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I. Sunimary of Progress

The previous phase of thís study afforded evidence for a model of the electrodermal response which implied that the recovery limb contained information of velue. An approximnate method for obtaining a characteristic measure of this limb, the recovery half-time, was adopted and used for initial explorations into possible applications of the new measure. Results wers very cacouraging and as a consequence a major effort has since been exerted toward the development of a more refined measure for characterizing the recovery limb and toward the evaluation of its bebavioral indications. At the same time a parallel effort was maintained to continue experiments aimed at clarifying the nature of the peripheral mechanism of the response. The following summarizes progress made in these areas.

The subsequent section on Specific Findings (ID), details the quantitative data of those items whose analysis has proceeded far enough for reporting-

A. Recovery Limb Measures

1. A superior manual method was developed for obtaining the time constant of the recovery limb, Its reliability betwveen scorers and in repeated measures exceeds 0.90.

Apprcved,for 2 T FES Date

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2. The basis for two automated systens for cvaluating the time constunt was established; one of thiese is an analog system, the other digital. Both are relatively simple,

3. The discrint, irg power of the new measure as an indicator of stínulus situation has been tcsted on several populations, using the manual methoj. It succcssfully distinguished between several paired categories of stimulus conditiors with remarkable reliability.

4. The recovery limb time constant for a given individuel during a standard stimulus situation was found to be characteristic and was correlated with his rate of habituation to a series of repeated stimuli. Individuals who had a short time constant also tended to have a slower habituation in their electrodermal response to a series of reaction time tests but not to a series cf tones.

5. The variation in time constant was examined in a population of subjects in which each was exposed to a succession of eight conditions ranging from resting with eyes closed through a series of simple to complex tasks. A cold pressor test was also included. The time constant varied with the situation in a characteristic manner, being longest for the rest situation and becoming shorter as the task becomes more involving. This finding was a consistant one across subjects and was independent of amplitude. The cold pressor test, although producing high activation, was accompanied by a long time constant (about the same order as that of spontaneous responses during rest). These results strongly supported the interpretation of short time constants as accompaniments of goal directed bchavior.

6. Shorter time constants were found, as predicted by the model, to be associated with positive skin potential responses and with reabsorption responses.

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B. Studies of the Peripheral Mechanism

1. A major question regarding the nature of the absorbtion reflex (and presumably, thercfore of the origin of the positive skin potentiai response believea to be related to it) is whether it depends upon absorption through the horny layer, medisted by the underlying epidermis, or upon sweat duct activity. An optical device for observing surface moisture has supported the hvpothesis that reabsorption occurs via the sweat duct.

2. The local potential response (LPR) produced by stretching the skin was previously shown to contain a fast and a slow component which often respond differentty to changes in surface conditions. A given variable may produce either potentiation or attenuation of the LPR in a manner which defies prediction at this stage, but the variation in amplitude of the experimental site is consistently greater than the control and an effeet of the surface variable is consequently statistically significant. However, only three effects are consisrant in direction of change:

a. Reducing surface temperature produces an iacrease in LPR amplitude.

b. Exsanguination produces an increase in LPR amplitude.

c. Backgtound negative electrodermal potential activity produces an increase in LPR amplitude.

3. The striking effect of the aluminum ion in selectively potentiating the positive wave of the skin potential response was utilized as an aid in an attempt to identify which component of the biphasic potential response was primarily responsible

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for the conductance change in the exosonatic response. Since indiyiduals show a rather wide va ríatfon in their response to local application of AlClg concordance between effeets upon positive potential responses cnd effects upon conduetanee responses was exanincd. The results of tis study on 20 subjects:. raised more questions than It answered. Although potentiation of thie zonductance response was correlated with the potenriation of the potential response aeross subjecrs, the as specific relation to SPRs of negative opposed to positive direction, and the relation of polarity of current flow to degrce of potentiation presented a confused picture. Moreover, the associated measurements of capacitance and impedance revealed no significant effect of $\mathbf { A l C l } _ { 3 }$ on these for the group as a whole. These results are presently undergoing intensive examination and will not be reported here.

4. The report of a finding of sweat clands under the nail plate was clarfied 一 indicating that these were observed only at the distal tip near the margin with the naked skin. A new method for insuring that the nail plate site was confined to the center of the nail and for precluding spurious 1 contributions by activity of the reference site demopstrated the following:

a, Positive or negative potential responses may be observed from ts COCLELAENA AMRD the center of the nail plate.

b. These are not appreciably influenced (if at all) by the application of varinus surface electroiytes.

c. Local potential responses of high magnitude (all positive) are readily elicited from this same arca.

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d. Exosomatic nail resnonses showing the typical increase in conductance are not obseryed. Responses showing a decrease in resistance are not unusual, but entirc records in which the nearby skin is active may show none of these. They are thought to represent the vasomotor effect upon conductance typically seen in the impedance plethysmogram. The lack of covariation between 2 these conductance responses and the nail pctential responses suggests that thev represent different. phencmena. At this stage it is believed that the nail potential responses because thev correlate highly with skin potentiai responses (SPR), reoresent a component found in the SPR which is not of sweat gland origin.

C. Study of Bio-Psychological Adaprability

Initial exploration of the possibility of using the adaptability of autonomic behavior as an index of adaptability of psychological behavior has been started on a population of 60 suSjccts. These were run through a battery of psychological tests and then exposed to a behavioral situation which exaniined their rate of habituation to a series of repeated stimuli, their rate of activation from a rest state to a tüsk state, and their rate of relaxation following the end of the task, Analyses completed to date have shown that individuals who demonstrate a capacity to maintain a high degree of appropriate inhibition during motor task performance also show rapid recovery of electrodermal levels after high activation. Morcover, post-activation recovery to original rest levels for pulse volume and for electrodermal activity pro-PAS ceed at different rates, and a large fraction of the test population shows a reciprocal 2 relation between these two rates.

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II. Specific Findings

A. Recovery Limb of the Skin Conductance Response

1. Manual measurement of the recovery limb time constant.

Gildemeister (1923) and Darrow (1937) bad described te recovery limb as an exponential decay curve. All responses whose recovery limb has the same time constant should fall along this curve independent of amplitude as shown in figure I. In actuality only the first portion of this limb falls upon an exponential slope, since the latter portion apparently represents a separate component as described in the previous report. Because this second component may come in at various levels, the half-time measure previously described is subject to considerable variation in the activity of the slow component (figure 2). In addition, if a second wave occurs during the recovery of the wave in question, measurement of the half-time is often precluded. For these reasons, a method for examining the time constant of the early portion of the recovery limb was developed. In this method a transparent template consisting of a' family of exponential curves, each having a slightly Ionger time constant than the one to its left, is slid sideways over the response, its baseline at the level of response onset, until one of the calibrated slopes corresponds with the early portion of the recovery limb (figure 3). Interpolation is easily accomplished. A xeading takes about 7 seconds, and reliability both for repeated measures and between scores is high (berter than 0.9). If the bascline (during inactive periods) has an appreciable slope, a correction must be applied. This is acccmplished by lowering the baseline of the template to a level half way between the level of wave onset and the

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level at which it takes on thic slope of the resting base\_z. In practice this is a simple operation which is not commonly necessary.  less to say DCrscordings are mandatory whenever quantitative treatinent : time constant is attenpted.

2. Autonatic determination of the time cczznt.

a. Analog method:

(1) Since the equation for an expozl curve is

$$
\frac { d E } { d t } = - k E
$$

whiere E is the voltage, t is time e=i x is a rate constant which

is the reciprocal of the time const=.

$$
\frac { d ^ { 2 } E } { d t ^ { 2 } } = - k \frac { d E } { d t }
$$

cr

$$
\mathbf { k } = \mathbf { \frac { - y ^ { \alpha } } { Y ^ { \alpha } } }
$$

where Y' and Y" are the first and sec:ad derivatives of the recovery ${ \bf \nabla } { \bf \vec { Y } ^ { \prime } }$ $\pmb { \gamma } "$ limh with respect to time. These z ze readily obtained by the use of operational amplifiers as show= ≈ gure 4. Y\* and Y" are fed into $\gamma ^ { \tt t }$ $\gamma "$ a simple division circuit which taiss zivantage of the logarithmic characteristics of a silicon diode z, H. L. Review of Scientific $\dot { \mathbf { s } } _ { i }$ Instruments 33, 235-233, 1962. T =formnation of interest in the output will be the negative peaks c =: rate constant which may be neasured by a digital voitmeter.

(2) Another form of the exponent: ezation,

$$
\mathbf { \nabla \cdot \log } \bar { \mathbf { E } } = - \mathbf { k } \mathbf { \cdot } \mathbf { \nabla } \mathbf { c }
$$

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suggests that the rate constant ean be obtained by the slope of log E against time or d(log E)/dt. Unforturately this would be useful only if E represents voltage referrec to final asymptotic . Ievel (i.e., to baseline), an arrangement wich would be conı- plicated, if indeed attainable.

b. Digital method:

An approximate solution for obtaining the rate constant Iends itself readily to analysis by digital voltmeter and simple digital computation. It is based on the fact that exponential decay is essentialy a percentage rclation, i.e., in a small increment of sime, the percent recovery is constant regardless of the amplitude chosen. From this it follows that the ratio of the absolute increments of recovery in two successive increments of time is related to the time constant, Thus if recovery is taking place at 5 percent per millisecond, the recovery rate may be obtained, for example at the 1 volt level, by taking

$$
\Delta E _ { \perp } = \ . 0 5 \times 1 \ \mathrm { v o l t } \ = \ . 0 5 0 0
$$

$$
\Delta ~ E _ { 2 } = ~ . 0 5 \times 0 . 9 5 ~ \mathrm { v o l t } = ~ . 0 \dot { . } 7 5
$$

To calculate the rate constant, take

$$
1 - \frac { \Delta 1 } { \Delta 2 } = 1 - \frac { 0 5 0 0 } { 0 . 7 5 } = . 0 5
$$

In practice, voltages are sampled by a digital voltmeter at 3 successive points on the recovery limb, e.g., at 0.2 second intervals, (figure 5) starting 0.5 seconds after peak and the

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appropriate calculation made cither manually or by computer.

3. Testing the discrininating power of the time constant measure.

The t/2 measure was previously slown to be capable of discrininating be- $t / 2$ tween rest and task performance and betveen the response to án alerting signal and the response to a task execution signal (for some subjects). The ncw time constant measure was tested on additional populations and under different conditions. One was a comparison on 35 subjects of the time constant associated with the orienting response to a series of tones as compared with that to a series of reaction time tests. Figure 6 shows the characteristic acceleration of the recovery limb attending the reaction time effort. Figure 7 s.lows the results for the entire population $( P < . 0 0 1 )$ . Only two subjects failed to sliow the acceleration.

In another eyaluation (this one of the power of the t/2 measure) a population of $t / 2$ 16 subjects was exposed to a series of moderate light flashes and their orienting responses obtained. They were then instructed that when the light flashed (same light) they were to observe the position of a moving pointer, but to withhold reporting until requested. Thus no motor activity was overtly invoived in this perceptual task. Table 1 shows the result and also suinmarizes other tests for comparative purposes. All but 3 of the 16 subjects showed an acceleration of the recovery limb during the perceptual task.

Another example of the ability of the recovery limb to discriminate is seen in figure 8 which shows simultaneous recordings from the dorsal (hand) and palmar surfaces of two individuals. The letter A indicates an alerting signal for a forthcoming

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TONES

RT

Figure 6. Recordings of responses to a series of tones and a series of reaction time signals, showing acceleration of recovery limb during reaction time series.

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Table 1. Effect of various stimulus conditions upon recovery limb time constant.

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reaction time effort; E is the execution signal and S denotes a spontancous wave occurring during the forepcriod, Below these responses are shown the time constants. In the dorsal trace of the first subject, the time ccnstant of the spontaneous response is approximately equal to that of the alerting response while the execution response has a, time constant of approximately half this length. Although the absolute levels for the palmar and dorsal traces are different, the same relationships hold. The second subject (right hand panel) shows a different sort of relation. This subject has a short rime constant in the alerting response. That of the spontaneous response is almost twice as long. The execution response for this subject has a considerably slower recovery limb than does his alerting response. Here again the palmar responses though of different absolute value are in the same ratio as those from the dorsal surface. These autonomic pattern differences will be examined for possible use as an indicator of characteristic behavior patterns in an individual.

Figure 9 exemplifies the application of this measure in the identification of qualitatively different states, despite similarities in response amplitude. In the upper trace a subject is being presented with his first series of reaction time (RT) and word association (WA) stimuli. There was a forewarning signal for the reaction time and the subject in each case responded to this alerting signal as well as to the execution signal. In trace B which occurred 8 minutes later, the subject has appaxently habituated to the situation and has ceased responding to the alerting signal. Notice the marked slowing of the recovery limbs, and especially that the response to the word association, thougi of similar amplitude co that in A, has a greatly differing time constant.

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4. Correlation of an individun l's tine constan sith his behuvioral partern.

One naturally wonders whether this measure which can differentiate betveea conditions within a subject independently of response amplitude can also differentiate between subjects having different behavior patterns in similar situations. To answer thiis question, the recovery time constants of responses to reaction time efforts were used to characterize the individual subjects. Also determined for each subject was a measure of the rate of habituation of their responses either to a series of toncs or a series of reaction tine efforts as seen in figure 6. The measure of habituation was the quotient of the amplitude of the second response of the series divided by thet of the third response. The larger this ratio, the more rapid the habituation, Table 2 shows the results of comparísons across subjects. (Square root transformation was used in some cases ;o obtain a linear regression.) Ln all cases the time constant (SCR) measure was that of the skin conductance response obtained during the reaction time 2 series. Various measures of habituation rate were compared with this. In the first case it was the skin conductance response during the reaction time series. This showed a 0,33 correlation with the recovery time constant, $( p < . 0 \dot { 2 } )$ which is interpreted as indicating that a short time constant is associated with sustained activation (motivation?) in the RT task.

In another comparison, the habituation rate for SCR was obtained during the tone series and compared with the same time constants as above. There was no significant correlation.

Surprisingly the time constant obtained during the reaction time series did correlate significanily with the rate of habituation of the finger pulse volume response

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Table 2. Correlation of recovery limub time constants obtained during reaction time with various habituation measures taken across subjects.

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obtained duríng the same tone series examined above (r = 0.30, P.05). This relation of SCR recovery rate to an entirely different autonomic measure in a different stimulus situation is viewed as an indicatíon of the basic significance of this measure.

5. Relation of time constant length to quality of stimulus situation.

To shed light upon the behavioral significance of changes in the time constant its relation to a series of S graded stimulus situations was examined. Although data on 21 subjects are available, only 9 have been analyzed to date. The situations were:

Relaxing - Eyes open - 2 minutes

Relaxing - Eyes closed - 2 minutes

Counting aloud - 2 minutes

Reading aloud - 1.5 minutes

Counting backwards by 7's - 2 minutes

Deep breaths, 3 at 20 second intervals

Cold pressor test (ice bath) - 2 minutes

Mirror drawing - to completion

Average time constants were determined for each sitiation acd the 8 categories rank-ordered for each individual, using a rank of 1 for the longest. These ranks were then averaged for each condition. Results were in the following order:

Situation

Average Rank

Rest, eyes open Cold pressor

2.2 ± 0.8 (Longest)

3.1 ± 1.2

Rest, eyes closed

3.3 ±1.2

Deep breathis

4.2 ± 1.5

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Situation

Average Rank

Count, forwa rd

4.4±1.2

Count, backward

$$
6 \pm 1 . 9
$$

Read aloud

6.1 ± 1.3

Micror tracing

Two features of this ranking are most significant, first that time constant becomes shorter apparently as the goal direction of the behavior increases. The second is AN that the cold prcssor test, though it produced high activation showed waves with time constants as long as those under resting conditions. This seems consistent with the above inference regarding the association of rapid recovery limbs with goal directed behavior. It is suggestive of a system in which mobilization for goatdirected activity, involves activation of a rcflex mechanism which hastens elećtrodermal recovery.

Tests of statistical significance have not been made on this sample because of the additional analysis in progress. Nevertheless, inspection of the means and deviations makes it clear that the extreme categories are significantly different.

6. The biological basis for the variation in time constant was investigated
on the basis of relations suggested in the last report. It had been hypothesized that
the fast component cf the recovery limb might represent an epidermal membrané
process, associated with the reabsorption phenomenon and with the positive skin (SPE)
potential response, Records from 11 subjects were examined, and two "pure"
negative SPRs and two with significant positive components were chosen from each.
The time constants of the associated conductance responses were measured and for

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all 11 subjeets, were shorter when asscciated with positivc SPRs (8.7 vs 14.9 seconds, $ { \mathbf { P } } { } < . 0 0 1 )$ . An example of a recording is scen in figure 10.

Since the reabsorption reflex had previously been shown to be assoclated with the positive wave, the association of short recovery times with reabsorption was to. be expected. Figure 1l shows an example (panel B) of the faster recoveries associated with the activation of reabsorption (Hydration increases upward). Note the concomitant change in skin potential activity from negative to biphasic with a positive (downward) component appearing. The average time constant for the left hand panel was 7.4 seconds, for the righit, 4.8. A comparison on 12 subjects showed that reabsorption waves were associated with steeper recovery limbs at the .01 evel of significance.

B. Peripheral Mechanism

Because of the implicit involvement of the reabsorption reflex as a possible cause of the variation in recovery limb slope, efforts were made to clarify its mechanism. It had been previously postulated that this phenonenon represented a reflex increase in epidermal permeability. When this permeability increase occurred, the passlve moveirent of water down its concentration gradient would appear as an inward movement if surface vapor tension were high enough. However, data on the low permeability of the corneum cast doubt that the route was through this layer (and then across the epidermis). It was considered more likely that the moisture was returning via the sweat duct. This possibility was investigated by a modification of the Netsky prism method described by Thomas and Korr (1957) which is sensitive to frank sweat (droplets). In this modificacion, a photocell was substituted for the

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HYD

SPR

SRR

A

Figure 11. Relation of recovery limb time constant to presence or absence of absorption reflex (upper trace, absorpcion is downward). Note acceleration of recovery limb with appearance of reabsorption responses.

[PAGE 28]
photographic cquipment so thiat continuous recordings of sweat droplet concentration could be made. Unlike the photographic metliod it is very important in this method that the light be we'l collimated to prevent contamination of the records with vascular changes (figure 12). It is also necessary that there be no possibility of variation in skin contact at the edge of the masked area. Test of contamination by vasomotor activity were accomplished by inflation of venous and arterial cuffs on the arm to produce artificial vascular changes in the fingers. The system finally adopted was demonstrated to be free of such contamination. The recordings (figure 13) showed increases in sweat and also reabsorption. Although the device has been used thus far on only 5 subjects, all have manifested the phenomenon. It is now being used in conjunction with recordings of SPR, SCR, and hydration (electrical method). The implications of the findings with this device Is that the droplets of sweat formed at the sweat pore rather suddenly disappear. This has been confirmed by microscopic observation of the finger tip. This would indicate that te cause of the reflex reduction of hydratlon previouslv observed is not due to drving of a uniformnly moist,ed corneum but rather to draining of the sweat droplets back into the sweat duct. This may perhaps represent activity of the sweat duct wall at a relatively superficial level, e.g., at the germinating layer.

Local Potential Responses

The collection of data on the effects of variation in surface conditions upon LPR amplitude has been completed.· As discussed in the summary, a relative range measure is a better indicant of effects than is an absolute comparison because of variation in direction of these effects. The data may be summarized as folows:

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(The control sites were subjected to a blank proccdure.)

In addition, of 7 sukjects examined for effect of background negative activity upon LPR amplitude, all showed a substantial increase for both fast and slow components (average 430%, P<.001).

C. Bio-Psychological Adaptability

In the initiaì examination of adaptability or "gear-shifting" capacity, a population of 60 subjects was run through a battery consisting of the following:

a) Several paper and pencil psychological evaluations including personality trait inventories, and manifest anxiety ratings.

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b) Performaace tests: designed to examine rigidity - flexilility characteristics.

c) A knob-turning test desigued to examine maintainance of appropriate motor inhibition over an extended period, The subject was instructed to turn a large knob as slowly as possible througlı 180 degrees. The time course of this effort was recorded and a comparison made of the angula= velocity in the first third with that in the last third to detect breakdown of inhibition. This was expressed as a ratio K; a large ratio signifies a speeding up in the last third (i.e., loss of inhibition). Following these tests the subject was fitted with electrodermal electrodes and ectaace plethysmograph. He was exposed in sequence to:

a) 3 minutes of rest

b) a series of 5 tones, ca s0 db, 1000 cps

c) a seríes of 5 similar tones for reaction time test effort

d) 3 minutes of rest

e) a difficult discrimination task

f) 5 mintes of rest

Although analysis is not yet completed, it appears that the psychological and performance tests, except for the knob-turning task showed low correlation with the physiological data. The relation of SCR recovery Iimb time constant to habituation rate in these runs has already been described. A relation between performance and physiological behavicr was also found, In these runs, as a measure of the "gearshifting" ability of the subject, his time for 50% recovery from the difficuit

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discrinination tusk to basc level during the final rest period was determined for skin conductance, skin potential and finger pulse volume, The recovery balftine for the electrodermal lcvel measures (not responses) was significantly related to K, the inhibitory index in the knob-turning task $( \overrightarrow { r } < 0 . 5 )$ . Longer recovery times were associated with a tendeney to speed up toward the end of the task. Put another way, the capacity to maintain inhibitory motor control over an extended period was associated with an ability to shift autonomic gears rapidly.

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