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Lie detection mechanism is used to evaluate the ethical and moral values of people. In general, these moral and ethical values are difficult to determine. Earlier technique like polygraph does not provide accuracy in determining mental behaviour. Lately, it is possible to study psychological response of a person using electroencephalogram (EEG). Based on this, we develop a standalone solution that can detect brain signals using EEG. To this end, we extract the desired features from the brain signals acquired through sixteen electrodes using various extraction techniques. Then, we implement linear discriminant analysis (LDA) classification technique to differentiate the positive and negative samples from the signals obtained from sensors in order to achieve a decision for either guilty subject or innocent subject accordingly. The whole work is designed with the help of MATLAB and Xilinx tool. For efficiency, the whole system is implemented on FPGA. The amount of correct deception detection in guilty and innocent subjects are 85%. It is easy and more convenient approach than other previously used methods.
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Electrical and Electronic Engineering 2017, 7(3): 69-76
DOI: 10.5923/j.eee.20170703.01
Evaluation of P300 based Lie Detection Algorithm
Syed Kamran Haider1,*, Malik Imran Daud2, Aimin Jiang1, Zubair Khan1
1Department of Internet of Things, Hohai University, Changzhou, China
2Department of Electrical Engineering, Foundation University, Rawalpindi, Pakistan
Abstract Lie detection mechanism is used to evaluate the ethical and moral values of people. In general, these moral
and ethical values are difficult to determine. Earlier technique like polygraph does not provide accuracy in determining
mental behaviour. Lately, it is possible to study psychological response of a person using electroencephalogram (EEG).
Based on this, we develop a standalone solution that can detect brain signals using EEG. To this end, we extract the desired
features from the brain signals acquired through sixteen electrodes using various extraction techniques. Then, we
implement linear discriminant analysis (LDA) classification technique to differentiate the positive and negative samples
from the signals obtained from sensors in order to achieve a decision for either guilty subject or innocent subject
accordingly. The whole work is designed with the help of MATLAB and Xilinx tool. For efficiency, the whole system is
implemented on FPGA. The amount of correct deception detection in guilty and innocent subjects are 85%. It is easy and
more convenient approach than other previously used methods.
Keywords Event Related Potential, Linear Discriminant Analysis, P300 Features Extraction
1. Introduction
Deception detection has drawn much value from scientific
society in the past decades. It has found many applications
related to psychological implications. In present, the older
technique polygraph are widely used for the justification of
deceptive and truthful behavior of subject [1]. A
researchable analysis gives us an idea that, with the help of
EEG signals we can easily monitor the psychological
variations, brain activities and deception detection related
features [2, 3].
In decision making situation where scientific study gives
us best solution which is relevant to the measurement of
P300 event related potentials (ERP). The reason is to do so
far is that cognitive disability is often associated with
variations in the P300 potentials, the waveform can be
helpful in treatments of cognitive task. There is a variety of
uses for the P300 potential in scientific study, leading from
study of depression and drug infatuation to anxiety
dis-orders.
Currently designed Brain Computer Interface (BCI)
systems and prototypes are facing problems in slow
communication channel. The transfer rate (ITR) between
human brain and BCI prototypes are lower than 100 bits per
minute [4]. A systematic framework for hardware BCI is
implemented using FPGA [5]. The system utilizes a BCI
hardware modular architecture based on FPGA and allows
* Corresponding author:
kamranhaider85@yahoo.com (Syed Kamran Haider)
Published online at http://journal.sapub.org/eee
Copyright © 2017 Scientific & Academic Publishing. All Rights Reserved
integrating the complete BCI on a single FPGA device. Our
research aims to explore the possibilities of the high-speed
recognition from EEG signals, and a standalone system that
can be used as a lie detector with less processing time
without any software involvement. But this achievement is
reached at a price of implementing the whole work process
on MATLAB and as well as on FGPA chip.
In this research a system is designed to prove the
feasibility of the whole concept of lie detector. The
implementation of lie detector algorithm on FPGA and its
interfacing with blue tooth module is the most critical step in
our work. To reduce the development time that takes place at
feature extraction and signal classification stage, high level
synthesis approach is used. This approach is much better
than the Register Transfer Language (RTL) flow, which can
generate small enough design, such that it can fit the
complete BCI pipeline into one FPGA device. Usage of LDA
classifier synthesis speeds up the design process and allows
us to work on a fairly high level of abstraction during the
development of new algorithms. Further, high available
computational power of FPGA device will allow us to
integrate progressive non-linear signal processing algorithms
like Principal Component Analysis (PCA) and Independent
Component Analysis (ICA) for feature extraction. Compared
to other known solutions of Transmit (Tx) part, Bluetooth
Low Energy radio interface is proposed to keep the system
power consumption as low as possible.
The remaining paper is arranged as follows. In Section II,
the methodology of proposed approach is discussed. Section
III focuses on implementing results and some discussions are
made. In the end, the conclusion is given in Section IV.
70 Syed Kamran Haider et al.: Evaluation of P300 based Lie Detection Algorithm
2. Test Based for Implementation
using FPGA
2.1. Participants
Twenty subjects (15 males and 5 females, ages between
20-25 years) that were generally universities students
(undergraduate and postgraduate) and all had good health
with stable psychological behavior participated in this study.
Fig.1 shows the step-wise methods for the understanding of
lie detector we have developed with some overview of the
methodological analysis of this research.
Figure 1. Lie Detector Implementation flow chart
2.2. Lie Detection Based Scenario
We have recorded data of over 15 to 20 subjects. In one
scenario, some precious items (e.g., jewelry, cash, smart
phones, etc.) were placed in front of some subjects. Those
subjects were not informed about the scenario and the
subject can be any random person. Another person called as
Subject-2 intended to perform this test come and stole that
item that was placed in front of person called as Subject-1. It
can be any person but suggestively that can be his/her close
friend. As this test was performed in university, university
authorities would handle the case of that stolen item [6]. This
was done only to put our subject under pressure for lie and
truth response. While conducting test in the presence of
authorities our subject wore Emotiv EPOC headset. Some
training data was collected to define the correct lie and truth
classes. Training slides were prepared on MATLAB with
defined time period (in our case 5 to 6 seconds for each
question) of each image and questionnaire set. First some
obvious questions were asked that everybody would answer
the obvious answers, i.e., the true answer [7]. The
instructions was also given to the subjects during the process
to count the total number of questions asked by the
investigator. This was essential to keep a record that our
subject was mentally attentive and fluctuating thoughts did
not come during the data acquisition process. Authenticity of
data was achieved through counting. At the end, the subject
was asked to inform about the total number of questions
displayed [8].
2.3. Desired Signal Acquisition
The brain signals were recorded with the sample rate of
128 samples per second. The recorded signals which were
digitized and amplified can be monitored offline with the
help of MATLAB software. Pass band filter were used with
the range of 0.3-30 Hz prior to data analysis. For P300-based
study about Guilty Knowledge Test (GKT) the previous
mentioned pass band filter range were used [9]. The EEG
signals from EPOC headset are itself digitized because
headset contains the built-in analog to digital converter
(ADC). The data can be received through the headset using
Bluetooth receiver at reception end.
The electroencephalogram (EEG) signals were recorded
using 16 channels Emotiv EPOC headset. The position of the
sensors is shown in Fig.2.
Figure 2. Placement of electrodes
The Emotiv EPOC headset provide the features like high
resolution and multi-channel and used in various
applications in the field of research. The raw EEG waveform
can be monitor on the software provided by the company.
Moreover, it has the detection libraries: Mental Commands,
Performance Metrics & Emotional States and Facial
Expressions.
The Emotiv EPOC headset is specially designed headset
& provides the following features shown in the Table 1.
The Emotiv has a control panel kit which provides the
easy access to explore more about EPOC headset. It provides
the facility to the user to create their own profile and train
thoughts. The Emotiv graphical user interface includes:
Expressive suite, Affective suits and mental suits as well. In
addition it has Mouse Emulator latest feature to control the
mouse pointer by moving their head by utilizing the EPOC
gyroscope. Two modes of recording the EEG signals, known
as differential and referential, are used. In differential mode
two inputs directly feed from two electrodes towards each
differential amplifier. On the other hand, in referential mode,
one or two reference electrodes are used.
Electrical and Electronic Engineering 2017, 7(3): 69-76 71
Table 1. Features of Headset
Features Specifications of EEG Headset
Total Channels 14 sensors
Channel names AF3,F7,F3,FC5,T7,P7,O1,O2,P8,T
8,FC6,F4,F8,AF4
Sampling approach Sequential sampling. ADC
Sampling rate 128 SPS (2048 Hz internal)
Resolution
14 bits 1 LSB=0.51µV (16 bit
ADC, 2 bits instrumental noise
floor discarded)
Bandwidth 0.2-45 Hz, digital notch filters at
50Hz and 60Hz
Filtering Built in digital 5th order Sinc filter
Dynamic amplitude range 8400µV(pp)
Coupling mode AC coupled
Battery life (typical) 12 hours
Impedanc Measurement Real-time contact quality using pat
2.4. Pre-Processing
After applying pass band filter on EEG signals, each
continuous subject record is divided into single sweep as per
the times known by stimulus presentation [10]. The total
length of each single sweep is 1000ms, and contains 128
samples. Then the signal pattern recognition technique
includes special features extraction and features selection.
After that apply classification method on the signals to assess
the detection rate. It should be noticed that, in all cases
related to P300 ERP the Pz is the prime location where P300
can be monitored maximal and therefore visual related
experiments were performed only on Pz data [11].
2.5. Optimal Features Extraction
The original recorded EEG signal is in time domain and
the whole signal energy distribution is dispersed. The
optimal features are suppressed with the noise. In order to
dig out the features, EEG signal is observed under the signal
energy in the form of time domain or frequency domain. The
frequency domain analysis is the best for those features
utilized in the mental task related to EEG signals [12].
Two types of features were observed in this evaluation.
These extracted features were also involved in similar
studies and shown good performance and it is also useful for
our application too.
2.5.1. Morphological Features
Several morphological features (based on shape) were
extracted and evaluated. It has; Latency time, Maximum
Peak value of signal, Positive value in the signal, Total Area
and some others as discussed in [14]. These optimal
features were previously used in to identify depressive
subjects by using P600 ERP of the signal [13].
2.5.2. Frequency Features
This group of features has the frequency related
characteristic of the signal [14]. It contains the features;
mode, median and mean of the frequency.
2.6. Features Abstraction
To determine the guilty and innocent response of the
subject all the defined features from the probe sweeps were
save in European data format (.edf) file. Then the analysis
was applied to find out the most related features for the guilty
subjects (G-Probes) and innocent subjects (I-Probes) at
signal classification stage [15].
2.7. Signal Classification
Extracted features were referred towards the LDA [16, 17].
This method has less computational requirement and it is
more appropriate method for many pattern recognition
related problems. In addition, LDA classifier is very simple
to use and provides better results. The popularity of this
classifier has been involved EEG processing, ERP related
researches such as motor imagery based BCI systems, P300
speller and P300 component detection. This classification
technique is more perfect and best practical processing
method on data collected for P300 speller paradigm.
Moreover, same like other classifier, LDA also share some
drawbacks. Before applying P300 classifier on EEG signals,
LDA needs to take the average of several trials to de-noise
the background noise and increase the magnitude of P300
response for better results. Taking average of several trials is
a time consuming step which greatly slows down the
classification process and therefore it is not appropriate for
real time P300 classification with single trial. It becomes our
interest to implement algorithms for the detection of P300 in
lie detection scenario [18].
In our research we are following class depend approach.
The mathematical model of the class depend transformation
we adopted as follow:
For better understanding of two-class problem, this
concept is applied on 2-D data points. Mathematical
interpretation of this classification method in cooperate with
the MATLAB implementation allied with this work. The
representation of 2-D data sets in the matrix containing
features [19]:
set1 =
a11 a12
a21 a22
am1
am2
,set2 =
b11 b12
b21 b22
bm1
bm2
(1)
(1) Calculate mean for individual data sets and mean for
complete data set. Let 1 represents mean of data
set1 and 2 represents be the mean of data set2,
respectively, and 3 represents the entire data mean,
which is calculated by inclusion of set1 and set2:
3=1×1+2×2 (2)
72 Syed Kamran Haider et al.: Evaluation of P300 based Lie Detection Algorithm
where 1 and 2 shows the two-class a prior probabilities.
In our scenario of deception detection, the probability index
is consider to be 0.5.
(2) All the covariance matrices hold the symmetric
property. Let cov1 represents the covariance of data
set1 and cov2 represents the covariance of data set2.
Covariance matrix is calculated with the help of
following equation.
=   (3)
Therefore, for the two-class problem:
(3) Calculate the with-in class variance
= 0.5  1+ 0.5  2 (4)
(4) The between-class distribution is calculated by using
following equation:
= 3   3
(5)
can be represented as the covariance of data sets whose
elements belongs to mean vector of each class. As defined
before, formulation of optimization criterion in classification
of LDA is the proportion of between-class distribution to
within-class distribution. The solution achieved by
maximizing this criterion represent the axes of new
transformed space. Moreover in class-dependent case the
optimizing criterion is calculated by using mention above
equations. It should be verified that in class dependent LDA
type, for L-class type L separate optimizing criterion are
needed for each single class as calculated in Eq (6).
(5) The optimizing index in case of class dependent type
are computed as:
j=()  (6)
(6) To obtain the transformation matrices, we transform
the data sets using single LDA transform.
 _= (
)T×set_j (7)
where (
)T is the transpose of the Eigen vector which is
obtained from the  of each sets and set_j are the
data set 1 and data set 2.
(7) Once the transformation are concluded using LDA
transformation, then Euclidean distance or Root mean
square (RMS) distance is used for the classification of
data points.
= ×   (8)
where  is the mean of the transformed data set, n is
the class index and x is the test vector. For n classes ,
Euclidean distances are obtained for each test point. The
smallest Euclidean distance among the distances classifies
the test vector as belonging to class n.
2.8. FPGA Implementation
The contribution presents a novel high performance, low
power BCI architecture allowing a single-chip
implementation of a BCI device. FPGA platform is used to
reach high performance and low power consumption; to
speed up the classification process, high-level synthesis of
signal processing algorithms is employed by research
scientists. FPGA architecture has many advantages i.e.
configurability, possibility of independent development,
topological compatibility, scalability, and high
computational power as proposed for P300 based lie detector
implementation [20].
Usage of developing the whole system on FPGA synthesis
speed up the design process and allows us to work on a fairly
high level of abstraction during development of new
algorithms. Further, high available computational power of
the FPGA device will allow us to integrate progressive
non-linear signal processing algorithms like PCA and ICA
for feature extraction. Compared to other known solution of
the Transmit (Tx) part, Bluetooth Low Energy radio
interface is proposed to keep the system power consumption
as low as possible.
Hardware descriptive language (HDL) model needs to be
transformed into binary stream before it can be coded to
FPGA. ELBERT series related chips can only accepts binary
(.bin) data bit stream created by XILINX software tool kit.
Once HDL model is synthesized, it is more easy and
convenient to produce a binary data bit stream out of it. The
Papilio Pro board uses the FT2232 dual channel interface
USD chip that helps for the easy reprogramming of SPI flash
[21]. The .mat extension file load from the host application
(MATLAB) and program it in to SPI Flash memory and then
lets the FPGA boot from the flash.
3. Results and Discussion
3.1. MATLAB Simulation Results
As given in first scenario, the training data sets of two
classes i.e. the lie & truth data sets are plotted corresponding
to one another. Set1 is the truth data set class whereas set2
belongs to lie data sets.
Data sets are transformed through LDA classifier. Mean,
variances, co-variances are calculated. Increase of
separability criterion by the calculation of between and
within class variances. In this project, class dependent
transformation is applied because the objective is to
maximize adequate class separability measure. Test vector is
the target data, which need to be calculated that to which
class it belongs. In the following figure it is clearly shown
that vector set lies at minimum distance to the transformed
set1 which is data set of truth class. This shows honest
behavior of subject. On the other hand if the test vector lies at
minimum distance to the transformed set2 i.e. lie data set, the
subject is lying.
The Figure 3. indicates the data sets of lie and truth classes.
The data sets of two classes are scattered randomly which
would not provide the required information needed to
separate the classes. The values are also normalized in
feature vector set to remove the noise content of EEG signal.
LDA maximizes the separability measure of the two
classes, which are shown in the next figure.
Electrical and Electronic Engineering 2017, 7(3): 69-76 73
Figure 3. Training data of truth & lie sets (subject 1)
Figure 4. Target data indicating it belongs to transformed set 1 (the truth
response)
In Figure 4. target data set lies to the transformed set1, this
is trained innocent set. This is measured by minimum mean
distance of the target data set to the innocent and guilty
vector sets. The vector to which the targeted vector placed
closely is the outcome of innocent and guilty response. Here,
it is clearly shown that the subject has not concealed the
information, which is our innocent subject.
Similarly the guilty response shows that sort of plots
where evidently target set depicts that our response is
dishonest.
Likewise, Figure 5. Indicates the data sets of lie and truth
classes. The data sets of two classes are scattered randomly
which could not provide the required information needed to
separate the classes. The values are also normalized in
feature vector set to remove the noise content of EEG signal.
LDA maximizes the separability measure of the two classes,
which are shown in the next figure.
In Figure 6. target data set lies close to the transformed
set2, this is the trained guilty set. This is measured by the
minimum mean distance of the target data set to the innocent
and guilty vector sets. The vector to which the targeted
vector placed closely is the outcome of innocent and guilty
response. Here, it is clearly shown that the subject has
concealed the information, which is our anticipated guilty
subject.
Figure 5. Training data of truth & lie sets (subject 2)
Figure 6. Target data indicating it belongs to transformed set 2 (the Lie
response)
3.2. FPGA Implementation Results
After the implementation of algorithm on MATLAB the
next step is move towards the FPGA. The main theme is to
implement the algorithm on FPGA to make a standalone
system for lie detector. Software based implementation
needs much time to execute the code based on complex
equation. The processing speed of FPGA is faster due to data
flow programming and even we can perform all of those
steps simultaneously and control the specific timing for each
step. Moreover, because FPGA prototypes run faster, larger
data sets can be used, potentially exposing bugs that would
not be uncovered by a simulation model. Model-Based
Design using HDL code generation enables teams to produce
the first prototype faster than a manual workflow. That’s the
74 Syed Kamran Haider et al.: Evaluation of P300 based Lie Detection Algorithm
reason behind the evaluation of lie detector on FPGA chip. If
we connect headset with the FPGA using Bluetooth then
there is no need for the intermediate device to monitor the
signals. We can display the result on output port of FPGA
using red and green light using with the help of screen
display. In this section using Verilog coding the lie detection
algorithm were implemented after verifying the MATLAB
results. The FPGA kit is of Xilinx Company (Papilio Pro) is
used. We used ISE 14.2 suit of Xilinx for writing the Verilog
Coding.
The first case is about the innocent person and the below
results shows the execution of first case. In the same manner
like MATLAB after extracting the desired features from
training data and testing data all values were stored on (.mat)
file.
Figure 7. FPGA reset state
In Figure 7. Operations of LDA were adjusted on clock
cycle, each clock leading edge one operation related to LDA
will be performed on training and testing data sets. Before
going to execute the LDA technique, Fig.8. Shows to set the
initial parameters like clock period, leading edge value etc.
Figure 8. FPGA clock frequency adjustment
On each leading edge of clock one by one all tasks will be
performed. On the first leading edge clock execute “RESET”
command, everything is reset at that time. Status register
shows “0000”.
On the Second leading edge of clock “Test vector, Set 1,
Set 2” files were read. Status register were changed to
“0001”.
Figure 9. Reading the Test vector, set1 & set2 data on the next leading
edge of clock
After calculating the classification algorithm, “Euclidean
distance” is calculated for the “set 1 & set 2”.
Figure 10. Calculate Euclidean distance for both set1 & set2
After calculating Euclidean distance on the next leading
edge the message were displayed “Subject is innocent”. This
shows that the samples are of innocent person.
Figure 11. Output of FPGA (Innocent response of subject)
In the above Figure 9. mean_dis_set1 shows distance of
innocent samples from the target and similar as
mean_dis_set2 shows distance of guilty samples as
Electrical and Electronic Engineering 2017, 7(3): 69-76 75
compared to target data. Innocent samples are closer than the
guilty samples. Distance of set2 is greater than set1, which
shows that the subject is innocent. The next case is about
guilty subject.
In the Fig.10 mean_dis_set1 shows distance of innocent
samples from the target and similar as mean_dis_set2 shows
distance of guilty samples as compared to target data. Guilty
samples are closer than the innocent samples. Distance of set
is greater than set2, which shows that the subject is guilty.
Figure 12. Output of FPGA (Guilty response of subject)
4. Conclusions
In this research, it becomes the determination and
motivation to hardware (FPGA) implementation of the
algorithm; P300 component analysis based on LDA
classification technique with P300 peak values
corresponding to each channel of electrode. We have
achieved 85% accuracy in detecting lie and truth subjects.
Simulation results on MATLAB is achieved by acquiring
signals on Emotiv headset whereas on FPGA simulation is
attained by converting the .edf format into .mat format and
loaded it into the Papilio pro. Emotiv headset is the latest
device that can map the EEG signal more accurately and with
good signal to noise ratio. The filters that are used in headset
digitized the signal and send to the Bluetooth receiver and we
can monitor the signals on our systems. Our research is
targeted to the evaluation of the high processing speed
recognition from the EEG signals and makes a standalone
system, which can be used as a lie detector. However, this
achievement was reached at a price of implementing the
whole algorithm on MATLAB and FPGA.
In terms of cost analysis the FPGA device is cheaper than
the super computers to execute the heavy programs and the
execution time of hardware is better than the software
simulation of code. In the old methodology like polygraph to
detect lie heavy machines were used to generate the reports.
This new system eliminates the cost of heavy machines and
gives the idea to build a standalone system using a small
hardware device with good performance ability. However,
with the emerging technology of latest products new
methods are still under consideration to give the better
output.
ACKNOWLEDGMENTS
This work was supported in part by the National Nature
Science Foundation of China under grants 61101158,
61471157, and 61401148, and the Natural Science
Foundation of Jiangsu Province, China under grants
BK20130238, BK20141159 and BK20141157, and Science
&Technology Program of Changzhou, China under Grant
CJ20159039.
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