​Even as Uber talks up its determination to treat drivers more humanely, it is engaged in a behind-the-scenes experiment in behavioural science to manipulate them in the service of its corporate growth – an effort whose dimensions became evident in interviews with several dozen current and former Uber officials, drivers and social scientists, as well as a review of behavioural research.

Uber's innovations reflect the changing ways companies are managing workers amid the rise of the freelance-based "gig economy". Its drivers are officially independent business owners rather than traditional employees with set schedules. This allows Uber to minimise labor costs but means it cannot compel drivers to show up at a specific place and time. And this lack of control can wreak havoc on a service whose goal is to seamlessly transport passengers whenever and wherever they want.

Uber helps solve this fundamental problem by using psychological inducements and other techniques unearthed by social science to influence when, where and how long drivers work. It's a quest for a perfectly efficient system: a balance between rider demand and driver supply at the lowest cost to passengers and the company.

Employing hundreds of social scientists and data scientists, Uber has experimented with video game techniques, graphics and non-cash rewards of little value that can prod drivers into working longer and harder.

To keep drivers on the road, the company has exploited some people's tendency to set earnings goals, alerting them that they are ever so close to hitting a precious target when they try to log off.

"We show drivers areas of high demand or incentivise them to drive more," said Michael Amodeo, an Uber spokesman. "But any driver can stop work literally at the tap of a button – the decision whether or not to drive is 100 per cent theirs."

Uber's recent emphasis on drivers is no accident. As problems have mounted at the company, from an allegation of sexual harassment in its offices to revelations that it created a tool to deliberately evade regulatory scrutiny, Uber has made softening its posture towards drivers a Litmus test of its ability to become a better corporate citizen.

Because Uber's drivers are independent contractors, they lack most of the protections associated with employment.

"We're talking about this kind of manipulation that literally affects people's income," said Ryan Calo, a law professor at the University of Washington who studies the way companies use data and algorithms to exploit psychological weaknesses. Uber officials, he said, are "using what they know about drivers, their control over the interface and the terms of transaction to channel the behaviour of the driver in the direction they want it to go".

Uber was increasingly concerned that many new drivers were leaving the platform before completing the 25 rides that would earn them a signing bonus. To stem that tide, Uber officials in some cities began experimenting with simple encouragement: You're almost halfway there, congratulations!

While the experiment seemed warm and innocuous, it had in fact been exquisitely calibrated. The company's data scientists had previously discovered that once drivers reached the 25-ride threshold, their rate of attrition fell sharply.

And psychologists and video game designers have long known that encouragement toward a concrete goal can motivate people to complete a task.

"It's getting you to internalise the company's goals," said Chelsea Howe, a prominent video game designer who has spoken out against coercive psychological techniques deployed in games. "Internalised motivation is the most powerful kind."

Mr Amodeo defended the practice. "We try to make the early experience as good as possible, but also as realistic as possible," he said. "We want people to decide for themselves if driving is right for them."

Of course, managers have been borrowing from the logic of games for generations, as when they set up contests and competition among workers. More overt forms of gamification have proliferated during the past decade.

But Uber can go much further. Because it mediates its drivers' entire work experience through an app, there are few limits to the elements it can gamify. Uber collects staggering amounts of data that allow it to discard game features that do not work and refine those that do. And because its workers are contractors, the gamification strategies are not hemmed in by employment law.

When asked whether Uber's product managers and data scientists were akin to developers at a social gaming company like Zynga, Jonathan Hall, Uber's head of economic and policy research, accepted the analogy but rejected the implication.

"I think there's something to that, but ultimately Zynga should worry mostly about how fun its games are rather than trying to get you to play a little bit more by some trick," he said. He argued that exploiting people's psychological tics was unlikely to have more than a marginal effect on how long they played Zynga's games or drove for Uber. It is "icing on the cake", he said.

There are aspects of the platforms that genuinely do increase drivers' control over their work lives, as Uber frequently points out. Unlike most workers, an Uber driver can put in a few hours each day between dropping children off at school and picking them up in the afternoon.

Uber is even in the process of developing a feature that allows drivers to tell the app in advance that they need to arrive at a given location at a given time. "If you need to pick up your kids at soccer practice at 6pm," said Nundu Janakiram, the Uber official in charge of products that improve drivers' experiences, "it will start to give you trips to take you in the general direction to get to a specific place in time."