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Cardiac-somatic changes during a simple reaction time task: A developmental study
.TOl;RSAL
OF EXPERIMENTAL
CHILD
PSYCHOLOGY
Cardiac-Somatic
Changes Reaction
A PAUL School
A. R.
OBRIST,’ STZRLINO
16, 34&362
during
Time
HENAX,
L.
Study1
HOWARD, AND
a Simple
Task:
Developmental .JAMES
(1973)
DORIS
*JAMES
J.
R.
SUTTERER,
MURRELL
of Merlicine, School oj Bducrrtzon. nnrl Biologicd Sciences, Resenrch CetlteT of the Child Dce~elopment Institzcte, Uniuersit?/ of Norih C’awliua, Chapel Hill
The relationship during a simple reaction time task between heart, rate and four measures of task irrelevant somatic activity was evaluated in four age groups of children, i.e., 4-, 5, 8-, and lo-year-olds and young adults, in order to evaluate further a hypothesized coupling of cardiac and somatic activity. At, all age levels. phasic decreases in both heart rate and somatic activity coincident with performance were found with the magnitude of the effect increasing with age only on three somatic measures. However, tonic levels of both heart rate and somatic activity dccreasrd with age. Performance on the reaction task was found to be inversely related to the age-related phnsic somatic effects as well as age-related tonic heart rate and somatic activity.
The purpose of this research was to utilize a developmental strategy to evaluate within the confines of the simple reaction time (RT) paradigm the relationship between cardiac and somatic events and to evaluate a hypothesis concerning the behavioral relevance of these effects. The observation that the direction and magnitude of heart rate changes, in both the classical conditioning and a simple RT situation, are concomitant with the direction and magnitude of change in ongoing somatic activities has been viewed as representing a biological linkage or coupling, achieved primarily by common CNS mechanisms, between cardiac and somatic events necessitated by the metabolic function of the heart (Obrist, 1968; ’ This research was supported by Research Grant MH-07995, National Institute of Mental Health, United States Public Health Service to P. A. Obrist and Institutional Grant HD-03110. National Institute of Child Health and Development, United States Pub’ic Health Service, with the Biological Sciences Resrarch Center of the Child Cevelopmental Institute, University of North Carolina, Chap?1 Hill. ‘Requests for reprints should bc sent to: Paul A. Obrist, Ph.D., Department of Psychiatry, University of North Carolina School of Medicine, Chapel Hill, North Carolina. 346 Copyright @ 1973 by Academic Prrss. Inc. All rights of reproduction in any form reserved.
HEART
RATE
AND
SOMANTIC
ACTIVITT
347
Obrist & Webb, 1967; Obrist, Webb, & Sutterer, 1969; Webb & Obrist, 1970; Obrist, Webb, Sutterer, 8: Howard, 1970a, 1970b; Sutterer & Obrist, 1972). In the simple RT situation with a fixed foreperiod, heart rate deceleration, and a cessation of task irrelevant, ongoing somatic events have been found in adult man to be coincident with responding. Furthermore, performance speed has been found to be directly related t’o the magnitude of these effects (e.g., see Obrist et al., 197Oa). The decrease in somatic activity has been viemcd as representing the inhibition of task-irrelevant activities necessitated for efficient execution of the behavioral response with the cardiac deceleration being a visceral counterpart of this somatic change. In this context, these cardiac and somatic changes can be viewed as peripheral manifestations of CM proccsscs associated with attention, in which the cessation of somatic events and its concomitant visceral counterpart reflect a facilitation of attention by an inhibition of irrelevant activity. In the previous RT studies cited using adult Ss, the relationship between heart rate and somatic activity as well as the behavioral significance of these effects has been evaluated in several ways. For example, the experimental manipulation of forcpcriod duration and certainty influenced cardiac, somatic, and performance effects in a similar manner (Webb & Obrist, 1970). Within S analyses of the data revealed that on trials in which heart rate was slowest there occurred the largest decrease in somatic act,ivity and fastest reaction times (Obrist et cd., 1970b). Also, an alternative position which views the cartliac deceleration and its relationship to performance as due to the involvement, of heart rate in the afferent control of CNS processes (Lacey, 19671, rather than due to its cfferent association with somatir processes,was not supported when directly evaluated by the pharmacological manipulation of the cardiac response (Obrist et al., 1970b). In the present study, a devclopmentnl strategy was chosen to evaluate further the relationship between cardiac and somatic activity, because it appeared to be another yet unexplored way to manipulat,e the relationship. That is, the developing organism would provide a naturalistic way to manipulate somatic activity and hence attentional processesin that, younger Ss were expcctctl to show more background somatic activity, i.e., be more restless and have less facility to inhibit such activity (Elliott, 1964, 1966; Shapiro, 1973), effects which should covary with age, In turn, any age-related cliffercnccs in background somatic activity, i.e., tonic levels and the facility to inhibit such activity, i.e., phasic changes, should be reflect,ed in similar age-related differences in heart rate and performance, if the cardiac, somatic, and performance effects are interrelated as hypothesized.
348
OBRIST
ET
AL.
Specifically, it was expected in the light of these considerations that: (1) In any age group in which there was found a reliable decrease in phasic somatic activities, there would be a reliable phasic deceleration of heart rate. Conversely, if any age group showed no change or an increase in phasic somatic activity, such as was anticipated might be the case in the youngest age groups, there would be no phasic deceleration of heart rate. (2) Any effect of age on either tonic levels of somatic activity or the magnitude of the phasic decrease in somatic act,ivities associated with responding would be directly related to tonic levels of heart rate or the phasic deceleration of heart, rate associated with responding, respectively. (3) Performance on the RT task should parallel the somatic and cardiac changes with a decrease in RT being associated with a greater inhibition of, or lower level of, somatic activity and heart rate. We also evaluated one other issue with regard to cardiac and somatic effects. This concerned whether one parameter of somatic activity, eye movements and blinks, would dcmonstratc a greater sensitivity with age to the manipulation of attention than would heart rate. In two previous studies (Webb Q Obrist, 1970; Obrist et al., 1970b) occular activity was found to decrease more consistently than heart rate at shorter PIs, whereas at longer PIs, both effects decreased in an equally consistent manner. Because attentional requirements would be expected to be at least as great at short PIs, these effects would suggest t’hat occular activity can have a greater sensitivity to attentional processes than heart rate. It was anticipated that if a sufficiently broad age range of children were used it could be determined whether there is a transition in cardiac, somatic, and performance effects between the youngest group and an adult reference group. Initially, 5- and g-year-old groups were used. However, when a reliable cardiac deceleration and a decrease in somatic activities were still found in the 5-year-old group, a sample of 4-year-olds was then used in the expectation that the decreases in heart rate and somatic activity would be attenuated. Younger samples were not used since it appeared they would be unable to perform the task. Finally, a lo-year-old group was evaluated so as to provide a further transitional group between the younger groups and adults. METHOD
Subjects The 4- and &year-old samples were drawn from privately run nursery schools and kindergartens in the city of Chapel Hill, North Carolina. The 8- and lo-year-old samples were drawn from the 3rd and 5th grades of
HEART
RATE
Ah-D
SOMANTIC
ACTIVITY
349
one public elementary school. Parents of all children in each private school or grade in the public school selected were sent a letter requesting their permission for the children to participate in the experiment. Approximately 5070 of the parents agreed. In order to abtain 40 Ss in each age group, two to three school classes at any one age level were selected. The adult sample was volunteers from b0t.h an introductory psychology course and an intermediate level undergraduate education course at the University of North Carolina, Chapel Hill. bpproximately equal numbers of males and females were used in each age group. The mean age in years and months and standard deviation in months of each group at the time the S participated in the experiment were: 4 year olds, j: = 4-6, (T = 3.2; 5 years olds, C = 5-8, (T = 4.4; 8 years olds, Z = 8-9, (T = 6,.7; 10 years olds, f = 10-7, (T = 6.2; adult, z = 19-11, (T = 14.2. Owing to either equipment, failure or the failure of Ss to show up for the experiment, the final iV in each age group was: 4 year old* , S = 38 ; 5 year olds, IV = 34 ; 8 year olds, N = 38; IO year olds, ,I: = 39 ; adults, :V = 33. No S was used who at the time of testing was on any medication which might influence either performance or t’lie biological measures. Apparatus All physiological measures were recorded on a Beckman Type R Dynograph using Beckman biopotcntial electrodes to measure EKG, chin EMG, and eye movements. Two high-sensitivity (O-5 cm Hg) Statham strain gauges were used to transduce the pneumatic signals necessary to measure general activity and respiration. The RT stimuli, foreperiod duration, and intertrial intervals were all automatically programmed, and performance time measured to the nearest millisec with a combination of specially built solid state circuitry, plynch paper tape, and commercial Digi-bit circuitry. A standard telegraph key was used as the RT manipulandum. In order to minimize the medical atmosphere of the laboratory, the S room was decorated with posters and drawings and the Es wore pastel smocks. Physiological
Measures
Five measures of somatic activity were employed to insure that somatic activity was reliably evaluated. Two measures, vertical eye movements and blinks, have been found in previous studies with adults (Obrist et al., 1969) to show fairly high levels of background activity as compared to EMG measures and thus a more obvious decrease concomitant with responding. Chin EMG was used as it has been found (Obrist et al., 1969) to be associated with postural movements as well as discrete movements of the muscles in and around the mouth-a kind of somatic activity corn-
350
OBRIST
ET
AL.
monly seen. General activity, i.e., movements of the limbs and torso, was also assessed as it was expected to be elevated in younger children. Finally, respiration was measured as has been routinely done in all previous studies. The methods for measuring heart rate, respiration, and chin EMG activity were similar to those previously described (Obrist et al., 1969; Webb & Obrist, 1970). Vertical eye movements and blinks were recorded from electrodes placed just above the eye brow and just below the lower eye lid and centered over the middle of the right eye. General activity was recorded from pneumatic sensors located in the back and seat of the S chair. Procedure Instructions. All age groups received identical instructions, except that with the youngest age groups the instructions were commonly repeated, and the X shown by manipulating his arm and hand what was to be done when the respond stimulus came on. The instructions stressed that the S was to release the key as rapidly as possible. No incentives or feedback of results were provided with the exception that the youngest two age groups were told that if they stayed with the experiment until the end they would be given a bonus toy. The youngest three age groups were given an age and sex appropriate $2.00 toy for participation. The 10 year olds were given $2.00 and adults either $2.00 or experimental credit for participation. Reaction time task. A visual preparatory stimulus or ready signal was used which had a duration of 1 sec. It consisted of a 6-V jewel light placed at eye level and approximately 3-ft directly in front of the S. The respond signal was a clearly audible 100%Hz tone presented through a speaker over a low level of white noise. The respond signal terminated when the S responded. The foreperiod or preparatory interval (PI), i.e., the time between the onset of the ready and respond stimuli, was 4 set and the intertrial interval, i.e., the t’ime between ready stimuli, was 20 sec. Subjects were instructed to keep the reaction time key depressed at all times except when they were signaled to release it.. Throughout the experiment, a young adult female research assistant stayed with the S, except for adult Ss, to provide reassurance and any necessary assistance. Sixty reaction time trials were used with a short rest period after 30 trials. The first five trials were practice, which was found to be a sufficient number of trials for all Ss to learn the task requirements. The only time the Ss were further instructed after five trials was if they failed to depress the key immediately after release or if they released the key prematurely on two
HEART
RATE
AND
SOMANTIC
ACTIVITY
consecutive trials. After five trials, Ss were never told to prepare respond signal or to release the key. Data
Analysis
351 for the
and Quantification
A second-by-second analysis of the physiological data was performed on alternate trials beginning with trial 6, providing a total of 28 trials (see Wood $ Obrist, 1964; Obrist et al., 1969). The only exception to this was when a premature release or artifact occurred at which time the next trial was selected. On each trial, the second-by-second analysis was carried out in (1) the last 5 set before the ready signal, a base !>eriod, (2) the 4 set of the PI, and (3) the first 2 set following the onset of the respond signal, except for heart rate where the analysis was extended to 3 see following the respond stimulus. This analysis involved determining the value of each biological parameter coincident with each second of the measurement period. For heart rate, the time in millisec of a given R-R interval was assigned to the second in which the R wave integrator discharged. Where two R-R intervals were integrated in a given second, the average of the two values was used. Because of t.he time lag between where the R-R interval actually occurs and where it is integrated can be between 0.5 and 1.0 set, the second-by-second changes in heart rate depicted in the figures were corrected by 1 sec. This involved omit’ting the data from the first second of the PI and moving all following second values up 1 see toward the ready signal. In order to bc consistent with current convcntion, R-R, interval is depicted in the tables and figures as beats per minute. The EMG and general activity were quantified only with respect to presence or absenceof somatic activity in any 1 WCrather than responseamplitude, because the latter is more difficult to quantify and tends to increase with age. EMG activity was considered present in any 1 set if a distinguishable spindle-shaped burst of activit,y occurred which had a duration of at least l/z SW and a peak a,mplitude of at least 60 ~LV.The latter value was chosen because the EMG baseline was usually in the range of 2030 pY. Where the baseline exceeded 30 p,V, the criterion for peak amplitude was increased accordingly. Whcrc an EMG burst extended into 2 set, it was scored as present in both secondsonly if the duration in each was clearly 1/z set or more. General activity was scored as present in any second if the amplitude of the pen displacement associated with a movemcnt was at least 3 mm greater than the base level. A constant amplifier gain was used for all Ss and the sensitivity of the pneumatic chair checked on cacb S prior to the beginning of the RT trials. Occular activity WRS quantified in two ways: (1) As an amplitude
352
OBRIST
ET
AL.
score which combines vertical movements and blinks such that in any 1 see the difference in millimeters between the highest and lowest level of pen displacement is obtained and (2) as a frequency score where the presence or absence of eye blinks was determined within each second. For occular activity, a constant amplifier gain was used with the sensitivity of the recording checked on each S prior to the beginning of the R.T trials. The respiration data were not quantified. The data were summarized on each S over the 28 trials as follows. A base period value was obtained which indicated the average amount of activity per second. Similarly, a mean value for each second of the forcperiod and each second of the respond period was determined. Thus, the second-by-second changes depicted in the figures indicate the average values for each second of the PI and respond period as well as t,he average amount of act,ivity in any 1 see of the base period. RESULTS
The data will be presented first in regard to phasic changes associated with responding and then in regard to tonic effects. Because of large differences between age groups in base level (tonic activity) on all but one measure, which could act to obscure any influence of age on phasic effects, the data will then be presented with base level differences controlled by covariance techniques. 1. Phasic Effects At all age levels, reliable decreases in somatic activity and heart rate were observed either just to anticipate or to be coincident with the execution of the RT task. The mean second-by-second values for each experimental group are depicted for heart rate in Fig. 1, EMG in Fig. 2, and the amplitude of eye movements and blinks in Fig. 3. The second-bysecond changes for general activity and the frequency of eye blinks are not depicted, since the former tends to parallel EMG activity and the latter parallel eye movement amplitude. On each of the somatic measures, the decrease in activity was generally largest during the fourth or last second of the foreperiod, with the exception of EMG activity where the decrease also extended into the first second of the respond period. The other somatic measures showed increases in activity in this second, which is probably associated with the execution of the motor response.The heart. rate deceleration associated with responding was maximum on the first 2 set of the respond period. The reliability of the heart rate and somatic changes associated with responding was evaluated within each age group and on each measure as
HEART
RATE
AND
SOMANTIC
353
ACTIVITY
nWSELINE 5YR’o -BASELINE
4YRc 0
EASE UNE IO YR..
1
I x BASELINE
1 I
I 1 2 3 PREPARATORY INTERVAL
0 I 4 I RESPOND
1 2 PERIOD
SECONDS FIG.
1. Second-by-second
changes
in heart
rate.
the differences between the base period and second(s) of maximum decrease coincident with responding, as indicated by the second-by-second group averages. For a11somatic measures, the fourth second of the PI was used as the maximum decrease value. The maximum heart rate deceleration used the average of the heart rate values in the first 2 set of the respond period. Table 1 presents for each measure and age group, the mean values for the base period and period of maximum change, and the difference between these mean values. The reliability of these base-periodmaximum-change-period differences and any influence of age on these differences was evaluated by a repeated-measures analysis of variance (Type I, Linguist, 1953) done separately on heart rate and each of the somatic measures, With regard to base-level-maximum-change-level differences as assessedacross age groups, significant decreasesin all measures were found [heart rate, F(1,177) = 114.99, p < .OOOl; EMG, F(1,177) = 141.30, p < BOO1; general activity, F(lJ77) = 85.28, p < .OOOl; eye movement, F(1,177) = 111.37, p < .OOOl; eye blink, F(1,177) = 88.09, p < .OQOlJ. A breakdown of this effect by groups revealed that
354
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AL.
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ADULTS&
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PREPARATORY INTERVAL
RESPbND
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SECONDS FIG. 7.2 608 6-4
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PERIOD
SECONDS FIG.
3. Second-by-second
changes
in eye movement
amplitude.
HEART
MEDIAN
RATE
AND
SOMANTIC
355
ACTIVITY
TABLE 1 REACTION TIME (RT) AND MEAN BASE LEVEL (BASE) AND MEAN LEVEL OF MAXIMUM DECI~EASE (MAX) FOR HEART RATE AND SOMATIC ACTIVITY AT EACH AGE LEVEL A&+ ___4 Av =
Mdn Heart BPM
RT (msec) rate
EMG y. Trials
present
General activity (y. Trials present Eye movement Mag (mm pen displacement) Eye blink frequency To Trials present
Base Max d Base Max d Base Max d Base Max d Base Max d
5
s
10
38
34
38
39
611 101.9 100.1 -1.8 32 25 -7 25 20 -5 5.2 4.7 -0.5 30 31 +1
581 104.2 102.6 -1.6 26 18 -8 24 17 -7 5.3 4.5 -1.2 33 28 -5
345 90.4 68.0 -2.4 26 15 -11 15 9 -6 5.0 3.5 -1.5 35 22 -13
290 86.1 84.4 -1.7 13 7 -6 9 6 - 3 4.4 3.6 -0.8 32 21 -11
Adult
231 75.8 74.7 -1.1 6 3 - 3 10 5 -5 4.2 2 2 -2.0 34 15 - 19
of the 25 possible base-max differences, i.e., five measures within each of five age groups, 23 were found to be a significant decrease as evaluated by either a Tukey (A) test (Kurtz, Link, Tukey, & Wallace, 1965) or t-tests. The two instances where no reliable change was found were eye movement amplitude and eye blink frequency in 4 year olds. Although these phasic effects are consistent with the hypothesized relationship between cardiac and somatic effects, the attempted manipulation of phasic effects by age, with one exception, was not successful. That is, there was not found any relationship between age and the magnitude of the phasic effects, even though it had been anticipated that in the younger age groups phasic effects would either be eliminated or at least attenuated. The exception was on the two measures of occular activity, i.e., eye movement amplitude and frequency, where the magnitude of the phasic decrease associated with responding increased with age. This effect, was evaluated by the interaction between age and base-levelmaximum-change-level differences. With both measures, the interaction was significant [eye movement, F(4,177) = 6.84, p < .OOOl; eye blink F(4,lW = 12.26, p < .OOOl]. A breakdown of this interaction with a
356
OBRIST
ET
AL.
Tukey (A) test indicates that on both occular measures the basis for the interaction was due to the 4- and 5-year-olds showing significantly, i.e., p < .05, smaller decreases in occular activity than the other three groups during the period of maximum change associated with responding. The 8 and 10 year olds also showed significantly smaller decreases than adults on three of the four comparisons. Base levels, on the other hand, are not significantly different for eye blinks but are significantly higher for the younger three age groups for eye movements, effects which could not account for the larger phasic differences seen in the older groups. That is, if base levels influenced the magnitude of the phasic effect, then the phasic effect would be expected to be larger wit’h higher base levels not smaller. Tonic Effects Reliable differences were found between age groups in tonic levels of activity, both base levels and maximum change levels, on all measures except eye blink frequency. The reliability of these differences were assessed by the analysis of variance, which indicates significant age or group differences in tonic levels of heart rate, EMG, GBM, and eye movement amplitude [heart rate F(4,177) = 36.70, p < .0001; EMG, F(4,177) = 24.88, p < .OOl; general activity, P(4,177) = 15.95, p < .OOOl; eye movement F(4,177) = 7.09, p < .OOOl] . Most importantly, inspection of Table 1 and Figures 1, 2, and 3 indicates that on all four measures tonic levels decrease with age. The reliability of t,he differences between any two age groups was assessed by a Tukey (A) test (Kurtz et al., 1965)) which indicates that 4 and 5 year olds are not reliably different from each other on any measure except EMG, but are reliably more active on most measures than the older three age groups. For example, of the 24 comparisons that could be made between 4 and 5 year olds and the other three age groups on these four measures, 21 were significant at the .05 level or less. Similarly, 8 and 10 year olds tend to have significantly higher levels of activity than adults on most of these four measures, but are not reliably differentiated from each other except on EMG. Of the eight comparisons that could be made between 8 and 10 year olds and adults, six were significant at the .05 level or less. The overall consistency with which the age groups are differentiated by all five measures of tonic base and maximum change levels was evaluated by multiple rank order correlations (coefficients of concordance, Siegal, 1956), which were computed between levels of activity on all measures and age groups. A marked consistency was found for both base levels (W = .50, p < .05) and for maximum change levels, (W = .94, p < .Ol). Therefore, these data, with the exception of eye blink frequency, demonstrate a consistent relationship between age and tonic levels of heart rate and somatic activity.
HEART
Influence
RATE
AND
SOMANTIC
of Age with Base Level Differences
ACTIVITY
Comected
In order to minimize any influence that base level differences between groups might have on phasic effects, analysis of covariance was applied to all four measures which showed a significant base level difference between groups, i.e., heart rate, general activity, EMG, and eye movements. The covariant was the maximum change level associated with responding (Lacey, 1956), and any age-related influence on phasic activity was indicated by the difference between the adjusted mean scores of the period of maximum change using a group correction (see Bruning & Kintz, 1968, for computat,ional procedures). A significant age effect was now found with two somatic measures, eye movements [F(4,170) = 22.50, p < .OOl] and EMG [8’(4,173) = 3.59, p < .Ol]. In each case, the adjusted mean scores during the last second of t’he PI decreased with age. It should be noted that with eye movements a similar but less pronounced effect was seen when no correction was used for base level differences, whereas with EMG a somewhat reverse effect had been seen when no correction had been applied. On the other hand, even with the influence of age corrected, heart rate and one somatic measure, general activity, still showed no influence of age on the phasic decreases associated with responding [F(4,174) = 1.07, p < .20, heart rate; F(4,171) = 1.83, p < .20, general activity]. Therefore, what seems to emerge in regard to the relationship between heart rate and somatJic activity is that heart rate is most consistently related to general activity; all age groups show reliable phasic decreases in both heart rate and general activity that are unrelated to age, but large agerelated differences in tonic. or base Ievels of activity. Phasic heart rate changes do not reflect age-related differences in phasic activity in the other three somatic measures; yet age-related differences in tonic effects seen in t,wo of these somatic measures, EMG and eye movements, are consistently related to tonic heart rate and general activity. Perjormance
Eflects
Performance on the RT task was also found to be inversely related to age. Performance time decreased as age increased (see Table I), an effect that paralleled the relationship of age and tonic levels of somatic and cardiac activity as well as phasic age-related somatic effects. The median RT values based on all but the first six practice trials are presented in Table 1. A highly significant age effect was found as revealed by a simple analysis of variance [F(4,177) = 44.00, p < .OOOl]. Any two age groups were differentiated consistently with how they were differentiated on heart rate and the somaCe measures. For example, the differences between 4 and
358
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ET
AL.
5 year olds are the smallest in performance, the somatic measures, and heart rate. Thus, reaction time is fastest where tonic levels of somatic activit’y are less and heart rate lowest or where phasic somatic effects are largest. DISCUSSION
The results of this study can be summarized as follows: (1) A deceleration of heart rate and a decrease in the several parameters of ongoing task-irrelevant somatic activities were found to be coincident with responding in adults and all four age groups of children. (2) Developmental or age-related differences among these measureswere seenin two respects: (a) Phasic effects: On three somatic measures, eye movements, frequency of eye blinks, and chin EMG, the magnitude of the phasic decrease associated with performance increased with age. Such an age-related phasic effect was not evidenced with heart rate and general activity. (b) Tonic effects: Large age-related differences were found with tonic levels of heart rate, general activity, chin EMG, and eye movements with tonic levels of activity decreasing with age. (3) Performance was found to be inversely related with age in the same manner as was the magnitude of the phasic decreases in the somatic measures and the change in tonic levels of heart rate, general activity, chin EMG, and eye movements. The data are consistent with the hypothesized coupling of heart rate and somatic activity in several respects. The phasic decrease in both cardiac and somatic activity associated with performance is seen in all age groups. There are no instances where there were reliable phasic changes in both somatic and cardiac activity which did not mirror each other directionally. There was a consistent relationship between age and tonic levels of heart rate, general activity, EMG, and the magnitude of eye movements, an effect that does not appear to have been previously reported. On the other hand, there is one aspect of the data that could be considered inconsistent with this hypothesis. The attempt to manipulate the magnitude of the phasic heart rate changes associated with responding by the use of the developing organism was not successful, even though age-related phasic effects were observed in three of the four somatic measures. However, it is proposed that this failure to find age-related influences on phasic heart rate changes is not so much a contradiction of the hypothesized relationship between cardiac and somatic effects, but as indicative of the basis of this relationship and of the limitations in the use of phasic heart rate as an index of somatic inhibition. The observation that general activity and chin EMG, as heart rate, demonstrate no agerelated differences on phasic changes associated with responding, except
HEART RATE AND SONANTIC
AcTfVfTY
359
for a small EMG effect once base level differences were corrected, suggests that phasic heart rate changes are primarily related to the more extensive somatic acts as is characterized by general activity. This possibility has been supported in the first completed stage of a study now in progress, where attention during a RT task has been manipulated in 10 year olds by the use of incentives. Although significant phasic decreases in heart rate, general activity, and chin EMG were again found, the magnitude of the phasic changes did not differentiate low and high incentive conditions. But again, as in the present study, the magnitude of the phasic decreases in occular activity was significantly greater in the high attention condition where performance speed was also significantly faster (Meyers & Obrist, 1972). There was no evidence that heart rate, either the phasic changes associated with responding or the phasic changes at any point during the PI, was reliably altered without concomitant somatic effects. If anything, decreases in somatic activity were noted in the absence of heart rate effects such as during the early part of the PI.3 Such effects, as well as the influence of age on phasic eye movement changes, can be argued not to reflect an independence of heart rate from somatic activity as they do a greater sensitivity of preparatory somatic activity t.o the experimental manipulations. An independence of heart rate from somatic activity would have been demonstrated if reliable phasic decreases in heart rate had been found either without changes in somatic activity or in the presence of increases in somatic activity. In such a case, heart rate may then provide uniquely useful information about preparatory activity, i.e., information about behavioral processesother than the state of the striate musculature (seeObrist et al., 1973). There are several implications of these data for behavioral processes. To the extent that phasic changes in heart rate and inhibition of taskirrelevant somatic activities reflect biological processes associated with attent,ion, then the phasic heart rate changes will be sensitive to alterations in attentional states only to the extent that phasic changes in general activity are influenced by attentional states. It would appear that in the developing organism under the conditions of the present study 3Differences from base level were also evaluated in each of the 4 WC of thr PI for heart rate since inspection of Figure 1 suggested a possible age-related effect. Base level differences were again corrected by covariance analyses using the maximum change level in each second of the PI or the covariant. A significant age effect (p < .05) was found in each of the first 3 sec. However, it was attributable to the adult group failing to show any change in heart rate from base level during this period. The four age groups of children were not significantly different. Thus, phmic heart, rate effects again failed to differentiate age groups in a manner one might expect if heart rate was influenced by attentional processes.
360
OBRIST
ET
AL.
that phasic changes in heart rate and somatic activity, other than for occular activity, are not sensitive to the heightened state of attention that -older Ss presumably have as they prepare to respond. This, in part, may be due to the age-related differences in tonic levels of activity. That is, older children and adults showed less background or base level somatic activity. Thus, in order for Ss to show greater phasic decreases in somatic activity, they would have to decrease an already lower level of somatic activity. If heart rate is coupled to these aspects of somatic activity as the evidence from the present as well as other studies indicate, then the same limitation is placed on heart rate as on somatic activity. However, tonic levels of activity might provide some useful information. If the incidence of body movements and other task-irrelevant activities is directly related to the general attentive state of the organism, t’hen the older Ss would be considered in a more constant state of attentiveness or vigilance. Also, if one assesses the frequency of general activity and EMG in the last second of the PI, the older Ss show less somatic activity. Thus, either tonic base levels of somatic activity or the incidence of taskirrelevant activity coincident with performance might provide some useful information about attentive states. The influence of age on phasic changes in occular activity indicates that older Ss did show a greater momentary increase in attentiveness and thus suggest that of the various types of phasic changes, occular activity is the more sensitive index of attentional processes. Occular activity offers the advantage over other somatic measures, particularly in older children and adults, of having a higher base level. Thus, conditions which result in a decrease in somatic activity can be more sensitively detected by eye movements and blinks. Also, it is an easier measure to obtain than EMG and can be more reliably quantified since it is not as subject to various types of electronic artifact. The principal limitation of eye movements as an index of somatic inhibition is in tasks where either eye movements or fixation are relevant to behavioral activity. The results of this experiment as well as that of work now in progress indicate that the magnitude of the phasic heart rate decreases is not influenced by the manipulation of at,tention in the developing organism. However, there are several reports that the manipulation of attention in a RT paradigm has influenced phasic heart rate changes, both in adults (e.g., Higgins, 1971; Jennings, Averill, Opton, & Lazarus, 1971) and children (Sroufe, 1971). In the latter study, both the magnitude and regularity of the phasic cardiac deceleration was found to increase with age over the range of 6-10 years’, using both a simple and a disjunctive RT task but only with a 5- not a lo-set foreperiod. On the other hand, Elliott (1973) was unable to find any effect on the phasic deceleration in
HEART
RATE
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ACTIVITY
361
7 year oIds when attention was manipulated by incentives. There are several differences between studies, particularly in those using children, which could account for the inconsistency of the results as to the effects of attentional manipulations. For example, Sroufe (1971) in contrast to the present study used fewer trials and his Ss were apparently more motivated. In any case, the use of the phasic heart rate changes to assess attention in the developing organism needs to be further evaluated, particularly in regard to the conditions in which heart rate might provide useful information about attentional processes. REFERENCES & KINTZ, B. L. Computational handbook of statistics. Glenview, Ill.: Foresman and Company, 1968. CHASE, W. G., GRAHAM, F. K., & GRAHAM, D. T. Components of HR response in anticipation of reaction time and exercise tasks. Journal of Experimental Psychology, 1967,76, 642-648. EI,LIOTT, R. Physiological activity and performance: A comparison of kindergarten children and young adults. Psychological Monographs, 1964, 78, No. 10, l-33. ELLIOTT, R. Physiological activity and performance in children and adults: A twoyear follow-up. Journal of Ezperimental Child Psychology, 1966, 4, 58-80. ELLIOTT, R. The motivational significance of heart rate. In P. A. Obrist, A. II. Black, J. Brener, and L. DiCara (Eds.), Contemporary trends in cardiouascttlnr psychophysiology. Chicago : Aldine-Atherton, 1973. HERRINGTON, L. P. The relation of physiological and social indices of activity level. Studies in personality, contributed in honor of Lewis M. Terman. New York: McGraw-Hill, 1942. Pp. 125-146. HIGGINS, J. D. Set and uncertainty as factors influencing anticipatory cardiovascular responding in humans. Journal of Comparative and Physiological Psychology, 1971, 74, 272-283. JENNINGS, J. R., AVERILL, J. R., OPTEN, E. M., & LXARUS, R. S. Some parameters of heart rate change: Perceptual versus motor task requirements, noxiousness, and uncertainty. Psychophysiology, 1971, 7, 194-212. KURTZ, T. E., LINK, R. F., TUKEY, J. W., & WALLACE, D. L. Short cut multiple comparison for balanced single and double classifications. Part 2: Derivations and approximations. Biomet~ika, 1965, 52, 485-498. LACEY. J. I. The evaluation of autonomic responses: Toward a general solution. Annals of New York Academy of Science, 1956,67, 12%164. L.~cEY, J. I. Somatic response patterning and stress: Some revisions of activation theory. In M. H. Appley and R. Trumbull (Eds.), Psychological stress: Issues in Tesearch. New York: Appleton-Century-Crofts. 1967. Pp. 14-42. LINDQUIST, E. F. Design and analysis of experiments in Psychology and Education. Boston : Houghton Mifflin Company, 1953. MALMO, R. B. Cognitive factors in impairment: A neuropsychological study of divided set. Journal of Experimental Psychology, 1966,71, 184-189. MEYERS, K. A., & ORRIST. P. A. Psychophysiological correlates of attention in children. Paper presented at the annual meeting of the Society for Psychophysiological Research, Boston, 1972. BRUNING,
Scott,
J. L.,
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P. A. Heart rate and somatic-motor coupling during classical aversive conditioning in humans. Journal of Experimental Psychology, 1968, 77, 180-193. OBRIST, P. A., & WEBB, R. A. Heart rate during conditioning in dogs: Relationship to somatic motor activity. Psychophysiology, 1967,4, 7-34. OBRIST, P. A., WEBB, R. A., & SUTTERER, J. R. Heart rate and somatic changes during aversive conditioning and a simple reaction time task. Psychophysiology, 1969, 5, 696723. OBRIST, P. A., WEBB, R. A., SUTTERER, J. R., & HOWARD, J. L. The cardiac-somatic relationship : Some reformulations. Psychophysiology, 197Oa, 6, 569587. OBRIST, P. A., WEBB, R. A., SUTTERER, J. R., & HOWARD, J. L. Cardiac deceleration and reaction time: An evaluation of two hypotheses. Psychophysiology, 1970b, 6, 695-706. OBRIST, P. A., HOWARD, J. L., LAWLER, J. E., GALOSY, R. W., MEYERS, K. A., & GAEBELEIN, C. J. The cardiac-somatic interaction. In P. A. Obrist, A. H. Black, J. Brener, and L. DiCara (Eds.), Contemporary trends in cardiovascular psychophysiology, Chicago: Aldine-Atherton, 1973. SHAPIRO, A. H. Verbalization during the critical interval of a reaction time task and development of motor control. Child Development, 1973, 44, In press. SIEGAL. S. Nonparametric statistics for the behavioral sciences. New York: McGrawHill, 1956. SROUFE, L. A. Age changes in cardiac deceleration within a fixed foreperiod reaction time task: An index of attention. Developmental Psychology, 1971, 5, 338-343. SUTTERER, J. R., & OBRIST, P. A. Heart rate and general activity alterations of dogs during several aversive conditioning procedures. Journal of Comparative and Physiological Psychology, 1972. 80, 314-326. WEBB, R. A.. & OBRIST. P. A. Physiological concomitants of reaction time performance as a function of preparatory interval. Psychophysiology, 1970, 6, 389403. WOOD, II. M., & OBRIST, P. A. The effects of controlled and uncontrolled respiration on the conditioned heart rate response in human beings, Journal of Erperimental Psychology, 1964, 68, 221-229. OBRIST,
OF EXPERIMENTAL
CHILD
PSYCHOLOGY
Cardiac-Somatic
Changes Reaction
A PAUL School
A. R.
OBRIST,’ STZRLINO
16, 34&362
during
Time
HENAX,
L.
Study1
HOWARD, AND
a Simple
Task:
Developmental .JAMES
(1973)
DORIS
*JAMES
J.
R.
SUTTERER,
MURRELL
of Merlicine, School oj Bducrrtzon. nnrl Biologicd Sciences, Resenrch CetlteT of the Child Dce~elopment Institzcte, Uniuersit?/ of Norih C’awliua, Chapel Hill
The relationship during a simple reaction time task between heart, rate and four measures of task irrelevant somatic activity was evaluated in four age groups of children, i.e., 4-, 5, 8-, and lo-year-olds and young adults, in order to evaluate further a hypothesized coupling of cardiac and somatic activity. At, all age levels. phasic decreases in both heart rate and somatic activity coincident with performance were found with the magnitude of the effect increasing with age only on three somatic measures. However, tonic levels of both heart rate and somatic activity dccreasrd with age. Performance on the reaction task was found to be inversely related to the age-related phnsic somatic effects as well as age-related tonic heart rate and somatic activity.
The purpose of this research was to utilize a developmental strategy to evaluate within the confines of the simple reaction time (RT) paradigm the relationship between cardiac and somatic events and to evaluate a hypothesis concerning the behavioral relevance of these effects. The observation that the direction and magnitude of heart rate changes, in both the classical conditioning and a simple RT situation, are concomitant with the direction and magnitude of change in ongoing somatic activities has been viewed as representing a biological linkage or coupling, achieved primarily by common CNS mechanisms, between cardiac and somatic events necessitated by the metabolic function of the heart (Obrist, 1968; ’ This research was supported by Research Grant MH-07995, National Institute of Mental Health, United States Public Health Service to P. A. Obrist and Institutional Grant HD-03110. National Institute of Child Health and Development, United States Pub’ic Health Service, with the Biological Sciences Resrarch Center of the Child Cevelopmental Institute, University of North Carolina, Chap?1 Hill. ‘Requests for reprints should bc sent to: Paul A. Obrist, Ph.D., Department of Psychiatry, University of North Carolina School of Medicine, Chapel Hill, North Carolina. 346 Copyright @ 1973 by Academic Prrss. Inc. All rights of reproduction in any form reserved.
HEART
RATE
AND
SOMANTIC
ACTIVITT
347
Obrist & Webb, 1967; Obrist, Webb, & Sutterer, 1969; Webb & Obrist, 1970; Obrist, Webb, Sutterer, 8: Howard, 1970a, 1970b; Sutterer & Obrist, 1972). In the simple RT situation with a fixed foreperiod, heart rate deceleration, and a cessation of task irrelevant, ongoing somatic events have been found in adult man to be coincident with responding. Furthermore, performance speed has been found to be directly related t’o the magnitude of these effects (e.g., see Obrist et al., 197Oa). The decrease in somatic activity has been viemcd as representing the inhibition of task-irrelevant activities necessitated for efficient execution of the behavioral response with the cardiac deceleration being a visceral counterpart of this somatic change. In this context, these cardiac and somatic changes can be viewed as peripheral manifestations of CM proccsscs associated with attention, in which the cessation of somatic events and its concomitant visceral counterpart reflect a facilitation of attention by an inhibition of irrelevant activity. In the previous RT studies cited using adult Ss, the relationship between heart rate and somatic activity as well as the behavioral significance of these effects has been evaluated in several ways. For example, the experimental manipulation of forcpcriod duration and certainty influenced cardiac, somatic, and performance effects in a similar manner (Webb & Obrist, 1970). Within S analyses of the data revealed that on trials in which heart rate was slowest there occurred the largest decrease in somatic act,ivity and fastest reaction times (Obrist et cd., 1970b). Also, an alternative position which views the cartliac deceleration and its relationship to performance as due to the involvement, of heart rate in the afferent control of CNS processes (Lacey, 19671, rather than due to its cfferent association with somatir processes,was not supported when directly evaluated by the pharmacological manipulation of the cardiac response (Obrist et al., 1970b). In the present study, a devclopmentnl strategy was chosen to evaluate further the relationship between cardiac and somatic activity, because it appeared to be another yet unexplored way to manipulat,e the relationship. That is, the developing organism would provide a naturalistic way to manipulate somatic activity and hence attentional processesin that, younger Ss were expcctctl to show more background somatic activity, i.e., be more restless and have less facility to inhibit such activity (Elliott, 1964, 1966; Shapiro, 1973), effects which should covary with age, In turn, any age-related cliffercnccs in background somatic activity, i.e., tonic levels and the facility to inhibit such activity, i.e., phasic changes, should be reflect,ed in similar age-related differences in heart rate and performance, if the cardiac, somatic, and performance effects are interrelated as hypothesized.
348
OBRIST
ET
AL.
Specifically, it was expected in the light of these considerations that: (1) In any age group in which there was found a reliable decrease in phasic somatic activities, there would be a reliable phasic deceleration of heart rate. Conversely, if any age group showed no change or an increase in phasic somatic activity, such as was anticipated might be the case in the youngest age groups, there would be no phasic deceleration of heart rate. (2) Any effect of age on either tonic levels of somatic activity or the magnitude of the phasic decrease in somatic act,ivities associated with responding would be directly related to tonic levels of heart rate or the phasic deceleration of heart, rate associated with responding, respectively. (3) Performance on the RT task should parallel the somatic and cardiac changes with a decrease in RT being associated with a greater inhibition of, or lower level of, somatic activity and heart rate. We also evaluated one other issue with regard to cardiac and somatic effects. This concerned whether one parameter of somatic activity, eye movements and blinks, would dcmonstratc a greater sensitivity with age to the manipulation of attention than would heart rate. In two previous studies (Webb Q Obrist, 1970; Obrist et al., 1970b) occular activity was found to decrease more consistently than heart rate at shorter PIs, whereas at longer PIs, both effects decreased in an equally consistent manner. Because attentional requirements would be expected to be at least as great at short PIs, these effects would suggest t’hat occular activity can have a greater sensitivity to attentional processes than heart rate. It was anticipated that if a sufficiently broad age range of children were used it could be determined whether there is a transition in cardiac, somatic, and performance effects between the youngest group and an adult reference group. Initially, 5- and g-year-old groups were used. However, when a reliable cardiac deceleration and a decrease in somatic activities were still found in the 5-year-old group, a sample of 4-year-olds was then used in the expectation that the decreases in heart rate and somatic activity would be attenuated. Younger samples were not used since it appeared they would be unable to perform the task. Finally, a lo-year-old group was evaluated so as to provide a further transitional group between the younger groups and adults. METHOD
Subjects The 4- and &year-old samples were drawn from privately run nursery schools and kindergartens in the city of Chapel Hill, North Carolina. The 8- and lo-year-old samples were drawn from the 3rd and 5th grades of
HEART
RATE
Ah-D
SOMANTIC
ACTIVITY
349
one public elementary school. Parents of all children in each private school or grade in the public school selected were sent a letter requesting their permission for the children to participate in the experiment. Approximately 5070 of the parents agreed. In order to abtain 40 Ss in each age group, two to three school classes at any one age level were selected. The adult sample was volunteers from b0t.h an introductory psychology course and an intermediate level undergraduate education course at the University of North Carolina, Chapel Hill. bpproximately equal numbers of males and females were used in each age group. The mean age in years and months and standard deviation in months of each group at the time the S participated in the experiment were: 4 year olds, j: = 4-6, (T = 3.2; 5 years olds, C = 5-8, (T = 4.4; 8 years olds, Z = 8-9, (T = 6,.7; 10 years olds, f = 10-7, (T = 6.2; adult, z = 19-11, (T = 14.2. Owing to either equipment, failure or the failure of Ss to show up for the experiment, the final iV in each age group was: 4 year old* , S = 38 ; 5 year olds, IV = 34 ; 8 year olds, N = 38; IO year olds, ,I: = 39 ; adults, :V = 33. No S was used who at the time of testing was on any medication which might influence either performance or t’lie biological measures. Apparatus All physiological measures were recorded on a Beckman Type R Dynograph using Beckman biopotcntial electrodes to measure EKG, chin EMG, and eye movements. Two high-sensitivity (O-5 cm Hg) Statham strain gauges were used to transduce the pneumatic signals necessary to measure general activity and respiration. The RT stimuli, foreperiod duration, and intertrial intervals were all automatically programmed, and performance time measured to the nearest millisec with a combination of specially built solid state circuitry, plynch paper tape, and commercial Digi-bit circuitry. A standard telegraph key was used as the RT manipulandum. In order to minimize the medical atmosphere of the laboratory, the S room was decorated with posters and drawings and the Es wore pastel smocks. Physiological
Measures
Five measures of somatic activity were employed to insure that somatic activity was reliably evaluated. Two measures, vertical eye movements and blinks, have been found in previous studies with adults (Obrist et al., 1969) to show fairly high levels of background activity as compared to EMG measures and thus a more obvious decrease concomitant with responding. Chin EMG was used as it has been found (Obrist et al., 1969) to be associated with postural movements as well as discrete movements of the muscles in and around the mouth-a kind of somatic activity corn-
350
OBRIST
ET
AL.
monly seen. General activity, i.e., movements of the limbs and torso, was also assessed as it was expected to be elevated in younger children. Finally, respiration was measured as has been routinely done in all previous studies. The methods for measuring heart rate, respiration, and chin EMG activity were similar to those previously described (Obrist et al., 1969; Webb & Obrist, 1970). Vertical eye movements and blinks were recorded from electrodes placed just above the eye brow and just below the lower eye lid and centered over the middle of the right eye. General activity was recorded from pneumatic sensors located in the back and seat of the S chair. Procedure Instructions. All age groups received identical instructions, except that with the youngest age groups the instructions were commonly repeated, and the X shown by manipulating his arm and hand what was to be done when the respond stimulus came on. The instructions stressed that the S was to release the key as rapidly as possible. No incentives or feedback of results were provided with the exception that the youngest two age groups were told that if they stayed with the experiment until the end they would be given a bonus toy. The youngest three age groups were given an age and sex appropriate $2.00 toy for participation. The 10 year olds were given $2.00 and adults either $2.00 or experimental credit for participation. Reaction time task. A visual preparatory stimulus or ready signal was used which had a duration of 1 sec. It consisted of a 6-V jewel light placed at eye level and approximately 3-ft directly in front of the S. The respond signal was a clearly audible 100%Hz tone presented through a speaker over a low level of white noise. The respond signal terminated when the S responded. The foreperiod or preparatory interval (PI), i.e., the time between the onset of the ready and respond stimuli, was 4 set and the intertrial interval, i.e., the t’ime between ready stimuli, was 20 sec. Subjects were instructed to keep the reaction time key depressed at all times except when they were signaled to release it.. Throughout the experiment, a young adult female research assistant stayed with the S, except for adult Ss, to provide reassurance and any necessary assistance. Sixty reaction time trials were used with a short rest period after 30 trials. The first five trials were practice, which was found to be a sufficient number of trials for all Ss to learn the task requirements. The only time the Ss were further instructed after five trials was if they failed to depress the key immediately after release or if they released the key prematurely on two
HEART
RATE
AND
SOMANTIC
ACTIVITY
consecutive trials. After five trials, Ss were never told to prepare respond signal or to release the key. Data
Analysis
351 for the
and Quantification
A second-by-second analysis of the physiological data was performed on alternate trials beginning with trial 6, providing a total of 28 trials (see Wood $ Obrist, 1964; Obrist et al., 1969). The only exception to this was when a premature release or artifact occurred at which time the next trial was selected. On each trial, the second-by-second analysis was carried out in (1) the last 5 set before the ready signal, a base !>eriod, (2) the 4 set of the PI, and (3) the first 2 set following the onset of the respond signal, except for heart rate where the analysis was extended to 3 see following the respond stimulus. This analysis involved determining the value of each biological parameter coincident with each second of the measurement period. For heart rate, the time in millisec of a given R-R interval was assigned to the second in which the R wave integrator discharged. Where two R-R intervals were integrated in a given second, the average of the two values was used. Because of t.he time lag between where the R-R interval actually occurs and where it is integrated can be between 0.5 and 1.0 set, the second-by-second changes in heart rate depicted in the figures were corrected by 1 sec. This involved omit’ting the data from the first second of the PI and moving all following second values up 1 see toward the ready signal. In order to bc consistent with current convcntion, R-R, interval is depicted in the tables and figures as beats per minute. The EMG and general activity were quantified only with respect to presence or absenceof somatic activity in any 1 WCrather than responseamplitude, because the latter is more difficult to quantify and tends to increase with age. EMG activity was considered present in any 1 set if a distinguishable spindle-shaped burst of activit,y occurred which had a duration of at least l/z SW and a peak a,mplitude of at least 60 ~LV.The latter value was chosen because the EMG baseline was usually in the range of 2030 pY. Where the baseline exceeded 30 p,V, the criterion for peak amplitude was increased accordingly. Whcrc an EMG burst extended into 2 set, it was scored as present in both secondsonly if the duration in each was clearly 1/z set or more. General activity was scored as present in any second if the amplitude of the pen displacement associated with a movemcnt was at least 3 mm greater than the base level. A constant amplifier gain was used for all Ss and the sensitivity of the pneumatic chair checked on cacb S prior to the beginning of the RT trials. Occular activity WRS quantified in two ways: (1) As an amplitude
352
OBRIST
ET
AL.
score which combines vertical movements and blinks such that in any 1 see the difference in millimeters between the highest and lowest level of pen displacement is obtained and (2) as a frequency score where the presence or absence of eye blinks was determined within each second. For occular activity, a constant amplifier gain was used with the sensitivity of the recording checked on each S prior to the beginning of the R.T trials. The respiration data were not quantified. The data were summarized on each S over the 28 trials as follows. A base period value was obtained which indicated the average amount of activity per second. Similarly, a mean value for each second of the forcperiod and each second of the respond period was determined. Thus, the second-by-second changes depicted in the figures indicate the average values for each second of the PI and respond period as well as t,he average amount of act,ivity in any 1 see of the base period. RESULTS
The data will be presented first in regard to phasic changes associated with responding and then in regard to tonic effects. Because of large differences between age groups in base level (tonic activity) on all but one measure, which could act to obscure any influence of age on phasic effects, the data will then be presented with base level differences controlled by covariance techniques. 1. Phasic Effects At all age levels, reliable decreases in somatic activity and heart rate were observed either just to anticipate or to be coincident with the execution of the RT task. The mean second-by-second values for each experimental group are depicted for heart rate in Fig. 1, EMG in Fig. 2, and the amplitude of eye movements and blinks in Fig. 3. The second-bysecond changes for general activity and the frequency of eye blinks are not depicted, since the former tends to parallel EMG activity and the latter parallel eye movement amplitude. On each of the somatic measures, the decrease in activity was generally largest during the fourth or last second of the foreperiod, with the exception of EMG activity where the decrease also extended into the first second of the respond period. The other somatic measures showed increases in activity in this second, which is probably associated with the execution of the motor response.The heart. rate deceleration associated with responding was maximum on the first 2 set of the respond period. The reliability of the heart rate and somatic changes associated with responding was evaluated within each age group and on each measure as
HEART
RATE
AND
SOMANTIC
353
ACTIVITY
nWSELINE 5YR’o -BASELINE
4YRc 0
EASE UNE IO YR..
1
I x BASELINE
1 I
I 1 2 3 PREPARATORY INTERVAL
0 I 4 I RESPOND
1 2 PERIOD
SECONDS FIG.
1. Second-by-second
changes
in heart
rate.
the differences between the base period and second(s) of maximum decrease coincident with responding, as indicated by the second-by-second group averages. For a11somatic measures, the fourth second of the PI was used as the maximum decrease value. The maximum heart rate deceleration used the average of the heart rate values in the first 2 set of the respond period. Table 1 presents for each measure and age group, the mean values for the base period and period of maximum change, and the difference between these mean values. The reliability of these base-periodmaximum-change-period differences and any influence of age on these differences was evaluated by a repeated-measures analysis of variance (Type I, Linguist, 1953) done separately on heart rate and each of the somatic measures, With regard to base-level-maximum-change-level differences as assessedacross age groups, significant decreasesin all measures were found [heart rate, F(1,177) = 114.99, p < .OOOl; EMG, F(1,177) = 141.30, p < BOO1; general activity, F(lJ77) = 85.28, p < .OOOl; eye movement, F(1,177) = 111.37, p < .OOOl; eye blink, F(1,177) = 88.09, p < .OQOlJ. A breakdown of this effect by groups revealed that
354
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\-------------BASELHE4YR.0
ASELINE ASELINE
BASELINE
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ADULTS&
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I I
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3
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PREPARATORY INTERVAL
RESPbND
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SECONDS FIG. 7.2 608 6-4
5 g
changes
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PERIOD
SECONDS FIG.
3. Second-by-second
changes
in eye movement
amplitude.
HEART
MEDIAN
RATE
AND
SOMANTIC
355
ACTIVITY
TABLE 1 REACTION TIME (RT) AND MEAN BASE LEVEL (BASE) AND MEAN LEVEL OF MAXIMUM DECI~EASE (MAX) FOR HEART RATE AND SOMATIC ACTIVITY AT EACH AGE LEVEL A&+ ___4 Av =
Mdn Heart BPM
RT (msec) rate
EMG y. Trials
present
General activity (y. Trials present Eye movement Mag (mm pen displacement) Eye blink frequency To Trials present
Base Max d Base Max d Base Max d Base Max d Base Max d
5
s
10
38
34
38
39
611 101.9 100.1 -1.8 32 25 -7 25 20 -5 5.2 4.7 -0.5 30 31 +1
581 104.2 102.6 -1.6 26 18 -8 24 17 -7 5.3 4.5 -1.2 33 28 -5
345 90.4 68.0 -2.4 26 15 -11 15 9 -6 5.0 3.5 -1.5 35 22 -13
290 86.1 84.4 -1.7 13 7 -6 9 6 - 3 4.4 3.6 -0.8 32 21 -11
Adult
231 75.8 74.7 -1.1 6 3 - 3 10 5 -5 4.2 2 2 -2.0 34 15 - 19
of the 25 possible base-max differences, i.e., five measures within each of five age groups, 23 were found to be a significant decrease as evaluated by either a Tukey (A) test (Kurtz, Link, Tukey, & Wallace, 1965) or t-tests. The two instances where no reliable change was found were eye movement amplitude and eye blink frequency in 4 year olds. Although these phasic effects are consistent with the hypothesized relationship between cardiac and somatic effects, the attempted manipulation of phasic effects by age, with one exception, was not successful. That is, there was not found any relationship between age and the magnitude of the phasic effects, even though it had been anticipated that in the younger age groups phasic effects would either be eliminated or at least attenuated. The exception was on the two measures of occular activity, i.e., eye movement amplitude and frequency, where the magnitude of the phasic decrease associated with responding increased with age. This effect, was evaluated by the interaction between age and base-levelmaximum-change-level differences. With both measures, the interaction was significant [eye movement, F(4,177) = 6.84, p < .OOOl; eye blink F(4,lW = 12.26, p < .OOOl]. A breakdown of this interaction with a
356
OBRIST
ET
AL.
Tukey (A) test indicates that on both occular measures the basis for the interaction was due to the 4- and 5-year-olds showing significantly, i.e., p < .05, smaller decreases in occular activity than the other three groups during the period of maximum change associated with responding. The 8 and 10 year olds also showed significantly smaller decreases than adults on three of the four comparisons. Base levels, on the other hand, are not significantly different for eye blinks but are significantly higher for the younger three age groups for eye movements, effects which could not account for the larger phasic differences seen in the older groups. That is, if base levels influenced the magnitude of the phasic effect, then the phasic effect would be expected to be larger wit’h higher base levels not smaller. Tonic Effects Reliable differences were found between age groups in tonic levels of activity, both base levels and maximum change levels, on all measures except eye blink frequency. The reliability of these differences were assessed by the analysis of variance, which indicates significant age or group differences in tonic levels of heart rate, EMG, GBM, and eye movement amplitude [heart rate F(4,177) = 36.70, p < .0001; EMG, F(4,177) = 24.88, p < .OOl; general activity, P(4,177) = 15.95, p < .OOOl; eye movement F(4,177) = 7.09, p < .OOOl] . Most importantly, inspection of Table 1 and Figures 1, 2, and 3 indicates that on all four measures tonic levels decrease with age. The reliability of t,he differences between any two age groups was assessed by a Tukey (A) test (Kurtz et al., 1965)) which indicates that 4 and 5 year olds are not reliably different from each other on any measure except EMG, but are reliably more active on most measures than the older three age groups. For example, of the 24 comparisons that could be made between 4 and 5 year olds and the other three age groups on these four measures, 21 were significant at the .05 level or less. Similarly, 8 and 10 year olds tend to have significantly higher levels of activity than adults on most of these four measures, but are not reliably differentiated from each other except on EMG. Of the eight comparisons that could be made between 8 and 10 year olds and adults, six were significant at the .05 level or less. The overall consistency with which the age groups are differentiated by all five measures of tonic base and maximum change levels was evaluated by multiple rank order correlations (coefficients of concordance, Siegal, 1956), which were computed between levels of activity on all measures and age groups. A marked consistency was found for both base levels (W = .50, p < .05) and for maximum change levels, (W = .94, p < .Ol). Therefore, these data, with the exception of eye blink frequency, demonstrate a consistent relationship between age and tonic levels of heart rate and somatic activity.
HEART
Influence
RATE
AND
SOMANTIC
of Age with Base Level Differences
ACTIVITY
Comected
In order to minimize any influence that base level differences between groups might have on phasic effects, analysis of covariance was applied to all four measures which showed a significant base level difference between groups, i.e., heart rate, general activity, EMG, and eye movements. The covariant was the maximum change level associated with responding (Lacey, 1956), and any age-related influence on phasic activity was indicated by the difference between the adjusted mean scores of the period of maximum change using a group correction (see Bruning & Kintz, 1968, for computat,ional procedures). A significant age effect was now found with two somatic measures, eye movements [F(4,170) = 22.50, p < .OOl] and EMG [8’(4,173) = 3.59, p < .Ol]. In each case, the adjusted mean scores during the last second of t’he PI decreased with age. It should be noted that with eye movements a similar but less pronounced effect was seen when no correction was used for base level differences, whereas with EMG a somewhat reverse effect had been seen when no correction had been applied. On the other hand, even with the influence of age corrected, heart rate and one somatic measure, general activity, still showed no influence of age on the phasic decreases associated with responding [F(4,174) = 1.07, p < .20, heart rate; F(4,171) = 1.83, p < .20, general activity]. Therefore, what seems to emerge in regard to the relationship between heart rate and somatJic activity is that heart rate is most consistently related to general activity; all age groups show reliable phasic decreases in both heart rate and general activity that are unrelated to age, but large agerelated differences in tonic. or base Ievels of activity. Phasic heart rate changes do not reflect age-related differences in phasic activity in the other three somatic measures; yet age-related differences in tonic effects seen in t,wo of these somatic measures, EMG and eye movements, are consistently related to tonic heart rate and general activity. Perjormance
Eflects
Performance on the RT task was also found to be inversely related to age. Performance time decreased as age increased (see Table I), an effect that paralleled the relationship of age and tonic levels of somatic and cardiac activity as well as phasic age-related somatic effects. The median RT values based on all but the first six practice trials are presented in Table 1. A highly significant age effect was found as revealed by a simple analysis of variance [F(4,177) = 44.00, p < .OOOl]. Any two age groups were differentiated consistently with how they were differentiated on heart rate and the somaCe measures. For example, the differences between 4 and
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5 year olds are the smallest in performance, the somatic measures, and heart rate. Thus, reaction time is fastest where tonic levels of somatic activit’y are less and heart rate lowest or where phasic somatic effects are largest. DISCUSSION
The results of this study can be summarized as follows: (1) A deceleration of heart rate and a decrease in the several parameters of ongoing task-irrelevant somatic activities were found to be coincident with responding in adults and all four age groups of children. (2) Developmental or age-related differences among these measureswere seenin two respects: (a) Phasic effects: On three somatic measures, eye movements, frequency of eye blinks, and chin EMG, the magnitude of the phasic decrease associated with performance increased with age. Such an age-related phasic effect was not evidenced with heart rate and general activity. (b) Tonic effects: Large age-related differences were found with tonic levels of heart rate, general activity, chin EMG, and eye movements with tonic levels of activity decreasing with age. (3) Performance was found to be inversely related with age in the same manner as was the magnitude of the phasic decreases in the somatic measures and the change in tonic levels of heart rate, general activity, chin EMG, and eye movements. The data are consistent with the hypothesized coupling of heart rate and somatic activity in several respects. The phasic decrease in both cardiac and somatic activity associated with performance is seen in all age groups. There are no instances where there were reliable phasic changes in both somatic and cardiac activity which did not mirror each other directionally. There was a consistent relationship between age and tonic levels of heart rate, general activity, EMG, and the magnitude of eye movements, an effect that does not appear to have been previously reported. On the other hand, there is one aspect of the data that could be considered inconsistent with this hypothesis. The attempt to manipulate the magnitude of the phasic heart rate changes associated with responding by the use of the developing organism was not successful, even though age-related phasic effects were observed in three of the four somatic measures. However, it is proposed that this failure to find age-related influences on phasic heart rate changes is not so much a contradiction of the hypothesized relationship between cardiac and somatic effects, but as indicative of the basis of this relationship and of the limitations in the use of phasic heart rate as an index of somatic inhibition. The observation that general activity and chin EMG, as heart rate, demonstrate no agerelated differences on phasic changes associated with responding, except
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for a small EMG effect once base level differences were corrected, suggests that phasic heart rate changes are primarily related to the more extensive somatic acts as is characterized by general activity. This possibility has been supported in the first completed stage of a study now in progress, where attention during a RT task has been manipulated in 10 year olds by the use of incentives. Although significant phasic decreases in heart rate, general activity, and chin EMG were again found, the magnitude of the phasic changes did not differentiate low and high incentive conditions. But again, as in the present study, the magnitude of the phasic decreases in occular activity was significantly greater in the high attention condition where performance speed was also significantly faster (Meyers & Obrist, 1972). There was no evidence that heart rate, either the phasic changes associated with responding or the phasic changes at any point during the PI, was reliably altered without concomitant somatic effects. If anything, decreases in somatic activity were noted in the absence of heart rate effects such as during the early part of the PI.3 Such effects, as well as the influence of age on phasic eye movement changes, can be argued not to reflect an independence of heart rate from somatic activity as they do a greater sensitivity of preparatory somatic activity t.o the experimental manipulations. An independence of heart rate from somatic activity would have been demonstrated if reliable phasic decreases in heart rate had been found either without changes in somatic activity or in the presence of increases in somatic activity. In such a case, heart rate may then provide uniquely useful information about preparatory activity, i.e., information about behavioral processesother than the state of the striate musculature (seeObrist et al., 1973). There are several implications of these data for behavioral processes. To the extent that phasic changes in heart rate and inhibition of taskirrelevant somatic activities reflect biological processes associated with attent,ion, then the phasic heart rate changes will be sensitive to alterations in attentional states only to the extent that phasic changes in general activity are influenced by attentional states. It would appear that in the developing organism under the conditions of the present study 3Differences from base level were also evaluated in each of the 4 WC of thr PI for heart rate since inspection of Figure 1 suggested a possible age-related effect. Base level differences were again corrected by covariance analyses using the maximum change level in each second of the PI or the covariant. A significant age effect (p < .05) was found in each of the first 3 sec. However, it was attributable to the adult group failing to show any change in heart rate from base level during this period. The four age groups of children were not significantly different. Thus, phmic heart, rate effects again failed to differentiate age groups in a manner one might expect if heart rate was influenced by attentional processes.
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that phasic changes in heart rate and somatic activity, other than for occular activity, are not sensitive to the heightened state of attention that -older Ss presumably have as they prepare to respond. This, in part, may be due to the age-related differences in tonic levels of activity. That is, older children and adults showed less background or base level somatic activity. Thus, in order for Ss to show greater phasic decreases in somatic activity, they would have to decrease an already lower level of somatic activity. If heart rate is coupled to these aspects of somatic activity as the evidence from the present as well as other studies indicate, then the same limitation is placed on heart rate as on somatic activity. However, tonic levels of activity might provide some useful information. If the incidence of body movements and other task-irrelevant activities is directly related to the general attentive state of the organism, t’hen the older Ss would be considered in a more constant state of attentiveness or vigilance. Also, if one assesses the frequency of general activity and EMG in the last second of the PI, the older Ss show less somatic activity. Thus, either tonic base levels of somatic activity or the incidence of taskirrelevant activity coincident with performance might provide some useful information about attentive states. The influence of age on phasic changes in occular activity indicates that older Ss did show a greater momentary increase in attentiveness and thus suggest that of the various types of phasic changes, occular activity is the more sensitive index of attentional processes. Occular activity offers the advantage over other somatic measures, particularly in older children and adults, of having a higher base level. Thus, conditions which result in a decrease in somatic activity can be more sensitively detected by eye movements and blinks. Also, it is an easier measure to obtain than EMG and can be more reliably quantified since it is not as subject to various types of electronic artifact. The principal limitation of eye movements as an index of somatic inhibition is in tasks where either eye movements or fixation are relevant to behavioral activity. The results of this experiment as well as that of work now in progress indicate that the magnitude of the phasic heart rate decreases is not influenced by the manipulation of at,tention in the developing organism. However, there are several reports that the manipulation of attention in a RT paradigm has influenced phasic heart rate changes, both in adults (e.g., Higgins, 1971; Jennings, Averill, Opton, & Lazarus, 1971) and children (Sroufe, 1971). In the latter study, both the magnitude and regularity of the phasic cardiac deceleration was found to increase with age over the range of 6-10 years’, using both a simple and a disjunctive RT task but only with a 5- not a lo-set foreperiod. On the other hand, Elliott (1973) was unable to find any effect on the phasic deceleration in
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7 year oIds when attention was manipulated by incentives. There are several differences between studies, particularly in those using children, which could account for the inconsistency of the results as to the effects of attentional manipulations. For example, Sroufe (1971) in contrast to the present study used fewer trials and his Ss were apparently more motivated. In any case, the use of the phasic heart rate changes to assess attention in the developing organism needs to be further evaluated, particularly in regard to the conditions in which heart rate might provide useful information about attentional processes. REFERENCES & KINTZ, B. L. Computational handbook of statistics. Glenview, Ill.: Foresman and Company, 1968. CHASE, W. G., GRAHAM, F. K., & GRAHAM, D. T. Components of HR response in anticipation of reaction time and exercise tasks. Journal of Experimental Psychology, 1967,76, 642-648. EI,LIOTT, R. Physiological activity and performance: A comparison of kindergarten children and young adults. Psychological Monographs, 1964, 78, No. 10, l-33. ELLIOTT, R. Physiological activity and performance in children and adults: A twoyear follow-up. Journal of Ezperimental Child Psychology, 1966, 4, 58-80. ELLIOTT, R. The motivational significance of heart rate. In P. A. Obrist, A. II. Black, J. Brener, and L. DiCara (Eds.), Contemporary trends in cardiouascttlnr psychophysiology. Chicago : Aldine-Atherton, 1973. HERRINGTON, L. P. The relation of physiological and social indices of activity level. Studies in personality, contributed in honor of Lewis M. Terman. New York: McGraw-Hill, 1942. Pp. 125-146. HIGGINS, J. D. Set and uncertainty as factors influencing anticipatory cardiovascular responding in humans. Journal of Comparative and Physiological Psychology, 1971, 74, 272-283. JENNINGS, J. R., AVERILL, J. R., OPTEN, E. M., & LXARUS, R. S. Some parameters of heart rate change: Perceptual versus motor task requirements, noxiousness, and uncertainty. Psychophysiology, 1971, 7, 194-212. KURTZ, T. E., LINK, R. F., TUKEY, J. W., & WALLACE, D. L. Short cut multiple comparison for balanced single and double classifications. Part 2: Derivations and approximations. Biomet~ika, 1965, 52, 485-498. LACEY. J. I. The evaluation of autonomic responses: Toward a general solution. Annals of New York Academy of Science, 1956,67, 12%164. L.~cEY, J. I. Somatic response patterning and stress: Some revisions of activation theory. In M. H. Appley and R. Trumbull (Eds.), Psychological stress: Issues in Tesearch. New York: Appleton-Century-Crofts. 1967. Pp. 14-42. LINDQUIST, E. F. Design and analysis of experiments in Psychology and Education. Boston : Houghton Mifflin Company, 1953. MALMO, R. B. Cognitive factors in impairment: A neuropsychological study of divided set. Journal of Experimental Psychology, 1966,71, 184-189. MEYERS, K. A., & ORRIST. P. A. Psychophysiological correlates of attention in children. Paper presented at the annual meeting of the Society for Psychophysiological Research, Boston, 1972. BRUNING,
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