Thursday, April 23, 2009

Basic Human Factors For Multitouch/Interactive Displays

Yet another prospect came to me today looking to reenact the displays in Minority Report.

Don't get me wrong. I'm huge fan of the movie, but the requests for unusable interfaces have become so frequent that I am putting together a little "Human Factors 101" pamphlet for marketers.

I would really appreciate your comments and help getting the word out about good design.

4 Reasons You Don't Want to Be Tom Cruise:
Basic Human Factors for Interactive Displays

Minority Report, Microsoft Surface and Jeff Han's touch demos have created a global sensation. These compelling videos represent the technology that marketers dream of: it is big, splashy and visceral. While these massive interactive displays are really cool in movies, real life solutions need to take the needs and limitations of users into account.

When selecting a multitouch solution, there three human factors issues that you should take into account when choosing a screen size for your interactive display.

Distance From Screen/Foveal View

While we thing we see the world in a “panoramic view”, this is an illusion that is created by our brains. Behind the scenes, our eyes are constantly scanning and updating this view. Our foveas, the part of our eyes that see in “Technicolor” only scans about 5% of our field of view at any given time. The rest of our eye is primarily built to detect motion...changes in the environment that should be updated.

While we may be able to “sense” a 5’ screen at arm’s length, we can only really pay attention to about 18-24” of it at any given time.

Try this experiment. Look in a mirror and stare into your own eyes. Put both hands out in front of you and wiggle your fingers. Continue to move them away from each other, you will feel your eyes pulling to try to track your fingers instead of staring into the mirror when they come in line with your shoulders.

Arm Fatigue

While typing and mousing might cause mild fatigue, making your upper arms defy gravity for hours or even minutes on end is straight up painful. In fact, this position is so painful that CIA used this "Stress Position" to break Guantanamo Detainees.

In extended usage situations, it's important that there be proper support for the users arms and fingers.

In tabletop situations, it is important to avoid scenarios where users need to hover for extended periods of time and where the wrist is hyper-extended (the hand and fingers should be as parallel to the forearm as possible). Top two situations to watch out for here are placing the table at too low (like Microsoft Surface) or placing content too close to the user (so that their wrists need to move perpendicular to the forearm to access it).

In wall mounted situations, interactive content should be above chest height and controllers should be placed as low on the screen as possible. Ideally, users should be able to support their elbows on a table or similar when the device is not in use.

Neck Fatigue

30 years of industrial research by furniture manufacturers has led to commonly available guidelines for table/chair heights, keyboard trays, monitor heights and lighting that make computers comfortable to use. Use it.

One of the findings of the research is that neck pain is a primary causes of decreased task efficiency in the office. Hyper-extending the neck by looking down as one might when typing with a notebook computer on one’s lap is a prime example of poor ergonomics.

A number of typical multitouch formfactors, including the Tabletop computer, the handheld tablet and wall-mounted displays that have content below chest height. This can cause intense pain if used for extended periods of time.

Eye Fatigue

The normal human eye likes to focus at ~28 inches in front of it (approximately the length of a human arm). If type sizes, task patterns or physical factors require users to be closer or farther away, your application will be hard to use. It’s important to note that older users in particular prefer larger point sizes.

While we would all like to look like Tom Cruise, Minority Report should be viewed as the cautionary tale that it is. In reality, none of us want his job. It's a pain in the neck.

If you have other thoughts about content to include, I'd really appreciate your comments. ~Jonathan


  1. Excellent post, Johnathan! I'm going to link to it.

    I think its also important to point out that multitouch on standard desktop monitors and notebook computers is not going to work all that well. For desktop its going to be uncomfortable to sit in your chair with your hands waving in front of you all day. For lap tops, and this is a point you made to me a while back, the hings on the screens will give as you press with your fingers; that or the whole laptop will tip back words. In either case it doesn't work.

    Nice post.

  2. Just to add this :

    Talk about unboxing experience ...

  3. There are certain contexts of use where multi-touch displays will be quite useful; these are in part the same contexts where current touch-screen technology is useful, but multi-touch capabilities will extend the kinds of interactions possible in these environments, and the technology also opens up additional use contexts. To roundly dismiss multi-touch UI's is overly-generalized I think. While I do agree that for many uses these UI's are not truly appropriate and can even be considered to be gimmicks, there are a lot of very powerful applications for these technologies where they can dramatically open up the user experience and empower the user. Large scale public displays are one use, for example, as are institutional information displays which, while not public, have large user bases but feature specific and discreet information architectures. When a large display is an information point accessed by many, intended to provided limited and specific access to content, then in these contexts multi-touch / touch technologies are quite valuable.

    Thanks, and warmest regards.