IEEE Consumer Electronics Magazine - October 2016 - 48

Table 1. A comparison of ECG systems. Technologies
ECg system

software

real time

lead Count

Connectivity

Portable

additional Features

Biopac
+
ecG2-r Bionomadex tX/rX [43]

acqknowledge

yes

2 (ecG)
+ 1 (GNd)

Wireless (2.4-GHz
digital rF)

●

Shimmer3 + consensys Base [46]

consensys

yes

3 (ecG)
+ 1 (GSr)
+ 1 (eMG)

Wireless
(Bluetooth)

yes

●
●

MP150a

Lead iii data can be inferred
based on lead i and lead ii data
● can be used simultaneously
with other Biopac modules
eMG add-on
9doF sensor

aBiopac

MP150 is considered to be the ecG gold standard.
eeG: electroencepholagraphy, ecG: electrocardiography, eMG: electromyography, GSr: galvanic skin response, 9doF: nine degrees of freedom.

Brain activity and eeG
BraiN activity
The brain is the epicenter of all nerve stimuli. Thus, monitoring brain activity is complimentary to detecting stress
response. Stress response originates in the amygdala, which
communicates with the hypothalamus to initiate an ANS
response [28]. This stimulation of the ANS provokes subsequent physiological and physical manifestations of stress.
Evoked potentials at the cerebral cortex correspond to signals
sent between the amygdala and hypothalamus making it possible to record brain activity at the scalp [29]. Specifically,
the frontal cortex is examined, usually by means of EEG.

eeG
Several different technologies are used for measurements of
direct brain activity including positron emission tomography
(PET), functional magnetic resonance imaging (fMRI), and
EEG. Both PET and fMRI use blood flow as indicators of
brain activity, whereas EEG uses electrical potentials.
Although both PET and fMRI are effective means for measuring brain activity with high spatial resolution, both are
very slow in response and involve expensive equipment [50].
Therefore, our focus here is on EEG technology.
EEG measurements involve a matrix of electrodes placed
on the head that record event-related potentials at the occurrence of brain stimulation. These electrodes are most commonly fitted into a cap according to the international 10/20
system. This system is based on 19 electrode placements
spaced at 10% and 20% intervals across the cranium. Each
percentage is of the total length of the cranium either front to
back or ear to ear. The nasion (bridge of the nose) and inion
(occipital protuberance) are used as boundary markers for the
perimeter of the electrode system. [51]. The system is used to
allow for a comparison of results from research conducted all
over the world [50], [51]. Figure 2 shows the top view of the
10/20 system (see the Figure 2 caption for more details on
electrode labeling).
Similar to ECG analysis, measurements are filtered into
frequency bands and can be analyzed according to power
through a technique that calculates power spectrum ratios.
48 IEEE Consumer Electronics Magazine

OCTOBER 2016

The extracted frequency bands are categorized across a range
of approximately 30 Hz as delta band (d, 0.5-4 Hz), theta
band ( i, 4-8 Hz), alpha band (a, 8-13 Hz), and beta band
( b, 13-30 Hz) [55]. When using the power spectrum ratio
technique for accessing EEG data, filtered measurements are
then translated to PSD via FFT. An energy spectrum density
can then be calculated by dividing the PSD area of each band
by the respective frequency range of each band [55].
Among the systems frequently used in research are the
B-Alert X10 by Advanced Brain Monitoring (ABM); the
EPOC+ from Emotiv; and the gold standard, the wired
ActiveTwo EEG system by BioSemi. The Emotiv EPOC+
and ABM B-Alert are both highly ranked wireless EEG systems that are commercially available. The two have been
compared against the gold standard several times and have
proven to be comparable [52]-[54] (see Table 2).

Skin conductance and GSr
SkiN coNductaNce
More recent research focuses on skin measurements for stress
detection because they provide an easy interface for
instrumentation. The skin response primarily focused on is
EDA, more commonly known as GSR, which measures skin
conductance. Skin conductance is the susceptibility of the skin
to conduct electricity. This conductivity is based on sweat
gland activity that often activates in response to high stress or
fight-or-flight situations [24]. During increased stress, perspiration increases, causing resistance to current flow to drop,
inversely affecting conductivity of skin. This relationship is
the reason that conductance is used as opposed to resistance.
Conductance has a directly proportional relationship to the
increase in perspiration and is indicative of increased stress.
Although GSR has been used to detect stress, it is also worthwhile to note that GSR, like other biomarkers, is a response to
arousal, which could be positive (e.g., elation) or negative
(e.g., fight or flight) [25].

GSr
GSR, which relies on conductivity of skin in response to stimuli, measures skin conductance level while monitoring activity

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