The Secret Behind Angry Birds

The usual question: Over the past 30+ years as a consultant in the field generally known as human factors engineering (aka usability engineering), I have been asked by hundreds of clients why users don’t find their company’s software engaging. The answer to this persistent question is complex but never truly elusive. This question yields to experience and professional usability analysis.

The unusual question: Surprisingly, it is a rare client indeed who asks the opposing question: why is an interface so engaging that users cannot stop interacting with it? This is a difficult question because it requires cognitive reverse engineering to determine what interaction attributes a successful interface embodies that result in a psychologically engaging user experience. This question pops up when products become massively successful based on their user experience design – think iPhone, iPad, Google Instant Search, Nintendo Wii, Microsoft Kinect.

The interesting question: Recently clients have asked about the phenomenally successful casual computer game Angry Birds, designed for mobile phones, tablets and other platforms. For those who don’t have a clue what Angry Birds is all about, here is a quick synopsis. The game involves employing a sling shot to propel small cannonball-shaped birds with really bad attitudes at rather fragile glass and timber houses populated by basically catatonic green pigs. The basic thrust of the game is to bring about the demise of the pigs as quickly and expertly as possible by collapsing the pigs’ houses on top of their (sometimes) helmeted heads. Obviously, this sounds like a truly dumb concept. However, there is a catch.

Why is it that over 50 million individuals have downloaded this simple game? Many paid a few dollars or more for the advanced version. More compelling is the fact that not only do huge numbers download this game, they play it with such focus that the total number of hours consumed by Angry Birds players world-wide is roughly 200 million minutes a DAY, which translates into 1.2 billion hours a year. To compare, all person-hours spent creating and updating Wikipedia totals about 100 million hours over the entire life span of Wikipedia (Neiman Journalism Lab). I say these Angry Birds are clearly up to something worth looking into. Why is this seemly simple game so massively compelling? Creating truly engaging software experiences is far more complex than one might assume, even in the simplest of computer games. Here is some of the cognitive science behind why Angry Birds is a truly winning user experience.

Simple yet engaging interaction concept: This seems an obvious point, but few realize that a simple interaction model need not be, and rarely is, procedurally simple. Simplification means once users have a relatively brief period of experience with the software, their mental model of how the interface behaves is well formed and fully embedded. This is known technically as schema formation. In truly great user interfaces, this critical bit of skill acquisition takes place during a specific use cycle known as the First User Experience or FUE. When users are able to construct a robust schema quickly, they routinely rate the user interface as “simple”. However, simple does not equal engaging. It is possible to create a user interface solution that is initially perceived by users as simple. However, the challenge is to create a desire by users to continue interaction with a system over time, what we call user “engagement”.

What makes a user interface engaging is adding more detail to the user’s mental model at just the right time. Angry Birds’ simple interaction model is easy to learn because it allows the user to quickly develop a mental model of the game’s interaction methodology, core strategy and scoring processes. It is engaging, in fact addictive, due to the carefully scripted expansion of the user’s mental model of the strategy component and incremental increases in problem/solution methodology. These little birds are packed with clever behaviors that expand the user’s mental model at just the point when game-level complexity is increased. The process of creating simple, engaging interaction models turns out to be exceedingly complex. Most groups developing software today think expansion of the user’s mental model is for the birds. Not necessarily so.

Cleverly managed response time: A universal law of user interface design is “the faster the response time, the better”. True enough, there are applications where this is patently true. For example, Google has made this a mantra for their systems. However, surprisingly few software developers realize that response time management is actually a resource that can be leveraged to add to the quality and depth of engagement of a user interface. The surprising point that is often misunderstood is that not every aspect of the user interface needs to be or should be as fast as possible. Programmers uniformly have a really hard time with this one and few game designers take advantage of this potent variable. In most commercial software interfaces, response time management is completely overlooked even by those who claim to be UI design experts. The developers of Angry Birds managed response time in a way that goes far beyond simply “faster is better”.

For example, in Angry Birds, it was possible for the programmers to have made the flight of the birds fast – very fast, but they didn’t. Instead they programmed the flight of the angry flock to be leisure pace as they arc across the sky heading for the pigs’ glass houses. This slowed response time, combined with a carefully crafted trajectory trace (the flight path of the bird), solves one huge problem for all user interfaces – error correction. The vast majority of software user interfaces have no consideration for how users can be taught by experience with the system to improve their performance. This problem is a vast and complex issue for screen-based trading systems where error correction is not only essential, but also career threatening.

In Angry Birds game play the pigs also take a long time to expire once their houses are sent to bits. In many play sequences, seconds are consumed as the pigs teeter, slide and roll off planks or are crushed under slow falling debris. This response time of  3-5 seconds, in most user interfaces, brings users to the point of exasperation, but not with Angry Birds. Again, really smart response time management gives the user time to relax and think about how lame they are compared to their 4 year old who is already at the 26th level. It also gives the user time to structure an error correction strategy (more arc, more speed, better strategy) to improve performance on the next shot. The bottom line on how Angry Birds manages response time: fast is good, clever is better.

Short-term memory management: It is a well-known fact of cognitive science that human short-term memory (SM), when compared to other attributes of our memory systems, is exceedingly limited. This fact has been the focus of thousands of studies over the last 50 years. Scientists have poked and prodded this aspect of human cognition to determine exactly how SM operates and what impacts SM effectiveness. As we go about our daily lives, short-term memory makes it possible for you to engage with all manner of technology and the environment in general. SM is a temporary memory that allows us to remember a very limited number of discrete items, behaviors, or patterns for a short period of time. SM makes it possible for you to operate without constant referral to long-term memory, a much more complex and time-consuming process. This is critical because SM is fast and easily configured, which allows one to adapt instantly to situations that might otherwise be fatal if one were required to access long-term memory. In computer-speak, human short-term memory is also highly volatile. This means it can be erased instantly, or more importantly, it can be overwritten by other information coming into the human perceptual system. Where things get interesting is the point where poor user interface design impacts the demand placed on SM. For example, a user interface design solution that requires the user to view information on one screen, store it in short-term memory, and then reenter that same information in a data field on another screen seems like a trivial task. Research shows that it is difficult to do accurately, especially if some other form of stimulus flows between the memorization of the data from the first screen and before the user enters the data in the second. This disruptive data flow can be in almost any form, but as a general rule, anything that is engaging, such as conversation, noise, motion, or worst of all, a combination of all three, is likely to totally erase SM. When you encounter this type of data flow before you complete transfer of data using short-term memory, chances are very good that when you go back to retrieve important information from short-term memory, it is gone!

One would logically assume that any aspect of user interface design that taxes short-term memory is a really bad idea. As was the case with response time, a more refined view leads to surprising insights into how one can use the degradation of short-term memory to actually improve game play engagement. Angry Birds is a surprisingly smart manager of the player’s short-term memory.

By simple manipulation of the user interface, Angry Birds designers created significant short-term memory loss, which in turn increases game play complexity but in a way that is not perceived by the player as negative and adds to the addictive nature of the game itself. The subtle, yet powerful concept employed in Angry Birds is to bend short-term memory but not to actually break it. If you do break SM, make sure you give the user a very simple, fast way to accurately reload. There are many examples in the Angry Birds game model of this principle in action. Probably one of the most compelling is the simple screen flow manipulation at the beginning of each new play sequence. When the screen first loads, the user is shown a very quick view of the structure that is protecting the pigs. Just as quickly, the structure is moved off screen to the right in a simple sliding motion.

Coming into view on the left is a bevy of bouncing, chatting and flipping birds sitting behind the slingshot. These little characters are engaging in a way that for the most part erases the player’s memory of the structure design, which is critical to determining a strategy for demolishing the pig’s house. Predictably, the user scrolls the interface back to the right to get another look at the structure. The game allows the user to reload short-term memory easily and quickly. Watch almost anyone play Angry Birds and you see this behavior repeated time and again. One of the main benefits of playing Angry Birds on the iPad is the ability to pinch down the window size so you can keep the entire game space (birds & pigs in houses) in full view all the time. Keeping all aspects of the game’s interface in full view prevents short-term memory loss and improves the rate at which you acquire skills necessary to move up to a higher game level. Side note: If you want the ultimate Angry Birds experience use a POGO pen on the iPad with the display pinched down to view the entire game space. This gives you finer control, better targeting and rapidly changing game play. The net impact in cognitive terms is a vastly superior skill acquisition profile. However, you will also find that the game is less interesting to play over extended periods. Why does this happen?

Mystery: You probably do not know how to recognize it, but Angry Birds has it. To add context to this idea, mystery is all around us in the things we find truly compelling. The element or attribute of mystery is present in all great art, advertising, movies, products, and not surprisingly, interactive games. The idea of mystery in a user experience as an attribute for increasing user engagement is embedded in the idea of mystery (conceptual depth). We all experience the impact of mystery when we view a cubist period Picasso, recall the famous Apple 1984 super bowl ad, or listen to Miles Davis.  He is said to have described jazz as playing the spaces between the notes, not the notes themselves. Mystery is present when you pick up an iPad for the first time. Why are the icons spaced out across the screen when they could be clustered much closer together to save space. Why does the default screen saver look like water on the inside of the screen?

Mystery is that second layer of attributes that are present but undefined explicitly, yet somehow created with just enough context to consume mental resources in subtle and compelling ways. At its most basic level, experiencing mystery in what we interact with makes you ask the question, “Why did they do that?”.  What we mean here is, “Why did they do that? – A good thing, not “What were they thinking? – A bad thing.  If you think carefully about the experiences you have in the ebb and flow of life, you realize that the most compelling are those that force you to think long and hard about why a given thing is the way it is. For example, why did Frank Gehry create the Guggenheim Museum Bilboa using the shapes he did? The famous architect could have created any shape concept, but why did he choose those shapes? It’s a mystery – we do not know and probably neither does he. What we do know is that his creation is cited as one of the most important works of contemporary architecture. In the same way that a building can captivate millions of sightseers, the element of mystery (conceptual depth) can help sell a few million copies of a simple interactive game.

Angry Birds is full of these little mysteries. For example, why are tiny bananas suddenly strewn about in some play sequences and not in others? Why do the houses containing pigs shake ever so slightly at the beginning of each game play sequence? Why is the game’s play space showing a cross section of underground rocks and dirt? Why do the birds somersault into the sling shot sometimes and not others? One can spend a lot of time on the Acela processing these little clues, consciously or subconsciously. When users of technology process information in this way, it is very likely that they are more deeply engaged than without these small questions.

How things sound: Over the past 15 years, the neuroscience of music has taken a huge leap forward. This new research is just beginning to tell us why music adds such a strong emotional component to movies, advertising, theater, and of course, new media of all types, including casual computer games. Employing the power of audio stimuli including structured music often adds a critical level of engagement for users of all forms of technology. Angry Birds’ audio effects and music seem simple but are, in fact, very complex. The use of audio effects and carefully varied melodic music lines works to enhance the game play engagement level. Many games do this but few do it expertly. The audio in Angry Birds serves to enhance the user’s experience by mapping tightly to the user’s simple mental model of conflict between the angry birds and the loathsome pigs. This concept, known in film production as “action syncing”, provides enhanced levels of the feedback for users at just the right time. For example, in Angry Birds, we hear the birds chatter angry encouragement to their colleagues as each prepares for launch. We hear avian dialogue as the birds arc toward their targets and hear the pained response from their victims when they strike their targets. The pigs are by no means silent. When the avian interlopers fail, they are often egged on to try just one more time by the snickering, grinning pigs. These consistently applied audio elements reinforce the player’s interactions and deepen engagement by emphasizing the anthropomorphic qualities of the main characters of the game and providing clever enhanced feedback during critical on-screen behaviors. What about the actual melodic music shifting from the foreground to the background without apparent reason? This musical thread running through the game play experience is mysteriously familiar and easily understood in the context of the overall theme of the game. Where have I heard that melody before? This combination of audio feedback is varied just enough that parents sitting in the next room are rarely prone to demanding an end to game play based on distracting musical repetition. Perhaps this explains the high number of hours spent playing the game!

How things look: Angry Birds has a look. One might characterize the visual style of Angry Birds as a combination of “high-camp cartoon” with a bit of greeting card graphics tossed in for good measure.

This leads to a more interesting question: How does visual design impact success in the marketplace? I routinely get this question from clients who are undertaking large redesign or new development projects. Decades after it first surfaced in automobile design, visual design is still the most contentious aspect of designing compelling user experiences. Designers (mostly of the UX stripe) routinely sell clients on the concept that the visual design (graphic style) of a given interface solution is a critical factor in success. This assumption seems to make good intuitive sense. However, the actual working principle is counter-intuitive. In most user experience design solutions, visual design (how things look) is technically a hygiene factor. You get serious negative points if it is missing, but minimal positive lift beyond first impression, if a user interface has great visual design. When we conduct user engagement studies for clients (not the same as usability testing), we routinely see data that strongly supports this theory. This concept does not apply to all user experience design problems, but in most cases it holds well. The ultimate question is how much visual design is enough?  Even more important than good or bad visual design is appropriate visual design. On this metric, Angry Birds again has just the right set of attributes. The concept of appropriate visual design is in itself complex as designers generally apply too much rendering and engineers apply none, which often leaves the actual user staring at the equivalent of an engineering prototype (Google) or alternatively, World of Warcraft. After decades of experience in user interface design, I can predict fairly accurately the corporate software development bias of clients by simply examining the user interfaces of their products. I cannot imagine Google as anything but engineering-driven, despite the apparently large number of UX designers hired in recent years.

Measuring that which some say cannot be measured: How does one measure visual design in this context? There are several well-understood methodologies for assessing the appropriateness of visual design that we employ in development projects. These research methods make objective that which is thought to be only subjective. Visual design can be measured, rated, and scaled to the benefit of users and those who develop such interfaces. The actual dimensions of appropriate and winning visual design vary widely, depending on the application but in game design two factors reign supreme. First, the visual design must be memorable and second, it must convey the desired attributes of the game play model.

So memorable is Angry Birds that the developers have deals for real world “brand extensions”, including Angry Birds stuffed toys, t-shirts, and all matter of off-the-wall consumer goods that make BIG profits. The simple visual design of those tiny cartoon-ish birds is so compelling and simple, it brings an additional level of continuous interest to the game play experience. Of note too is the world the birds and pigs inhabit which changes in strange and subtle ways with every level. Visual design is another critical dimension of the success of Angry Birds, which leads to the ultimate question: Is Angry Birds the best it can be? Not by a long shot!

We are left with the notion that a cognitive teardown of a truly compelling user experience is vastly more interesting and insightful than simply answering the opposite question: why is a given user interface dysfunctional? To summarize, in the context of Angry Birds, success is bound up in slowing down that which could be fast, erasing that which is easily renewable, and making visual that which is mysterious and memorable. Over the past 10 years, our firm has conducted user engagement studies on hundreds of user interfaces. The vast number did not get one principle right, much less six.  You go Birds! Your success certainly makes other Angry and envious.