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Because pupil dilation is correlated with so many different mental and emo-
tional states, it's difficult to say whether pupillary changes indicate successes or
failures in everyday usability testing. However, measuring pupil diameter may be
useful in certain situations where the focus is on the amount of mental concen-
tration or emotional arousal. For example, if you are interested mainly in eliciting
an emotional response to a new graphic on a website, then measuring changes
in pupil diameter (from baseline) may be very useful. To do this, simply measure
the percentage deviation away from a baseline for each participant and then aver-
age those deviations across the participants. Alternatively, you can measure the
percentage of participants who experienced dilated pupils (of a certain amount)
while attending to a particular graphic or performing a specific function.
7.3 MEASURING EMOTION
Measuring emotion is difficult. Emotions are often fleeting, hidden, and con-
flicted. Asking a participant about what she is feeling through an interview or
survey may not always be effective. Many participants tell us what they think
we want to hear or simply have difficulty articulating what they are really feel-
ing. Some are even hesitant or afraid to admit their true feelings to a perfect
stranger.
Despite the difficulty in measuring emotions, it is still very important for the
UX researcher to understand the emotional state of the participant. The partici-
pant's emotional state while experiencing something is almost always a concern.
Most UX researchers use a combination of probing questions, as well as inter-
pretation of their facial expressions, and even body language to infer the partici-
pant's emotional state. This may be acceptable for some products; however, it
does not always suffice. Some products or experiences are relatively much more
emotional and have a greater bearing on the overall user experience. Simply
think about the range of emotions a participant might experience when calcu-
lating how much money he will have when he retires, reading about a health
condition he has, or just playing an action game with friends.
There are essentially three different ways to measure emotions. Emotions can
be inferred based on facial expressions, by skin conductance, or by use of EEG.
This section highlights three different companies that used these three different
approaches. All of these products and services are currently available commercially.
7.3.1 Affectiva and the Q-Sensor
Based on an interview with Daniel Bender, product manager, Affectiva (
www.
The Affective Computing Research group at MIT's Media Lab was founded in
1998 by Professor Rosalind Picard Sc.D. in an effort to develop technologies that
advance understanding of emotions. The aim of the research group is to restore a
proper balance between emotion and cognition in the design of technologies for
addressing human needs (
http://affect.media.mit.edu/
). Picard and coinvestigator
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