Page 395 -

13.4 Physiological tools 385

FIGURE 13.5
An electroencephalography (EEG) recording cap.
From https://commons.wikimedia.org/wiki/File:EEG_Recording_Cap.jpg.

with differences between locations or relative to some average baseline used as
indicators of various types of activity (Stern et al., 2001). Evoked response mea-
surements involve measurements of differentials between electrodes in two lo-
cations (perhaps earlobe and scalp), in response to auditory or visual responses
(Stern et al., 2001).
Functional near-infrared spectroscopy (fNIRS) uses the reflectivity characteris-
tics of the skull, scalp, and brain to measure mental activity. Near-infrared light can
travel 2–3 cm into the brain before being either absorbed or reflected. Wavelengths
that are reflected by hemoglobin can be used to measure mental activity (Izzetoglu
et al., 2004; Hirshfeld et al., 2007). An fNIRS measurement system generally in-
cludes light sources and detectors mounted on a flexible headband.
Preliminary applications to HCI research have examined the ability of fNIRS
to measure mental effort. An examination of the mental effort involved in solving
rotating cube puzzles found that fNIRS measured distinguishable differences when
comparing tasks with a graphical cube on a screen to tasks involving a physical cube.
fNIRS was able to distinguish between tasks at three different levels of difficulty,
with better-than-random accuracy (Hirshfeld et al., 2007). The application of fNIRS
to a military command-and-control task found that fNIRS could be used to predict
workload (Izzetoglu et al., 2004). The results from these studies were interpreted as
demonstrating the utility of fNIRS for HCI research. fNIRS has subsequently been
used in a number of HCI studies, addressing topics such as the impact of think-aloud
protocols (Pike et al., 2014) and web-form layout (Lukanov et al., 2016) on mental
workload; evaluating information visualization systems (Peck et al., 2013); and even
as a form of input (Solovey et al., 2012; Afergan, 2014).
Functional magnetic resonance imaging (fMRI) has also been used in HCI re-
search. fMRI works by tracking blood flow through the brain: as blood will flow to