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.An important technical limitation is the necessity forhaving S in a shielded room (for example, grounded fly screen), which could be easily provided only insome central laboratory.Of course, the skeletal muscle can be activated intentionally by S.If S wished he could contract themeasured muscle upon each ques--150-tion and thus confuse the record, although the strategy would probably not occur to him.Such amovement would also have the effect of disturbing all the usual measures of lie detection, and evidentlyis not a common occurrence.The use of the method has some interesting possibilities since conflictbetween two responses can be recorded (17).OCULAR MOVEMENTSSomewhat similar in operation to the EMG the ocular movements permit the study of a choice ofresponses.If two or more visual targets are provided the eyes may unconsciously turn toward one oranother in response to a question.The method lends itself well to the map or picture exploration method(see the following).A substudy of the Indiana lie detection research tested the power of the ocular movements as adetector with good results.At least under special experimental conditions good discrimination can beobtained.This method, however, has the handicap of being rather cumbersome and slow.It involvesphotographing the eye movements with art ophthalmograph and evaluating the record after it has beendeveloped.Proposed Variables Not Yet TestedVELOCITY OF PULSE WAVESpeed of transmission of the pulse wave along an artery has been proposed by the group atWashington State University (5) as a possible indicator of deception.The variable measured is primarilythe pressure increase in the artery that follows a heart systole and is propagated through the fluid in theartery in a manner fairly well described by a known equation.(This propagation of pressure wave is quitea different matter from the flow of blood.) If the pressure wave is picked up at two points a knowndistance apart, its velocity can be calculated.The Washington State group has worked on a device thatwould do this automatically.The velocity, according to the equation, depends on the level of blood pressure, and it would seem thatin the same individual, variations in pressure would be the principal source of variation in velocity.Consequently, the scheme would be an indirect measure of blood pressure.Since the pickups would be activated by pulse pressure, and since pulse pressure is quite variableitself, it seems probable that such-151-a device would require a good deal of monitoring of sensitivity to give suitable readings.The scheme isalso rather complex and seems to be an alternative to the simpler method of recording pressure describedpreviously.GASTROINTESTINAL REACTIONSRecent instrumental developments (11, 12, 36) make possible the use of the gastrointestinal reactionsas a means of detection.According to one method, gastric or intestinal activity is recorded from surfaceelectrodes attached to S, one on the abdomen and one on the arm.Stimulus effects upon GI activity havebeen demonstrated (11), though much remains to be discovered about them.A probable handicap of themethod is the extreme slowness of response and recovery in this sector; it might be necessary to spacequestions several minutes apart.Nevertheless, the variable might turn out to be highly discriminative.THE ELECTROENCEPHALOGRAMThe EEG is a possible response variable for use in detection although it has never been tested.Theproblem expected is that under interview conditions the alpha rhythm would probably be blocked most ofthe time, and there would be very little opportunity for it to exhibit the "arousal" or "alerting" reaction.Inother words, the variable may be too sensitive to all sorts of stimuli and reach its maximum response, as itwere, too readily, but no one can be certain this would happen without a trial.Equipment for recordingthe EEG is basically the same as that described for the EMG.An integrator is not generally used inconnection with it, though such a transformation might in fact be useful.Interrogation ProceduresCertain general facts and a few known particulars indicate how prior conditions may affect detectionresults.Adaptation EffectsA general effect that needs to be taken into account is the rule of adaptation.Almost all the responsevariables discussed are known to become less responsive with repeated stimulation, some at a greater,-152-some at a lesser rate (10).Beyond influencing the choice of variable this fact should also regulateprocedure.Interrogation would be expected to become progressively less effective as it proceeds, and thediminishing returns would limit length of session: one cannot detect a difference between responses thatare practically nonexistent.In other words, instrumental detection would not be expected to combine wellwith a "wear-them-down" procedure.Profitable sessions would then probably be an hour or less.Furthermore, questioning or stimulation of other sorts before the instrumental session wouldundoubtedly also produce a deadening of response.For example, there is considerable transfer ofadaptation from one stimulus to another in the GSR.Immediately following a period of highly disturbingevents it is possible that an S might be induced to tell the truth, but the situation would be a poor one forinstrumental methods, since S is already in such a high state of excitement that increments in the responsevariables would be small.This can be inferred from experimental results, but it would be well to havedirect confirmation.For similar reasons, possibly because of the same adaptation mechanism, a condition of fatigue orprolonged sleeplessness would be unfavorable in discriminating truth from falsehood.Physiologicreactions are likely to be reduced in such circumstances.This suggestion accords with the commonexperience of being "too tired to care one way or the other." The stimulus threshold is raised and theperson eventually falls asleep  a state of relative indifference to all ordinary stimuli.By the same tokenone would expect alcohol and barbiturates, and perhaps tranquilizers, to be unfavorable to detection.Because of these considerations there may actually be a contradiction between trying to secure anadmission and detecting lying by instruments [ Pobierz całość w formacie PDF ]