Emotional Interactions 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 [email protected]
We used the Ultimatum Game to investigate two
person social decision making. The Ultimatum
Game offers the experimental model to estimate the
fairness, mind reading, conflict between emotion
and cognition, and strategic behavior. We recorded
simultaneous activity of the EEG from 64 scalp
electrodes in 26 healthy participants (13 pairs of
proposers and responders) and estimated the timefrequency analysis and nonlinear interdependence
between the two players’ brain regions. We found
that the face to face interactions modulate the
Ultimatum Game behavior compared to the
previous studies. We also found that the high
frequency oscillations of frontocentral regions of
the brain are closely related to the social interaction.
Furthermore, information flow among frontocentral
areas between the brains is stronger than that of
other regions. This is the first study to analyze
temporal dynamics and functional connectivity in
human social decision-making using EEGs.
offer the smallest amount possible and responder
should accept any amount offered. This is hardly
the case in human subjects in the empirical settings.
They offer what they think is the fair amount and
they accept that they think is the fair amount. Thus,
the Ultimatum Game is the apt tool for the
investigation of human emotional interactions,
especially fairness monitoring and can focus on the
irrational behavior ensued from it.
The purpose of this study is to find and confirm
the location of electrophysiological basis of
emotion and cognition (fairness and reason) in the
Ultimatum Game. Furthermore, we aim to
investigate social and emotional interactions
between the two players by EEG simultaneous
recording (EEG hyperscanning), and then to assess
the underlying dynamics and the functional
connectivity between the brain regions of the two
players.
Introduction
Methods
Interactive social decision making is ubiquitous
in our everyday lives. An interactive decision
making involves goal-directed behavior, using
cognitive skills such as working memory and
executive function. Moreover, this requires ability
of ‘theory of mind’ and social cognition.
To investigate social interaction in experimental
settings, we adapted Ultimatum Game. In the
Ultimatum Game, two players, proposer and
responder, are offered a certain sum of money. The
proposer has to suggest 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.
However, if the deal is rejected, neither player gets
anything. The rational and optimal solution,
suggested by game theory, is that proposer should
We recorded simultaneous activity of the EEG
from 64 scalp electrodes (Quik-cap, Compumedics
Neuroscan, USA) in 26 healthy participants (13
pairs of proposers and responders). Electrode
positions included the standard 10-20 system
locations and additional intermediate positions.
Electrode impedance was below 5 kOhm. EEG
was continuously recorded, digitized at a rate of
1000 Hz with a linked mastoids reference. The
signal was amplified by SynAmps2 (Compumedics
Neuroscan, USA), band-pass filtered at 0.1-300 Hz.
Abstract
100
90
80
Offer rates (%)
70
60
50
40
30
20
10
Figure 1: High resolution EEG hyperscanning
(simultaneous recording) system.
0
5:5
6:4
7:3
8:2
9:1
Offer
Results
We found that the offer amount of money of the
proposer is decreased compared to the previous
report (Oosterbeek et al. 2003) (Figure 1). 63.75%
of offers is 5:5. Other offer rates (6:4 - 8.75%; 7:3 3.75%; 8:2 - 5%; 9:1 - 3.75%) are significantly
decreased compared to 5:5 offer.
Figure 1: Distribution of offers by each ratio.
In the single trial Ultimatum Game, the
responder accepts 5:5 offers by 100% and 7:3
offers by 55.56%. Acceptance rates of unfair offers
such as 8:2 and 9:1 are both 5.56%. Unfair offers
were significantly rejected by the responder.
However, in serial trials Ultimatum Game, which
requires more strategic decision making than the
single trial game, acceptance rates were
significantly decreased in 7:3 offers and increased
in 8:2 offers compared to the single trial game.
100
a single trial
serial trials
80
Acceptance rates (%)
Subsequently, 60 Hz and 120 Hz notch filters
were applied to minimize line noise artifacts. Trials
with strong eye movement or other movement
artifacts were manually removed by inspection.
Ocular artifact reduction and baseline correction
were performed using Scan 4.4 (Compumedics
Neuroscan, USA). We selected -2 ~ 2 secs of each
proposer offer period and responder decision
period.
The reformatted data were than processed by
means of a windowed Fourier transform (window
length, 192 ms; step, 20 ms; window overlap, 90%).
Signal windows were zero-padded to 512 points to
obtain an interpolated frequency resolution of ~1
Hz/frequency bin.
Nonlinear interdependence is also estimated.
This is a nonlinear method used to characterize the
dynamical interdependence with additional
information of the strength and direction of
functional connectivity for bivariate time series,
regardless of the frequency bands (Breakspear &
Terry, 2002).
Correlations between the current offer amount
and the next offer amount were determined with
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.
60
40
20
0
5:5
7:3
8:2
9:1
Offer
Figure 2: Behavioral results from the Ultimatum
Game. These are the offer acceptance rates of the
responders averaged over all trials. Each of 16
responders played both a single trial game and 10
sequential games with one proposer.
In the sequential interaction, the current offers
and the next offers of the proposer have significant
correlation when the current offer was accepted
(Figure 3). No significant correlation was found in
the currently rejected offer. The slope of the linear
regression is less than one (slope: 0.86), indicating
that the proposer tends to offer less money in the
next offer compared to the current offer.
Figure 4: Time-frequency analysis of the
proposer and responder’s brain in the right
frontocentral region. Timing of the proposer offer
and the responder decision are indicated by red
dashed lines.
5
Next offer
4
3
Figure 5: Information flow in the social
interaction in the Ultimatum Game using nonlinear
interdependence index.
2
1
0
0
1
2
3
4
5
Current offer
Figure 3: 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).
Time frequency spectrograms were estimated in
the timing of the proposer offer and the timing of
the responder decision (Figure 4). The results
found that beta and gamma oscillations are
significantly increased in the timing of the decision
in both players, especially in the right frontocentral
regions (p<0.01).
Proposer’s brain
Proposer offer
Responder decision
Responder’s brain
Nonlinear interdependence prediction error is
calculated for the interaction in the proposer offer.
Smaller prediction error from channel X to Y
indicates stronger dependency from X to Y,
meaning that stronger information flow is from Y
to X. Figure 5 represents the information flow both
within and between each player’s brains.
Prediction errors of all 128 EEG channels (each 64
EEG channels) were estimated and only the
significantly correlated channels were indicated
(Table 1). The right frontocentral regions of the
proposer and the left frontocentral regions of the
responder are the main regions of information flow
in the social interaction.
Discussion
In this study, we found that the face to face
interactions modulate the Ultimatum Game
behavior compared to the previous studies
(Oosterbeek et al. 2003; Sanfey et al. 2003). We
also found that the high frequency oscillations of
frontocentral regions of the brain are closely
related to the social interaction. Furthermore,
information flow among frontocentral areas
between the brains is stronger than that of other
regions.
Behavioral results suggest that the face to face
interactions in the Ultimatum Game can affect their
social interactions and fairness evaluation.
Moreover, the single trial game and the sequential
game showed different responder decision
behavior. The results reflect the different strategies
related to the evaluation of reasoning and fairness.
The responder in the single trial game placed a
value more on the fairness, while the responder in
the sequential game thought more importantly on
the reasoning.
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
P6
to
offer rate and timing is needed to draw definitive
conclusions about the information transmission.
Since there was strong social interaction between
the players, the rejection rate is very low and more
than 60% of the proposers offered 5:5 fair amount
of money. The relatively small size of 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 the two person social
interaction
by
measuring
simultaneous
electrophysiological activity of the two brains. This
is the first study to analyze temporal dynamics and
social interactions in human decision-making using
simultaneous EEG recordings. The reported
findings provide evidence for behavioral and
electrophysiological approaches to social cognition
and decision-making that stress the fundamental
role of frontal areas in neural networks that support
deliberative and emotional processes in human
social decision-making.
References
F5
FC3
FC3
F5
FC3
C1
C1
FC3
FC3
CP1
CP1
FC3
FC3
P1
P1
FC3
Synchronized high oscillations in right
frontocentral regions of both players indicate that
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sent the information signal to the right
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