Biological Psychology 8 (1979) 1-29 © North-Holland Publishing Company
T H R E E EXPERIMENTS ON THE E F F E C T S OF INFORMATION F R E Q U E N C Y AND FEEDBACK TIMING ON INSTRUCTED H E A R T R A T E SPEEDING CRAIG T. TWENTYMAN *
State University of New York at Binghamton, Binghamton, New York, U.S.A. Accepted for publication 12 October 1978
Three experiments are reported comparing different biofeedback displays in a heart rate speeding task. The first experiment examined the effects of heart rate feedback presented at three frequencies in a fixed-time format. Information was given at 0.5-see, 2-see and 8-see intervals. Results indicated that both the 0.5-see and 8-see groups' speeding performances were superior to that of the 2-see group. The second experiment compared a 1-see fixed-time group with groups receiving displays in which feedback was presented synchronously with systole. Feedback was synchronized either with every heart beat or every tenth beat. The one-beat group was superior to both the 1-see and 10-beat groups. Experiment III again presented displays which terminated with every beat or every tenth beat. However, in the previous experiment heart interval information was presented only briefly at the systole ending the sample period. In Experiment III, criterion terminations remained on the feedback screen throughout the subsequent interval. Thus, subjects did not have the additional task of attending to very briefly presented information. Nevertheless, speeding performances of the one-beat group were again superior to that attained by the 10-beat group. In all experiments a relationship between increased respiratory and skin conductance levels and heart rate speeding performances was found, suggesting that heart rate speeding was part of a generalized pattern of arousal. It was concluded that instructed heart rate speeding is highly sensitive to changes both in the frequency of feedback presentation, and to the type of display (fixed-time or heart-time) presented.
1. Introduction (Experiment I) Recently, several experiments have demonstrated that more frequent presentation of information produces greater performance during instructed heart rate speeding tasks. Lang and Twentyman (1974) reported that a group receiving proportional visual feedback was superior to a group receiving binary feedback * Reprint requests should be sent to Craig T. Twentyman, State University of New York at Binghamton, Binghamton, New York, 13901. This research was conducted in fulFfllrnent of PhD requirement at University of Wisconsin Madison and was supported in part by a Grant to Peter J. Lang from the National Institute of Mental Health (MH 10993). The assistance of Michael Falconer in the development of computer software is gratefully acknowledged.
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during heart rate speeding tasks. Interestingly, group differences were found only during heart rate speeding and no differences were present during slowing. In an extension of Lang and Twentyman's (1974) study, Colgan (1977) presented three groups of subjects with binary, proportional or a combination of the two types of visual displays. Subjects attempted to increase and decrease heart rate over 10 sessions. The groups receiving proportional feedback demonstrated significantly better performances during both the speeding and slowing tasks than did the group receiving only binary feedback. As in the Lang and Twentyman (1974) report, no group respiratory effects were present. Finally, Gatchel (1974) reported that performances in a heart rate speeding task varied with the frequency of feedback presented to subjects. In this experiment subjects were presented feedback in which the lenght of a oscilloscope line was proportional to the amount of time between a specified number of heart cycles. Subjects in different feedback groups were presented feedback at the termination of every beat, every fifth beat or every tenth beat in both heart rate speeding and slowing sessions. Frequency of speeding did not effect performances during the slowing task. However, when heart rate performance scores for the speeding sessions were analyzed, a linear trend was found with the more frequent presentations of information producing greater speeding. Although several authors report that greater heart rate speeding can be achieved with more frequent presentations of information, the results of frequency manipulations during slowing tasks is less clear. That is, both Gatchel (1974) and Lang and Twentyman (1974) found that more frequent presentation of information did not produce greater slowing performances while Colgan (1977) reported group differences during both speeding and slowing tasks. The magnitude of slowing performances in all of these studies, however, were considerably smaller than those achieved during speeding. Although one might be tempted to interpret the relative lack of slowing effects as due to low baseline levels, another possibility also exists: factors inherent to the feedback displays might have disrupted slowing performances. In the one-beat displays employed in this laboratory (Gatchel, 1974, Lang and Twentyman, 1974), subjects in the speeding tasks received more frequent reinforcement (presentation of the word GOOD) across trials as they were successful. For example, across trial periods during a speeding task, subjects who uniformly increased their heart rate from 60 to 70 and then 80 bpm would receive increases in the number of reinforcements first by 10 and then by 20 presentations per minute. During slowing trials, however, if subjects slowed their heart rate first by 10 and then by 20 bpm across trials, they would receive 10 and then 20 fewer presentations of reinforcement each minute. Thus, rate of reinforcement may have adversely affected slowing performances. In addition, Colgan's (1977) Finding that a proportional display was superior to a binary display in facilitating heart rate slowing is of considerable interest because his display did not include specific verbal reinforcement (the word GOOD) for task success. In other respects his display was
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similar to both the Gatchel (1974) and Lang and Twentyman (1974) display. In a test of whether the reduction of reinforcement across trials disrupted the learning of heart rate slowing, Lang and Twentyman (1977) presented fixed-time feedback displays to subjects. These proportional displays were generated by a small laboratory computer and consisted of visual information about averaged heart rate. The fixed-time displays exployed in this study differed from the standard beat-by-beat displays (Lang and Twentyman, 1974) in two ways. First, changes in the vertical marker line which provided information about task success and failure were not coincidental with systole. Secondly, informational changes were presented at the end of fixed-time periods rather than with the occurrence of a specified number of physiological events (e.g., at 1-sec or 6-sec intervals rather than at systole or at every fifth or tenth systole). Subjects were assigned to one of four groups: A standard one-beat group; a 1-sec fixed-time group; a 6-sec fixed-time group; or to a control group which participated in a perceptual-motor tracking task. Results indicated that all feedback groups differed from the control group during the slowing task but no differences between feedback groups were found. In the speeding task, however, significant differences between feedback groups were present. Surprisingly, both the one-beat and the 6-sec groups increased their speeding performances in the second session whereas the 1-sec groups performance fell off dramatically. Although it is unclear why the 1-sec group's performance deteriorated, one possibility is that subjects attempted to match respiration or heart rate changes to the frequency of the feedback display. Lang and Twentyman (1977) suggested that several physiological variables such as heart rate and respiration inspiratory period occur at periods of approximately 1 sec. It is possible that the rate of feedback may have interacted with the rate of one of the physiological variables to disrupt speeding performances. In the present experiment three separate fixed-time frequencies were used which were not employed in the Lang and Twentyman (1977) study. One group of subjects received feedback every 0.5 sec. Thus, this group was presented feedback displays which could provide information about changes in each heart cycle unless heart rate exceeding 120 bpm during feedback trials. A second group of subjects received feedback every 2 sec while the third group received feedback every 8 sec. The purpose of including feedback displays at these frequencies was to roughly match the rate of presentation in Gatchel's (1974) one.beat, five-beat, and 10-beat displays. The 0.5-sec and 2-sec frequencies displays were also selected because they were faster and slower than resting heart typically found ha college subjects. 2. Method Z l. Subjects
Subjects were 45 male undergraduate volunteers who received points to be applied towards a course grade for participation in the experiment. Prior to the
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experiment subjects were screened for a history of cardiovascular disease, medications, or druguse. 2.2. Apparatus
Heart rate, skin conductance, the various measures of respiratory activity (respiration period, expiration period, total period, inspiration/expiration ratio, and respiration amplitude) were continuously recorded on a Beckman Type R Dynograph. Subjects were seated in a reclining chair facing a DEC VR-12 oscilloscope which was slaved to a DEC PDP-12 computer. The subject's room was adjacent to that in which the polygraph and computer were housed and was illuminated by a small light placed to one side of the subject's chair. This room was sound-shielded from the adjacent equipment room. The analogue EKG signals from the polygraph was channelled through a Tek. tronix Model RM 503 oscilloscope which was utilized to trigger off of successive R-waves. These triggers drove an external register on a Digital Equipment Corporation PDP-12 laboratory computer, which measured the time between successive R - R intervals to the nearest 0.004 sec. A Schmitt trigger, connected to the voltage output of the respiration channel of the polygraph, drove another external register on the PDP-12 which measured the time between successive respiration cycles. Skin conductance levels were amplified and the output was sent to an analogue to digital converter. The computer sampled the SCL 10 times per second and the range of 0-20/amhos was divided into 512 units. 2.3. Physiological measures
Heart rate was recorded with two Beckman miniature electrodes placed over the lower anterolateral ribs. Electrodes were attached after the skin was prepared by a thorough scrubbing with rubbing alcohol. Skin conductance was recorded with two Beckman silver-silver chloride electrodes attached to the thenar and hypothenar eminences of the subject's nondominant hand. These .electrodes were attached first to allow time for hydration to occur and were placed on the subject's hand after a rubbing with tissue wetted distilled water. K - Y surgical jelly was used as a conducting medium. Respiration was measured by two Parks 3-inch mercury strain gauges wired in series which were taped over the sternum and diaphragm. The signals were sent to a 9853 mercury strain gauge coupler set on the DC position. The output from this channel was sent to the computer for analysis of respiration depth and period mea. sures. Inspiratory and expiratory periods were recorded on-line to the nearest tenth of a second while amplitude measures were scored in A/D units. 2. 4. Heart rate display
With each of the three feedback presentation rates, analogue information about the subject's heart rate during the averaging period was visually presented in the
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form of a horizontal line extending from the extreme left edge of the oscilloscope and terminating at some point on the scope face, with its end marked by a short vertical slash. The length of the line was directly proportional to the average of the subject's heart rate for the time period averaged. At the termination of an averaging interval, the next average was computed by the computer and it caused the termination line to jump immediately to a new length. This line was longer and extended further to the right if the inter-beat interval was slower than that of the previous interval or shorter if the average heart rate of the current" interval was faster than the previous interval. Identical averages over consequetive periods were indicated by a brief disappearance of the short vertical slash. This also occurred if no R - R interval was present within a specific interval. The display also contained a fLxed vertical line, running from the top to the bottom of the screen. This line served as a criterion marker for the subject. When the subject was requested to speed his heart rate, his task was to terminate the horizontal line to the left of the marker. If the subject was successful the word GOOD was illuminated on the screen for each success. This occurred coincident with the horizontal line jumping to a position on the left of the criterion line. The criterion line was initially set at the subject's median R - R interval which was established during the 1-min period during which the subject was initially asked to perform the speeding task but was not presented with feedback (i.e., the try period). The target could be altered subsequently, depending on subject performance, and was modified as in previous experiments from this laboratory (Lang and Twentyman, 1974).
2. 4.1. Tracking display This display was similar to that used in the heart rate sessions with the following differences. First, the line was a moving display such that a sweeping line was generated by the computer beginning at the far left of the screen and terminating somewhere near the center of the screen. Secondly, this display was presented on the average of 60 sweeps per minute. Individual sweeps, however, terminated either on the left or the right of the vertical center line and were programmed to do so in a random order. The subject's task was to monitor the lines and press a microswitch whenever the line terminated on the lefthand side of the display. The work GOOD was illuminated on the screen if the subject's button press occurred within 400 msec of the termination. 2.5. Experimental design Subjects were randomly assigned to one of three experimental groups: (1) a group which received feedback every 0.5 see; (2) a group which received feedback every 2 sec; (3) a group which received feedback every 8 seconds. Each subject came to the laboratory for three separate sessions. The initial session for all subjects consisted in monitoring the tracking task display and participating in time estimation
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trials. Following the tracking session all subjects participated in two sessions of heart rate speeding. Both the tracking session and the two heart rate control sessions followed a standard time-phase format which allowed for comparisons across groups and sessions. 2.6. Procedure
All subjects were individually interviewed during an initial session. At this time the general purpose of the experiment was described and subjects were questioned regarding any history of cardiac, psychiatric or other disorders and were asked about medicine or drug usage. Subjects who were free of cardiovascular and other disorders and were willing to participate in the experiment were then assigned to one of the experimental groups. The time of day was held constant for each subject thus avoiding systematic changes in circadian rhythms. The three experimental sessions were conducted within a week. The procedure for each of the three experimental sessions was as follows. Subjects were seated in a comfortable chair and the electrodes and strain gauges were attached. Following this, the experimenter left the room to adjust the polygraph settings and set the triggering in an adjacent room. The experimenter returned to demonstrate the display and read a standard set of instructions according to the experimental group in which the subject was assigned. Instructions for all subjects included statements to breathe normally and not to move in the chair as movements might disrupt the physiological recording. Following any questions by the subjects the experimenter left the room and the experimental control of the session was turned over to the PDP-12. The format of all the sessions involved 18 cells, the content of which varied as a function of the session (tracking or heart rate control). The arrangement of the cells is exemplified by the pattern for the heart rate control sessions. Each session began with a 3-min baseline period during which no display was present. The subject was then asked to speed his heart for 1 min during which no display was present. This attempt is designated as the try period. The subject was then asked to speed for 3 min during which the feedback display was presented. After the feedback period, subjects were instructed to continue speeding their heart rate but feedback was withheld. This transfer period was 1 min and was also followed by a 1-min rest period. The cycle of tasks was then repeated four more times, for a total of five trials. The final period in each session was a 3-min final baseline period. The format of the tracking sessions were comparable to the heart rate sessions except that during feedback periods subjects pressed a small microswitch whenever a computer generated display line terminated on the left side of the verticle criterion line. During the initial try and subsequent transfer periods, subjects estimated 10-see time periods. At the termination of each of the estimated 10-sec periods, subjects pressed a small microswitch.
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3. Results 3.1. Tracking session The heart rate baseline and deviation scores for the initial tracking session, in which all subjects tracked a computer-generated display, were analysed. No median differences in heart rate were found among the groups either during the initial baseline period or during the first 'time estimation' procedure. Group effects were also not present fo~,"the heart rate median scores during any of the feedback, transfer or rest periods. Analysis of data from the other physiological response systems also indicated that no significant group differences were found in the respiration or skin conductance measures during baseline, tracking or time estimation periods.
3.2. Heart rate control sessions 3.2.1. Baseline and try periods Separate analysis for baseline periods and for the initial try periods were carried out for the heart rate control sessions. No significant differences were found between groups during the initial baseline periods in any of the physiological response systems. There were also no differences between groups during the initial try periods except for heart rate median deviation scores. For these scores, a significant Group X Session interaction was found (F = 4.23, df = 2.42, p < 0.05) indicating that the 2-sec group's performance was disrupted even prior to feedback during the second session whereas the 0.5-sec group's performance increased substantially. 3.2.1.1. Analysis o f feedback, transfer and rest periods. Heart rate performance scores were analysed and a significant Group X Session interaction was found during the feedback trial periods (F = 5.17, df = 2, 42, p < 0.01). As canbe seen in fig. 1, there were virtually no differences between groups during the first speeding session. It can also be seen that in the second speeding session the 2-sec group's performances falls off relative to the other groups which are about equal. Analysis for individual sessions indicated that no group differences were present during the first speeding session but significant group effects were found during the second session (F = 3.95, df = 2, 42, p < 0.05). Subsequent t tests indicated that the 2-sec group significantly differed from each of the other groups (0.5-sec and 2-sec group t = 2.62, d f = 4 2 , p < 0 . 0 5 ; 2-sec and 8-sec t = 2 . 1 8 , d f = 4 2 , p < O . 0 5 ; 0.5-sec and 8-sec t = 0.44, df = 42, p > 0.05) which did not differ from each other. A similar pattern was also found for the transfer periods with the exception of the fact that a significant Group effect (F = 3.54, df = 2, 42, p < 0.05) was found in addition to the Group X Session interaction (F = 3.87, df = 2, 42, p < 0.05). Again, there was little difference between groups during the first session but by the second session the 2-sec group's performance deteriorated while the other group's perfor-
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C.T. Twentyman ~Instructed heart rate speeding
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TRIALS Fig. 1. Mean change during feedback trials of physiological variables assessed in Experiment I.
mances increased. Individual session analysis indicated that significant differences were only found during the second speeding session (F = 6.28, df = 2, 42, p < 0.01). Subsequent t tests again demonstrated that the 2.sec group's performance fell off relative to the other groups (0.5-see and 2-sec group t = 3.43, df = 42, p < 0.05; 2-sec and 8-sec group t = 3.42, df = 42, p < 0.05; 0.5-sec and 8-sec group t = 0.01, df = 42, p > 0.05). When rest period median heart rates were analyzed no significant group or session effects were found. A significant trial effect was present (F = 3.46, df = 4, 168, p < 0 . 0 1 ) indicating that decreases in heart rate generally occurred across a session. Heart rate inter-quartile-range (IQR) was also analyzed during feedback, transfer and rest periods. No group or session effects were present but significant trial effects were found during each of these periods (F's respectively of 9.30, 4.00 and 3.87, dfs = 4 , 1 6 8 , all ps less than 0.01). In general, heart rate variability decreased
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during the feedback and transfer trials but increased across the session during rest periods. 3.2.2. Skin conductance Analysis of the other physiological response systems was also accomplished. Although some of these measures show differences between the groups, this pattern is not consistently found across the responses measured. For example, no group differences were found in skin conductance levels and only some of the respiration measures show group differences. During feedback trials only a Session X Trial interaction was found for skin conductance (F = 2.63, df = 4, 168, p < 0.05) indicating that during the first speeding session the change in skin conductance decreased across the session whereas in the second session, skin conductance increased slightly. 3. 2.3. Respiration measures
When analyses of respiration were conducted a more complex picture emerged. Respiration inspiratory period median analysis yielded no significant group effects during any of the trial periods. Respiration total period scores yielded no group differences during feedback trials although the 2-sec group demonstrated somewhat smaller decreases than the other groups. The only significant effect for this measure was during the transfer periods when medians were analysed. A significant group effect was demonstrated (F = 6.36, df = 2, 42, p < 0.005) indicating that the 2-see group showed smaller changes than the other groups (2-sec vs. 0.5-sec and 8-sec, ts of 2.62, 2.42, dfs = 42, p < 0.05). No group effects were found for respiration average amplitude median scores. Respiration ratio Group effects were found during both the feedback (F = 6.11, df = 2, 42, p < 0.005) and transfer periods (F = 4.92, df = 2, 42, p < 0.025). In general, these effects indicate that the pattern of respiration remained virtually the same for the 2-sec group while the other groups showed increased inspiratory patterns during the second session. No systematic differences were found in the standard deviation scores of the respiration ratio measure except for a significant Session effect (F = 4.72, df = 1, 42, p < 0.05) during the transfer periods indicating that variability was greater during the first session. Analyses of respiratory expiration period medians indicated that significant Group (F = 6.15, df = 2, 42, p < 0.005) and Group X Trial effects (F = 2.35, df = 8,168, p < 0.025) were present but this was only during the transfer periods. In comparison to the other groups the 2-sec group had smaller decreases in expiration periods (0.5-see vs. 2 sec t = 2.30, df= 42, p < 0.05; 0.5 see vs. 8 see t = 1.92, df= 42, p < 0 . 0 5 ; 2sec vs. 8sec t = 0 . 3 5 , p > 0 . 0 5 ) . Although heart rate changed dramatically between sessions for the different groups, respiratory expiration period did not systematically vary across sessions.
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3. 2. 4. Cell-type analyses Each of the physiological responses was also subjected to analysis with type of trial (feedback, transfer or rest) being a factor in addition to the group, session and trial factors. No group by cell-type interactions were found. However, a number of significant cell-type factors were present. That is, heart rate was higher during feedback trials than during transfer (F = 7.37, df = 1, 42, p < 0 . 0 1 ) or rest trials (F = 41.93, df= 1,42, p < 0.001) and transfer trials heart rate was in turn also greater than that found during rest trials (F = 46.12, df = 1,42, p < 0.01). Similar findings were also present for skin conductance level (F's respectively of 9.76, 22.28 and 10.81, df = 1, 42, all ps < 0.005); respiration inspiratory period (F's respectively of 5.89, 12.39 and 1.08, dfs = 1, 42, all ps < 0.025) and total respiratory period (F's respectively of 12.18, 67,13 and 24.18, dfs = 1,42,all ps < 0.005). No cell-type differences were found between feedback and transfer periods in respiration average amplitude. However, transfer-rest (F = 12.18, df = 1, 42, p < 0 . 0 0 5 ) and feedback-rest differences (F = 10.61, df = I, 42, p < 0.005) were present for this measure. 3.2.5. Correlational data All the physiological variables were correlated for each of the two speeding sessions during baseline, try, feedback, transfer and rest periods. A number of findings were consistent for both the individual group correlations as well as for the combined sample of subjects from all three groups. The highest correlations were generally found for the same measure when feedback and transfer periods were correlated. For example, correlations of the same measure (heart rate, skin conductance, respiration periods, etc.) during these periods ranged from 0.69 to 0.97. Correlations between response systems during the same trial periods were generally modest and ranged from 0.34 to 0.52 for the combined groups. In general, changes in one system were related to changes in other systems. Thus, elevations in heart rate can be seen as part of a more generalized trophotropic response in which multiple systems are involved. 3.2.6. Base levels Little evidence for an initial values effect was found when the combined group scores were correlated. That is, heart rate correlations were examined during both sessions and median scores during the initial baseline correlated --0.07, -0.08 with the same measure during the feedback and transfer periods in the first session. These correlations increase during the second session to -0.33 and -0.11. When individual groups were examined, however, stronger evidence appeared. For the 0.5-see group baseline HR medians correlated -0.30 and -0.17 during the first session with performance scores from the feedback and transfer periods and -0.58 (p < 0.05) and -0.16 during the second session. A similar pattern was also found for the 8-sec group, with correlations of -0.19 and - 0 . 3 0 during the first session and -0.45 (p < 0.07) and -0.33 during the second session although none of the cor-
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relations achieved significance. It is interesting to note that similar patterns were not evident in the 2-sec group. Correlations of 0.25 and 0.16 were found during the first session and 0.10 and 0.34 during the second session. This suggests that during feedback trials, the type of feedback presented differentially affected subjects with high and low initial heart-rate. Subjects with high initial heart rate were more likely to show greater increases in the 2-sec group whereas the law of initial value held for the other groups. This finding suggests a possible explanation for the disrupted speeding performances in the 2-sec group. That is, subjects whose heart periods were longest might have been in a critical frequency range in which the feedback display disrupted their speeding performances because it was presented at a rate slightly slower than their heart cycle. 3.2. 7. Skin conductance
Skin conductance measures were not strongly related to any of the heart rate measures in the entire sample or in each of the subgroups. When all the groups were combined the baseline SC median scores were negatively correlated with skin conductive level during the feedback and transfer periods during the second session (first session, +0.13 and +0.09; second session, -0.27 and -0.32). Individual groups differed but the correlations between baseline skin conductance and skin conductance during the feedback and transfer periods was not strong (0.5-sec group, first session, -0.10 and -0.02; second session, -0.11 and -0.20; 2-see group, first session, +0.11 and +0.37, second session -0.30 and -0.34; 8.sec group, -0.11 and -0.13, second session, -0.44 and -0.46). 3.2.8. Respiration measures
Respiration measures were also included in the correlations. Total respiration period during the initial baseline period was negatively correlated with respiration during the feedback and transfer sessions (first session, -0.49, p < 0.05, and -0.24; second session, -0.35, p < 0.05, and -0.16) when all groups were combined. A different pattern emerged when one looked at the separate groups. The 0.5-sec group showed the strongest negative correlations between these periods (first session, -0.59 and -0.72; second session, -0.70 and -0.56, all ps < 0.05) while the 2-sec group had correlations of (first session, -0.32 and 0.32; second session, -0.20 and -0.08). The 8-sec group showed correlations of (first session, -0.46, p < 0.05, and -0.36; second session, -0.30 and -0.27). These correlations suggest that the 2-sec group's respiratory changes were related the least to initial base levels. Thus, as in heart rate, the pattern of respiratory changes varied across groups for subjects with high and low initial levels. 4. Discussion
The results from this experiment demonstrate that subjects presented with fixedtime feedback displays can increase their heart rate. Greater speeding was produced
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during feedback than during transfer trials, indicating that feedback augments performances achieved when subjects are merely instructed to increase heart rate. Performance during transfer was also greater than during rest indicating that some speeding can be achieved even when feedback displays are removed. Two Findings in this experiment are particularly striking. First, heart rate performances in the 2-sec group fell off substantially during the second speeding session. This is similar to the results of Lang and Twentyman (1977) who reported that a 1-sec flExed-time feedback display disrupted speeding performance during the second speeding session. Although the correlation between baseline heart rate and performances were small, a complex picture emerges. In the 0.5-sec group especially, subjects with higher heart rates produced smaller increases whereas the pattern was reversed for subjects in the 2-sec group. This suggests that a feedback display presenting information at rates slightly slower than the subject's heart rate may produce performance decrements. Another possibility, that the 2-sec group matched respiration rate to the frequency of the display and thus affected heart rate, is also possible. Correlational evidence exists suggesting that a pattern of changes between respiration and heart rate was disrupted for the 2-sec group. That is, heart rate performances were closely related to changes in total respiratory period for the 0.5-sec group during feedback trials (rs = 0.60 and 0.60 for speeding sessions one and two, both ps < 0.05) whereas the 2-sec group demonstrated reversed or smaller correlations (rs = -0.23 and 0.38, ps > 0.05). This finding suggests that the 2-sec display may have disrupted a complex cardiopulminary pattern which was established in subjects who were more successful in speeding their heart rate. The second surprising finding is that the 8-sec group's performance was comparable to a group receiving feedback every 0.5-sec. A number of authors have reported that subjects who received frequent feedback have produced greater speeding results than subjects who were presented information at less frequent intervals (Gatchel, 1974; Lang and Twentyman, 1974). It should be noted that these studies presented feedback which was tied to a cardiovascular event (i.e., systole). There are several differences between the 8-sec fixed-time group and the subjects who received feedback every five or 10 beats (Gatchel, 1974). In the fixed-time format the target line cannot sweep across the screen. Instead, the marker jumps instantaneously from one position to another with changes in the periods' average heart rate. Thus, fixed-time subjects are provided with a knowledge of exact amount of change produced during each 8-sec feedback period relative to the preceding 8-see period. In contrast, subjects receiving 10-beat feedback (Gatchel, 1974) may not have been able to determine how much improvement occurred during consecutive 1-beat intervals because the display swept across the screen and the demands of the task may have interfered with the subjects' memory of the exact location of the previous sweep. Another major difference between the displays is the fact that the FExed-time groups did not receive feedback coincident with systole. Although the jump dis-
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play may have served to increase speeding performances in the 8-sec group, it should be noted that the lack of a linear relationship between feedback frequency and speeding performances may also have been due to small performances in the 0.5-see group. Although results have been varied from study to study, when subjects have been given beat by beat information (Gatchel, 1974) larger performances have been achieved than were found in the 0.5-sec group in the present experiment. This suggests that any information about heart rate or interval may be effective in producing some speeding. What is most effective, however, is a display which presents specific temporal information about changes in the organ in addition to information about performance changes. Results from the other physiological responses are inconsistent with respect to the specificity of heart rate increases. No group differences were found in measures of skin conductance. Several measures of respiration, however, revealed significant group effects which were similar to the results found in heart rate. This suggests that respiratory maneuvers and especially those related to respiratory period, varied more closely with heart rate performances than did changes in skin conductance.
5. Introduction (Experiment II) The results of the previous study suggest that fixed-time displays differ from feedback displays which present information on a beat by beat basis. The purpose of this experiment is to replicate the Findings of both Gatchel (1974) and Lang and Twentyman (1977). Three groups of subjects were employed and received Onebeat, 10.beat and 1-sec feedback displays. Although Gatchel (1974) reported finding no group effects in a measure of respiration period, he suggested that respiration amplitude or other physiological measures may have been more sensitive to changes in the heart rate speeding tasks. Consistent with this view, Sroufe (1971) demonstrated that respiration amplitude greatly affects both heart rate and heart rate variability whereas respiration period effects were smaller. In the present study, several measures of respiration in addition to the two (total respiratory period and total respiration period interquartile range) employed by Gatchel (1974) were recorded. Skin conductance level was also included in the present study. The additional physiological measures were recorded to determine whether changes in respiratory or skin conductance levels occurred during the speeding tasks and were related to changes in heart rate. In the previous experiment differences were only found on some of the respiration measures. This suggests that the use of only one response measure such as total respiratory period may not provide sufficient information about the change in respiratory patterns which occur with changes in heart rate.
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6. Method 6.1. Subjects 36 males recruited from bulletin boards at the Phychology Building served as subjects. Each person was paid $2.00 per session for participating in the experiment. All subjects were screened during the initial interview for any history of cardiovascular or other diseases and for drug use.
6.2. Apparatus and physiological measures The apparatus was identical to that described in Experiment I. The same physiological measures that were recorded during the first experiment were also obtained in this experiment.
6.3. Experimental design Subjects were randomly assigned to one of three groups. The first group received a 1-sec fixed-time feedback display in which heart rate was averaged every second. This display was identical to that described in the previous experiment. The second and third groups received feedback displays in which the horizontal lines began sweeping across the screen from the far left side and was terminated by either the next R wave of the cardiac cycle or by the tenth R wave. Thus, all groups saw an analogue feedback display but only the second and third groups were presented with a display in which the termination of the cycle was coincident with an event in the cardiac waveform (i.e., the R wave). In all other respects, such as the presentation of the word GOOD or the setting of the criterion marker line, the one-beat and 10-beat groups saw an identical display to that presented to the 1-sec subjects. Prior to the two sessions of heart rate control all subjects participated in one session of a perceptual motor tracking display which was identical to that described in the previous experiment with the following exception: one-third of the subjects tracked a sweeping display which was randomly generated at the rate of approximately 60 sweeps per minute. Another third of the subjects tracked a display which was generated at the rate of 10 sweeps per minute. The remaining third of the subjects in each group tracked a visual display which changed at the rate of approximately 60 times per minute but this display instantaneously jumped from position to position in a manner visually identical to that seen in the 1-sec display. This display was, of course, randomly generated by the computer. The rationale behind presenting the different displays was to ensure that familiarity with a display did not augment the ability of any group of subjects to control their heart rates relative to the other groups.
C T. Twentyman /Instructed heart rate speeding
15
6.4. Procedure
The procedure was identical to that described in the previous experiment.
7. Results 7.1. Tracking session
No significant simple Group differences were found On any of the heart rate baseline measures or during the feedback transfer or rest periods. There were also no significant Group differences in any of the skin conductance or respiration measures. 7.2. Heart rate speeding sessions
Initial baseline periods and try periods were analysed for all physiological responses. No significant Group or Group X Session interactions were found. When heart rate performance scores were analysed, significant Group differences were found during the feedback trials (F = 4.88, df = 2, 33, p < 0.025). As can be seen in fig. 2, no differences between groups were found during the first speeding session. During the second speeding session, however, the one-beat group showed greater performances during feedback trials than either the 1-see or 10-beat groups (t's respectively of 3.03, 3.04, df = 33, p < 0.05) which did not differ. Similar but somewhat smaller differences were found during the transfer periods (Group F = 4.27, df -- 2, 33, p < 0.025). Again, these differences were largely due to the effects of the one-beat group (one-beat vs. 1-see and lO-beat t's of 3.10, 2.79, df = 33, p < 0.05). 7.Z 1. Skin conductance Several group effects were also found in the measures of skin conductance level. All groups increased conductance over the initial base periods but the one-beat showed increased conductance relative to the other groups during feedbacl~ trials (group F = 7.55, df = 2, 33, p < 0.005). Group effects were also found during the transfer and rest trials (F values respectively of 5.95 and 4.31, df's = 2, 33, p's less than 0.025). Subsequent analyses indicated that the one-beat group differed from the other two groups which did not show differences (feedback t's = 2.59, 2.16, transfer t's = 2.45, 1.92, df's = 33, p's < 0.05). Significant trial effects during the feedback periods (F = 2.27, df = 4, 132, p < 0 . 0 5 ) indicated greater conductance across the session whereas the significant rest trial effects (F--7.08, df--4, 132, p < 0.025) indicated a general reduction of conductance during these periods. The only difference found in skin conductance level variability was a significant trial effect (F =3.51, d f = 4 , 132, p < 0 . 0 1 ) which was present during transfer periods. This indicates that a generally smaller variability was present during later trials.
16
C.T. Twentyman /Instructed heart rate speeding
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7.Z2. Respiration measures Although respiration measures also followed the pattern of heart rate changes, these results were not consistent. Only a Group X Session interaction was found for respiration inspiratory period medians during the feedback trials (F = 3.27, df = 2, 33, p less than 0.05) and indicates that the one-beat group had relatively greater decreases in inspiratory period during the second session whereas the other groups had relatively greater increases in the second session. When individual sessions were analysed, however, differences were not found and comparisons of individual groups revealed no differences. There were few systematic changes in respiration expiratory period scores. During feedback trials there was a significant session effect (F = 7.02, df = 1.33, p less than 0.025) indicating that the expiratory period decreases were generally smaller during the second session. Significant group effects were found for expira-
c.T. Twentyman / Instructed heart rate speeding
17
tory period IQR during the transfer (F = 4.06, df = 2, 33, p less than 0.025)and rest periods (F = 4.25, df = 2, 33, p less than 0.025). In general, the one-beat group demonstrated more variability than the other groups which did not differ from each other. The measure of respiration total period did not show differences between groups. While patterns similar to those found in respiration inspiratory period were present in this measure, analyses did not reveal significant differences. Total respiration period, however, did demonstrate a significant session effect (F = 8.04, df= 1, 33, p less than 0.01) with greater decreases present during the first session. The respiration I/E ratio mean revealed only a significant session effect (F = 4.79, df = 1,33, p < 0.05) during feedback trials which indicated a relative movement toward less expiration during the second session. During the transfer periods a group effect was present (F = 4.81, df = 2, 33, p < 0.025) with the one-beat group demonstrating greater relative expirations when compared to the lO-beat or 1-sec group (t's = 2.01, 2.00, df's = 33, p's < 0.05). Again, the 10-beat and 1-sec groups did not differ. 7. 2. 3. Cell- type analyses
Analyses of variance including cell.type (feedback, transfer and rest trials) indicated that no group X cell-type interactions were significant for any of the response measures. Cell-type was not a significant factor for heart rate when feedback and transfer trials were compared but was a significant factor when feedback-rest and transfer-rest trials were compared (F's respectively of 22.84 and 21,32, df's = 1, 33, p's < 0.001) Differences between feedback-rest and transfer rest trials were also found for respiration inspiratory period (F's of 16.86 and 14.29, df's = 1,33, p's < 0.001), total respiratory period (F's of 29.71 and 19.83, df's = 1, 33, p's < 0.001) and for skin conductance levels (F's of 7.14 and 4.61, df's = 1, 33, p ' s < 0.05). In addition, feedback-transfer cell-type differences were also significant or marginally significant for respiratory inspiration period (F = 3.43, df = 1, 33, p < 0.10), total respiratory period (F = 20.05, df= 1, 33, p
T H R E E EXPERIMENTS ON THE E F F E C T S OF INFORMATION F R E Q U E N C Y AND FEEDBACK TIMING ON INSTRUCTED H E A R T R A T E SPEEDING CRAIG T. TWENTYMAN *
State University of New York at Binghamton, Binghamton, New York, U.S.A. Accepted for publication 12 October 1978
Three experiments are reported comparing different biofeedback displays in a heart rate speeding task. The first experiment examined the effects of heart rate feedback presented at three frequencies in a fixed-time format. Information was given at 0.5-see, 2-see and 8-see intervals. Results indicated that both the 0.5-see and 8-see groups' speeding performances were superior to that of the 2-see group. The second experiment compared a 1-see fixed-time group with groups receiving displays in which feedback was presented synchronously with systole. Feedback was synchronized either with every heart beat or every tenth beat. The one-beat group was superior to both the 1-see and 10-beat groups. Experiment III again presented displays which terminated with every beat or every tenth beat. However, in the previous experiment heart interval information was presented only briefly at the systole ending the sample period. In Experiment III, criterion terminations remained on the feedback screen throughout the subsequent interval. Thus, subjects did not have the additional task of attending to very briefly presented information. Nevertheless, speeding performances of the one-beat group were again superior to that attained by the 10-beat group. In all experiments a relationship between increased respiratory and skin conductance levels and heart rate speeding performances was found, suggesting that heart rate speeding was part of a generalized pattern of arousal. It was concluded that instructed heart rate speeding is highly sensitive to changes both in the frequency of feedback presentation, and to the type of display (fixed-time or heart-time) presented.
1. Introduction (Experiment I) Recently, several experiments have demonstrated that more frequent presentation of information produces greater performance during instructed heart rate speeding tasks. Lang and Twentyman (1974) reported that a group receiving proportional visual feedback was superior to a group receiving binary feedback * Reprint requests should be sent to Craig T. Twentyman, State University of New York at Binghamton, Binghamton, New York, 13901. This research was conducted in fulFfllrnent of PhD requirement at University of Wisconsin Madison and was supported in part by a Grant to Peter J. Lang from the National Institute of Mental Health (MH 10993). The assistance of Michael Falconer in the development of computer software is gratefully acknowledged.
2
C.T. Twentyman/Instructed heart rate speeding
during heart rate speeding tasks. Interestingly, group differences were found only during heart rate speeding and no differences were present during slowing. In an extension of Lang and Twentyman's (1974) study, Colgan (1977) presented three groups of subjects with binary, proportional or a combination of the two types of visual displays. Subjects attempted to increase and decrease heart rate over 10 sessions. The groups receiving proportional feedback demonstrated significantly better performances during both the speeding and slowing tasks than did the group receiving only binary feedback. As in the Lang and Twentyman (1974) report, no group respiratory effects were present. Finally, Gatchel (1974) reported that performances in a heart rate speeding task varied with the frequency of feedback presented to subjects. In this experiment subjects were presented feedback in which the lenght of a oscilloscope line was proportional to the amount of time between a specified number of heart cycles. Subjects in different feedback groups were presented feedback at the termination of every beat, every fifth beat or every tenth beat in both heart rate speeding and slowing sessions. Frequency of speeding did not effect performances during the slowing task. However, when heart rate performance scores for the speeding sessions were analyzed, a linear trend was found with the more frequent presentations of information producing greater speeding. Although several authors report that greater heart rate speeding can be achieved with more frequent presentations of information, the results of frequency manipulations during slowing tasks is less clear. That is, both Gatchel (1974) and Lang and Twentyman (1974) found that more frequent presentation of information did not produce greater slowing performances while Colgan (1977) reported group differences during both speeding and slowing tasks. The magnitude of slowing performances in all of these studies, however, were considerably smaller than those achieved during speeding. Although one might be tempted to interpret the relative lack of slowing effects as due to low baseline levels, another possibility also exists: factors inherent to the feedback displays might have disrupted slowing performances. In the one-beat displays employed in this laboratory (Gatchel, 1974, Lang and Twentyman, 1974), subjects in the speeding tasks received more frequent reinforcement (presentation of the word GOOD) across trials as they were successful. For example, across trial periods during a speeding task, subjects who uniformly increased their heart rate from 60 to 70 and then 80 bpm would receive increases in the number of reinforcements first by 10 and then by 20 presentations per minute. During slowing trials, however, if subjects slowed their heart rate first by 10 and then by 20 bpm across trials, they would receive 10 and then 20 fewer presentations of reinforcement each minute. Thus, rate of reinforcement may have adversely affected slowing performances. In addition, Colgan's (1977) Finding that a proportional display was superior to a binary display in facilitating heart rate slowing is of considerable interest because his display did not include specific verbal reinforcement (the word GOOD) for task success. In other respects his display was
C.T. Twentyman /Instructed heart rate speeding
3
similar to both the Gatchel (1974) and Lang and Twentyman (1974) display. In a test of whether the reduction of reinforcement across trials disrupted the learning of heart rate slowing, Lang and Twentyman (1977) presented fixed-time feedback displays to subjects. These proportional displays were generated by a small laboratory computer and consisted of visual information about averaged heart rate. The fixed-time displays exployed in this study differed from the standard beat-by-beat displays (Lang and Twentyman, 1974) in two ways. First, changes in the vertical marker line which provided information about task success and failure were not coincidental with systole. Secondly, informational changes were presented at the end of fixed-time periods rather than with the occurrence of a specified number of physiological events (e.g., at 1-sec or 6-sec intervals rather than at systole or at every fifth or tenth systole). Subjects were assigned to one of four groups: A standard one-beat group; a 1-sec fixed-time group; a 6-sec fixed-time group; or to a control group which participated in a perceptual-motor tracking task. Results indicated that all feedback groups differed from the control group during the slowing task but no differences between feedback groups were found. In the speeding task, however, significant differences between feedback groups were present. Surprisingly, both the one-beat and the 6-sec groups increased their speeding performances in the second session whereas the 1-sec groups performance fell off dramatically. Although it is unclear why the 1-sec group's performance deteriorated, one possibility is that subjects attempted to match respiration or heart rate changes to the frequency of the feedback display. Lang and Twentyman (1977) suggested that several physiological variables such as heart rate and respiration inspiratory period occur at periods of approximately 1 sec. It is possible that the rate of feedback may have interacted with the rate of one of the physiological variables to disrupt speeding performances. In the present experiment three separate fixed-time frequencies were used which were not employed in the Lang and Twentyman (1977) study. One group of subjects received feedback every 0.5 sec. Thus, this group was presented feedback displays which could provide information about changes in each heart cycle unless heart rate exceeding 120 bpm during feedback trials. A second group of subjects received feedback every 2 sec while the third group received feedback every 8 sec. The purpose of including feedback displays at these frequencies was to roughly match the rate of presentation in Gatchel's (1974) one.beat, five-beat, and 10-beat displays. The 0.5-sec and 2-sec frequencies displays were also selected because they were faster and slower than resting heart typically found ha college subjects. 2. Method Z l. Subjects
Subjects were 45 male undergraduate volunteers who received points to be applied towards a course grade for participation in the experiment. Prior to the
4
C.T. Twentyman/Instructed heart rate speeding
experiment subjects were screened for a history of cardiovascular disease, medications, or druguse. 2.2. Apparatus
Heart rate, skin conductance, the various measures of respiratory activity (respiration period, expiration period, total period, inspiration/expiration ratio, and respiration amplitude) were continuously recorded on a Beckman Type R Dynograph. Subjects were seated in a reclining chair facing a DEC VR-12 oscilloscope which was slaved to a DEC PDP-12 computer. The subject's room was adjacent to that in which the polygraph and computer were housed and was illuminated by a small light placed to one side of the subject's chair. This room was sound-shielded from the adjacent equipment room. The analogue EKG signals from the polygraph was channelled through a Tek. tronix Model RM 503 oscilloscope which was utilized to trigger off of successive R-waves. These triggers drove an external register on a Digital Equipment Corporation PDP-12 laboratory computer, which measured the time between successive R - R intervals to the nearest 0.004 sec. A Schmitt trigger, connected to the voltage output of the respiration channel of the polygraph, drove another external register on the PDP-12 which measured the time between successive respiration cycles. Skin conductance levels were amplified and the output was sent to an analogue to digital converter. The computer sampled the SCL 10 times per second and the range of 0-20/amhos was divided into 512 units. 2.3. Physiological measures
Heart rate was recorded with two Beckman miniature electrodes placed over the lower anterolateral ribs. Electrodes were attached after the skin was prepared by a thorough scrubbing with rubbing alcohol. Skin conductance was recorded with two Beckman silver-silver chloride electrodes attached to the thenar and hypothenar eminences of the subject's nondominant hand. These .electrodes were attached first to allow time for hydration to occur and were placed on the subject's hand after a rubbing with tissue wetted distilled water. K - Y surgical jelly was used as a conducting medium. Respiration was measured by two Parks 3-inch mercury strain gauges wired in series which were taped over the sternum and diaphragm. The signals were sent to a 9853 mercury strain gauge coupler set on the DC position. The output from this channel was sent to the computer for analysis of respiration depth and period mea. sures. Inspiratory and expiratory periods were recorded on-line to the nearest tenth of a second while amplitude measures were scored in A/D units. 2. 4. Heart rate display
With each of the three feedback presentation rates, analogue information about the subject's heart rate during the averaging period was visually presented in the
C.T. Twentyman /Instructed heart rate speeding
5
form of a horizontal line extending from the extreme left edge of the oscilloscope and terminating at some point on the scope face, with its end marked by a short vertical slash. The length of the line was directly proportional to the average of the subject's heart rate for the time period averaged. At the termination of an averaging interval, the next average was computed by the computer and it caused the termination line to jump immediately to a new length. This line was longer and extended further to the right if the inter-beat interval was slower than that of the previous interval or shorter if the average heart rate of the current" interval was faster than the previous interval. Identical averages over consequetive periods were indicated by a brief disappearance of the short vertical slash. This also occurred if no R - R interval was present within a specific interval. The display also contained a fLxed vertical line, running from the top to the bottom of the screen. This line served as a criterion marker for the subject. When the subject was requested to speed his heart rate, his task was to terminate the horizontal line to the left of the marker. If the subject was successful the word GOOD was illuminated on the screen for each success. This occurred coincident with the horizontal line jumping to a position on the left of the criterion line. The criterion line was initially set at the subject's median R - R interval which was established during the 1-min period during which the subject was initially asked to perform the speeding task but was not presented with feedback (i.e., the try period). The target could be altered subsequently, depending on subject performance, and was modified as in previous experiments from this laboratory (Lang and Twentyman, 1974).
2. 4.1. Tracking display This display was similar to that used in the heart rate sessions with the following differences. First, the line was a moving display such that a sweeping line was generated by the computer beginning at the far left of the screen and terminating somewhere near the center of the screen. Secondly, this display was presented on the average of 60 sweeps per minute. Individual sweeps, however, terminated either on the left or the right of the vertical center line and were programmed to do so in a random order. The subject's task was to monitor the lines and press a microswitch whenever the line terminated on the lefthand side of the display. The work GOOD was illuminated on the screen if the subject's button press occurred within 400 msec of the termination. 2.5. Experimental design Subjects were randomly assigned to one of three experimental groups: (1) a group which received feedback every 0.5 see; (2) a group which received feedback every 2 sec; (3) a group which received feedback every 8 seconds. Each subject came to the laboratory for three separate sessions. The initial session for all subjects consisted in monitoring the tracking task display and participating in time estimation
6
C.T. Twentyman/Instructed heart rate speeding
trials. Following the tracking session all subjects participated in two sessions of heart rate speeding. Both the tracking session and the two heart rate control sessions followed a standard time-phase format which allowed for comparisons across groups and sessions. 2.6. Procedure
All subjects were individually interviewed during an initial session. At this time the general purpose of the experiment was described and subjects were questioned regarding any history of cardiac, psychiatric or other disorders and were asked about medicine or drug usage. Subjects who were free of cardiovascular and other disorders and were willing to participate in the experiment were then assigned to one of the experimental groups. The time of day was held constant for each subject thus avoiding systematic changes in circadian rhythms. The three experimental sessions were conducted within a week. The procedure for each of the three experimental sessions was as follows. Subjects were seated in a comfortable chair and the electrodes and strain gauges were attached. Following this, the experimenter left the room to adjust the polygraph settings and set the triggering in an adjacent room. The experimenter returned to demonstrate the display and read a standard set of instructions according to the experimental group in which the subject was assigned. Instructions for all subjects included statements to breathe normally and not to move in the chair as movements might disrupt the physiological recording. Following any questions by the subjects the experimenter left the room and the experimental control of the session was turned over to the PDP-12. The format of all the sessions involved 18 cells, the content of which varied as a function of the session (tracking or heart rate control). The arrangement of the cells is exemplified by the pattern for the heart rate control sessions. Each session began with a 3-min baseline period during which no display was present. The subject was then asked to speed his heart for 1 min during which no display was present. This attempt is designated as the try period. The subject was then asked to speed for 3 min during which the feedback display was presented. After the feedback period, subjects were instructed to continue speeding their heart rate but feedback was withheld. This transfer period was 1 min and was also followed by a 1-min rest period. The cycle of tasks was then repeated four more times, for a total of five trials. The final period in each session was a 3-min final baseline period. The format of the tracking sessions were comparable to the heart rate sessions except that during feedback periods subjects pressed a small microswitch whenever a computer generated display line terminated on the left side of the verticle criterion line. During the initial try and subsequent transfer periods, subjects estimated 10-see time periods. At the termination of each of the estimated 10-sec periods, subjects pressed a small microswitch.
C.T. Twentyman / Instructed heart rate speeding
7
3. Results 3.1. Tracking session The heart rate baseline and deviation scores for the initial tracking session, in which all subjects tracked a computer-generated display, were analysed. No median differences in heart rate were found among the groups either during the initial baseline period or during the first 'time estimation' procedure. Group effects were also not present fo~,"the heart rate median scores during any of the feedback, transfer or rest periods. Analysis of data from the other physiological response systems also indicated that no significant group differences were found in the respiration or skin conductance measures during baseline, tracking or time estimation periods.
3.2. Heart rate control sessions 3.2.1. Baseline and try periods Separate analysis for baseline periods and for the initial try periods were carried out for the heart rate control sessions. No significant differences were found between groups during the initial baseline periods in any of the physiological response systems. There were also no differences between groups during the initial try periods except for heart rate median deviation scores. For these scores, a significant Group X Session interaction was found (F = 4.23, df = 2.42, p < 0.05) indicating that the 2-sec group's performance was disrupted even prior to feedback during the second session whereas the 0.5-sec group's performance increased substantially. 3.2.1.1. Analysis o f feedback, transfer and rest periods. Heart rate performance scores were analysed and a significant Group X Session interaction was found during the feedback trial periods (F = 5.17, df = 2, 42, p < 0.01). As canbe seen in fig. 1, there were virtually no differences between groups during the first speeding session. It can also be seen that in the second speeding session the 2-sec group's performances falls off relative to the other groups which are about equal. Analysis for individual sessions indicated that no group differences were present during the first speeding session but significant group effects were found during the second session (F = 3.95, df = 2, 42, p < 0.05). Subsequent t tests indicated that the 2-sec group significantly differed from each of the other groups (0.5-sec and 2-sec group t = 2.62, d f = 4 2 , p < 0 . 0 5 ; 2-sec and 8-sec t = 2 . 1 8 , d f = 4 2 , p < O . 0 5 ; 0.5-sec and 8-sec t = 0.44, df = 42, p > 0.05) which did not differ from each other. A similar pattern was also found for the transfer periods with the exception of the fact that a significant Group effect (F = 3.54, df = 2, 42, p < 0.05) was found in addition to the Group X Session interaction (F = 3.87, df = 2, 42, p < 0.05). Again, there was little difference between groups during the first session but by the second session the 2-sec group's performance deteriorated while the other group's perfor-
8
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mances increased. Individual session analysis indicated that significant differences were only found during the second speeding session (F = 6.28, df = 2, 42, p < 0.01). Subsequent t tests again demonstrated that the 2.sec group's performance fell off relative to the other groups (0.5-see and 2-sec group t = 3.43, df = 42, p < 0.05; 2-sec and 8-sec group t = 3.42, df = 42, p < 0.05; 0.5-sec and 8-sec group t = 0.01, df = 42, p > 0.05). When rest period median heart rates were analyzed no significant group or session effects were found. A significant trial effect was present (F = 3.46, df = 4, 168, p < 0 . 0 1 ) indicating that decreases in heart rate generally occurred across a session. Heart rate inter-quartile-range (IQR) was also analyzed during feedback, transfer and rest periods. No group or session effects were present but significant trial effects were found during each of these periods (F's respectively of 9.30, 4.00 and 3.87, dfs = 4 , 1 6 8 , all ps less than 0.01). In general, heart rate variability decreased
C.T. Twentyman / Instructed heart rate speeding
9
during the feedback and transfer trials but increased across the session during rest periods. 3.2.2. Skin conductance Analysis of the other physiological response systems was also accomplished. Although some of these measures show differences between the groups, this pattern is not consistently found across the responses measured. For example, no group differences were found in skin conductance levels and only some of the respiration measures show group differences. During feedback trials only a Session X Trial interaction was found for skin conductance (F = 2.63, df = 4, 168, p < 0.05) indicating that during the first speeding session the change in skin conductance decreased across the session whereas in the second session, skin conductance increased slightly. 3. 2.3. Respiration measures
When analyses of respiration were conducted a more complex picture emerged. Respiration inspiratory period median analysis yielded no significant group effects during any of the trial periods. Respiration total period scores yielded no group differences during feedback trials although the 2-sec group demonstrated somewhat smaller decreases than the other groups. The only significant effect for this measure was during the transfer periods when medians were analysed. A significant group effect was demonstrated (F = 6.36, df = 2, 42, p < 0.005) indicating that the 2-see group showed smaller changes than the other groups (2-sec vs. 0.5-sec and 8-sec, ts of 2.62, 2.42, dfs = 42, p < 0.05). No group effects were found for respiration average amplitude median scores. Respiration ratio Group effects were found during both the feedback (F = 6.11, df = 2, 42, p < 0.005) and transfer periods (F = 4.92, df = 2, 42, p < 0.025). In general, these effects indicate that the pattern of respiration remained virtually the same for the 2-sec group while the other groups showed increased inspiratory patterns during the second session. No systematic differences were found in the standard deviation scores of the respiration ratio measure except for a significant Session effect (F = 4.72, df = 1, 42, p < 0.05) during the transfer periods indicating that variability was greater during the first session. Analyses of respiratory expiration period medians indicated that significant Group (F = 6.15, df = 2, 42, p < 0.005) and Group X Trial effects (F = 2.35, df = 8,168, p < 0.025) were present but this was only during the transfer periods. In comparison to the other groups the 2-sec group had smaller decreases in expiration periods (0.5-see vs. 2 sec t = 2.30, df= 42, p < 0.05; 0.5 see vs. 8 see t = 1.92, df= 42, p < 0 . 0 5 ; 2sec vs. 8sec t = 0 . 3 5 , p > 0 . 0 5 ) . Although heart rate changed dramatically between sessions for the different groups, respiratory expiration period did not systematically vary across sessions.
10
C.T. Twentyman / Instructed heart rate speeding
3. 2. 4. Cell-type analyses Each of the physiological responses was also subjected to analysis with type of trial (feedback, transfer or rest) being a factor in addition to the group, session and trial factors. No group by cell-type interactions were found. However, a number of significant cell-type factors were present. That is, heart rate was higher during feedback trials than during transfer (F = 7.37, df = 1, 42, p < 0 . 0 1 ) or rest trials (F = 41.93, df= 1,42, p < 0.001) and transfer trials heart rate was in turn also greater than that found during rest trials (F = 46.12, df = 1,42, p < 0.01). Similar findings were also present for skin conductance level (F's respectively of 9.76, 22.28 and 10.81, df = 1, 42, all ps < 0.005); respiration inspiratory period (F's respectively of 5.89, 12.39 and 1.08, dfs = 1, 42, all ps < 0.025) and total respiratory period (F's respectively of 12.18, 67,13 and 24.18, dfs = 1,42,all ps < 0.005). No cell-type differences were found between feedback and transfer periods in respiration average amplitude. However, transfer-rest (F = 12.18, df = 1, 42, p < 0 . 0 0 5 ) and feedback-rest differences (F = 10.61, df = I, 42, p < 0.005) were present for this measure. 3.2.5. Correlational data All the physiological variables were correlated for each of the two speeding sessions during baseline, try, feedback, transfer and rest periods. A number of findings were consistent for both the individual group correlations as well as for the combined sample of subjects from all three groups. The highest correlations were generally found for the same measure when feedback and transfer periods were correlated. For example, correlations of the same measure (heart rate, skin conductance, respiration periods, etc.) during these periods ranged from 0.69 to 0.97. Correlations between response systems during the same trial periods were generally modest and ranged from 0.34 to 0.52 for the combined groups. In general, changes in one system were related to changes in other systems. Thus, elevations in heart rate can be seen as part of a more generalized trophotropic response in which multiple systems are involved. 3.2.6. Base levels Little evidence for an initial values effect was found when the combined group scores were correlated. That is, heart rate correlations were examined during both sessions and median scores during the initial baseline correlated --0.07, -0.08 with the same measure during the feedback and transfer periods in the first session. These correlations increase during the second session to -0.33 and -0.11. When individual groups were examined, however, stronger evidence appeared. For the 0.5-see group baseline HR medians correlated -0.30 and -0.17 during the first session with performance scores from the feedback and transfer periods and -0.58 (p < 0.05) and -0.16 during the second session. A similar pattern was also found for the 8-sec group, with correlations of -0.19 and - 0 . 3 0 during the first session and -0.45 (p < 0.07) and -0.33 during the second session although none of the cor-
C.T. Twentyman /Instructed heart rate speeding
11
relations achieved significance. It is interesting to note that similar patterns were not evident in the 2-sec group. Correlations of 0.25 and 0.16 were found during the first session and 0.10 and 0.34 during the second session. This suggests that during feedback trials, the type of feedback presented differentially affected subjects with high and low initial heart-rate. Subjects with high initial heart rate were more likely to show greater increases in the 2-sec group whereas the law of initial value held for the other groups. This finding suggests a possible explanation for the disrupted speeding performances in the 2-sec group. That is, subjects whose heart periods were longest might have been in a critical frequency range in which the feedback display disrupted their speeding performances because it was presented at a rate slightly slower than their heart cycle. 3.2. 7. Skin conductance
Skin conductance measures were not strongly related to any of the heart rate measures in the entire sample or in each of the subgroups. When all the groups were combined the baseline SC median scores were negatively correlated with skin conductive level during the feedback and transfer periods during the second session (first session, +0.13 and +0.09; second session, -0.27 and -0.32). Individual groups differed but the correlations between baseline skin conductance and skin conductance during the feedback and transfer periods was not strong (0.5-sec group, first session, -0.10 and -0.02; second session, -0.11 and -0.20; 2-see group, first session, +0.11 and +0.37, second session -0.30 and -0.34; 8.sec group, -0.11 and -0.13, second session, -0.44 and -0.46). 3.2.8. Respiration measures
Respiration measures were also included in the correlations. Total respiration period during the initial baseline period was negatively correlated with respiration during the feedback and transfer sessions (first session, -0.49, p < 0.05, and -0.24; second session, -0.35, p < 0.05, and -0.16) when all groups were combined. A different pattern emerged when one looked at the separate groups. The 0.5-sec group showed the strongest negative correlations between these periods (first session, -0.59 and -0.72; second session, -0.70 and -0.56, all ps < 0.05) while the 2-sec group had correlations of (first session, -0.32 and 0.32; second session, -0.20 and -0.08). The 8-sec group showed correlations of (first session, -0.46, p < 0.05, and -0.36; second session, -0.30 and -0.27). These correlations suggest that the 2-sec group's respiratory changes were related the least to initial base levels. Thus, as in heart rate, the pattern of respiratory changes varied across groups for subjects with high and low initial levels. 4. Discussion
The results from this experiment demonstrate that subjects presented with fixedtime feedback displays can increase their heart rate. Greater speeding was produced
12
C.T. Twentyman / Instructed heart rate speeding
during feedback than during transfer trials, indicating that feedback augments performances achieved when subjects are merely instructed to increase heart rate. Performance during transfer was also greater than during rest indicating that some speeding can be achieved even when feedback displays are removed. Two Findings in this experiment are particularly striking. First, heart rate performances in the 2-sec group fell off substantially during the second speeding session. This is similar to the results of Lang and Twentyman (1977) who reported that a 1-sec flExed-time feedback display disrupted speeding performance during the second speeding session. Although the correlation between baseline heart rate and performances were small, a complex picture emerges. In the 0.5-sec group especially, subjects with higher heart rates produced smaller increases whereas the pattern was reversed for subjects in the 2-sec group. This suggests that a feedback display presenting information at rates slightly slower than the subject's heart rate may produce performance decrements. Another possibility, that the 2-sec group matched respiration rate to the frequency of the display and thus affected heart rate, is also possible. Correlational evidence exists suggesting that a pattern of changes between respiration and heart rate was disrupted for the 2-sec group. That is, heart rate performances were closely related to changes in total respiratory period for the 0.5-sec group during feedback trials (rs = 0.60 and 0.60 for speeding sessions one and two, both ps < 0.05) whereas the 2-sec group demonstrated reversed or smaller correlations (rs = -0.23 and 0.38, ps > 0.05). This finding suggests that the 2-sec display may have disrupted a complex cardiopulminary pattern which was established in subjects who were more successful in speeding their heart rate. The second surprising finding is that the 8-sec group's performance was comparable to a group receiving feedback every 0.5-sec. A number of authors have reported that subjects who received frequent feedback have produced greater speeding results than subjects who were presented information at less frequent intervals (Gatchel, 1974; Lang and Twentyman, 1974). It should be noted that these studies presented feedback which was tied to a cardiovascular event (i.e., systole). There are several differences between the 8-sec fixed-time group and the subjects who received feedback every five or 10 beats (Gatchel, 1974). In the fixed-time format the target line cannot sweep across the screen. Instead, the marker jumps instantaneously from one position to another with changes in the periods' average heart rate. Thus, fixed-time subjects are provided with a knowledge of exact amount of change produced during each 8-sec feedback period relative to the preceding 8-see period. In contrast, subjects receiving 10-beat feedback (Gatchel, 1974) may not have been able to determine how much improvement occurred during consecutive 1-beat intervals because the display swept across the screen and the demands of the task may have interfered with the subjects' memory of the exact location of the previous sweep. Another major difference between the displays is the fact that the FExed-time groups did not receive feedback coincident with systole. Although the jump dis-
C.T. Twentyman /Instructed heart rate speeding
13
play may have served to increase speeding performances in the 8-sec group, it should be noted that the lack of a linear relationship between feedback frequency and speeding performances may also have been due to small performances in the 0.5-see group. Although results have been varied from study to study, when subjects have been given beat by beat information (Gatchel, 1974) larger performances have been achieved than were found in the 0.5-sec group in the present experiment. This suggests that any information about heart rate or interval may be effective in producing some speeding. What is most effective, however, is a display which presents specific temporal information about changes in the organ in addition to information about performance changes. Results from the other physiological responses are inconsistent with respect to the specificity of heart rate increases. No group differences were found in measures of skin conductance. Several measures of respiration, however, revealed significant group effects which were similar to the results found in heart rate. This suggests that respiratory maneuvers and especially those related to respiratory period, varied more closely with heart rate performances than did changes in skin conductance.
5. Introduction (Experiment II) The results of the previous study suggest that fixed-time displays differ from feedback displays which present information on a beat by beat basis. The purpose of this experiment is to replicate the Findings of both Gatchel (1974) and Lang and Twentyman (1977). Three groups of subjects were employed and received Onebeat, 10.beat and 1-sec feedback displays. Although Gatchel (1974) reported finding no group effects in a measure of respiration period, he suggested that respiration amplitude or other physiological measures may have been more sensitive to changes in the heart rate speeding tasks. Consistent with this view, Sroufe (1971) demonstrated that respiration amplitude greatly affects both heart rate and heart rate variability whereas respiration period effects were smaller. In the present study, several measures of respiration in addition to the two (total respiratory period and total respiration period interquartile range) employed by Gatchel (1974) were recorded. Skin conductance level was also included in the present study. The additional physiological measures were recorded to determine whether changes in respiratory or skin conductance levels occurred during the speeding tasks and were related to changes in heart rate. In the previous experiment differences were only found on some of the respiration measures. This suggests that the use of only one response measure such as total respiratory period may not provide sufficient information about the change in respiratory patterns which occur with changes in heart rate.
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C.T. Twentyman / Instructed heart rate speeding
6. Method 6.1. Subjects 36 males recruited from bulletin boards at the Phychology Building served as subjects. Each person was paid $2.00 per session for participating in the experiment. All subjects were screened during the initial interview for any history of cardiovascular or other diseases and for drug use.
6.2. Apparatus and physiological measures The apparatus was identical to that described in Experiment I. The same physiological measures that were recorded during the first experiment were also obtained in this experiment.
6.3. Experimental design Subjects were randomly assigned to one of three groups. The first group received a 1-sec fixed-time feedback display in which heart rate was averaged every second. This display was identical to that described in the previous experiment. The second and third groups received feedback displays in which the horizontal lines began sweeping across the screen from the far left side and was terminated by either the next R wave of the cardiac cycle or by the tenth R wave. Thus, all groups saw an analogue feedback display but only the second and third groups were presented with a display in which the termination of the cycle was coincident with an event in the cardiac waveform (i.e., the R wave). In all other respects, such as the presentation of the word GOOD or the setting of the criterion marker line, the one-beat and 10-beat groups saw an identical display to that presented to the 1-sec subjects. Prior to the two sessions of heart rate control all subjects participated in one session of a perceptual motor tracking display which was identical to that described in the previous experiment with the following exception: one-third of the subjects tracked a sweeping display which was randomly generated at the rate of approximately 60 sweeps per minute. Another third of the subjects tracked a display which was generated at the rate of 10 sweeps per minute. The remaining third of the subjects in each group tracked a visual display which changed at the rate of approximately 60 times per minute but this display instantaneously jumped from position to position in a manner visually identical to that seen in the 1-sec display. This display was, of course, randomly generated by the computer. The rationale behind presenting the different displays was to ensure that familiarity with a display did not augment the ability of any group of subjects to control their heart rates relative to the other groups.
C T. Twentyman /Instructed heart rate speeding
15
6.4. Procedure
The procedure was identical to that described in the previous experiment.
7. Results 7.1. Tracking session
No significant simple Group differences were found On any of the heart rate baseline measures or during the feedback transfer or rest periods. There were also no significant Group differences in any of the skin conductance or respiration measures. 7.2. Heart rate speeding sessions
Initial baseline periods and try periods were analysed for all physiological responses. No significant Group or Group X Session interactions were found. When heart rate performance scores were analysed, significant Group differences were found during the feedback trials (F = 4.88, df = 2, 33, p < 0.025). As can be seen in fig. 2, no differences between groups were found during the first speeding session. During the second speeding session, however, the one-beat group showed greater performances during feedback trials than either the 1-see or 10-beat groups (t's respectively of 3.03, 3.04, df = 33, p < 0.05) which did not differ. Similar but somewhat smaller differences were found during the transfer periods (Group F = 4.27, df -- 2, 33, p < 0.025). Again, these differences were largely due to the effects of the one-beat group (one-beat vs. 1-see and lO-beat t's of 3.10, 2.79, df = 33, p < 0.05). 7.Z 1. Skin conductance Several group effects were also found in the measures of skin conductance level. All groups increased conductance over the initial base periods but the one-beat showed increased conductance relative to the other groups during feedbacl~ trials (group F = 7.55, df = 2, 33, p < 0.005). Group effects were also found during the transfer and rest trials (F values respectively of 5.95 and 4.31, df's = 2, 33, p's less than 0.025). Subsequent analyses indicated that the one-beat group differed from the other two groups which did not show differences (feedback t's = 2.59, 2.16, transfer t's = 2.45, 1.92, df's = 33, p's < 0.05). Significant trial effects during the feedback periods (F = 2.27, df = 4, 132, p < 0 . 0 5 ) indicated greater conductance across the session whereas the significant rest trial effects (F--7.08, df--4, 132, p < 0.025) indicated a general reduction of conductance during these periods. The only difference found in skin conductance level variability was a significant trial effect (F =3.51, d f = 4 , 132, p < 0 . 0 1 ) which was present during transfer periods. This indicates that a generally smaller variability was present during later trials.
16
C.T. Twentyman /Instructed heart rate speeding
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TRIALS Fig. 2. Mean change during feedback trials of physiological variables assessed in Experiment II.
7.Z2. Respiration measures Although respiration measures also followed the pattern of heart rate changes, these results were not consistent. Only a Group X Session interaction was found for respiration inspiratory period medians during the feedback trials (F = 3.27, df = 2, 33, p less than 0.05) and indicates that the one-beat group had relatively greater decreases in inspiratory period during the second session whereas the other groups had relatively greater increases in the second session. When individual sessions were analysed, however, differences were not found and comparisons of individual groups revealed no differences. There were few systematic changes in respiration expiratory period scores. During feedback trials there was a significant session effect (F = 7.02, df = 1.33, p less than 0.025) indicating that the expiratory period decreases were generally smaller during the second session. Significant group effects were found for expira-
c.T. Twentyman / Instructed heart rate speeding
17
tory period IQR during the transfer (F = 4.06, df = 2, 33, p less than 0.025)and rest periods (F = 4.25, df = 2, 33, p less than 0.025). In general, the one-beat group demonstrated more variability than the other groups which did not differ from each other. The measure of respiration total period did not show differences between groups. While patterns similar to those found in respiration inspiratory period were present in this measure, analyses did not reveal significant differences. Total respiration period, however, did demonstrate a significant session effect (F = 8.04, df= 1, 33, p less than 0.01) with greater decreases present during the first session. The respiration I/E ratio mean revealed only a significant session effect (F = 4.79, df = 1,33, p < 0.05) during feedback trials which indicated a relative movement toward less expiration during the second session. During the transfer periods a group effect was present (F = 4.81, df = 2, 33, p < 0.025) with the one-beat group demonstrating greater relative expirations when compared to the lO-beat or 1-sec group (t's = 2.01, 2.00, df's = 33, p's < 0.05). Again, the 10-beat and 1-sec groups did not differ. 7. 2. 3. Cell- type analyses
Analyses of variance including cell.type (feedback, transfer and rest trials) indicated that no group X cell-type interactions were significant for any of the response measures. Cell-type was not a significant factor for heart rate when feedback and transfer trials were compared but was a significant factor when feedback-rest and transfer-rest trials were compared (F's respectively of 22.84 and 21,32, df's = 1, 33, p's < 0.001) Differences between feedback-rest and transfer rest trials were also found for respiration inspiratory period (F's of 16.86 and 14.29, df's = 1,33, p's < 0.001), total respiratory period (F's of 29.71 and 19.83, df's = 1, 33, p's < 0.001) and for skin conductance levels (F's of 7.14 and 4.61, df's = 1, 33, p ' s < 0.05). In addition, feedback-transfer cell-type differences were also significant or marginally significant for respiratory inspiration period (F = 3.43, df = 1, 33, p < 0.10), total respiratory period (F = 20.05, df= 1, 33, p
