a picture with the caption “Which animals are most like each other?” and the answer “Rabbit and duck”. In a 1915 issue of the American magazine Puck, the cartoonist Ely William Hill published “My wife and my mother-in-law”, based on an 1888 German postcard. The image can be seen either as a young lady looking back over her shoulder, or as an elderly woman facing forwards. Several of Salvador Dalí’s paintings include illusions; especially Slave Market With the Apparition of the Invisible Bust of Voltaire, where a number of figures and everyday objects, carefully arranged, combine to give the impression of the French writer’s face.

Illusions offer insights into how the visual system processes images. The first few stages are fairly well understood. The top layer in the visual cortex detects edges of objects and the direction in which they are pointing. This information is passed to lower layers, which detect places where the direction suddenly changes, such as corners. Eventually some region in the cortex detects that you are looking at a human face and that it belongs to Aunt Matilda. Other parts of the brain are alerted, and you belatedly remember that tomorrow is her birthday and hurry off to buy a present.

These things don’t happen by magic. They have a very definite rationale, and that’s where the mathematics comes in. The top layer of the visual cortex contains innumerable tiny stacks of nerve cells. Each stack is like a pile of pancakes, and each pancake is a network of neurons that is sensitive to edges that point in one specific direction: one o’clock, two o’clock and so on.

For simplicity, call this network a cell; it does no harm to think of it as a single neuron. Roughly speaking, the cell at the top of the stack senses edges at the one o’clock position, the next one down corresponds to the two o’clock angle, and so on. If one cell receives a suitable input signal, it “fires”, telling all the other cells in its stack: “I’ve seen a boundary in the five o’clock direction.” However, another cell in the same stack might disagree, claiming the direction is at seven o’clock. How to resolve this conflict?

Neurons are linked by two kinds of connection, excitatory and inhibitory. If a neuron activates an excitatory connection, those at the other end of it are more likely to fire themselves. An inhibitory connection makes them less likely to fire. The cortex uses inhibitory connections to reach a definite decision. When a cell fires, it sends inhibitory signals to all of the other cells in its stack. These signals compete for attention. If the five o’clock signal is stronger than the seven o’clock one, for instance, the seven o’clock one gets shut down. The cells in effect “vote” on which direction they are detecting and the winner takes all.

Many neuroscientists think that something very similar is going on in visual illusions and rivalry. Think of the duck and rabbit with two possible interpretations. Hugh R Wilson, a neuroscientist at the Centre for Vision Research at York University, Toronto, proposed the simplest model, one stack with just two cells. Rodica Curtu, a mathematician at the University of Iowa, John Rinzel, a biomathematician then at the National Institutes of Health, and several other scientists have analysed this model in more detail. The basic idea is that one cell fires if the picture looks like a duck, the other if it resembles a rabbit. Because of the inhibitory connections, the winner should take all. Except that, in this illusion, it doesn’t quite work, because the two choices are equally plausible. That’s what makes it an illusion. So both cells want to fire. But they can’t, because of those inhibitory connections. Yet neither can they both remain quiescent, because the incoming signals encourage them to fire.

One possibility is that random signals coming from elsewhere in the brain might introduce a bias of perception, so that one cell still wins. However, the mathematical model predicts that, even without such bias, the signals in both cells should oscillate from active to inactive and back again, each becoming active when the other is not. It’s as if the network is dithering: the two cells take turns to fire and the network perceives the image as a duck, then as a rabbit, and keeps switching from one to the other. Which is what happens in reality.

Generalising from this observation, Wilson proposed a similar type of network that can model decision-making in the brain – which political party to support, for instance. But now the network consists of several stacks. Maybe one stack represents immigration policy, another unemployment, a third financial regulation, and so on. Each stack consists of cells that “recognise” a distinct policy feature. So the financial regulation stack has cells that recognise state regulation by law, self-regulation by the industry, or free-market economics.

The overall political stance of any given political party is a choice of one cell from each stack – one policy decision on each issue. Each prospective voter has his or her preferences, and these might not match those of any particular party. If these choices are used as inputs to the network, it will identify the party that most closely fits what the voter prefers. That decision can then be passed to other areas of the brain. Some voters may find themselves in a state akin to a visual illusion, vacillating between Labour and Liberal Democrat, or Conservative and Ukip.

This idea is speculative and it is not intended to be a literal description of how we decide whom to vote for. It is a schematic outline of something more complex, involving many regions of the brain. However, it provides a simple and flexible model for decision-making by a neural network, and in particular it shows that simple networks can do the job quite well. Martin Golubitsky of the Mathematical Biosciences Institute at Ohio State University and Casey O Diekman of the University of Michigan wondered whether Wilson’s networks could be used to model more complex examples of rivalry and illusions. Crucially, the resulting models allow specific predictions about experiments that have not yet been performed, making the whole idea scientifically testable.

The first success of this approach helped to explain an experiment that had already been carried out, with puzzling results. When the brain reassembles the separate bits of an image, it is said to “bind” these pieces. Rivalry provides evidence that binding occurs, by making it go wrong. In a rivalry experiment carried out in 2006 by S W Hong and S K Shevell, the subject’s left eye is shown a horizontal grid of grey and pink lines while the right eye sees a vertical grid of grey and green lines. Many subjects perceive an alternation between the images, just as della Porta did with his books. But some see two different images alternating: pink and green vertical lines, and pink and green horizontal lines – images shown to neither eye. This effect is called colour misbinding; it tells us that the reassembly process has matched colour to grid direction incorrectly. It is as if della Porta had ended up seeing another book altogether.

Golubitsky and Diekman studied the simplest Wilson network corresponding to this experiment. It has two stacks: one for colour, one for grid direction. Each stack has two cells. In the “colour” stack one cell detects pink and the other green; in the “orientation” stack one cell detects vertical and the other horizontal. As usual, there are inhibitory connections within each stack to ensure a winner-takes-all decision.

Following Wilson’s general scheme, they also added excitatory connections between cells in distinct stacks, representing the combinations of colour and direction that occur in the two “learned” images – those actually presented to the two eyes. Then they used recent mathematical techniques to list the patterns that arise in such a network. They found two types of oscillatory pattern. One corresponds to alternation between the two learned images. The other corresponds precisely to alternation between the two images seen in colour misbinding.

Colour misbinding is therefore a natural feature of the dynamics of Wilson networks. Although the network is “set up” to detect the two learned images, its structure produces an unexpected side effect: two images that were not learned. The rivalry experiment reveals hints of the brain’s hidden wiring. The same techniques apply to many other experiments, including some that have not yet been performed. They lead to very specific predictions, including more circumstances in which subjects will observe patterns that were not presented to either eye.

Similar models also apply to illusions. However, the excitatory connections cannot be determined by the images shown to the two eyes, because both eyes see the same image. One suggestion is that the connections may be determined by what your visual system already “knows” about real objects.

Take the celebrated moving illusion called “the spinning dancer”. Some observers see the solid silhouette of a dancer spinning anticlockwise, others clockwise. Sometimes, the direction of spin seems to switch suddenly.

We know that the top half of a spinning dancer can spin either clockwise or anticlockwise. Ditto for the bottom half. In principle, if the top half spins one way but the bottom half spins the other way, you would see the same silhouette, as if both were moving together. When people are shown “the spinning dancer”, no one sees the halves moving independently. If the top half spins clockwise, so does the bottom half.

Why do our brains do this? We can model that information using a series of stacks that correspond to different parts of the dancer’s body. The brain’s prior knowledge sets up a set of excitatory connections between all cells that sense clockwise motion, and another set of excitatory connections between all “anticlockwise” cells. We can also add inhibitory connections between the “clockwise” and the “anticlockwise” cells. These connections collectively tell the network that all parts of the object being perceived must spin in the same direction at any instant. Our brains don’t allow for a “half and half” interpretation.

When we analyse this network mathematically, it turns out that the cells switch repeatedly between a state in which all clockwise cells are firing but the anticlockwise ones are quiescent, and a state in which all anticlockwise cells are firing but the clockwise ones are quiescent. The upshot is that we perceive the whole figure of the dancer switching directions. Similar networks provide sensible models for many other illusions, including some in which there are three different inputs.

These models provide a common framework for both rivalry and illusion, and they unify many experiments, explain otherwise puzzling results and make new predictions that can be tested. They also tell us that in principle the brain can carry out some apparently complex tasks using simple networks. (What it does in practice is probably different in detail, but could well follow the same general lines.)

This could help make sense of a real brain, as new experiments improve our ability to observe its “wiring diagram”. It might not be as ambitious as trying to model the whole thing on a computer, but modesty can be a virtue. Since simple networks behave in strange and unexpected ways, what incomprehensible quirks might a complicated network have?

Perhaps Dalí, and Escher, and the spinning dancer can help us find out. 

Ian Stewart is Emeritus Professor of Mathematics and Digital Media Fellow at the University of Warwick

Laura Hynd for New Statesman
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Having the last laugh

How Diane Abbott – overlooked, mocked and marginalised by her own party for three decades – ended up as the closest ally of a Labour leader

“I don’t think you’re up to it.” It is 1970, and Diane Julie Abbott, aged 17, is keen to apply to Cambridge University, but her history teacher has other ideas.

“I was an omnivorous reader,” she says now, sitting in her parliamentary office, in a prime spot overlooking the Thames, “and in all these books, particularly these novels between the wars, if you went to university, you went to Oxford or Cambridge.”

The teachers at Harrow County School for Girls, where Abbott was the only black girl in her class, were not supportive. Her memories are less happy than those of her contemporary Michael Portillo, who attended the affiliated boys’ grammar school, and who played Macduff to her Lady Macduff in a school play.

Even when Abbott succeeded, she was regarded with suspicion. She remembers getting an A-minus in an English class – a mark that disappointed her – and being asked to stay behind by the teacher. “She picked up my essay between her thumb and her forefinger and said: ‘Where did you copy this from?’ I was genuinely shocked.”

The story suggests that she acquired her ability to shrug off criticism early. It is also a reminder of how often she is underestimated. The Times journalist Matt Chorley once described a successful day for Labour as one in which “Diane Abbott was on TV a bit less”. Julie Burchill described her in the Spectator as a “preposterous creature” who “blotted the landscape of English politics, speaking power to truth in order to advance her career”. In the Guardian, Michael White dubbed her a “useful idiot”.

She has been endlessly dismissed as stupid, untalented and bad at politics – an obvious “diversity hire”. These criticisms are immune to evidence: her time at Cambridge, the only black British student from a state school in the entire university; her 12 years on the sofa with Portillo on BBC1’s This Week; her time in the shadow cabinet under Ed Miliband; her reliable ability to hold the line in television interviews; and now her status as Jeremy Corbyn’s closest political ally. She is largely ignored by lobby journalists, even as they lament their failure to secure a line into the Labour leader’s thinking. In 2017, Diane Abbott celebrates her 30th year in parliament. Should we take her seriously?

 

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Abbott’s mother, a nurse, and her father, a welder, were born in the same village in Jamaica, but met and married in London and lived in Notting Hill “before it was a fashionable place to live”. Abbott was born there in 1953, 12 years before the phrase “race relations” first made its way on to the statute books. “My father was very aspirational,” she recalls, “and so every weekend, he and my mother would drive round houses in Pinner, and every Monday they’d ring the estate agent, and the estate agent would say the house had gone. But, of course, the house wasn’t gone.”

Eventually, they did buy a house, not in Pinner but in Edgware, north London. “My brother – his best friend was Jewish,” she tells me, “and he’d attend the Jewish youth club with his friend, and one day his friend said in a really embarrassed way: ‘I’m really sorry, I’m afraid you can’t continue to attend the club, because they’re afraid it will encourage the girls to marry out.’

“The thing was,” she continues, “my brother was upset about this. We were all upset on his behalf but it was just part of life.” And in 1970, a black straight-A student being told that she wasn’t good enough to go to Cambridge was, again, part of life. It was her response that was out of the ordinary: “Well, I do think I’m up to it. And that’s what matters, isn’t it?”

At university, Abbott didn’t get involved in politics, and she found the Cambridge Union off-putting. Her hall tutor advised her to go into the civil service, and so she arrived at the Home Office in 1976, the lone black graduate trainee on what she now describes as “a quixotic quest to do good”.

In turn, that took her to the National Council for Civil Liberties, now Liberty. Believing it to be a hotbed of communist sympathisers, MI5 tapped the office phones, an action that was ruled unlawful in 1990. “One of the things that Diane still talks about,” a friend tells me, “is her experience not only of the Home Office, but of being the subject of official surveillance. She has a cynicism about the state that hasn’t gone away.”

Abbott also joined local campaigns on some of the issues that have defined her career, such as the abolition of the “sus laws”, the informal provision that allowed the police to stop and search anyone under the ­Vagrancy Act, which activists claim was used to target ethnic minorities in Britain. After joining the Labour Party, she became a councillor in Westminster in 1982.

In the 1970s and 1980s, as today, Labour took the lion’s share of the ethnic minority vote. But no one from an ethnic minority had ever sat as a Labour MP. In the 1983 election, just one person from a minority was selected as a parliamentary candidate, and in an ultra-safe Conservative seat. In response, Labour’s minority activists formed the Black Sections, a campaign to secure ethnic minority representation.

It was through these that Abbott met Linda Bellos, who was the leader of Lambeth Council, where Abbott worked as a press officer – her last job before entering parliament. “I was born here in 1950, one of 50,000 black people [living in the UK],” Bellos tells me. “We might have talked about going home but home for me was bleeding London, wasn’t it? Hence the need to make sure we were involved in all of the parts of the state. Someone like Diane had been to Cambridge, she’d been a councillor, she knew the democratic process, she was friends with a number of MPs, she knew the score. If someone like her couldn’t be selected, what was the point of any of us being here?”

The Black Sections wanted affiliated status, similar to that of the Fabians. But there were concerns that black candidates would not appeal to Labour’s presumed core white working-class vote. Some on the left saw “identity politics” as a distraction from the class struggle; and some on the right thought the Black Sections were too radical. At the 1984 conference, their plan was thrown out by a margin of ten to one.

Despite this setback, the fight had an important legacy. In the 1987 elections, four ethnic minority MPs entered the Commons for Labour: Paul Boateng in Brent South, Keith Vaz in Leicester East, Bernie Grant in Tottenham – and, in Hackney North and Stoke Newington, there was the 33-year-old Diane Abbott.

 

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She was the first black woman to be selected for a safe parliamentary seat. The Times marked the occasion with a leader denouncing her “rhetoric of class struggle and skin-colour consciousness”.

A few months later, the Sun profiled the “ten looniest Labour candidates” in Britain. “We were all there,” Abbott recalls. “Jeremy [Corbyn], the rest of us, and I was number eight.”

The local party in Stoke Newington was delighted with this firebrand reputation. “They said: ‘Stick with us, and we’ll take you right to the top!’”

The voters of north London were less welcoming. A brick was thrown through the office window of her local party. With Abbott as the candidate, some traditional Labour voters switched to the SDP-Liberal Alliance, taking the Labour vote below 50 per cent for the first time in the seat’s history (the second occasion was in 2005, just after the invasion of Iraq).

In parliament, the intake of ethnic minority MPs was regarded with caution. Abbott recalls that the then speaker of the House of Commons, Bernard Weatherill, was “very anxious”. She adds: “He thought we’d be like the Fenians and disrupt and collapse parliamentary process. So he invited Bernie [Grant], who was regarded as our leader, for port. And Bernie came for port and the speaker was very nice to him. And I imagine the speaker thought this was what stopped us being like the Fenians.”

Those Labour MPs who were disruptive – such as Corbyn the serial rebel – were in low spirits for other reasons. The marginalisation of Abbott and her allies during the late 1980s and 1990s explains why they have so little sympathy for the party’s beleaguered centrists in the current power struggle.

At the Labour conference in Liverpool this year – where she spoke as shadow health secretary – Abbott told me: “I came to party conference every year for 20 years, and we would lose and lose and lose. These people have lost twice and they’re complaining!”

Her thick skin was toughened during the New Labour years – and it reaffirmed her close friendship with Corbyn. (The two had a short sexual relationship in the early 1980s, which ended amicably. Abbott was married for two years to a Ghanaian architect from 1991 to 1993; her son, James, was born in 1992.) “She’s always had an odd hold on Jeremy,” one Labour MP tells me. “You would see them having lunch together and her bossing him about. I think people underestimate how influential she
is on his thinking.”

When David Lammy, her neighbouring MP in Tottenham, entered parliament in 2000 following the death of Bernie Grant, he found her “vilified, ostracised and exiled by the Blairites”. There were several attempts to remove her as an MP – another reason why the Corbyn camp is unconcerned by complaints from MPs such as Stella Creasy and Peter Kyle about their local parties threatening to deselect them.

Abbott retains a network of friends from her time before politics, including from her stint as a television producer. They urged her to quit in the Blair years – or to end her association with the left-wing Socialist Campaign Group. “I never thought I was willing to trade what I thought was right for some position in the party,” she says.

Some allies see it differently. “I don’t think Diane is someone who can quit [politics],” a friend told me. “I see her tweeting at all hours. She has interests, books and so forth, but she couldn’t walk away.”

Abbott says that Keith Vaz convinced her to stay, telling her, “You have forgotten what it took for us to get here.” (Some of Corbyn’s allies believe that this is what made the leader so supportive of Vaz during his latest scandal.) This sense of solidarity with other ethnic minority MPs has led to the long-standing rumour that Abbott would have nominated Chuka Umunna had Corbyn not stood for the Labour leadership.

“Diane is absolutely loyal to Jeremy,” one MP who knows them both well tells me. “She’s loyal to the project, yes, but she’s also loyal to him, in a way I don’t think you could honestly say about John McDonnell or Clive Lewis.” During the coup attempt against Corbyn last summer, Abbott spoke forcefully in favour of Corbyn remaining in place, rather than striking a deal to put Lewis or McDonnell on the ballot. “Her position,” one insider recalls, “was that we’d got a candidate we knew could win, and that candidate was Jeremy.”

Not that they always agree. Abbott advocated a less conciliatory approach after Corbyn’s first victory in 2015. “The thing that can be infuriating about Jeremy is that he likes to think the best of everyone,” she says. “I’m always perfectly straight with him as to what I think, and even if he doesn’t believe me at the time, he always does come round to my point of view.”

Abbott is one of the few people in the Parliamentary Labour Party whom Corbyn trusts completely. In their relationship, it’s hard to see who is the senior partner.

In the late 1990s and early 2000s, Corbyn and Abbott settled into a pattern of dissent, followed by defeat. Corbyn spent the time attending to foreign and human rights campaigns and signing thousands of early day motions. Abbott carved out a niche as a reliable critic of the Labour government under Tony Blair, with a month-long slot at the launch of the BBC’s This Week in 2003 blossoming into a regular gig alongside Michael Portillo. But away from Westminster, Abbott was making a decision that she knew could destroy her political career.

 

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The London borough of Hackney is today a national leader in schooling, but in 2002, just a third of students received five or more A*-C grades. That prompted Abbott to send her ten-year-old son, James, to City of London, a leading private school.

“I knew I could lose the seat over it,” she told me. “I was a single parent, and time after time, I had not been there for things at school, or I was too tired to take him out somewhere . . . I just thought, just this once, I should be prepared to make a sacrifice for him. If I lost the seat, then I lost the seat.”

She kept the seat. “Other things do annoy Diane – reporters saying things about her that aren’t true, people talking down to her,” one friend tells me. “But with [the schooling] I think she was very happy with that deal and to take that blow.”

Then, in 2010, Abbott’s career began a surprising second act: a bid for the party leadership. Activists and commentators felt uninspired by the choice in front of them – Ed Miliband, David Miliband, Andy Burnham and Ed Balls, four former special advisers from the New Labour era. Abbott called them “geeky men in suits”. Harriet Harman, in particular, was keen that the contest should not be an all-male field. Her support swayed Abbott. “If you had to pick one person, it was her,” she says, “because she was more mainstream.”

David Lammy set up a meeting between Abbott and David Miliband. The front-runner told her that, if she were a vote short in the nominations from MPs, he would vote for her. “But because it was David Miliband, I didn’t believe him.”

The elder Miliband had his own reasons for backing her. He believed that having her on the ballot would deprive his brother, Ed, of valuable support from the left. This was also the calculation that allies of Yvette Cooper made about Corbyn in 2015. “David’s legacy,” the Wakefield MP, Mary Creagh, wrote five years later, “made it normal – Blairite, even – to put a left-winger on the ballot to ‘have a broad debate’.’’

Of Corbyn’s campaign, Abbott says now: “I knew he’d do well, because what people missed is that had it been one person, one vote [in 2010], I’d have come third.”

Had the unions and the MPs not had a disproportionate influence on the result, she says, “I’d have beaten Andy Burnham, I’d have beaten Ed Balls. I’d been to 53 hustings – most Labour people are where Jeremy and I were. I knew there was much more left-wing sentiment in the Labour Party than the lobby thought.”

As a result of Corbyn’s victory in 2015, she is shadowing one of the great offices of state in what once looked like her final term in parliament. Her policy priorities as shadow home secretary are broad but include her favoured subjects of police reform and anti-racism. “I want to help shape the debate on migration,” she tells me. “I think we’ve had a very vacuous debate.”

That has put her at odds with the shadow chancellor, John McDonnell. Though both are long-time friends of Corbyn, their relationship is not warm. Allies believe that the division stretches back to the late 1980s, when McDonnell – then outside parliament – gloried in not going “soft” in the manner of Neil Kinnock. Abbott attracted suspicion, in part because of her early conversion to a pro-European position. Many believe that McDonnell never embraced the European project. He has ruled out opposition to Brexit and is behind the toughening of the party’s line on immigration. Abbott, privately and publicly, is determined to hold Labour to a more open and pro-immigration position. She has said that Labour cannot win as “Ukip-lite”, a coded rebuke to McDonnell.

The shadow chancellor is the only MP with a comparable influence to Abbott’s on Jeremy Corbyn and, thus far, the Labour leader has struck a middle path on migration, supporting Abbott’s line that the single market cannot be traded away for restrictions on the free movement of people but stopping short of a full-throated defence of free movement in principle.

As well as winning that internal battle, Abbott faces the task of landing more blows on Amber Rudd than her predecessors – Andy Burnham, Yvette Cooper and Ed Balls – managed against Theresa May when she was the longest-serving home secretary in a century, transforming the reputation of a department once regarded as a political graveyard. Not many give Abbott much chance of success but, as always, she believes in herself and thinks that she’s up to it.

Stephen Bush is special correspondent of the New Statesman

Stephen Bush is special correspondent at the New Statesman. His daily briefing, Morning Call, provides a quick and essential guide to British politics.

This article first appeared in the 12 January 2017 issue of the New Statesman, Putin's revenge