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13.6 Examples 395

indicated that average response levels were lowest for the multimodal interface,
followed by speech and then gesture interfaces. For all three interfaces, the total
response increased with task complexity. This was interpreted as providing evi-
dence for the utility of using GSR to indicate cognitive loads. Analysis of specific
recordings found GSR peaks to be correlated with stressful or frustrating events,
with responses decreasing over time. Peaks were also correlated with major events
that were thought to be cognitively challenging, including reading instructions and
competing tasks (Shi et al., 2007).
Another study used both galvanic skin response (GSR) and blood-volume pres-
sure (BVP) to measure user frustration in an explicit attempt to develop methods for
using multiple sensing technologies. The experimental design involved a game with
several puzzles. Participants were told that the experimenters were interested in
how brightly colored graphics would influence physiological variables in an online
game. Unbeknown to the participants, the game software was rigged to randomly
introduce episodes of unresponsiveness. As participants were being timed and had
been offered a reward if they had the fastest task completion times, these delays
1
would presumably cause frustration. BVP and GSR responses were used to de-
velop models that could distinguish between frustrating and nonfrustrating states
(Scheirer et al., 2002).
Interaction with computer games is a natural topic for physiological data. As any-
one who has played video games knows, players can become excited while driving
race cars, hunting aliens, or playing basketball on the computer. However, the fast-
paced nature of these games limits the applicability of many techniques. Intrusive
data collection techniques, such as “think-aloud” descriptions, interfere with the
game-playing experience and posttest questionnaires fail to recapture all of the nu-
ances of the playing experience (Mandryk and Inkpen, 2004).
One study used various physiological data sources—GSR, EKG, cardiovascular
rate, respiration rate, and facial EMG—to measure responses to computer games
played against a computer and against a friend. Starting from the premise that the
physiological data would provide objective measures that would be correlated to
players' subjective reports of experiences with video games, the researchers hypoth-
esized that preferences and physiological responses would differ when comparing
playing against a computer to playing against a friend. Specifically, they hypoth-
esized that participants would prefer playing against friends, GSR and EMG values
would be higher (due to increased competition), and that differences between GSR
readings in the two conditions would correspond to subjective ratings (Mandryk and
Inkpen, 2004).
To test these hypotheses, they asked participants to play a hockey video game,
against the computer and against a friend. Participants were recruited in pairs
of friends, so each person knew their opponent. The hypotheses were generally

1
This experimental design is an example of deception (see Chapter 15). At the end of each session,
participant debriefing explained the true purpose of the experiment. Participants were offered the
opportunity to withdraw their data after the debriefing (Scheirer et al., 2002).