Transcript THE LIE DETECTOR - Northwestern University

THE LIE DETECTOR
Tim Fleck
Mike Gruener
Brian Halaburka
Chris Moskaites
OBJECTIVES
 To create a sensing device modeled after
a polygraph test
 Test would incorporate results from
several physiological sensors
 Create a Labview program to gather and
analyze subject data
POLYGRAPH THEORY
 Polygraphs measure:
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Heart rate
Respiratory rate
Blood pressure
Arm and leg motion
Electrodermal activity
INITIAL IDEAS
 Use real world polygraphs as design
models
 Assemble a polygraph which monitors
heart rate, breathing rate and
electrodermal activity
 Create a Labview program which would
self-analyze data and “detect” deceptive
behavior
FINAL LIE DETECTOR
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Incorporates two physiological sensors
detecting two phenomenon
1)electrodermal activity
2)motion
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Self analyzes received data
DETECTOR LOGIC
Subject
Electrodermal
Sensor/Motion
Sensor
DAQ
New Data
LABVIEW/CPU
Display Results
SENSORS
 Electrocardiogram or EKG
 Galvanic Skin Response Sensor
ELECTROCARDIOGRAM
 Measures the
electrical activity of
the heart
 Determines hearts
rate and rhythm
 Our project used it to
measure motion
GALVANIC SKIN
RESPONSE SENSOR
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Senses moisture
Stand-alone unit
Produces noise
Frequency was too
fast for the DAQ
CREATED SKIN SENSOR
 Based off the idea
that skin resistance
decreases with
moisture
 Used a voltage
difference circuit
 Amplified the voltage
difference to obtain
obvious results
LABVIEW LOGIC (EKG)
 Take initial readings visually from the
waveform graph
 Calibrate the high and low end of the
threshold based on the initial readings
 Every question after will be compared to
the threshold
 If a person’s motions go above the
threshold, a LED goes on, indicating a lie
LABVIEW LOGIC (GSR)
 Takes voltage readings of subject’s fingers until
button is pushed
 Then it computes and displays and average
voltage for the given time period
 Displays a waveform chart showing how much
the subject’s voltage is increasing from the
average as resistance decreases
 If the in average increase goes above a certain
predetermined value, a light goes on, indicating
a lie
DATA
 Thresholds were determined by
analyzing results gathered from group
testing
 Normalized against predetermined
values
DATA ANALYSIS AND
RESULTS
Galvanic Sensor:
 Computes voltage
average
 Determines a lie if
the subject’s voltage
goes above a
threshold
DATA ANALYSIS AND
RESULTS
EKG:
 Displays the electrical impulses generated by a
human body
 When a certain level of voltage is generated in
the body it rises above a predetermined value
indicating irregular behavior
 Detects movements from bodily extremities,
specifically the arms and legs
NORMAL EKG WAVEFORM
DECEPTIVE WAVEFORM
SOURCES OF ERROR
 Nervousness of test subject
 Calibration errors
Difficulties
 Heart Rate Monitor
 Galvanic Skin Response
 LABVIEW
 Lab Setup
CONCLUSIONS
 “Simple” circuitry increases in complexity
once work begins
 Check and recheck components before
and after assembly
 Start early
 Be flexible and constantly improve