Psychologically Tricked: Perceived Speed in an iPhone Game

In a recent iPhone game project I was involved with at itemis the player had to gain speed by tapping on the touch screen. Several game elements conveyed the impression of acceleration to motivate the player achieving this goal. The 3D game graphic of fly-by elements in a canyon were supported by a crescendo of game sounds and as with any serious racing game there was a speedometer, too.

Update: Read the follow-up post about the NIVEA FOR MEN WaterfallRace.

Different functions to separate actual and displayed speed values

During our first phase of interaction tests we constantly got the feedback that the speedo was not accurate, though. Players had the impression to be way faster than the value displayed by the gauge. Others complained about how hard it was to gain speed in the lower region.

We decided to separate the actual speed used for game logic from the displayed value as shown by the speedometer. The paper “Rethinking the Progress Bar” I stumbled across a while ago when I was improving the user experience of a desktop application came in handy to do so. Chris Harrison et. al. discuss how different update rates of ordinary progress bars change the user’s perception of progress duration. They come up with some simple, yet useful functions to map a real progress value x to the displayed value f(x).

Selection of functions as described in Rethinking the Progress Bar

Whereas the results in the paper highlight functions that produce an accelerating progress bar in the end we needed to achieve the opposite for our game.

My speed is quite good by now but I am not at top speed, yet. I will try harder.

On slow speed ranges our speedometer simulated a higher speed and greater variation on speed changes. Beginners got immediate feedback and felt success that way. High speed values on the other hand were visually more difficult to achieve. That behavior seemed to motivate advanced players.

We first used the Inverse Fast Power function but eventually settled on Late Pause. No player ever mentioned a mismatch between the actual and the displayed value after our adjustments and nobody seemed to recognize the fake.


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  1. Markus Klink says:

    Very nice article. I think the Hamburger public transport employs the same formula when calculating how long it takes for the next train to arrive. I never measured it, but the last minutes seem to fly by, whereas the first ones are always longer.

  2. [...] the iPhone game project I have written about before we had to implement a highly dynamic 3D scene in great detail here at itemis. From a third-person [...]

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