Phystology and Behavior, Vol. 14, pp. 575-578. Brain Research Publications Inc., 1975. Printed in the U.S.A.

Skin Color and Autonomic Nervous System Measures B E R N A R D K O R O L t ,2, G A R Y R. B E R G F E L D AND LYNN J. MCLAUGHLIN

St. Louis Veterans Administration Hospital and Department o f Psychiatry, St. Louis University School o f Medicine, St. Louis, MO 63125

(Received 8 March 1974) KOROL, B., G. R. BERGFELD AND L. J. MCLAUGHLIN. Skin color and autonomic nervous system measures. PHYSIOL. BEHAV. 14(5) 575-578, 1975. - A study has been performed in 50 subjects, 25 white and 25 black, measuring skin color (PI), basal skin resistance (SR) and amplitude of the galvanic skin response (GSR), and resting heart rate (HR) and the heart rate response (HRR) induced by a startle tone. A multiple correlation matrix revealed a statistically significant relationship between PI and SR and also GSR; between HR and HRR, and between SR and GSR. Analysis of the group differences revealed that blacks had significantly lower (darker) PI values, higher SR, greater GSR, and a higher HR and HRR. It is unclear from this study whether race or the intensity of skin color Influenced "the measured physiological responses. Skin color

Skin resistance

Galvanic skin response

Heart rate

NUMEROUS reports in the literature substantiate the earlier findings of Johnson and Corah [4] that negro subjects exhibited a significantly higher skin resistance (SR) than that shown by a comparable population of caucasians. Further study [5] revealed that the SR of oriental subjects was somewhat intermediate between that of the negro and caucasian groups. They also demonstrated that this difference in basal skin resistance between racial groups was not likely a consequence o f sweat gland activity, since there were not significant differences in the number of active sweat glands between the two groups. This latter finding is discordant with the results of Clark and Lhamon [ 1], which showed that the finger skin area of dark skinned subjects had a higher average number of seat glands per square centimeter o f skin than that of light skinned subjects. Studies by Malmo [9] suggested a positive correlation between skin resistance and pigment concentration. This conclusion is not in accordance with the findings of Kugelmass and Lieblich [7], who reported that Near Eastern Jewish and Bedouin subjects are darker on the average than Western Jews and also exhibit lower Sr. However, Lieblich, Kuglemass and Ben Shakhar [8], also reported that Israeli Bedouin negroes and Ghanese negroes exhibit higher Sr (lower conductance) than caucasian Bedouin and caucasian

Israelis. Most recently, Fisher and Kotses [2] found that negroes had a higher basal skin resistance; while the caucasian subjects demonstrated a significantly slower rate of habituation of the GSR when paired with black experimenters. The general consensus from these studies would appear to support the premise that darker skin color is associated with higher skin resistance. In a related study, Harburg and associates [3] reported that in black subjects, skin color was positively correlated with blood pressure. Black high stress males, coming from areas of low socio-economic status, high crime, high density, high residential mobility and high rates of marital break-up, had darker skin color than black middle class males, and also had the highest average blood pressure o f all groups examined. In the case o f the previously described studies, measurement of skin color was subjective and based upon a general visual assessment or at best a four-point scale by the nurseinterviewer taken from the area on the forehead between the eyes as the target skin area. Since we had recently developed an apparatus exhibiting high sensitivity and accuracy for the measurement of skin color over a continuous range [6], it was possible for us to perform a more definitive examination of the relationship between skin color and bas-

1Medical Research Information System No. 4675-01. 2Address reprint requests to: Bernard Korol, John Cochran VA Hospital, St. Louis, Missouri 63125. 575

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KOROL, BERGFELD AND MCLAUGHLIN

al skin resistance, basal heart rate and their responses to a non-stressful tone in a population of male and female caucasian and negro volunteers.

METHOD Sublects

The 50 subjects used m this study were recruited from the staff at the St. Louis VA Hospital and were divided into two groups of 25 black and 25 white subjects each. There were 9 white males, 16 white females, 5 black males and 20 black females.

A ppara tu s

The apparatus included a device developed for the measurement of skin color termed the pigmentometer [6]. This device was composed of a light source (12 V, DC) and a photocell pickup (minolta, Stock No. 9 0 2 1 - 6 3 1 1 ) housed m a V-shaped wooden box. There was a small hole (4.2 cm dla.) in the narrow end of the box over which reflectance cards or skin surface could be positioned. The device operated on the principle of the reflection of white light by different degrees of skin darkness or pigmentation. An Electro, Model NFB Filler DC power supply was used to energize the hght output. The photocell was connected to a Type 9853 voltage, pulse, pressure input coupler of a Beckman Type R Dynagraph recorder and a gain of the signal was accomplished through the preamplifier and driver amphfier units. The pigmentometer was calibrated using Kodak neutral test cards with gray calibrated for 18 percent reflectance and white calibrated for 90 percent reflectance when used with an exposure meter in artificial light. Thus, the intensity of skin color was expressed in absolute reflectance units. Skin color was taken from the skin on the ventral surface of the left forearm immediately distal to the elbow joint. Beckman silver-silver chloride electrodes, filled with Beckman electrode paste and held in position on the palmar surface of the right hand by Beckman adhesive collars, served as the sensor pickups for the measurement of basal skin resistance and the magnitude of the GSR. The Beckman GSR Couplera Type 9842, supplied a fixed direct current of 10 ~A]cm" of skin surface, and also allowed for the s:multaneous recording of the basal skin resistance and the magnitude of the GSR, both on the same channel of the Beckman Dynagraph. Heart rate, expressed as a function of the R wave interval of the electrocardiogram (ECG) between two successive cardiac ventricular beats was similarly obtained through Beckman silver-sliver chloride electrodes positioned and affixed to the ventral surface of the wrists and a ground electrode placed on the forehead. The inverted Lead I ECG pattern R-wave triggered the Beckman cardiotachometer coupler, Type 9857B, which monitored continuous beatto-beat rate of ventricular contraction. A 10 sec tone with the characteristics of 1000 Hz and 70 decibels intensity was delivered through earphones. The tone was generated by a Hewlett-Packard Model 200 AB audio oscillator and a Hunter timer was used to time-out the tone presentation. All recording was made by a Beckman Dynagraph recorder at a paper speed of 5.0 mm/sec.

Procedure

Upon entering the laboratory, each subject was informed of the nature of the experiment, the procedure to be followed, and shown the recorder, sensors, and other equipment. A sample polygraph record was also shown, and served as a descriptive explanation of the purpose of the study and procedure used as well as to demonstrate the physiological variables measured. The subject was then seated in an upright position in a conference table-type-chair and the recording electrodes positioned and affixed. The earphones were also placed in position. The subject's left forearm was placed over the light source-reflectance orifice of the plgmentometer. The 10min equilibration period then ensued. At the end of this equilibration period a 10-second tone, 1000 Hz of 70 db intensity, was delivered through the earphones. A subsequent 5-mm interval served as the poststimulus recovery period. RESULTS Measurements of basal levels and responses to the tone were taken as follows: S k m resistance. (1) Basal level - average resistance recorded m the five seconds preceding tone onset. (2) Responsivity - any deviation from baseline exceeding I00 ohms which occurred 1 - 4 secs following tone onset. Heart rate. (1) Basal level - average of the high and low heart rates recorded in the five seconds preceding tone onset. (2) Responsivxty - average of the high and low heart rates recorded in five second period following tone onset. Table 1 shows the mean values and standard errors for black and white subjects on pigmentation index (PI), basal skin resistance (SR), amplitude of the galvanic skin response (GSR), heart rate (HR) and heart rate response (HRR). Student's t-tests revealed significant population differences in PI (t = 12.43, d f = 48, p

Skin color and autonomic nervous system measures.

Phystology and Behavior, Vol. 14, pp. 575-578. Brain Research Publications Inc., 1975. Printed in the U.S.A. Skin Color and Autonomic Nervous System...
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