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Posted by Marty
- Aug 25, 2003, 03:36 PMQuote from: Skeptic on Aug 24, 2003, 04:20 PM
The thing is (in my experience, at least with Lafayette instrumentation) the transducers are actually in a box on the table, with pneumatic tubing running from the box to the cuff. I would bet the box is EMI shielded, at least.
And where would rectification come in? I'd think the transducers would be DC coupled, given the signals of interest...
Skeptic and AH:
I agree the box would be EMI shielded. In a commercial product the incoming leads would be shielded as well to prevent internal RF from escaping.
Rectification comes from rf on the bipolar amplifier inputs (most low noise, high sensitivity amps extant). They casue what lookes like an out of spec input EOS or IOS. Since it's at the inner most point on the loop, the offset gets directly amplified by the loop gain. I've seen significant effects from local FM radio on Analog Devices modules.
QuoteA rather simple way to look at it is this way. The capacitance between a 1m wire and a surface m^2 at a distance of 1m is going to be around 10^-12. Impedance at 1Hz is about 10^11. Assuming skin Z at 10^3, there would be a coupling reduction of the E field of approx 10^-8. Assuming a 1V DC operating point, a 1 Million volt, 1Hz E field would produce about a 1% modulation in measured skin Z. For impulse noise, anything more than a 1 pole filter would attenuate faster than the increased coupling at higher Hz's.
I'm not sure this sounds right to me, Marty. Although my EM education is at the undergrad level and RFI is hardly an area of my EE specialty, it seems to me that the long leads to the GSR measurement amplifiers would be good at picking up strong electric fields. And I would think that the input impedance to the amplifier would be on the order of skin Z, for best power coupling.
Out of band RF is a much bigger problem but easily contained, both by shielding and good bypass designs on the front end. The latter is typical of modern commercial designs but ad hoc lab work is far more variable - as the MRI-GSR descr. shows.
Wheatstone bridges have an advantage in reducing sensitivity to power supply variation and even working well with old, direct drive centered galvanometers. This has long been a non issue as high stability, cheap, voltage sources have been around 30 years or so.
-Marty
Posted by aldo_huxley
- Aug 24, 2003, 10:13 PMI see graphics is not the forte here. What methods are you guys use?
Aldo
Aldo
Posted by aldo_huxley
- Aug 24, 2003, 10:09 PMFood for thought. I know this is an MRI paper, hence the relationship to Tesla type fields, but anyone that has to go to this much trouble to prpoerly detect the human resistance response........got to be a fire in the somke somewhere......
Thus:
human skin conductance changes (SCRs)
Changes in human skin conductance are frequently used as an indirect measure of a subject's cognitive effort, emotional arousal, or level of attention. Recording skin conductance responses (SCRs) is useful during functional magnetic resonance imaging (fMRI) studies that hypothesize correlations between blood oxygen level dependent (BOLD) signals and anxiety levels or emotional responses. Because clinical MR scanners do not come equipped to monitor SCRs, one must independently acquire the apparatus to do so, and then adapt it for use in an MR scanner. The two main technical challenges are: a) obtaining SCR signals that are not corrupted by interference from the MR scanner's changing magnetic field gradients, and b) maintaining low background noise in the MR images. Recent studies reported monitoring SCRs during fMRI (1, 2), but the technical issues above are not addressed in detail. In addition, reference (1) reported that scanner-induced artifacts rendered SCR data useless in 4 out of 9 trials. Both studies reported normalized SCR data rather than amplitudes measured in S (S=1/), making it difficult to compare their SCR data to values reported in the literature. We therefore feel the need for an article that addresses the technical aspects of monitoring SCR on human subjects during fMRI. In this article we describe the construction, calibration, and testing of a versatile, low-cost system for monitoring SCRs in a clinical MR scanner. We show that the system suppressed scanner interference during fMRI to an acceptable level independently of the repetition time (TR) and slice orientation of the fMRI sequence. In addition, the presence of the SCR system inside the MR scanner did not adversely affect fMRI images as measured by the image background noise level.
SCR monitoring circuit: The design of our system was based on the frequency and amplitude characteristics of SCRs. The range of human SCR magnitudes is from SCRmin0.01 S to SCRmax 1 S (3,4). In order to ensure adequate resolution in measuring the smallest conductance responses, we required the SCR monitoring system to suppress interference during fMRI to a level , an order of magnitude below SCRmin
 =SCRmin/10=10-3 S
We hypothesized this could be accomplished by using a low-pass filter with cutoff frequency of 1 Hz (5), because SCR signals change relatively slowly compared to interference generated by the MR scanner. . Figure 2 shows the schematic diagram of the SCR monitoring circuit consisting of a Wheatstone bridge, a differential amplifier, and low-pass filter. The design of the bridge circuit was taken from Ref. 3, and a complete description of its use is given there. R1 is a 10-turn potentiometer, and all fixed resistors have 1% tolerance. The bridge output Vout (between points C and D of Fig. 2) is proportional to the change in the subject's skin conductance C4, as given by
(1)
(see Appendix) where C3=1/R3=5000 S, and Vin=0.488 V is the voltage from A to B, regulated by the LM113H reference diode. If one inserts the component values into Eqn. (1) and uses the lower limit of human SCR amplitudes C4=SCRmin, one finds an expected minimum bridge output voltage of Vmin=1 V. We adopt as a rule of thumb for determining adequate amplifier gain G that a minimum of 10 voltage steps Vres must be present over the lower limit of amplified output voltage GVmin, or GVmin/Vres10, yielding for G the criterion
(2)
We therefore calculated that the gain should satisfy G  610. We chose to use the differential amplifier chip AD624AD (Analog Devices, Norwood, MA) designed for a gain of 1000 (details are in Ref. 6). The amplifier output was fed to a low-pass filter with a 3 dB cutoff frequency of 1 Hz. We selected the 2-pole, Butterworth low-pass filter for its flat pass-band magnitude response and its moderately steep attenuation (-40 dB/decade) beyond the 3dB point. The filter circuit of Fig. 2 was designed using FilterProTM software for the universal filter circuit UAF42AP (Burr-Brown, Tucson, AZ), where R6=1.58 M and C=100 nF. NPO ceramic, silver mica, or metallized polycarbonate capacitors are recommended (6). Voltage supplies ranging from 6 to 18 V may provide power to the amplifier and filter circuits. The resistor R5 limits current through the LM113H, which maintains a constant voltage of 1.22 V, and satisfies
Cable shielding: Shielding the cable (shown schematically in Fig. 1) with braided copper sheath was another step we took to reduce scanner interference. This established a ground connection between the chassis of the electronics box, the custom-built aluminum door, and the scan room shielding, and reduced interference considerably. In our case shielding was particularly important because we put the 40 m data cable permanently in place over the scan room ceiling. The cable extended from the rear scan room door to the console room in front of the scan room. The length of the cable and its proximity to gradient power supplies made this step necessary.
Door: To prevent the SCR cable from picking up outside radio frequency (RF) interference, transferring the RF interference into the scan room, and degrading the quality of the functional MR images, we filtered the cable as it passed through the penetration ports on the custom-built door (Fig. 3(b)). The door itself was assembled from aluminum angle irons cut to the dimensions of the doorway, with allowance made on the sides and top for the addition of metal contact fingers (Lindgren, Glendale Heights, IL) compressed 70% of their width. The lower half of the door was covered with an aluminum plate 0.64 cm (0.25 in) thick, and the upper half with aluminum screen. Aluminum side handles were also added to make moving the door easier. A twin BNC connector was mounted to the aluminum plate (Amphenol #31-225) to mate with the SCR electrode cable on the immobilizer. Mounted to the aluminum plate was a filtered penetration port (Fig. 3(c)), consisting of an interior aluminum bulkhead through which two 400 Hz, low-pass, feed-through capacitors (Spectrum Control, Fairview, PA) were mounted.
Calibration: SCR amplitudes C4 are related to the amplified output voltage of the circuit by C4=-Vtotal  where = C3/(VinG) (see Appendix). Given that C3=5.00x10-3 S, Vin=0.488 V, and G=1000, one expects theoretically that =10.2 S/V. Further, because C3, Vin, and G are known to within 1% , one can show that  should have an uncertainty of 3%. We also determined  experimentally by sampling Vtotal while R4 was switched to the internal resistors 1 M and 0.1 M. Then =-C4/Vtotal was used to obtain
in good agreement with the expected value. We used the experimentally obtained  value, and programmed the data acquisition software to convert from volts to S. As a check of the system accuracy, we connected a precision resistor and potentiometer in series across the SCR leads and measured the difference between the maximum and minimum conductance. The difference in conductance was determined beforehand by digital multimeter to be 0.49 S. The calibrated SCR system yielded 0.46 S, in good agreement.
Thus:
human skin conductance changes (SCRs)
Changes in human skin conductance are frequently used as an indirect measure of a subject's cognitive effort, emotional arousal, or level of attention. Recording skin conductance responses (SCRs) is useful during functional magnetic resonance imaging (fMRI) studies that hypothesize correlations between blood oxygen level dependent (BOLD) signals and anxiety levels or emotional responses. Because clinical MR scanners do not come equipped to monitor SCRs, one must independently acquire the apparatus to do so, and then adapt it for use in an MR scanner. The two main technical challenges are: a) obtaining SCR signals that are not corrupted by interference from the MR scanner's changing magnetic field gradients, and b) maintaining low background noise in the MR images. Recent studies reported monitoring SCRs during fMRI (1, 2), but the technical issues above are not addressed in detail. In addition, reference (1) reported that scanner-induced artifacts rendered SCR data useless in 4 out of 9 trials. Both studies reported normalized SCR data rather than amplitudes measured in S (S=1/), making it difficult to compare their SCR data to values reported in the literature. We therefore feel the need for an article that addresses the technical aspects of monitoring SCR on human subjects during fMRI. In this article we describe the construction, calibration, and testing of a versatile, low-cost system for monitoring SCRs in a clinical MR scanner. We show that the system suppressed scanner interference during fMRI to an acceptable level independently of the repetition time (TR) and slice orientation of the fMRI sequence. In addition, the presence of the SCR system inside the MR scanner did not adversely affect fMRI images as measured by the image background noise level.
SCR monitoring circuit: The design of our system was based on the frequency and amplitude characteristics of SCRs. The range of human SCR magnitudes is from SCRmin0.01 S to SCRmax 1 S (3,4). In order to ensure adequate resolution in measuring the smallest conductance responses, we required the SCR monitoring system to suppress interference during fMRI to a level , an order of magnitude below SCRmin
 =SCRmin/10=10-3 S
We hypothesized this could be accomplished by using a low-pass filter with cutoff frequency of 1 Hz (5), because SCR signals change relatively slowly compared to interference generated by the MR scanner. . Figure 2 shows the schematic diagram of the SCR monitoring circuit consisting of a Wheatstone bridge, a differential amplifier, and low-pass filter. The design of the bridge circuit was taken from Ref. 3, and a complete description of its use is given there. R1 is a 10-turn potentiometer, and all fixed resistors have 1% tolerance. The bridge output Vout (between points C and D of Fig. 2) is proportional to the change in the subject's skin conductance C4, as given by
(1)
(see Appendix) where C3=1/R3=5000 S, and Vin=0.488 V is the voltage from A to B, regulated by the LM113H reference diode. If one inserts the component values into Eqn. (1) and uses the lower limit of human SCR amplitudes C4=SCRmin, one finds an expected minimum bridge output voltage of Vmin=1 V. We adopt as a rule of thumb for determining adequate amplifier gain G that a minimum of 10 voltage steps Vres must be present over the lower limit of amplified output voltage GVmin, or GVmin/Vres10, yielding for G the criterion
(2)
We therefore calculated that the gain should satisfy G  610. We chose to use the differential amplifier chip AD624AD (Analog Devices, Norwood, MA) designed for a gain of 1000 (details are in Ref. 6). The amplifier output was fed to a low-pass filter with a 3 dB cutoff frequency of 1 Hz. We selected the 2-pole, Butterworth low-pass filter for its flat pass-band magnitude response and its moderately steep attenuation (-40 dB/decade) beyond the 3dB point. The filter circuit of Fig. 2 was designed using FilterProTM software for the universal filter circuit UAF42AP (Burr-Brown, Tucson, AZ), where R6=1.58 M and C=100 nF. NPO ceramic, silver mica, or metallized polycarbonate capacitors are recommended (6). Voltage supplies ranging from 6 to 18 V may provide power to the amplifier and filter circuits. The resistor R5 limits current through the LM113H, which maintains a constant voltage of 1.22 V, and satisfies
Cable shielding: Shielding the cable (shown schematically in Fig. 1) with braided copper sheath was another step we took to reduce scanner interference. This established a ground connection between the chassis of the electronics box, the custom-built aluminum door, and the scan room shielding, and reduced interference considerably. In our case shielding was particularly important because we put the 40 m data cable permanently in place over the scan room ceiling. The cable extended from the rear scan room door to the console room in front of the scan room. The length of the cable and its proximity to gradient power supplies made this step necessary.
Door: To prevent the SCR cable from picking up outside radio frequency (RF) interference, transferring the RF interference into the scan room, and degrading the quality of the functional MR images, we filtered the cable as it passed through the penetration ports on the custom-built door (Fig. 3(b)). The door itself was assembled from aluminum angle irons cut to the dimensions of the doorway, with allowance made on the sides and top for the addition of metal contact fingers (Lindgren, Glendale Heights, IL) compressed 70% of their width. The lower half of the door was covered with an aluminum plate 0.64 cm (0.25 in) thick, and the upper half with aluminum screen. Aluminum side handles were also added to make moving the door easier. A twin BNC connector was mounted to the aluminum plate (Amphenol #31-225) to mate with the SCR electrode cable on the immobilizer. Mounted to the aluminum plate was a filtered penetration port (Fig. 3(c)), consisting of an interior aluminum bulkhead through which two 400 Hz, low-pass, feed-through capacitors (Spectrum Control, Fairview, PA) were mounted.
Calibration: SCR amplitudes C4 are related to the amplified output voltage of the circuit by C4=-Vtotal  where = C3/(VinG) (see Appendix). Given that C3=5.00x10-3 S, Vin=0.488 V, and G=1000, one expects theoretically that =10.2 S/V. Further, because C3, Vin, and G are known to within 1% , one can show that  should have an uncertainty of 3%. We also determined  experimentally by sampling Vtotal while R4 was switched to the internal resistors 1 M and 0.1 M. Then =-C4/Vtotal was used to obtain
in good agreement with the expected value. We used the experimentally obtained  value, and programmed the data acquisition software to convert from volts to S. As a check of the system accuracy, we connected a precision resistor and potentiometer in series across the SCR leads and measured the difference between the maximum and minimum conductance. The difference in conductance was determined beforehand by digital multimeter to be 0.49 S. The calibrated SCR system yielded 0.46 S, in good agreement.
Posted by Skeptic
- Aug 24, 2003, 04:20 PMQuote from: Marty on Aug 24, 2003, 06:04 AM
Transducers used in the BP cuff produce relatively small signals and would be most sensitive. The failure mechanism is rectification or other non linear interations with jamming RF. Shutting down a control CPU is best done with wide spectrum impulse noise.
The thing is (in my experience, at least with Lafayette instrumentation) the transducers are actually in a box on the table, with pneumatic tubing running from the box to the cuff. I would bet the box is EMI shielded, at least.
And where would rectification come in? I'd think the transducers would be DC coupled, given the signals of interest...
QuoteJamming with EM fields in the area of interest (in band) would require huge B or E fields. Given the wavelength here, all effects are near field. I would give B fields the biggest chance. Any effect would require B fields so large that they would vibrate metal of any significant cross section. In band E fields would not show since GSR would couple poorly (cap impedance is quite high compared to skin Z)
-Marty
I'm not sure this sounds right to me, Marty. Although my EM education is at the undergrad level and RFI is hardly an area of my EE specialty, it seems to me that the long leads to the GSR measurement amplifiers would be good at picking up strong electric fields. And I would think that the input impedance to the amplifier would be on the order of skin Z, for best power coupling.
Do you or anyone else have a schematic for a typical GSR meter? Are we talking a voltage source with a series current measurement resistor and instrumentation amplifiers, are things still done with a bridge, or some other mechanism?
Skeptic
Posted by Marty
- Aug 24, 2003, 06:04 AMQuote from: Skeptic on Aug 24, 2003, 02:10 AMTransducers used in the BP cuff produce relatively small signals and would be most sensitive. The failure mechanism is rectification or other non linear interations with jamming RF. Shutting down a control CPU is best done with wide spectrum impulse noise.
Actually, I think it stands to reason that the GSR instrument would be the most vulnerable to externally-generated electric fields. It's likely that those fields would need to be fairly strong and low frequency, though.
In my experience, the wires connecting the GSR (ohmmeter) to the fingers are not shielded, which would probably be the weak point for messing with the recorded signal.
Skeptic
Jamming with EM fields in the area of interest (in band) would require huge B or E fields. Given the wavelength here, all effects are near field. I would give B fields the biggest chance. Any effect would require B fields so large that they would vibrate metal of any significant cross section. In band E fields would not show since GSR would couple poorly (cap impedance is quite high compared to skin Z)
-Marty
Posted by Skeptic
- Aug 24, 2003, 02:18 AMQuote from: aldo_huxley on Aug 23, 2003, 09:48 PMSo how many manufactures are they? What components are common? Just curious. Mainly interested in the type of sensors and IC's utilized.
I'm not sure how many manufacturers there are, but Lafayette Instrument Co. is one of the biggest suppliers of polygraph instrumentation:
http://www.lafayetteinstrument.com
QuoteOh yes, a friend of mine is replacing a cap in an old stereo system. Question posed is which type is best, electrolytic, mylar, or ceramic? The former is best for filtering but I'm not sure about it's general effect on the sound. Any ideas?
Was the cap in the audio path to begin with, or in the power supply? In general, I would replace it with something close to what you took out.
For the record, electrolytics aren't necessarily "the best for filtering". Again, it depends: upon the frequency range of noise you're looking to filter, the noise amplitude, and how much you're looking to spend. Usually for power-supply-pin bypassing, you'll find both electrolytic and ceramic in parallel to cover a larger frequency range for noise filtering (most electrolytics are pretty much useless by the time you get into the tens-to-hundreds of kilohertz range).
QuoteGee, went off the subject.......
So you think the EMI protection within the unit exceeds the ability to disrupt it's functionality?
Absolutely not. But it all depends upon the strength of the disruption practially available, of course.
I would imagine some sort of high-voltage spark-gap device would likely induce significant noise in the GSR channel, at least. Whether the noise-induced nature would be obvious is another question.
It would be an interesting experiment to do, and could be tested using a common multimeter, unshielded leads and spade connectors strapped to the index and ring fingers using velcro straps (yes, I made my own crude GSR meter).
Skeptic
Posted by Skeptic
- Aug 24, 2003, 02:10 AMQuote from: Marty on Aug 22, 2003, 05:06 PM
The polygraph, including the galvanic skin resistance component, is not intrinsically vulnerable to electronic jamming measurement though each instrument may have defects that produce specific sensitivities. They would not be consistent from one design to another however due to the above.
-Marty
Actually, I think it stands to reason that the GSR instrument would be the most vulnerable to externally-generated electric fields. It's likely that those fields would need to be fairly strong and low frequency, though.
In my experience, the wires connecting the GSR (ohmmeter) to the fingers are not shielded, which would probably be the weak point for messing with the recorded signal.
Skeptic
Posted by Marty
- Aug 24, 2003, 01:57 AMThe oldest analog polygraphs are the least sensitive to external EMI. They didn't have any electronics except for the GSR which was typically passive, Wheatstone bridge based. The ones most sensitive were likely designed 30 years ago or so using electronic transducers (strain gauges) requiring significant amplification.. The types of capacitors make little difference, rather pcb layout and capacitor lead lengths (series inductance) are the important factors. Newer designs would have much more resistance as a side effect of stringent emitted EMI regulations.
As for the amplifier, resistors and capacitors in an RIAA equalization network should be highly accurate (or batch selected) and polystyrene types are quite good there. Low memory, linear, low leakage. For EMI, ceramic caps are normally best, available inline and with low series L.
-Marty
As for the amplifier, resistors and capacitors in an RIAA equalization network should be highly accurate (or batch selected) and polystyrene types are quite good there. Low memory, linear, low leakage. For EMI, ceramic caps are normally best, available inline and with low series L.
-Marty
Posted by aldo_huxley
- Aug 23, 2003, 09:48 PMSo how many manufactures are they? What components are common? Just curious. Mainly interested in the type of sensors and IC's utilized.
Oh yes, a friend of mine is replacing a cap in an old stereo system. Question posed is which type is best, electrolytic, mylar, or ceramic? The former is best for filtering but I'm not sure about it's general effect on the sound. Any ideas?
Gee, went off the subject.......
So you think the EMI protection within the unit exceeds the ability to disrupt it's functionality?
On the subject of conductivity sensors, what if you went to a poly with a tinge unit on?
Aldo
Oh yes, a friend of mine is replacing a cap in an old stereo system. Question posed is which type is best, electrolytic, mylar, or ceramic? The former is best for filtering but I'm not sure about it's general effect on the sound. Any ideas?
Gee, went off the subject.......
So you think the EMI protection within the unit exceeds the ability to disrupt it's functionality?
On the subject of conductivity sensors, what if you went to a poly with a tinge unit on?
Aldo
Posted by Marty
- Aug 22, 2003, 05:06 PMQuote from: aldo_huxley on Aug 21, 2003, 02:29 AMThe polygraph, including the galvanic skin resistance component, is not intrinsically vulnerable to electronic jamming measurement though each instrument may have defects that produce specific sensitivities. They would not be consistent from one design to another however due to the above.
I guess my main point is that polygraphs are sensitive pieces of equipment and should inherently be subject to EMI if purposely designed to do just that. Of course $$$ is always a driving force to any new innovation.
Electronic jamming is not new, nor confined to specific areas.
-Marty
Posted by aldo_huxley
- Aug 21, 2003, 02:29 AMNo relationship between Tesla coils and linear 13.56MHz amps, no experience with polys to date.
I guess my main point is that polygraphs are sensitive pieces of equipment and should inherently be subject to EMI if purposely designed to do just that. Of course $$$ is always a driving force to any new innovation.
Electronic jamming is not new, nor confined to specific areas.
Search the following:
Skin Conductance and Cardiac Responses to Masked Presentations of Fear-Relevant and
-Irrelevant Conditioned Stimuli
Changes in human skin conductance are frequently used as an indirect measure of a subject's cognitive effort, emotional arousal, or level of attention. Recording skin conductance responses (SCRs) is useful during
"Psychologists have been trying to identify universal patterns of physiological response since the early 1900s, but without success. We believe that the lesson to be learned there is that there are no such universal patterns," said Smith.
Galvanic Skin Response is a measure of the skin's conductance between two electrodes. Electrodes are small metal plates that apply a safe, imperceptibly tiny voltage across the skin. The electrodes are typically attached to the subject's fingers or toes using electrode cuffs (as shown on the left electrode in the diagram) or to any part of the body using a silver-Chloride electrode patch such as that shown on the EMG. To measure the resistance, a small voltage is applied to the skin and the skin's current conduction is measured.
Skin conductance is considered to be a function of the sweat gland activity and the skin's pore size. An individual's baseline skin conductance will vary for many reasons, including gender, diet, skin type and situation. Sweat gland activity is controlled in part by the sympathetic nervous system. When a subject is startled or experiences anxiety, there will be a fast increase in the skin's conductance (a period of seconds) due to increased activity in the sweat glands (unless the glands are saturated with sweat.)
After a startle, the skin's conductance will decrease naturally due to reabsorption. There is a saturation to the effect: when the duct of the sweat gland fills there is no longer a possibility of further increasing skin conductance. Excess sweat pours out of the duct. Sweat gland activity increases the skin's capacity to conduct the current passing through it and changes in the skin conductance reflect changes in the level of arousal in the sympathetic nervous system.
The electromyographic sensors measure the electromyographic activity of the muscle (the electrical activity produced by a muscle when it is being contracted), amplify the signal and send it to the encoder. In the encoder, a band pass filter is applied to the signal. For all our experiments, the sensor has used the 0-400 microvolt range and the 20-500 Hz filter, which is the most commonly used position.
Most people cannot mentally control their skin conductivity response in any kind of rapid and fine-tuned way. The response can take seconds to arise and longer to decay. However, you can experiment with thinking of exciting or calming thoughts and watch how your galvactivator responds. Once you have dialed it to your proper baseline, the galvactivator should be sensitive enough to respond to internally-generated imagery in a broad way.
The startle reflex is a characteristic spike in the galvanicskin response that usually occurs 1-3 seconds after the onset of a startleprobe or a novel stimulus. Typically, a startle probe refers to a loudnoise, bright light, or puff of air designed to "startle" or suddenly divert the attention of the subject. A similar spike in conductivity can be generated when a subject "orients" to a new stimulus -- a person suddenly standing next to you, for example.
Can someone tell if I am lying?
Not with the galvactivator, though the galvanic skin response is one of the measures commonly used as part of a lie detecting apparatus. However, detection of deception requires a thorough experimental setting which does not compare to everyday's use of the galvactivator.
More later, Nuff to chew on.
Aldo
I guess my main point is that polygraphs are sensitive pieces of equipment and should inherently be subject to EMI if purposely designed to do just that. Of course $$$ is always a driving force to any new innovation.
Electronic jamming is not new, nor confined to specific areas.
Search the following:
Skin Conductance and Cardiac Responses to Masked Presentations of Fear-Relevant and
-Irrelevant Conditioned Stimuli
Changes in human skin conductance are frequently used as an indirect measure of a subject's cognitive effort, emotional arousal, or level of attention. Recording skin conductance responses (SCRs) is useful during
"Psychologists have been trying to identify universal patterns of physiological response since the early 1900s, but without success. We believe that the lesson to be learned there is that there are no such universal patterns," said Smith.
Galvanic Skin Response is a measure of the skin's conductance between two electrodes. Electrodes are small metal plates that apply a safe, imperceptibly tiny voltage across the skin. The electrodes are typically attached to the subject's fingers or toes using electrode cuffs (as shown on the left electrode in the diagram) or to any part of the body using a silver-Chloride electrode patch such as that shown on the EMG. To measure the resistance, a small voltage is applied to the skin and the skin's current conduction is measured.
Skin conductance is considered to be a function of the sweat gland activity and the skin's pore size. An individual's baseline skin conductance will vary for many reasons, including gender, diet, skin type and situation. Sweat gland activity is controlled in part by the sympathetic nervous system. When a subject is startled or experiences anxiety, there will be a fast increase in the skin's conductance (a period of seconds) due to increased activity in the sweat glands (unless the glands are saturated with sweat.)
After a startle, the skin's conductance will decrease naturally due to reabsorption. There is a saturation to the effect: when the duct of the sweat gland fills there is no longer a possibility of further increasing skin conductance. Excess sweat pours out of the duct. Sweat gland activity increases the skin's capacity to conduct the current passing through it and changes in the skin conductance reflect changes in the level of arousal in the sympathetic nervous system.
The electromyographic sensors measure the electromyographic activity of the muscle (the electrical activity produced by a muscle when it is being contracted), amplify the signal and send it to the encoder. In the encoder, a band pass filter is applied to the signal. For all our experiments, the sensor has used the 0-400 microvolt range and the 20-500 Hz filter, which is the most commonly used position.
Most people cannot mentally control their skin conductivity response in any kind of rapid and fine-tuned way. The response can take seconds to arise and longer to decay. However, you can experiment with thinking of exciting or calming thoughts and watch how your galvactivator responds. Once you have dialed it to your proper baseline, the galvactivator should be sensitive enough to respond to internally-generated imagery in a broad way.
The startle reflex is a characteristic spike in the galvanicskin response that usually occurs 1-3 seconds after the onset of a startleprobe or a novel stimulus. Typically, a startle probe refers to a loudnoise, bright light, or puff of air designed to "startle" or suddenly divert the attention of the subject. A similar spike in conductivity can be generated when a subject "orients" to a new stimulus -- a person suddenly standing next to you, for example.
Can someone tell if I am lying?
Not with the galvactivator, though the galvanic skin response is one of the measures commonly used as part of a lie detecting apparatus. However, detection of deception requires a thorough experimental setting which does not compare to everyday's use of the galvactivator.
More later, Nuff to chew on.
Aldo
Posted by Marty
- Aug 21, 2003, 01:50 AMQuote from: aldo_huxley on Aug 19, 2003, 02:13 AMSorry Marty, I find that you are an EE. I'm an engineer producing 95nm gates curently running 37 GHz technology. How about you?
Aldo
That's nice. How does that relate to Tesla's disrupting polygraphs at 13 MHZ? I seem to have off put you. Sorry. Why not use a real name and not an alias? Perhaps you been subject to polygraphs? They sure have their downsides.
-Marty
Posted by aldo_huxley
- Aug 19, 2003, 02:13 AMSorry Marty, I find that you are an EE. I'm an engineer producing 95nm gates curently running 37 GHz technology. How about you?
Aldo
Aldo
Posted by aldo_huxley
- Aug 15, 2003, 09:41 PMgiving, sorry typo.......
Aldo
Aldo
Posted by aldo_huxley
- Aug 15, 2003, 09:40 PMGee Marty, methinks we got away from the suject here. Sorry everone!
So..........If we realistically look at a problem there is always a solution. I have been gining the Tesla as an example, but looking for real feed back as how to do it, not "it can't be done". I was always told can't can't do anything.
Anyway, other approaches to jamming can include harmonic amplification( as in h of n(x) = A of n cos(n omega t+thea of n) are the harmonics, let's see how about a 25ns 500V P-P spike in the line? on and on......
any EE's out there?
Aldo
So..........If we realistically look at a problem there is always a solution. I have been gining the Tesla as an example, but looking for real feed back as how to do it, not "it can't be done". I was always told can't can't do anything.
Anyway, other approaches to jamming can include harmonic amplification( as in h of n(x) = A of n cos(n omega t+thea of n) are the harmonics, let's see how about a 25ns 500V P-P spike in the line? on and on......
any EE's out there?
Aldo