C00022017

[PAGE 2]
I. Summery of Progress

A comprehenstve series of runs involving a variety of electrodermal and other physiological measures has been completed on a population of 26 subjects under a variety of task conditions and contrived psychological "sets" to assess the relative sensitivity and reliabllity of various electrodermal measures, Including the recovery limb time constant. Assessmeat of impulsivity and anxiety by psychological tests as well as a psychomotor test of inhibition have been obtained on the subjects. Data aralysis is still in progress, but some preliminary conclusions have already been drawn and are reported here as an interim progress note. Runs on a separate population of twenty subjects under a -different set of stimulus conditions have been used to examine the dependence of recovery limb time constant upon base conductance level and response amplitude. The initial study of the vascular compcnent in the skin poteztial response has been completed. Development of the automatic measurement of recovery limb time constant has progressed to the point at wiich a system is now availeble, using first derivatives, which overcome many of the difficulties of the earlier approach in which second derivatives were employed. The new system has been used to print out the time constants for 22 subjects whoee data had been stored on magnetic tape. These data are now being subjected to statistical evaluation.

I. Study of Characteristics of Recovery Limb in Relation to Other Electrodermal Measures

a. Dependence of Recovery Limb Time Constant on Base Level.

To detcrmine whether the apparent reiation of recoyery limb to nature of the stimulus condition was tc be explained by differences in base resistance level, comperisons

C00022017

Approved for Ralcas9 Dato 22FE3

151

[PAGE 3]
were made between base level and recovery li:nb time constant for 21 subjects in two condltions, each of which caused activation and conscquent decrease in base resistance, but with different degrees of goal oriented task demands.

Meaas for the two situations were as follows:

These data indicatc that despite the fact that the cold pressor task was, if anything, slightly more activating (difference in ievel not statiatically significant) the time constants were significantly different (p .01, paired comparison), the difference is thercfore no: ettributable to difference in base level.

It is to be expected, however, that subjects who show greater activation for performance of a task migint show a refiection of this 'mobilization both in base level and in recovery limb time constant. Accordlagly the correlntion between base conductance and time constant was determined for this same grcup c. subjects during the backward counting tesk, and it showed a signlflcant reletionship (r = -.49, F.05). For the cold pressor situation where the activation is presumed to be of a Cifferent cuality, the correlatioz was considerably less (r = -.23, N.S.)

C00022017

2

[PAGE 4]
b. Dependence of Recovery L.imb Time Constart on Responsc Amplitude

Although the time constant of an exponential decay should, if properly measured, be independent of amplitude of the curve, there are many conceivable reasons for suspecting that such may not be the case for the electrodermal response. Accordingly for each of 12 subjecte, time constants were compared with peak amplitudes (conductance change) for 30 sequeatial responses taken across four experimental conditions (rest, perceptual task, cognitive task, perceptual-motor taek). The Pearson's correlctions are shon below:

The independence of these two measures is well demonstrated. Some segative correlations migtt be expected because demanding tasks could produce higher responses and also, becauce of the narure of the activation, shorter time constants. For most of these subjects, however, such was clearly aot the case.

c. Denendence of Recovery Limb Time Constant on Quality of Task

A study was uadertaken to answer two questions.

1) Does the recovcry !imb vary as a function of the perceptua!, cognitive,

C00022017

3

[PAGE 5]
or motor aspects of a task.

2)  it does so, how does its specificlty and sensitivity compare with those of more conventlonal methods.

A. Method

Tweenty-six subjects were used in an experlment in which three tasks were performed, along wik associated rest periods. In order to exclude the variance kaowe to be due to the aperator's mod: ot Lastructloa and hls rciatioa to the subjact, the tasks were programmed on video tape.

1. Cognitive

Each of a series.of 12 Ravens Matrices Problems was presented fo. 30 seconds followed by a 15 second rest period. The subject was to choose the patterr which properly completed the matrix and was to report only after the given problem disappeared from the screen. Responses were chosea only from thé period in which te was solving the problem. Cbviously, contaminants such as visual perception, frustration. etc., were present, but it was hoped that the group result as a whole would be heavily weighted by the cognitive performance factor.

2. Percentual

A fixed pattern remained on the screen for three minutes. At random intervals during this period, it would disappear, momentarlly (40 msec) end for a total of 18 times. The subject was to continuously observe the pattern and after the ead of this task, upon command, report the number of disappecrances. All useable responses during the oservation period were anslyzed.

C00022017

[PAGE 6]
3. Reaction Time

A series of five reaction time trlals was used, cach having a warniag slgnal and a 10 second forcperiod. Measures werc taken at the time of the reaction key press.

4. Otncr Measures

a) Behavioral. . in addition to the above, two psychological tests were administered to these subjects, the Barrett Lnpuisivity Scale and the Spiclberger Trait Anxiety Scale. A behavioral test of motor inhibiion task wes aleo administered. In this task.: devised by tiis-investigator, the subject is told to turn a knob through 160 degrees, continuously, but as slowly as he can. Inhibitlon is assessed by the total time takea and by the degree to which rete is accelerated as the task progresses.

b) Physioloçical. La addition to the skin ccncuctance measure, skin potential, cardiotachometer recording, respiratton (mechanical prsumograph only) and frank persplration were measured. The last measure was ohtzined by a modification of the phozoelectric prism method previously described. The device has been improved to elininate vasomotor artifacts and to allow use of a lightweight unit secured to the inger tip.

5. Durig-the-above-runs;-tests-were·run-on-24 of-the subjects toidetermine the sensitivicy.of.the recovory limb time constant for-detecting subtle cháages-of emotional 1 sett ítest was adopted for this purpose and wes used-under three difierent-demand situations.- The use of vicco tape was agelo helpful in reduciag difrrences-in operator cfect...The subject was presented four, letters and asked to

C00022017

5

[PAGE 7]
cheose one and write !t dowt, to be turned in efter the task was over. łie was then presented a screen in which these four letters appeared ln a new order, the group being preceded by three other letters and followed by three πure. An arrow appeared and pointed to the first letter where it paused for 15 seconds. It then moved on to the next in the sequcnce and again paused for 15 scconds, etc. Thie subject kncw in advance that this would happen in regular scquence. In the first cuch test, the subject was to simply observe this scquence without any vorbal report. In the second test, the idcntical sequence 1 1

In a third series run on

13 of these 24 subjects, the subject was told that he would earn an extra dollar if he 1 managed to successfully An entirely new serles and new

were used. At the end c' tte previous two tests be had been told the operator's conclusion as to which of the letters was This time his "set" had been altered by his knowiedge of the operator's previous success and by the adced incentive Again he was to respond "no" to cach letter.

B. Results to Date

Analysis of these data is still in process, but some early results may be 1 presented. Follow-up progress reports will be made as calculations are completed.

1. Data Handling

The tapes were made primarlly so that analysis of these recordo could be made afer furtier development of elcctronic techaiques for calculation of the time constent. This development went on as ε paraliel effort during completion of the above series of ruas ard bas since been completed. The tapes have beer rua off

C00022017

[PAGE 8]
prieted out by usc of first

cerivative proceeslag. Mcans aad staadrd deviatiens of responses lor cach subject under each task condition are bcing calculatcd In preparatioa for t-tests cf ciffercnces betvcen cordltions. To dete calculatlons en 12 of the 26 suijects have been completed.

2. Cemparison Berween Conditions

No comparlsous acroso subjects caa be made urtil all means and standard doviations bave been calculated, but Latra-individual comparisons between tasks bave been made for those subiects completed. Of 32 posslble comparisons, only 3 reached sigaificance; 5 approached sigalficance. Ln 10 of the 1l subjects who showed reaction time responses, the time corstart for this task: was the shortest of the threc tasks.No consis: nt difference eppears between the cognitive and perceptual tsks for that part of the populatioa completed.

Using the the operator correctly icentified the ccn
cealed letter in the first ccries far 1s of the 24 subjects. Moreover, whes the subject --
was motivated to fby monetary reward, the operator ideatified it
correctly in 10 of the 13 cases. In 5 Lnstances. the operetor had fallcd to ideatify
the letter lo the first scrics, but when mcnetrirrevard was added be correctly
identified the nev: lotter for 4 of these 5 subjects. Tho comparison of -3

It is noteworthy that ia sone lastances in which skie conduetazee activity give ambigcous resclts, the optical sweet recording showed a grematic duerenttatioa.

C00022017

7

[PAGE 9]
4. Psvchological and Psychomotor Tests

These tests will later be used as a basis for sorting the population into different types of physiolcgical responders. To date, the Individual impulsivity ratings on the Barrett Scale have been compared with thie time taken for 180 degree knob rotation. The correlation was unpredictably a positive one for the 26 subjects (r = .37. p <.05), 1.e.. individuals judged more impulsive by the Barrett Scale took longer to rotate the kmob, lndlcating that the type of inhibition measured by the two tasks is different: The Barrett Scale was also demonstrated to give ratings which were independent of the Splelberger Anxiety ratings. Later calculations will examine the interaction of these scale ratings and physiological fiadings.

III. Study of a Possible Vascular Component in the Skin Potential Response

This study, involving the effect of arteriol or venous cuffs upon skin potential, has been completed on a total population of 24 subjects. Resuits are highly significant and show that the shiit in potential can be more easily demonstrated upon deflation than upon inflation of the cuff, and that the polarity of this post-deflation response differs according to the type of pressure cuff used. For venous (engorging) cuffs $\textcircled { 1 } = 6 0$ min Hg) the response positive. For axteriol (occluaive) cuffs (p = 180 mm Hg) the post-deflation response is negative. The conclusion that these represent vasomotor adjustments is supported by a follow-up pilot study oa the local potential responses reported earlier. It had been concluded thet the slow component of this positive responee to stretch is of vascular origin. If so, it should be demonstrable even when the epidermis is penetrated. Microelectrodes were pushed through the epidermis until the negative potentia! fell precipitously indicating penetration of the dermis. After allowing time for stabllization. increase of pressure on the

C00022017

8

[PAGE 10]
electrode causes a potential varlation. These experiments must be refined to eliminate the possibllity of the "responses" being only a reflection of variations in tip potentlal or sweat gland activity. If valid they will offer strong support for a vescular component in the skin potential response.

IV. Develooment of Automatic System

Comparisou of veluee for recovery limb time constant obtained by template matcliing with those cbtained by the use f first derivatives indicated the interchangeability of these two methods. The principle involved in the first derivative method is that the absolute steepzess of the recovery limb is a measure cf its time coastant for responses of equal amplitude. Respoases of higher amplitude having the same time constant will have a greater absolute steepness to the recovery limb. Hence the absolute slope of the recovery limh can be used as a measure of time constant if a correction for amplitude is made. In practice the simplest correction is to divide the cmplltude of the peak slope (first derivative) of the ascending limb by thet of the recovery limb. This ratlo. plotted agaiast the template readings, gives a good linear relationship.

To accomplish tiis electronically. the derivatives are obtcined by R-C differentiation and the output stored on capacitors with diode input so that peak values are obtained. Gating circuits are used to allow computation only aftcr both peaks have been stored and only if the time ciapsing between. successive wcves is long enough to allow the recovery limb to reach its peak. Lf the contingencies are met, a command signal feeds the two stored voltages into two voltage to frequency converters, and from tiiere to a counter having aa input for obtaining the ratio of

C00022017

9

[PAGE 11]
two frequencles. The output is prioted out upon command and the system reset. At the same time as the above occurs, the value of the peak first derivative of the ascending limb which is proportional to response amplitude is printed out after measurement Ly a separate counter. Thus the response amplitude and recovery limb time constant are measured in a single operation. It is presumed, however. that most facillties will not bave the luxury of two parallel voltage-to-frequency converters and counters and, therefore, an analog division circult is being tested. In this system the two volages to be divided are fed iato a diode division circuit and the quotient, as a voltage level is fed into an A-D conversion and printirg unit. This circuit is very simple, and as an alternative the output (proportional to time constant) can be written out on an ordinary analog recorder. The system thien approaches practical utility.

C00022017

10