The Case for Casual Biometrics

Plenty of triple-A productions use biometric testing of players -- but can it work for casual games, too? Developer Stefano Gualeni writes here about how he and his team tested iOS puzzle game Gua-Le-Ni using a simple lab setup.

Lecturer and developer Stefano Gualeni explains how his team employed biometric testing -- once the purview of big publishers and chiefly used to test action games -- to improve player response to a casual, indie iOS game.

"For the most part, the English and American whale draughtsmen seem entirely content with presenting the mechanical outline of things, such as the vacant profile of the whale; which, so far as picturesqueness of effect is concerned, is about tantamount to sketching the profile of a pyramid."

Herman Melville, Moby Dick; or, The Whale, Chapter LVI - Of the Less Erroneous Pictures of Whales, and the True Pictures of Whaling Scenes.

This article charts the history of a whale. Or rather, it is the story of my whale: the iPad video game titled Gua-Le-Ni; or, The Horrendous Parade.

I designed and developed Gua-Le-Ni between 2011 and 2012 with Italian development studio Double Jungle S.a.S. of Padova, Italy, and I call it "my whale" because one of the main tropes of such game, namely the fascination with mythological creatures, captured my curiosity since my early childhood.

I still remember my mother going through books with etchings of fantastic animals with me, and perhaps it is going through these early memories that the conception for a game involving fantastic beasts was first formed. I am sure it was a similar fascination that drove my decision to become an architect in the first place.

Toy cubes with animal parts printed on their faces constitute the main player-interface for Gua-Le-Ni.

This article tells the story of how my obsessions as an individual, as well as my inclinations as an independent game designer, became entangled with academic research. Specifically, it is about Gua-Le-Ni, and about how the development of the game was influenced by scientific experiments.

To begin with, the production of my game was slowed down and structured in a specific modular to accommodate the needs of the research team at NHTV Breda University of Applied Sciences. The coordinated effort of the Italian development team and the Dutch research team made Gua-Le-Ni the benchmark to assess the possibility to integrate psychophysiological (or biometric) experiments in the quick iterative production cycle of casual and independent game development.

Whereas on a personal level, Gua-Le-Ni is a work of love, a way to embrace my childhood experiences and to explore my understanding of the creative process, for the research team working on my game, it was an object of dispassionate observation reduced to its mechanical and quantifiable workings. Analogous to Melville's pyramid in the quote from Moby Dick, both perspectives are sketches of the same whale -- my whale.

From the point of view of a player, Gua-Le-Ni is an action-puzzle video game that takes place on the wooden desk of an old, befuddled British taxonomist. On his desk lies a fantastic book: a bestiary populated by impossible, finely drawn animals. Just like the monsters of myths and folklore, the impossible creatures in my game are combinations of parts of real animals. To understand what I mean, it might help to think of legendary creatures like the sphinx, the Minotaur, or South Park's Manbearpig.

Feeding the beasts in Gua-Le-Ni does not only temporarily stop their relentless stampeding, but can also modify the beasts' composition or increase their value in terms of points awarded upon their correct cataloguing.

My paper abominations walk across the illustrations of the old bestiary. Above, you can see a CA-BIT-DOR-STER: a four-module beast with the head of a camel, one body part of a rabbit, another of a condor, concluded with a lobster's tail. The main goal of Gua-Le-Ni is to recognize the components of the fantastic creatures and their relative order before one of them manages to flee from the page (which is the Game Over condition).

Mentored by the old taxonomist, the player pursues this purpose by rotating, moving and spinning toy cubes with pictures of animal parts printed on the six faces of the cubes. A paper beast is correctly recognized, and thus prevented from escaping the bestiary, when the player manages to match the illustrations on the top faces of the taxonomic cubes with the paper beast currently in play.

Departing from a player's perspective and taking yet another point of view, namely the academic framework that underlies my doctoral studies, Gua-Le-Ni is a creative artefact that complements my dissertation. It exemplifies the potential of video games for the explanation, the testing and the development of philosophical concepts and questions. In the specific case of my game, the playable philosophical notion is David Hume's understanding of the imaginative capabilities of the human mind. Luckily for you, neither this aspect of the game nor my sickeningly personal design process will be discussed here.

For the sake of the audience of Gamasutra, instead, this article will focus on one aspect of my whale, namely an aspect which has a practical dimension for people developing video games in short production cycles. More specifically, I will present some of the opportunities offered by biometric testing methods for the development of casual video games (the development of which are characterized by quick iterations).

The practical use of biometry in Gua-Le-Ni will be presented as a case study that clearly demonstrates the advantages offered by biometric testing. The benefits and the viability of a biometric approach for the developers of casual games are extensively discussed in the academic papers that discussed our methods and experiments (see references) and will be shortly presented to the reader in the conclusion of this article.

What is Biometry?

I find it useful, when introducing our work to people who are as yet unfamiliar with biometry, to begin explaining the basic functioning of lie detector machines. When utilizing lie detector machines, the body of a test subject is hooked to several sensors capable of recording changes in a range of physiological processes such as her heartbeat, the electrical conductivity of her skin, the frequency of her respiration, and so forth.

Observing variations in such dimensions, the discipline of biometry is capable of approximating an objective account of the test subject's internal state variations. In other words, by measuring how one's body reacts to a certain experience (which could be a set of questions, or the screening of an advertisement, a video game session, etcetera), we can determine one's level of stress, concentration, anxiety, fear, etcetera.

Whereas traditional quality assurance procedures generate highly subjective answers to research questions, biometry offers a method that produces results that are objective and quantifiable.

By monitoring changes in heart rate, skin conductivity, respiration and the contraction of certain key facial muscles, the lie detector-like setup we utilized was capable of providing valuable insights about game design choices as well as materializing the psychophysiological effects the game has on the players.

Employing biometric experiments and methodologies to analyze a video game, you can obtain scientific answers to several questions that are crucial for its development and commercial success. Examples of such questions include:

  • Is the initial speed of our video game too high for our target audience?
  • Did we reach a climax in emotional involvement where and when intended (this is likely to be at the end of our free demo)?
  • Does the tutorial of our video game succeed in keeping our players engaged while empowering them to perform well?
  • How does our target audience respond to the experience of their first Game Over?
  • Is our game too stressful for them? Is it perceived as too punishing?

The employment of biometric measurements is certainly not a new development in the field of video game design, tuning and testing: Triple-A titles such as Valve's Left 4 Dead and EA Sports' NBA Live 2010 have successfully demonstrated the viability and desirability of biometry as an analytical tool and as a factor of change for their products. Our research project and its benchmark video game Gua-Le-Ni pioneered and optimized the application of biometric technologies and methodologies with the objective of making them available for quicker iterations, exploring their viability as development tools for casual and independent video games.

The Initial Biometric Tests

To complement a wider quality assurance campaign based on questionnaires, interviews, blind-testing and hard-core performance tests, the Dutch research team at NHTV Breda University of Applied Sciences ran an initial series of biometric tests on Gua-Le-Ni. The aim of these initial tests was to structure a testing methodology incorporating the added perspective of biometry.

The first biometric analysis we ran on Gua-Le-Ni focused on its accessibility during the first few minutes of gameplay. The task that was assigned to the researchers was to determine biometrically the optimal speed of the game for the target audience indicated by the developers as soon as the player successfully completed the first tutorial. The game design goal in relation to the initial set of tests was that of achieving the feeling that the game was non-threatening and manageable at the most basic level of difficulty, hence likely resulting in an initially pleasant and positive experience for the casual audience we were developing for.

In terms of game logic, the initial speed of the game is determined by the initial walking speed of the beasts. In this sense, the results of the first test in terms of the walking speed of our bizarre creatures became a cornerstone for all the subsequent design decisions concerning the tuning of the speed and the complexity of the game.

The research team ran parallel tests on two slightly different versions of the game: In the first and harder version, the beasts crossed the screen rapidly (in 24 seconds), while in the second, easier version they would walk from one end of the page to the other more slowly (in 30 seconds). When the testers' stress patterns were analyzed and correlated with in-game questionnaires, we found that -- compared to the harder version -- the easier version showed fewer signs of stress in the participants.

Even in the slower version of the game, however, the recorded stress levels were much higher than expected in comparison with other successful casual games we tested biometrically with the same test subjects. The initial walking speed of the beasts was hence deemed still too high our intended players to simply enjoy the game. We could infer this outcome by combining the biometric data with the self-reported ones. As a result of this observation, the initial speed of the beta game was set -- for the tests that followed -- to 34 seconds. This value was further refined after the second set of biometric tests to the initial speed value of 36 seconds, with which the game was released.

A particular consistency in the Game Over pattern also highlighted difficulties for most testers in recognizing specific creature parts. Responding to the difficulties and the criticism of our test group, the graphics for the creature modules in question were redone.

In addition, we picked the lobster (the beast with the highest rate of stress and failures) as the creature to be used as an example in the tutorial, in order for players to familiarize themselves with its quirky appearance as early as possible in the learning curve of the game.

The Second Set of Biometric Experiments

A second series of tests was conducted two months after the initial experiments. The aim of this second series of tests was to understand how a player's performance develops during the first 10 minutes of gameplay.

An important point to clarify is that in the competitive version of the game, the walking speed of the paper creatures increases incrementally after a specific number of creatures have been correctly recognized. The idea behind this design parameter is that if our fantastic creatures are not properly fed, their actions become more frenzied as they grow hungrier in their search for food. In this phase of the testing, the development team wanted to find an ideal balance between the initial speed of the game and the rate of acceleration as players progressively gain skills during their advancement of the game. Specifically, we wanted to find answers to the following questions:

  • Does the game allow players in our target audience to be proficient enough to endure play-sessions of five minutes after three or four games?
  • Does the game make our players excited but not anxious?
  • Do players have a generally positive reaction to the reaching of the Game Over state (which needs to be perceived as fair and encouraging)?

Visual Results for the Second Set of Tests

The graphs below visualize the test results of one of the 14 test subjects that was tested in the second phase of experiments. Each dot on the graph represents a different beast. Blue dots represent beasts that were walking at basic speed, and red dots represent beasts that were wobbling faster than the basic speed.

In the test version of Gua-Le-Ni, the paper beasts were accelerated after the appearance of every four specimens. The vertical line on the graph represents a Game Over state, after which the game resets.

Skin Conductivity graph for test subject 35. Every Game Over (vertical red line) corresponded with a stress peak. As readable in the graph, the first game lasted a little more than one minute, the second a little less than two minutes, and the third almost three minutes.

The first graph tracked a dimension called skin conductivity of one of our test subjects. Skin conductivity provides a basic understanding of how tense or excited a test subject is by tracking the variation in moisture of his or her skin.

The results visualized in the graph above show that during the very first game, which lasted for approximately one minute and 10 seconds, Test Subject 35 was able to successfully categorize all of the beasts at the basic speed level, but failed at the first beast that would wobble faster than the initial speed. The results of the two following gameplay sessions show that excitement levels grow slightly as the difficulty level is increased, and reach extremes at Game Over states.

A game design reading of the skin conductivity graph of test subject 35 demonstrates that the ability to deal with complexity and speed progressively increases. In particular, subject 35 reached a three-minute gameplay session at her third game. This result corresponded with the aspirations of the development team and was regarded as an early success.

Overall, the test results showed that the duration and intensity of the game broadly matched the design intention of empowering the player to cope with slow beasts straight after the tutorial and to reach three-minute gameplay chunks within the first five minutes of gameplay. Nevertheless, combining the results of the biometric testing with the results of traditional questionnaires, I decided to make the game slightly slower. In the released version of the game, the rate of acceleration was also lowered and smoothed.

The second graph, by contrast, shows the variations of a second biometric parameter for the same gameplay session and in the same test subject tracked above. The second graph maps the electrical activity in the Zygomaticus Major muscle (responsible for smiling) during gameplay.

The activity of the Zygomaticus Major (smiling muscle) for test subject 35 during the same three games analyzed above. Every Game Over that was associated with stress peaks in the skin conductivity chart corresponds to a smile in this graph.

A combined reading of the graphs shows that the Game Over condition always invoked a smile in the test subject. When players were questioned about this in the post-gameplay interviews, we learned that such smiles were due to the fact that players could manipulate the cubes in an attempt to categorize the beasts until the very last pixel of the beast's tail is visible on the screen. This feature of the game produced a positive attitude that encouraged players to replay the game. The design feature gave the players a feeling of "almost having made it."

Another interesting conclusion that was inferred from the data is that beast configurations in which there was a large size disparity between heads and bodies generated more smiles. These configurations were perceived to be quirkier. The "WART-DOR" (warthog-condor) and the "RAB-PUS" (rabbit-octopus) were the configurations that elicited the most smiles in our test subjects. Although nothing was done with this information, in retrospect, we could have made these types of configurations appear more frequently in the game.

In Conclusion

Despite the successful employment of biometric testing in the highest strata of the video game industry, a review of recent publications on psychophysiology and video games reveals that it has not yet been adopted by the casual sector. It might be assumed that the costs involved in running biometric experiments make it affordable to the developers of high-end games only, but Gua-Le-Ni is proof that this is not the case.

We needed very little work and money to transform a simple air-conditioned research room in a viably neutral testing environment. Additionally, as witnessed by the release of Nintendo's Wii Fit balance board and its planned but unreleased vitality sensor hardware, biometric equipment is quickly becoming consumer technology -- that is to say, trivially inexpensive and more portable.

If biometric testing is really not economically prohibitive, then why have the developers of casual not embraced its technologies and methodologies games yet?

One possible answer lies in the focus of triple-A titles on action-oriented genres such as shooting, racing, and sports simulations. Whereas the qualities of such games give rise to easily detectable physiological patterns, the same is not always true of casual games such as puzzle games, hidden object games, point and click adventures, etcetera.

What I am arguing here is that the notable absence of biometry in the quality assurance methodologies of the casual sector of our industry can be accounted for by practical reasons as opposed to limitations in development budgets. Accordingly, there are no real obstacles that would prevent casual game developers from employing biometrics in testing action-oriented casual games or in investing in pursuing more research.

Biometric methodologies might, in the near future, also offer the capability of tracking internal states that are more relevant to the growing casual market, such as the level of concentration of the task at hand, the bafflement induced by a cognitive task beyond one's capabilities or the feeling of accomplishment.

The diffusion of expertise and the availability of the interpretative frameworks are also growing, and not only in obscure academic circles: several of our game design undergraduate students are developing graduation projects which involve the design their own biometric experiments, running their tests and the independent analysis of data.

As already hinted in my opening quote, I do not consider psychophysiology to be the ultimate video game analysis tool, nor I ever hoped or believed it could replace traditional game design and quality assurance approaches wholesale. An understanding of biometry as the "holy grail" of casual game development would be naively optimistic and blind to the partial, albeit deep, quality of the insights it provides.

Aside from the objective benefits explained above, and the large quantity of data that are possible to be harvested, working with the added lens of psychophysiology allowed me to talk to my testers about their feelings and intuitions with a more solid ground both when referencing a particular game event and when comparing results with those of other testers in the same target audience. Biometry made my process richer, more accurate, and also more interesting from an anthropological point of view, further fuelling my passion and my curiosity for game design. Personally, it was a refreshing and enriching experience that I am looking forward to repeating with my next, bizarre experiments in combinatorial game design.

From the outlined perspectives, the future of biometric and biofeedback applications in casual game development seems to me to be very promising. Applied research in biometrics is able to continue to attract funds and, even at the current level of economical affordability, the video-ludic employment of biometric technologies has proved capable of delivering both deep insights and objective advantages. Our benchmark case study Gua-Le-Ni, for instance, has received excellent reviews, attaining a current Metacritic score of 83 percent.

Once again, psychophysiology does not universally offer normative answers, but it does grant the possibility to understand players more thoroughly and to better 'draft' the games that we make -- and on these grounds, I believe that it will play an increasingly important role in the future of game development across all sectors of the games industry.

One of our test subjects wearing the complete set of sensors that were used during the second set of biometric tests.

Where whales can slow down their physiological processes when diving in the ocean depths, slowing down the development process of our benchmark title Gua-Le-Ni allowed the researchers to observe physiological processes in players to gain a far deeper understanding of game play experience.

With the more efficient methodologies now in place at NHTV Breda University of Applied Science, the development process would not even have to slow down, thus making the methodology even more viable to be integrated in casual game development iterations. With our efforts both in terms of research and game design we hoped to have opened a fresh, blue ocean for casual and independent developers: biometric game design.

In addition to the valuable information and inspiration that was gleaned from this method of testing, both researchers and test subjects had a whale of a time.


Gualeni, S., Janssen, D., Calvi, L., 2012. How psychophysiology can aid the design process of casual games: A tale of stress, facial muscles, and paper beasts. Full paper on biometry-aided casual game design presented at the 2012 Foundation of Digital Games Conference in Raileigh, NC, United States, May the 30th, 2012.

Gualeni, S., Janssen, D., Calvi, L., 2012. Psychophysiology and casual games: always a good match? Full paper on biometry-aided casual game design presented at the 2012 ECREA Conference in Istanbul, Turkey, October the 24th, 2012.

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