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13.4 Physiological tools 381

13.4 PHYSIOLOGICAL TOOLS

Our bodies are intricate devices, with numerous interrelated systems that change
their behavior as we are excited, frustrated, or otherwise aroused. Each cell in our
body is part of an electrical system, with voltage levels that differ across cell mem-
branes and change under the right conditions (Stern et al., 2001). Blood flow, heart
rate, rate of breathing, and electrical conductivity of various parts of the body are just
a few of the measures that have been studied in an attempt to better understand these
responses. The combination of these physiological measures with more traditional
study of task performance and subjective responses is known as psychophysiology
(Wastell and Newman, 1996).
Psychophysiology brings the possibility of using concrete measurements of the
state of the human body to accompany assessments captured through surveys or ob-
servations. Imagine a study of user frustration levels with a series of alternative inter-
face designs. You might start by asking participants to complete a series of tasks with
each interface. After they complete the tasks, you could ask the users to complete one
or more questionnaires aimed at understanding frustration levels. You might even ask
them which features of the designs were more or less frustrating.
Even though this might be a fine design for your study, it misses some potentially
important and interesting information. For example, when were the users most frus-
trated? Were they frustrated on the same task for each interface or did some designs
cause less frustration on some tasks and more frustration on others? Postfact ques-
tionnaires are simply too coarse-grained to address these questions. The retrospective
nature of questionnaires means that you are relying on the participants' fallible and
incomplete memories to get your results.
Suppose your careful and thorough reading of the appropriate literature tells you
that increases in frustration lead to increases in heart rate. With some sensors, re-
cording equipment, and appropriate training in their use, you could change your
experiment to monitor heart rate during task completion time. Appropriate tools
for synchronizing the physiological data with other data that you collect during the
tasks—such as task completion time or fine-grained records of all activities—will
let you see exactly what the participant was doing when he became most frustrated.
Correlating this information with feedback from the subjective questionnaire will
provide you with a much fuller picture than you would have been able to get from
only the task performance data and subjective responses.

13.4.1 PHYSIOLOGICAL DATA

Appropriate use of physiological data for research requires an understanding of
the types of data that can be collected, the tools required for data collection, and
the ways in which these data sources respond to various stimuli. Skin conductiv-
ity, blood flow, and respiration rate (to name a few examples) are very different
measures, each presenting a variety of challenges in terms of both collection and
interpretation.