Usability Evaluation for Video Games (Part 3): Psychophysiological Measures
Hello, and welcome to this third and final part of a series on Usability Evaluation for Video Games. In the first part of this series (here) I talked about the necessity to have a framework upon which to base our understanding of player actions. In the second part (here) I gave some examples and ideas on how to use different types of formal usability evaluation methods, to gauge how usable our games are. In this third part, I will talk about some more exotic methods of usability evaluation. These methods, are just now starting to become affordable by the masses, because the technology that is required to perform them used to be extremely expensive. However, as all things technology, the tools' prices are starting to fall, with a few tools out there that are actually in the affordable range, even by hobbyists. The measures that I will present here are all grouped under the name "psychophysiological measures".
So what are these things?These measures receive input from various places of the human body. Usually, measures that fall under this category are eye-tracking, pupilometry, electroencephalography (EEG), electromyography (EKG), and galvanic skin response (GSR). To understand these, I will present each measure together with its related technology, and what that technology actually measures.
Eye tracking allows us to see where the users have looked over a certain time period of working with a program. This technique used to involve having users restrain their heads with various types of restraining devices, so that their eyes' positions would remain stationary over the course of an observation, but now these restrictions are gone. This technique is difficult when using on a game that has rapidly changing visual structures, because eye tracking shines at showing where users look at most of the time. Thus, it is mostly used for website evaluations, and in marketing research.
However, all is not lost for eye-tracking. There are certain places where examining what our players look at is extremely helpful. For example, Key Lime Interactive used it to examine how players use the UI elements of their games (the UI is usually static over the course of a game). Read more about how they performed their study here.
Another measure that could be used during game evaluations is the measurement of pupil dilation over the course of playing a game. Pupils dilate as a response to emotional arousal, attention, and cognitive load (i.e., the amount of information a person is thinking about). Thus, this measure could be used to understand where players find things difficult, to the point of feeling like giving up. Usually, pupilometry can be performed with instruments that are found on good eye trackers.
The two measures together provide a good way of exploring games in terms of game analytics, and examining where players have problems that can turn an otherwise great game into a challenge nightmare, leading to players dropping the game and expressing dissatisfaction because of the game being too hard!
EEG together with EMG and GSR are more exotic (!) measures that require much more expensive equipment than eye-trackers. However, there are some limited functionality, affordable gear that may be used for EEG. The results from the EEG are brainwave data that voltage fluctuations resulting from ionic current flows within the neurons of the brain.
Measurements from the EEG can be used to examine the psychological state of a player, without resorting to the think-aloud protocol that tends to interrupt the thinking process, and distracts the player from the game. Thus, once more, this type of usability evaluation may not provide too much about usability problems in the game, but it will provide clues about how the player feels about our game. The other plus of the method is that the data are taken live during play, not through distracting the player, and not after the player finishes the play session.
EMG is another exotic measure, used to measure muscle tension. EMGs for game evaluation can be used to measure the tension of muscles on the face, which tense according to specific emotions. For example, we can measure muscle tension in muscles that tense when the players smile and frown, thus gaining significant insights about when the players have problems, when the players find the game funny, and when they are challenged, again during the play session.
Galvanic Skin Response (GSR)
One last measure that is used to gauge the emotions of players is GSR. The measurement of skin conductance provides us a way of looking at the players' emotional arousal, and more specifically their happiness level. It seems that the skin gives a different measurement when we are happy and when we are sad. Therefore, GSR is another way of getting live readings during a play session of the player's emotional state.
The evaluation techniques and measures that were presented in this post are more technically oriented than in my other posts. I hope that this post has shined a little more light into the obscure world of emotional measurements and eye-tracking, and has provided at least some ideas about how to receive more feedback about our game designs than those that are given verbally by game testers.