A convenient portable recording device, HGMl, which allows digital field recording of skin conductance and heart rate data with laboratory levels of precision, ...
In@rnational Journal of Psychophysiology, 11 (1991) 161-165 0 1991 Elsevier Science Publishers B.V. 0167-8760/91/$03.50
PSYCHO
161
00346
HGMl:
A research-oriented portable heart rate and galvanic skin response monitor
Robert J. Barry ‘, Robyn Moroney
‘- *, J.F. Orlebeke
* and Johan de Vries *
’ School of Education Studies, University of New South Wales, Kensington (Australia) and 2 Deparlment of Psychology, Free University, Amsterdam (Accepted
Key words: Portable
recording
(The Netherlands) 6 November
device; Skin conductance;
1990)
Heart rate monitor;
GSR monitor
A convenient portable recording device, HGMl, which allows digital field recording of skin conductance and heart rate data with laboratory levels of precision, is described. Examples of individual data are provided from a study of orienting response habituation, and from students participating in a study of examination anxiety, recorded while they sat scheduled class examinations. These illustrate the potential value of the device in field studies
INTRODUCTION The two autonomic measures most commonly used in studies of attentional processing in humans, particularly in those studies examining elicitation and habituation of the orienting response (OR), are heart rate (HR) and the galvanic skin response (GSR). Traditionally, such studies have been confined to the psychophysiological laboratory, because of the constraints imposed by the equipment needed to transduce and record the physiological data. Although there are a number of portable devices which allow the recording of cardiac information, usually in analog form, these
* Present address: Faculty of Nursing and Community Studies. University of Western Sydney, Hawkesbury, Richmond 2753, Australia. Correspondence: R.J. Barry, School of Education, University of New South Wales, Kensington 2033, Australia.
have emerged to meet a medical monitoring demand, and the temporal resolution involved may not be at the level required for psychophysiological research. In addition, there is an absence of portable equipment which can monitor electrodermal activity at resolutions comparable with standard research laboratory requirements. This technical note describes a portable Heartrate GSR Monitor, HGMl, developed z the Central Laboratory of the Department of Psychology at the Free University in Amsterdam, The Netherlands. This device, a combination of existing hardware elements, was developed to provide a portable research-quality digital instrument suitable for field study of these two important autonomic measures. The device, together with a microcomputer interface and appropriate software, forms a convenient package which should facilitate applied psychophysiological research. Following a description of the system elements, brief examples from work in progress are provided to illustrate the data format and use of the device.
162
DESCRIPTION
OF HGMl
Portuble monitor Dimensions: Weight: Power supply: Accuracy of built-in Microprocessor:
clock:
Free memory: Measuring time at 80 BPM * GSR sampling rate of * GSR sampling rate of Lifetime of stored data: Specifications, EKG part input impedance: common mode rejection: R-wave trigger:
timing basis: resolution R-R interval: refractory period after R-detection: resulting upper HR limit: Specifications, conductance resolution:
GSR part range:
sampling rate range: voltage at subject:
12.4 x 7.3 x 2.3 cm 215 g (without cells) 4 mercury cells (SP 675) 0.05% Hitachi HD63701 48 Kbyte HR with >lh 5 Hz: 0.1 Hz: > 4.5 h 2 days
> 100 MOhm > 80 dB auto-adjusting level detector interrupt 1 ms 200 ms 300 BPM
l-100 /.ls 0.025 PS (12 bit) 0.1-10 Hz 0.5 v
Microcomputer interface Available in Apple II or IBM versions. The Apple version employs an RS232 serial interface card which requires one slot in the microcomputer. The interface for the IBM version connects to the standard RS232 input. All required cabling is included. Software The proprietary data-acquisition software is ROM-based, and complemented by uncompiled
BASIC programs available in Apple II or IBM versions. These interactive programs control set-up of the device, recording of subject name and other details, times of starting and stopping of data collection, and data transfer for storage (in binary files on floppy disk) and/or hard copy print out. The software does not modify the data in any way, so that the integrity of raw data is ensured. Audible heart beats are available, with beat-bybeat HR and skin conductance displayed in real time, in a special monitor mode to assist initial setting-up with a subject. Cost and availubility The cost per package (portable monitor, interface, software disk, and manual with circuit diagram) is approx. US$ 3000, depending on fluctuations in exchange rates. For complete price lists and current information on availability/ ordering, contact J.F. Orlebeke, Department of Psychology, Free University, 1081 HV Amsterdam, The Netherlands (Phone: Amsterdam 5483870; Fax: Amsterdam 548-4443).
EXAMPLES
ILLUSTRATING
USE
The first example has been chosen to demonstrate the high resolution of the system, and its comparability with laboratory instruments, while the second demonstrates potential field applications. It should be emphasized that the information provided by the system is always raw GSR at nominated intervals, and raw beat-by-beat HR. Any desired data reduction is done outside the system. Example 1 A 14 year-old male participated in a study of OR habituation to 50 dB 1000 Hz tones of 2 s duration (rise time 20 ms) with a fixed interstimulus interval of 8 s. He was asked to count the tones to himself while sitting with eyes closed in a quiet room. Table I shows a hard copy of the formatted data obtained for a 10 s period starting at 15 : 18 : 23 (format of time is h: min: s). The onset of the first stimulus occurred at 15 : 18 : 25. GSR was sampled at 10 Hz, so that each line represents
163
TABLE
I
An example of the hard copy data format Identification: Michael Date: 15-12-.89 GSR rate: 10 HZ Starttime (storing data): Stoptime (storing data):
15:12:37 15:20:42
Time: 15:18:23 GSR:
3.600
3.600
3.600
3.600
3.600
3.625
3.625
3.600
HR: GSR: HR: GSR: HR: GSR: HR: GSR: HR: GSR: HR: GSR: HR: GSR: HR: GSR: HR: GSR: HR:
75.0 3.625
3.625
3.600
3.625
3.625
3.625
3.650
3.650
3.625
3.625
3.675 76.4 3.725
3.675
3.625 80.5 3.650
3.625 86.2 3.650
3.700
3.675
3.125
3.750
3.775
4.000
4.000
4.025
4.075
4.325
4.350
4.375
4.575
4.575
4.675 71.5 4.600
4.600
4.625 65.7 4.625
4.400 70.4 4.625
4.600
4.600
3.625
3.625 82.4 3.650
3.625
3.650
3.650
3.675
3.650
3.700
3.700
3.700
3.675
3.800
3.850
3.850
4.100 74.3 4.400
4.125
3.850 76.5 4.150
3.725 72.4 3.900
4.225
4.275
4.275
4.450
4.475
4.500
4.525
4.500
4.625
4.625
4.625
4.625
4.650
4.625
4.675
4.650
4.650
4.625
4.650
4.600
4.575
4.550
4.575
4.550 79.3
4.500
4.625 72.1 4.550
1 s of data. HR is shown at the 0.1 s interval following each R-wave. These HRs were used to obtain mean HR in real time intervals of 1 s
9. Heart
Rate (BPM)
T
66
I -2
I -1
Fig. 1. Individual
0
Tit& trot
stirktlus
kaet’(sI
6
7
8
heart rate data from the first four trials in an habituation study.
3.575
3.950
4.525
(Velden & Walk, 1987) which are shown in Fig. 1 as trial 1 data. Responses for trials 2 to 4 were obtained similarly, and are also displayed in Fig. 1. Fig. 2 shows the corresponding electrodermal responses. Raw data points are shown as small squares, and average data in 1 s intervals are included for comparison with the cardiac data of Fig. 1. The electrodermal data show the normal GSR waveform, particularly marked on the initial trial. There is clear evidence of sensitization of the prestimulus levels following trial 1, and marked phasic response habituation. Both these effects are compatible with previous reports (e.g., Barry, 1989). The cardiac responses shown in Fig. 1 are simple deceleratory responses, which fail to show either of the sensitization or habituation effects noted in the electrodermal data. Such findings of response fractionation are commonly reported (e.g., Barry & Tremayne, 1987).
164
5.5 Skin Conductance
I 5.0 -1_
-1
-2
0
TirnL fro:
stirhs
40n.set5
6
7
8
(s) Fig, 2. The corresponding
individual
electrodermal
data from the trials shown in Fig. 1
Skin Conductance (uSI
0
Heart Rate (BPM)
10
6
16
20
0
6
10
15
20
Measures Measures Fig. 3. Skin conductance and heart rate during examination periods for an anxious subject without relaxation training. The POST data were from an examination held approx. 4 weeks after that in which the PRE data were recorded. Each value is a mean over a 20 s period. The measures are evenly spaced over the examination time, which varied between subjects and examinations.
Skin Conductance (US)
8.0 T
Heart Rate (BPM)
loo-
8.0
-
a 0.0
1 0
5
Fig. 4. Skin conductance
PRE
+
POW
MeaZures and
heart
i 20
16
rate
~ -PM
1 b
data
from
-POST
1 I
0 0
an anxious subject examinations.
6
with
relaxation
IO
Measures training between
16
the PRE
20
and
POST
165
Example
2
Individual data are presented from two university students in a pilot study of the effects of relaxation training upon examination anxiety. A compulsory one-semester subject which employed monthly examinations in a continuous assessment program was utilised for the monitoring of physiological correlates of anxiety. Volunteers who reported marked examination anxiety were randomly allocated to either a control or experimental group. Following the first examination, the experimental group received relaxation training for a 4-week period, using commercially-available relaxation tapes. Subjects wore the portable monitoring devices to the preceding and following scheduled examinations. HR and GSR (at 10 s intervals) were recorded throughout the examination. Since subjects were free to leave the examinations whenever they finished, mean HR and GSR values were calculated for 20 s periods at the beginning and end of the examinations, and at eighteen equally-spaced intervening intervals. Fig. 3 shows these data for a typical control subject. The most obvious effect is the increase in skin conductance level from the first to the last examination, presumably reflecting an increase in stress/anxiety level during the semester. Every control subject showed such an increase. Fig. 4 shows the corresponding data for a typical experimental subject. There is no apparent increase in skin conductance level during the semester, suggesting that relaxation training was efficaceous in preventing the increase in electrodermal arousal, and presumably examination anxiety, noted in the control group. Each experimental subject similarly failed to exhibit an increase in skin conductance level over the semester.
DISCUSSION
AND
CONCLUSION
The first example presented above demonstrates the laboratory-quality data which can be obtained with the HGMl device due to its high sampling rate (up to 10 Hz) and precision (HR derived from interbeat intervals measured with 1 ms resolution, and skin conductance measured with 0.025 PS resolution). The second example illustrates its potential usage in field situations. In this case, physiological data were obtained from subjects sitting scheduled written class examinations with other students. In the context of a study of the effects of relaxation training on examination anxiety, the ability to record such data in situ must contribute to the validity of any conclusions reached. Tremayne and Barry (1990) have recently argued that the application of the OR concept to a wider range of real-world problems is necessary for it to retain its theoretical vitality and central position in modern psychophysiology. The HGMl system provides a convenient portable device which should facilitate high-quality scientific study of a range of such real-world problems in field situations.
REFERENCES Barry, R.J. (1989) Electrodermal indices of the phasic and tonic OR. Psychophysiology, 26, S13. Barry, R.J. & Tremayne, P. (1987) Separation of components in the evoked cardiac response under processing load. J. Psychophysiol., 1, 259-264. Tremayne, P. & Barry, R.J. (1990) Applied orienting response research: Some examples (with a comment by E.N. Sokolov). Pavlovian J. Biol. Ser. 25, 132-141. Velden, M. & Walk, C. (1987) Depicting cardiac activity over real time: A proposal for standardization. J. Psychophysiol., 1, 173-175.
