1. ICCS 2008 Proceedings
July 27 - 29 ㆍSeoul, korea
Emotional Interaction in Human Decision Making
using EEG Hyperscanning
Kyongsik Yun1, Dongil Chung1, Jaeseung Jeong1, 2, *
1
Department of Bio and Brain Engineering, Korea Advanced Institute of Science and Technology (KAIST),
Daejeon 305-701, Republic of Korea
2
Department of Psychiatry, Columbia College of Physicians and Surgeons, New York, NY 10032 USA
* Correspondence should be addressed to jsjeong@kaist.ac.kr
that the proposer should offer the smallest amount
possible and the responder should accept any
amount offered. This is not the usual case in
human subjects in the empirical settings: the
proposer offers what they consider is a fair amount
and the responder accepts that they think is a fair
amount. Thus, the Ultimatum Game is an apt tool
to investigate human emotional interaction,
especially fairness monitoring and can focus on
irrational behavior that ensues from fairness
monitoring.
The purpose of this study is to find and confirm
the location of the electrophysiological basis of
emotion and cognition (fairness and reason)
through the Ultimatum Game. Furthermore, we
aim to investigate the social and emotional
interaction between the two players by
simultaneously recording the players’ EEGs (EEG
hyperscanning) (Montague et al. 2002), and then
assessing the underlying dynamics and functional
connectivity between the brain regions of the two
players.
Abstract
We used the Ultimatum Game to investigate the
social decision making process between two. The
Ultimatum Game offers an experimental model to
estimate fairness, mind reading, conflict between
emotion and cognition, and strategic behavior. We
recorded the simultaneous activity from an EEG
using 64 scalp electrodes in 26 healthy participants
(13 pairs of proposers and responders). The timefrequency analysis and nonlinear interdependence
between the two players’ brain regions were then
estimated. We found that the face-to-face
interactions modulate the Ultimatum Game
behavior compared with previous studies. We also
found that the high frequency oscillations of the
frontocentral region of the brain are closely related
to the social interaction. Furthermore, the
information flow among the frontocentral areas
between the brains is stronger than that of other
regions. This is the first study to use to EEGs to
analyze temporal dynamics and functional
connectivity in human social decision making.
Introduction
Interactive social decision making is ubiquitous
in everyday life. Interactive decision making
involves goal-directed behavior using cognitive
skills such as working memory and executive
function. Moreover, this requires the abilities of
the mind reading and social cognition.
To investigate social interaction in experimental
settings, we used the Ultimatum Game. In the
Ultimatum Game, two players, a proposer and a
responder, are offered a certain sum of money.
The proposer suggests how to split the sum with
the responder, and the responder can accept or
reject the deal. If the responder accepts the offer,
the sum is split as accordingly between the two
players. However, if the deal is rejected, neither
player receives the money. The rational and
optimal solution, as suggested by game theory, is
Methods
We recorded the simultaneous EEG activities
using
64
scalp
electrodes
(Quik-cap,
Compumedics Neuroscan, USA) in 26 healthy
participants (13 pairs of proposers and responders).
The electrode positions included the standard 1020 system locations and additional intermediate
positions. The electrode impedance was below 5
kOhm. The EEG was continuously recorded and
digitized at a rate of 1000 Hz with a linked
mastoids reference. The signal was amplified
using SynAmps2 (Compumedics Neuroscan,
USA), band-pass filtered at 0.1-300 Hz. The EEG
hyperscanning system setup is shown in Figure 1.
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2. ICCS 2008 Proceedings
July 27 - 29 ㆍSeoul, korea
significantly decreased compared with the 5:5
offer.
100
90
80
Offer rates (%)
70
Figure 1: High resolution EEG hyperscanning
(simultaneous recording) system.
60
50
40
30
20
Subsequently, 60 Hz and 120 Hz notch filters
were applied to minimize line noise artifacts.
Trials with strong eye movements or other
movement artifacts were manually removed after
inspection. The ocular artifact reduction and
baseline correction were performed using Scan 4.4
(Compumedics Neuroscan, USA). We selected -2
~ 2 sec of each proposer offer period and
responder decision period.
The reformatted data were then processed using
a windowed Fourier transform (window length:
192 ms; step: 20 ms; window overlap: 90%). The
signal windows were zero-padded to 512 points to
obtain an interpolated frequency resolution of ~1
Hz/frequency bin.
The nonlinear interdependence was also
estimated. This is a nonlinear method used to
characterize the dynamical interdependence that
includes additional information of the strength and
direction of the functional connectivity for a
bivariate time series regardless of the frequency
bands (Breakspear & Terry, 2002).
The correlations between the current offer
amount and the next offer amount were
determined using the Pearson correlation
coefficients. A probability of 0.05 or less was
accepted as being significant. A statistical software
package (SPSS 11.0.1, SPSS Inc., Chicago, IL,
USA) was used.
10
0
5:5
6:4
7:3
8:2
9:1
Offer
Figure 2: Distribution of offers according to
each ratio.
In the single trial Ultimatum Game, the
responder accepts 5:5 offers at a rate of 100% and
7:3 offers at 55.56%. The acceptance rates of
unfair offers such as 8:2 and 9:1 were both 5.56%.
Unfair offers were significantly rejected by the
responder. However, in series trials of the
Ultimatum Game, which require more strategic
decision making than the single trials game, the
acceptance rates significantly decreased in 7:3
offers and increased in 8:2 offers compared with
the single trial game, as shown in figure 3.
100
a single trial
series trials
Acceptance rates (%)
80
60
40
20
0
5:5
Results
7:3
8:2
9:1
Offer
Compared with a previous report (Oosterbeek et
al. 2003) (Figure 2), we found that the amount of
money offered by the proposer is decreased.
63.75% of offers were 5:5. Other offer rates (6:4 8.75%; 7:3 - 3.75%; 8:2 - 5%; 9:1 - 3.75%) were
Figure 3: Behavioral results from the Ultimatum
Game. These are the offer acceptance rates of the
responders averaged over all trials. Each of the 13
responders played both a single trial game and 10
sequential games with one proposer.
328

3. ICCS 2008 Proceedings
July 27 - 29 ㆍSeoul, korea
In the sequential interaction, the current offers
and the next offers of the proposer have a
significant correlation when the current offer was
accepted (Figure 4). No significant correlation was
found in the current offer that was rejected. The
slope of the linear regression is less than one
(slope: 0.86), indicating that the proposer tended to
offer less money in the next offer compared with
the current offer.
of the responder are the main regions of
information flow in the social interaction.
Proposer’s brain
Proposer offer
Responder decision
5
Responder’s brain
Next offer
4
3
Figure 5: Time-frequency analysis of the
proposer’s and responder’s brain in the right
frontocentral region. Timing of the proposer offer
and the responder decision are indicated by the red
dashed lines.
2
1
0
0
1
2
3
4
5
Current offer
Figure 4: Correlations between the current offer
and the next offer in the sequential Ultimatum
Game when the current offer was accepted
(Pearson correlation; slope: 0.86, r = 0.73,
p < 0.0001).
The time frequency spectrograms were
estimated in the timing of the proposer offer and
the timing of the responder decision (Figure 5).
The results found that the beta and gamma
oscillations were significantly increased in the
timing of the decision in both players, especially in
the right frontocentral regions (p < 0.01).
The nonlinear interdependence prediction error
was calculated for the interaction in the proposer
offer. A smaller prediction error from channel X to
Y indicates a stronger dependency from X to Y,
meaning that the stronger information flow is from
Y to X. Figure 6 shows the information flow both
within and between each player’s brains. The
prediction errors of all 128 EEG channels (each
player’s 64 EEG channels) were estimated and
only significantly correlated channels were
indicated (Table 1). The right frontocentral regions
of the proposer and the left frontocentral regions
Figure 6: Information flow in the social
interaction in the Ultimatum Game using a
nonlinear interdependence index.
Discussion
In this study, using the Ultimatum Game, we
found that interpersonal behavior was modulated
by face-to-face interactions when compared with
previous studies (Oosterbeek et al. 2003; Sanfey et
al. 2003). We also found that the high frequency
oscillations of the frontocentral regions of the
brain were closely related to the social interaction.
Furthermore, the information flow among the
frontocentral areas between the brains was
stronger than that of other regions.
The behavioral results suggest that face-to-face
interactions in the Ultimatum Game can affect the
players’ social interactions and fairness
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4. ICCS 2008 Proceedings
July 27 - 29 ㆍSeoul, korea
evaluations. Moreover, the single trial game and
the sequential games showed different decision
behaviors from the responder. The results reflect
the different strategies related to the evaluation of
reasoning and fairness. In the single trial game, the
responder placed more value on the fairness, while
the responder in the sequential game thought that
reasoning was more important.
sent an information signal to the right frontocentral
regions of the proposer’s brain. Further nonlinear
interdependence analyses of each offer rate and
timing are needed to draw definitive conclusions
about the information transmission.
Since there was a strong social interaction
between the players, the rejection rate was very
low and more than 60% of the proposers offered a
fair amount of money (5:5). Moreover, the
relatively small size of the subjects and the small
rate of rejections limited the statistical power of
this study.
The aim of this study was to understand the
neural processes in a two person social interaction
by
measuring
the
simultaneous
electrophysiological activity of the two brains.
This is the first study to analyze the temporal
dynamics and social interactions in human
decision-making using simultaneous EEG
recordings. The reported findings provide
evidence for behavioral and electrophysiological
approaches in social cognition and decision
making that stress the fundamental role of the
frontal areas in neural networks that support
deliberative and emotional processes in human
social decision making.
Table 1: Information flow between the brain
regions (p < 0.01)
Proposer
from
Responder
to
from
FC4
FC3
FC4
CP1
FC4
P1
CP6
FP1
CP6
C6
C6
CP6
CP6
to
P6
F5
FC3
FC3
F5
FC3
C1
C1
FC3
FC3
CP1
CP1
FC3
FC3
P1
P1
FC3
References
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The synchronized high oscillations in the right
frontocentral regions of both players indicate that
these regions are closely related to social decision
making in the Ultimatum Game. The results are
consistent with a previous study that proposed that
the right dorsolateral prefrontal cortex is the center
of the cognitive reasonable decision making
process in the Ultimatum Game (Koenigs &
Tranel, 2007, Sanfey et al. 2003).
The information flow also showed that the right
frontocentral regions were highly correlated with
decision making in the two person interaction. The
left frontocentral regions of the responder’s brain
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