Category Archives: Forcing functions

Design with Intent presentation from Persuasive 2008

EDIT: I’ve now added the audio! Thanks everyone for the suggestions on how best to do it; the audio is hosted on this site rather than the Internet Archive as the buffering seemed to stall a bit too much. Let me know if you have any problems.

I’ve put my presentation from Persuasive 2008 on SlideShare, – because of the visual style it really needs to be listened to, or viewed alongside the text (below, or in the comments when viewing it on the SlideShare site). Alternatively, just download it [PPT, 11.6 Mb] – it comes with the notes.

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Getting someone to do things in a particular order (Part 3)

Continued from part 2

This series is looking at what design techniques/mechanisms are applicable to guiding a user to follow a process or path, performing actions in a specified sequence. The techniques fall roughly into three ‘approaches’. In this post, I’m going to examine the Poka-yoke approach. If you’ve been following the previous posts, you’ll probably have thought, “Well, all that’s pretty obvious.” And it is obvious – we encounter these kinds of design techniques in products and systems every day – but that’s part of the point of this bit of the research: understanding what’s out there already.

Poka-yoke approach

The mechanisms described in this approach are all based on technical (rather than explicitly human) factors, and involve designing the relationships between system elements.

Poka-yoke (Japanese: mistake-proofing) is an approach usually applied in manufacturing engineering, developed by Shigeo Shingo in the context of developing ‘zero defect’ assembly processes. The idea is to avoid slip-type errors by designing systems which prevent them occurring, prevent a user proceeding until the error condition has been rectified (control poka-yokes), or at the very least clearly warn the user of the error condition (warning poka-yokes).

Generally, when the design intent is for the user to follow a process or path in a specified sequence, a deviation from that sequence can be considered as an error, and thus the poka-yoke approach can be applicable outside its original field. Similar concepts, forcing functions, have been developed in interaction design, especially in the work of Donald Norman – the three main forcing function mechanisms, Interlock, Lock-in and Lock-out, broadly correspond to Shingo’s control poka-yoke category; all can help in assisting (or forcing) users to follow a process or sequence. In the warning poka-yoke category, the Arrangement detection mechanism is most relevant to this behaviour.

Interlock

An Interlock combines elements of both lock-ins and lock-outs (see below), and is probably the most familiar forcing function mechanism: the ability to use one function is dependent on another running or being started, another component (such as a guard) being in place, or some other condition being fulfilled.

Toyota Verso clutch-ignition interlockToyota Verso clutch-ignition interlockToyota Verso clutch-ignition interlock
Example: This Toyota Verso requires the clutch pedal to be depressed before the starter button will operate, to reduce the risk of starting in gear.

Car ignitions which cannot be operated unless the driver’s seat belt is fastened – a system originally promoted as ‘Interlock’ in the US – microwave ovens not operating unless the door is closed, and airline or train toilets where the lighting does not operate until the user has locked the door, are some of the highest profile everyday examples, but the principle of the interlock is extremely common in engineering and manufacturing industry, often in the context of a machine tool which will not start until a guard is in place, or where opening the case automatically cuts the power.

Interlocks are often specified when it is imperative – rather than merely desirable – that a user follow a particular sequence, or at least two steps of a sequence, in exactly the right order, but their use need not be limited to critical safety design problems. Ecodesign applications might include (for example) a car’s air conditioning system requiring the windows to be fully closed before operating, or a sink requiring the plug to be in before the tap can be left in a ‘running’ position.

Microwave oven door interlockMicrowave oven door interlock
Example: The ubiquitous interlock on a microwave oven ensures that the door is closed before the oven will start.

Lock-in

The Lock-in mechanism in this context (rather than an economic one) refers to a system arranged such that a process, procedure or operation is kept active – the user can’t exit the operation until a certain condition is met, or the ‘correct’ next step is taken. This can be implemented using sensors, logic processing, physical architecture, or a number of other ways.

As Norman puts it, this prevents “someone from prematurely stopping” an operation – this could mean letting some ongoing process run its course to completion before starting the next, or denying the user access to another function which might interfere with the current process. It can also prevent accidental cancelling of an operation – inadvertent deviation from a specified sequence – by introducing an extra ‘confirmation’ step.

Confirmation dialogue
Example: The confirmation dialogue displayed by some software when a user attempts to exit can be seen as a lock-in to prevent inadvertent ending of the application.

Lock-out

Lock-out is closely related to Lock-in: in this case, the mechanism makes it difficult or impossible for the user to start certain operations, or denies or impedes access to particular areas or functions. In the context of encouraging or forcing a user to follow a path or process in a specified sequence, a lock-out helps prevent inadvertent or mistaken steps in that sequence. It can also help prevent an operation being started too early in the sequence, and may also be implemented as an extra ‘confirmation’ step.

Lock-out dialogue
Example: This file backup application prevents a user modifying the properties of a scheduled backup task while it is running – ensuring that the correct sequence is followed.

Arrangement detection

Arrangement detection is a ‘warning’ rather than ‘control’ poka-yoke mechanism, and may be considered as a ‘feedback’ analogue of interlocks, lock-ins and lock-outs – providing a warning (audible, visual, tactile) when system elements are incorrectly arranged (physically or procedurally).

Arrangement detection is about warning the user that the path or process is occurring in an incorrect sequence, rather than actually forcing the user to follow the correct sequence. While there are a number of possible warning poka-yoke mechanisms alerting users to incorrect behaviour, arrangement detection is most relevant to the specific issue of sequencing.

Seatbelt warning
Example: The seat belt warning on car dashboards (in this case a Fiat Punto) is an arrangement detection poka-yoke, providing a visual (and often also audible) alert that a belt is not buckled while the engine is running, or the car is moving.

In part 4, we’ll look at the Persuasive Interface approach to getting someone to do things in a particular order.

Home-made instant poka-yokes

Everyday poka-yoke

Update: Also known as Useful Landmines in the 43 Folders world – thanks Pantufla!

Mistake-proofing – poka-yoke – can be as simple as encouraging/forcing yourself to do things in a sequence, to avoid forgetting or avoiding intermediate steps. If you’re the sort of person who hangs a jacket or bag on the door handle, so it can’t be forgotten on the way out, puts things in front of the door so you can’t forget them when you’re going out, or at the top or bottom of the stairs so you’ll remember to carry them to their intended destination next time you’re using the stairs, you’re engaged in mistake-proofing. You’re introducing a behaviour-shaping constraint to assist your own effectiveness.

In the above photo, putting the mobile phone (on-charge) inside a shoe makes it more likely that it will be remembered when going out: the act of putting the shoes on requires the user to pick up the phone, which could otherwise be easily forgotten. Similarly, Mark Hurst (of Good Experience and ‘Broken’ fame) regularly features two very simple poka-yoke procedures in his Uncle Mark’s Gift Guide & Almanac:

How to remember if the batteries aren’t in your camera

Summary: If the batteries are dead, or aren’t in the camera, keep the battery compartment open.

Description: When you’re charging your camera batteries (in a wall charger, say), keep the camera’s battery compartment open. That way, if you pick up your camera to put it in your pocket or purse, you’ll see that the battery compartment is open and will remember that the batteries aren’t in it.

Leaving the camera battery door open

There’s also this:

How to make sure they see the papers you dropped off

Summary: Put the papers on their chair.

Description: Here’s a tip I learned years ago and have used ever since. If you want to make sure that someone sees the papers you dropped off at their desk, put the papers on their chair. The natural inclination is to drop the files on the keyboard, or beside the mousepad. What’s the first thing the person does when they get back to their desk? They shove the papers aside, onto a nearby pile. They want to check their e-mail immediately, and those papers are in the way!

But put the papers on their chair, and watch what happens: the person refuses to sit on them! They take a second to pick them up, and while they’re in-hand, the person takes a look at the files while they get comfortable in the chair. Bingo: you guarantee attention to your drop-off.

Papers on chair

Of course the papers-on-chair method can also be used to remind (or discipline) yourself about dealing with important papers.

This kind of very simple sequencing poka-yoke comes almost naturally in our everyday lives, at least with certain tasks. Sometimes it’s simply reminding ourselves to do something (e.g. putting a Post-It note somewhere we can see it); other times it’s trying to prevent us proceeding until some action has been taken (e.g. putting a Post-It note right in the middle of the computer screen so we can’t ignore it). Donald Norman’s Things That Make Us Smart has some interesting discussion of the power of Post-It notes and their importance as “information in the world”, disburdening some of our mental load – also part of the whole Getting Things Done phenomenon.

Sometimes we even (consciously or otherwise) try to ‘trick’ ourselves into behaving how we want to (or know we should) – the random offset alarm clock (patent; Halfbakery discussion) and Gauri Nanda’s “runaway success” Clocky being examples that spring to mind. (I once had a bedside clock radio where the button to set the minutes no longer worked, which meant that I could only set it either on-the-hour, or, because I forgot to do it at the right moment, set it maybe between 5 and 30 minutes fast. That meant that there was an uncertainty built into every time I glanced at the display, and indeed every time the alarm went off. I was rarely late, as a result.)

I have a hunch that almost trivially simple sequencing poka-yokes (in particular) could be important in designing for sustainable behaviour, such as reducing energy use and waste generation. For example, if your rubbish bin had a recycling box built into the top, so that you had to lift it out of the way (hinged, perhaps, to make it hassle to remove entirely) before putting anything into the main bin, it would be difficult to ignore the recycling box. Hence, learning as much as possible about different methods people use to mistake-proof themselves, or shape their own everyday behaviour, is likely to be useful in exapnding this line of research.

So, what are the everyday home-spun (or otherwise) tricks you use to help mistake-proof yourself?

Spear’s Spellmaster: Poka-yoke in the classroom

Back in September we looked at Mentor Teaching Machines, a clever type of non-linear textbook from the early 1970s which guides/constrains the user’s progression, in the process diagnosing some common types of misunderstanding and ‘remedying’ them. The comments were enlightening, too: there’s a lot more history to programmed teaching texts and programmed instruction than I realised, and I will certainly be covering some of this, and what useful design principles and inspiration can be drawn from it, at some point.

Now, this is not in the same league, but interesting nonetheless: a ‘game’ to teach children (4 years onwards) spelling using a poka-yoke technique. The Spellmaster, from J W Spear & Sons – the example here is from 1980 (the Enfield factory was closed after a Mattel takeover in 1994) featured eighty plastic letter tiles, Scrabble-like but larger, with raised pegs underneath, a different pattern for each letter.

Spear's Spellmaster

Spear's Spellmaster

Spear's Spellmaster

Spear's SpellmasterSpear's Spellmaster

The letter tiles are used to spell the names of objects and concepts (colours, numbers) illustrated on punched cards which fit onto a backing board, the tiles only fitting in their spaces correctly if the pegs pattern aligns perfectly with the punched holes. If the wrong letter is used, the tile doesn’t fit properly and sits at an angle rather than snapping neatly into place. The ‘snap’ of a correctly positioned letter is actually pretty satisfying – surprisingly so, given the combination of plastic (urea formaldehyde, I think) and 30-year old cardboard.

Spear's Spellmaster

Spear's Spellmaster

Spear's SpellmasterSpear's Spellmaster
Left: The wrong tile – the pegs do not align with the punched holes. Right: The correct tile – everything lines up. Below: The wrong tile here – note the extra peg on the left-hand edge of the tile, which doesn’t match up with the punched hole, and leads to the tile not sitting down properly.
Spear's Spellmaster

Spear's Spellmaster

Letters which could work either way up, such as ‘o’ and ‘s’ have – as would be hoped – symmetrical peg patterns. It’s a simple system, but it’s clever and while not offering any ‘remedial’ function to the child, I would think it’s not too likely that many children would try all 25 other letters assuming the first one didn’t fit. Hence, there is some bias against pure trial-and-error. It’s interesting to think how immediately we might consider a computer-based solution to this kind of design brief today, where a purely physical one would work very well and give a different kind of tactile satisfaction.

Spear's Spellmaster

Spear's Spellmaster

I believe in mirror-queues

Meagan Call has written a very interesting piece examining the technique used in some (women’s) public restrooms* of moving the mirrors to the wall near the entrance/exit, rather than behind the sinks as might be expected (and is usually found in mens’ facilities), to lessen queueing and speed up throughflow:

No mirrors behind the sinks: photo by Meagan CallMirrors by exit instead: photo by Meagan Call

Women often linger, using the excess water from their recently scrubbed hands to squish, flatten, and fluff their hair. I’ve seen women who don’t bother to wash their hands bend over the sinks to play with their hair or re-touch makeup. And of course, some women go into the restroom for the sole purpose of looking into the mirror. No mirror equals less congestion, people washing their hands can get to the sinks more easily, and will leave more quickly.

Moving the mirror near the doors is actually an intelligent solution… by moving the mirrors away from the water, primping is less desirable. In addition, by placing it in the pathway of the door, people are more likely to feel foolish and in the way, and are therefore more likely to pass by quickly. The open space does not invite people to stay and look in the mirror.

Meagan’s analysis is spot-on – this is a clever technique which is subtle enough not to be noticed by the majority of users, but which nevertheless shapes their behaviour. The agenda is one of social benefit (for the greater good of the other users, reducing congestion) rather than explicitly commercial (in the context of the service area where the facilities are located), but it presumably has the effect of reducing complaints, hence increasing customer satisfaction even if only marginally.

We’ve looked before at some of the issues around mirrors in a retail environment, but in a confirmation/corollary of Meagan’s thoughts, I’ll end with two pertinent quotes:

Stand and watch what happens at any reflective surface – we preen like chimps, men and women alike… Mirrors slow shoppers in their tracks, a very good idea for whatever merchandise happens to be in the vicinity.

Paco Underhill, Why We Buy.

A large hotel in an American city received many complaints about the slowness of its elevators. It installed mirrors next to the elevator doors. The complaints ended.

Lawrence Lessig, Code and Other Laws of Cyberspace

………..

*/bathrooms/toilets/conveniences/other

Photos from Meagan Call.

Do you really need to print that?

Do you really need to print that?
Do you really need to print that?

This is not difficult to do, once you know how. Of course, it’s not terribly useful, since a) most people don’t read the display on a printer unless an error occurs, or b) you’re only likely to see it once you’ve already sent something to print.

Is this kind of very, very weak persuasion – actually worthwhile? From a user’s point of view, it’s less intrusive than, say, a dialogue box that asks “Are you sure you want to print that? Think of the environment” every time you try to print something (which would become deeply irritating for many users), but when applied thoughtfully, as (in a different area of paper consumption) in Pete Kazanjy’s These Come From Trees initiative, or even in various e-mail footers* (below), there may actually be some worthwhile influence on user behaviour. It’s not ‘micropersuasion’ in Steve Rubel’s sense, exactly, but there is some commonality.

Please consider the environment

I’m thinking that addressing the choices users make when they decide to print (or not print) a document or email could be an interesting specific example to investigate as part of my research, once I get to the stage of user trials. How effective are the different strategies in actually reducing paper/energy/toner/fuser/ink consumption and waste generation? Would better use of ‘Printer-friendly’ style sheets for webpages save a lot of unnecessary reprints due to cut-off words and broken layouts? Should, say, two pages per sheet become the default when a dicument goes above a certain number of pages? Should users be warned if widows (not so much orphans) are going to increase the number of sheets needed, or should the leading be automatically adjusted (by default) to prevent this? What happens if we make it easier to avoid printing banner ads and other junk? What happens if we make the paper tray smaller so the user is reminded of just how much paper he/she is getting through? What happens if we include a display showing the cost (financially) of the toner/ink, paper and electricity so far each day, or for each user? What happens if we ration paper for each user and allow him or her to ‘trade’ with other users? What happens if we give users a ‘reward’ for reaching targets of reducing printer usage, month-on-month? And so on. (The HP MOPy Fish – cited in B J Fogg’s Persuasive Technology – is an example of the opposite intention: a system designed to encourage users to print more, by rewarding them.)

Printing is an interesting area, since it allows the possibility of testing out both software and hardware tactics for causing behaviour change, which I’m keen to do.