AM 69-21
RECOVERY OF MOTOR PERFORMANCE FOLLOWING STARTLE
Richard I. Thackray, Ph.D. R. Mark Touchstone
Approved by Released by ~~ ~AM> J. RoBERT DILLE, M.D. P. v. SIEGEL, M.D. CmEF, CIVIL AEROMEDICAL FEDERAL Am SURGEON INSTITUTE
October 1969
Department of Transportation FEDERAL AVIATION ADMINISTRATION Office of Aviation Medicine Qualified requesters may obtain Aviation Medical Reports from Defense Documentation Center. The general public may purchase from Clearinghouse for Federal Scientific and Technical Information, U.S. Dept. of Commerce, Springfield, Va. 22151. RECOVERY OF MOTOR PERFORMANCE FOLLOWING STARTLE
I. Introduction. were found to be significantly more responsive to the startle stimulus on a number of autonomic Sudden, high-intensity sounds, such as those variables. While the study was not specifically produced by sonic booms, can be quite startling. concerned with determining the over-all mean In view of the increasing interest in possible response time to startle, it was estimated from detrimental effects of sonic booms, it would ap the data given to be approximately 950 msecs. pear important to consider what is presently Thackray18 obtained a mean response time of known concerning the general effects of startle 893 msecs. to a 120 db auditory stimulus on its on behavior. Although there have been numerous initial presentation, and also obtained evidence studies of autonomic or electromyographic re to support Sternbach's finding of a relationship sponse to startle/ 2 4 9 14 16 as well as the well between reaction time to startle and autonomic known work of Landis and Hunt8 on the mus response. In addition, Thackray found that cular reflex to startle, relatively few studies have startle tended to exaggerate the differences which been concerned with the effects of startle on exist between individuals in their "normal" speed performance. Thus, while it is generally be of response, such that Ss classified as slow re lieved that startle has a disruptive effect upon actors under nonstartle conditions tended to re performance, little data are available concerning spond more slowly to startle stimuli, while fast the actual extent of disruption resulting from startle, the rate of recovery, or the characteristics reactors responded more rapidly. This latter of subjects (Ss) who differ in their susceptibility finding, however, was significant only for the to startle. second of the two startle stimuli employed. Woodhead20 21 employed sudden bursts of The present study was designed to provide ad broad-band sound (100-110 db) and studied the ditional data on the extent and duration of per effects of such stimuli on a decision task in which formance disruption following startle, as well as moving symbols were matched against stationary to examine further the physiological and be ones. Performance was found to be significantly havioral correlates of Ss who differ in the extent impaired following stimulation, but recovered to of disruption. A tracking task requiring con pre-stimulus levels within 17 to 31 seconds. tinuous perceptual-motor coordination was chosen Woodhead, however, was more concerned with as the principal or primary task. Reaction times the use of sudden, intense noise as a "distractor" to both startle and nonstartle auditory stimuli and attempted to reduce the startle qualities of were also obtained as a secondary task. This the stimuli through pre-experimental adaptation. latter task was included for purposes of com Consequently there is some question as to whether parison with the previous studies of Sternbach17 these recovery rates would apply to completely and Thackray18 and to determine the relationship, unexpected, startling sounds. if any, between reaction time to startle and per Several other studies have examined the speed formance impairment on the tracking task. The with which individuals can react to startle, with startle stimulus was presented twice with suffi particular emphasis on identifying possible dif cient time between presentations to minimize ferences between fast and slow reactors. Stern adaptation effects. A final aspect of the study bach17 used a pistol shot and identified a group was the examination of possible relationships of slow reactors (mean response time of 1,695 between the recovery rate of perceptual-motor msecs.) and a group of fast reactors (mean re performance following startle and the rate of sponse time of 200 msecs.). The slow reactors autonomic recovery.
1 II. Method. and the leads connected to a Beckman Type 9857 cardiotachometer coupler. Skin resistance was Subjects. Thirty paid male college students obtained from two Fels zinc-zinc sulphate elec between the ages of 18 and 25 were employed. trodes leading to a Fels Model 22A Dermohm All were right-handed, had no known hearing meter. One electrode was attached to the palmar loss, and had no prior experience with tracking surface of the left hand and the other to the tasks. ventral surface of the left wrist. Current dens 2 Apparatus. The basic task apparatus con ity was 22.3 microampsjcm. • The output of the sisted of a console containing an oscilloscope Dermohmmeter led to another channel of the which constituted 'the display for a two-dimen recorder. Beckman miniature biopotential elec sional compensatory tracking task. The spot trodes were attached immediately above and be on the oscilloscope was driven in a random low the right eye and direct coupled to the manner by means of a cam-function generator recorder. This yielded a gross indication of eye which constantly varied the voltages to the hori closure as well as blinks. The electroencephalo zontal and vertical deflection plates of the gram was obtained from bipolar placements on oscilloscope. The S's task was to attempt to the left occipital and left midcentral regions. keep the spot continuously at the center of the Standard Grass electrodes with Grass electrode oscilloscope by means of a small control stick cream were employed. located at his right hand. Minimal muscular All equipment, with the exception of that effort was required to move the stick, and an equipment used by S in actually performing the excursion of approximately 1 inch in any direc tasks, was located outside the S's room. ~igure 1 tion from center was sufficient to move the spot shows a S instrumented for physiological record to the edge of the scope. Voltages defining the ing and performing the tracking task. position of the target on the oscilloscope (i.e., Procedure. Upon arrival each S received an the algebraic sum of the function generator and audiometric examination, was given a general control stick voltages) were fed to a PACE description of the tasks he was to perform, and TR-20 analog computer and the output voltages was told that the purpose of the experiment was (absolute horizontal and vertical error) were to investigate physiological changes during the separately integrated by Beckman Type 9873B learning and performance of perceptual-motor resetting integrator couplers. The entire track tasks. The various electrodes were attached and ing task was essentially a slightly modified ver S was given detailed instructions concerning the sion of one previously described by Pearson.U tasks. He was told that the first or training High-intensity noise served as the startle phase would consist of a series of 2-minute trials stimulus and was produced by amplifying the with a 35-second rest period between each. His output of a Grason-Stadler, Model 455B noise principal task was to try to keep the moving generator. Stimuli for measures of "nonstartle" spot on the oscilloscope as close to center as pos reaction time were produced by a General Radio, sible during the trials. He was further told that Model 1310 oscillator. All auditory stimuli were while tracking he would occasionally hear a tone presented through Sony Model DR-3A head through his headphones, and that he should re phones which had been previously calibrated spond to each tone by pressing the button located using an artificial ear. Stimulus levels were on top of the control stick. He was informed periodically monitored by means of a Ballantine that a small red warning light would come on Labs, Model 300-E voltmeter. Duration of all 5 seconds prior to the beginning of each trial. stimuli was 1% seconds, and a Friden Model The S then rested quietly for approximately 8 SP-2 tape reader was used for stimulus sequenc minutes while the physiological equipment was ing. Each stimulus activated a Hunter Klockoun adjusted and recordings made of "eyes open" ter which was stopped when S pressed a button and "eyes closed" electroencephalographic ac located on top of the control stick. tivity. A Beckman Type R Dynograph recorded the Fifteen 1,000 Hz, 75 db reaction time stimuli physiological variables as well as the integrated were presented during the 15-trail training tracking error. Beckman biopotential electrodes period. Although the temporal position of each were attached to the lateral walls of the S's chest of these stimuli within trials was randomly de-
2 FIGURE 1. Subject instrumented for physiological recording and performing tasks. The displays to the right on the console were not used in this experiment. termined, all Ss received them in the same after the phase began, the first 115 db startle positions. stimulus was presented. The same stimulus was Following completion of training, S was al again presented 15 minutes later. (These two lowed a 10-minute rest period. He was then high-intensity, "startle" stimuli will be subse informed that the next or test phase of the ex quently referred to as 81 and 82, respectively.) periment would be similar to the training phase Fifteen of the 1,000 Hz, 75 db stimuli were again just completed, except that he would have to presented at random intervals during this phase, perform both tasks without rest periods for 35 although as with the training phase, all Ss re to 40 minutes. He was also told to respond to all ceived them in the same temporal position. None auditory stimuli presented through the head of the 75 db stimuli was presented during the phones and that not all stimuli would be the 90-second periods immediately prior to or fol same. (No indication was given that any of the lowing 81 or 82. Upon completion of this phase stimuli would be loud or startling.) It was Ss were administered a post-experiment ques emphasized that S should try to maintain track tionnaire. Audiograms were also taken at this ing at all times even when making the button time to insure that no hearing loss had occurred. response to auditory stimuli. The test phase Scoring of the test and training phase data. actually lasted only 30 minutes. Two minutes Although the tracking task was essentially con-
3 tinuous in terms o£ the stimulus and response, was employed with the reaction time stimuli, the the measure of performance (integrator resets) individual distributions were often quite skewed, was a discrete measure. In order to plot the and thus the median yielded a better measure o£ recovery o£ tracking proficiency following startle, central tendency than the mean. Medians were the number o£ integrator resets had to be ob also used £or the reaction time data o£ the test tained £or successive periods o£ time. From phase. some initial pilot data, it appeared that a 1- The electroencephalographic and eye closure minute period following startle would be ade recordings were used only to monitor possible quate in terms o£ encompassing the duration o£ changes in levels o£ wakefulness during the 30- performance disruption. The same pilot data minute test period. No detailed analyses were also suggested that 5-second scoring intervals made o£ these data. would be reasonable £or plotting the recovery o£ tracking as well as the physiological data. Con III. Results. sequently, the 1-minute periods following sl and Training data. In plotting the data £or the S2 were each divided into twelve 5-second in tervals. The number o£ resets in each interval horizontal and vertical trac~ing error during o£ the horizontal and vertical integrators was training, it was found that the two curves essen then determined £or each S. Skin resistance was tially paralleled each other and were highly cor measured at the end o£ each interval and the related across trials ( r= .93; p < .01).. Conse values converted to conductance. In addition, quently, there appeared little to be gained by the minimum resistance occurring within the 10- considering them separately, and they were com second period following startle was also obtained bined in both the training and subsequent test £or each S and converted to conductance. This phase o£ the experiment. latter measure constituted a more precise deter The combined error data· over the 15 training mination o£ the magnitude o£ conductance change trials are shown in Figure 2. The scores are to startle and was used £or purposes o£ inter plotted in three-trial blocks with each block rep individual comparison. To determine the course resenting the mean number o£ integrator resets o£ heart rate recovery following stimulation, the per 5-second interval. It is apparent £rom the maximum heart rate (single fastest beat as meas figure that an asymptotic level o£ performance ured £rom the cardiotachometer recording) was was reached at or before the end o£ training. obtained within each interval. For the reaction time data, each S's median The mean number o£ horizontal and vertical response time to the 15 stimuli was obtained and integrator resets per 5-second interval was ob these values averaged across Ss. This yielded a tained £or the 2-minute f.>eriod immediately pre mean value o£ 516 msecs. ceding each startle stimulus. This was done £or Respome to startle. Figure 3 displays mean the purpose o£ obtaining a stable estimate o£ number of integrator resets £or the tracking data pre-startle tracking performance against which during successive 5-second intervals o£ the first to compare the change following stimulation. minute following S1. Also displayed are mean For heart rate, the maximum rate was obtained maximum heart rate and mean conductance level £or the 5-second interval immediately preceding £or each 5-second interval. In addition, mean S1 and S2. Skin resistance was measured at the .pre-stimulus values are given £or each variable. moment of stimulation and converted to con Relative to the pre-stimulus level, tracking error ductance. increased by 65 percent during the first 5-second For the training period, only the performance interval. This declined to a 16 percent increase data were scored. In order to make the tracking by the second interval. Both increases were sig data comparable to the test phase data, the num- , nificant with t-values of 5.35 (p<.01) and 3.34 ber of horizontal and vertical resets obtained (p<.01) respectively. Error continued to de during each 2-minute trial·. was expressed in cline up to the fourth interval, with an apparent terms o£ means per 5-second interval. Each S's rise in tracking error beginning at the fifth in distribution o£ reaction times to the 15 presenta terval and then a £all below the pre-stimulus tions o£ the 1,000 Hz stimulus was obtained and level by the seventh and £or most o£ the remain a median computed. Since no warning signal der o£ the minute. 0£ intervals three through
4 7.4 ....; -c u 7.2 Q) en I 7.0 &0...... en Q) 6.8 -en Q)...... 6.6 0 -c.... 6.4 at Q) .-..,..c 6.2 0 c 6.0 I>< -a:: 0 5.8 0:: 0:: LJ.J 5.6 (!) z 5.4 ::.::: u <( 5.2 a:: t-
2 3 4 5 THREE- TRIAL BLOCKS
FIGURE 2. Mean tracking error during the 15-trial training period. 12, only the eighth (t=3.43; p<.01) was sig Conductance level increased to a maximum nificantly different from the pre-stimulus level. during the first interval and then began a gen Maximum heart rate in beats per minute erally consistent decline throughout the remainder (b.p.m.) increased significantly from a pre of the minute. Comparisons of each interval stimulus value of 80.2 to 95.7 (t=7.57; p<.01) with the value at the time of stimulation yielded during the first interval, declined below the pre t-values which were significant (p<.05) for all stimulus value during the third and fourth in intervals. tervals, rose to about the pre-stimulus level during Of the two physiological measures, heart rate the fifth, sixth, and seventh intervals, and then was the only one which revealed any possible steadily declined during the remainder of the covariation with the curve of performance re minute. With the exception of the first interval, covery. This appeared to extend up to at least only intervals 11 and 12 differed significantly the sixth interval. Beyond this the fluctuations (p<.05) from the pre-stimulus value, although in tracking performance were not generally the t-values for intervals three (1.68) and four paralleled by any corresponding heart rate (1.81) approached significance (p<.10). changes. Because of the apparent relationship
5 TRACKING ERROR (TEl 96 •\ \ 13.6 -:: 8.8 o---o CONDUCTANCE (C) 94 c 13.4 u 8.4 MAX. HEART RATE (MHR) 92 cu ·----· en 13.2 J, 8.0 90 c 13.0 :g 88 ·e .1: ...... 12.8 ~.... 0 86!!0 Cl> ..0 12.6 ·e 84- UJ 12.4 ~ z 6.4 82 ~ FIGURE 3. Mean tracking error, maximum heart rate, and conductance level during successive 5-seeond intervals • following S1 Also shown are pre-startle values for each variable. between the initial heart rate and performance pattern similar to that obtained for S1. Of in changes, the rise in tracking error (interval four tervals two through 12, however, only the third to interval six) was compared with the heart rate interval was significantly different .from the pre increase during these same intervals. However, stimulus value (t=2.63; p<.05). neither the error increase (t=l.01; p>.05) nor Qgnductance level also showed a pattern which the heart rate increase (t=1.81; p>.05) was sig approximated that obtained for the earlier startle nificant. stimulus, and t-tests revealed all intervals to dif Figure 4 displays the same variables shown in fer significantly (p<.Ol) from the level at the Figure 2 except that the data are those for S2. time of stimulation. Tracking error during the first 5-second interval Once again, it is interesting to note the ap increased by only 29 percent over the pre-stimulus parent relationship between heart rate and track level. This increase, however, was significant ing error immediately following stimulation. (t=2.67; p<.05). By the second interval, error After the initial decline, however, the secondary had decreased below the pre-stimulus level and increase in both heart rate and tracking error remained below during the rest of the 1-minute occurred 5 seconds earlier than the corresponding period. Comparisons of each interval with the rise which appeared to follow S 1 • A comparison pre-stimulus value yielded t-values which were of the heart rate increase between intervals three significant (p<.05) for intervals three, five, six, and four yielded a significant t-value ( t=2.90; seven, eight, and 11. p<.01), but the increase in tracking error which Maximum heart rate increased significantly occurred during these intervals was not significant from a pre-stimulus level of 80.8 b.p.m. to 93.6 (t=1.77; p>.05). b.p.m. during the first interval following startle While the immediate effect of startle on track (t=7.65; p<.01). It then followed a recovery ing was a temporary impairment, startle appeared 6 ::: 8.8 TRACKING ERROR (TEl c:: 94 13.6 u 8.4 o---o CONDUCTANCE (C) 92 13.4 ...cu .;, 8.0 ...... MAX. HEART RATE (MHR) 90 13.2 ·----· ~ ... .: ... a; 7.6 88 ·e 0 cu... 'o 13.oe ..... 0 ..... 7.2 ...... ~-----o 2 -o, 12.8 .~ - E ~ 6 8 .. ,0 c:J>' 12.6: • TE -o ~ -·--o-. (,) 6.4 -o ·= -- -o 12.4 :i 0 • MHR -·-- 1- c:: -- (,) 6.0 I>C 12 ·a2;:) a:: ... z: 0 5.6 a:: 12.0 8 a:: ,,.. 1.&.1 5.2 11.8 (,!) z: 4.8 ::..:: 11.6 (,) <1: 4.4 a:: •C 11.4 1- 4.0 'fl Pre- 2 3 4 5 6 7 8 9 10 II 12 Stirn. FIVE - SECOND INTERVALS FIGURE 4. Mean tracking error, maximum heart rate, and conductance level during successive 5-second intervals • following 8 2 Also shown are pre-startle values for each variable. to have a facilitative effect on reaction time. relative to the pre-stimulus levels, tracking error Thus, mean reaction times to S1 and S2 were rose only 29 percent during the initial 5-second 402 msecs. and 401 msecs., respectively, while the interval following S 2 , but increased 65 percent mean of each S's median reaction time to the during the same interval following 8 1. Further, 15 nonstartle tones was 462 msecs. Separate com tracking error following S 2 was found to be sig parisons of this latter value with mean reaction nificantly less than the pre-stimulus level for times to the two startle stimuli yielded t-values most of the remaining minute; this was not the of 3.39 (p<.01) for S1 and 4.75 (p<.01) for S~. case with S1. These differences between S1 and The correlations of nonstartle reaction time with 8 2 , however, appeared to be due primarily to response time to S1 and Sz were 0.33 (p>.05) differences in the level of pre-stimulus tracking and 0.54 (p<.Ol) respectively. There was no error. A comparison of the mean levels revealed evidence of any relationship between either the the level prior to S 2 to be significantly greater nonstartle or startle reaction time measures and than the level prior to S1 (t=4.71; p<.01). This tracking performance as measured either prior increase is interesting in view of the fact that to S1 or Sz or during the first 5-second interval there were no significant differences between the following startle. The obtained product-moment pre-stimulus levels for maximum heart rate correlations ranged from 0.00 to 0.14. (t=0.29; p>.05) or conductance (t=0.12; p>.05) Although it was not intended to investigate which might have indicated a declining arousal adaptation effects to startle, and the startle level. Because of the difference in pre-stimulus stimuli were presented only twice with 15 minutes tracking performance, it was difficult to compare between presentations to deliberately minimize the two startle stimuli in terms of either their any possible adaptation, a comparison of Figures immediate effects on performance or possible dif 3 and 4 might suggest that the second startle ferences in the recovery patterns. There were stimulus was somewhat less disruptive in its ef several indications, however, which would sug fects on tracking behavior than the first. Thus, gest that S1 and Sz did not differ appreciably in 7 their immediate startle effect. For example, a tween the groups with regard to tracking error comparison of the absolute level of tracking error prior to startle. The pre-startle means for S1 (integrator resets) during the initial 5-second were 6.56 and 3.67 for the HE and LE groups interval following S1 with absolute level of error respectively. For 82 mean values for the two during the same interval following s2 yielded groups were 8.09 and 4.90. These differences no evidence of a difference (t=0.77; p>.05), nor, between the groups were significant for both pre as indicated earlier, was there any apparent dif startle periods (S1 (t=2.96; p<.05); S2 (t=2.51; ference between reaction times to S1 and 82. Also, p<.05) ). neither the maximum heart rates during the first In terms of response to the startle stimuli, 5-second interval nor the maximum conductance there were no significant differences between the levels following startle were different for sl and HE and LE groups in mean conductance change 8 2. The obtained t-values were 1.49 (p>.05) to either 81 or 8 2. This was not the case with and 0.76 (p>.05) for heart rate and conductance heart rate response, however. For S1 the heart level respectively. It should be noted, though, rate response (maximum heart rate during the that while there was little evidence from the 5-second interval following stimulation minus physiological or performance data to suggest any maximum heart rate in the 5-second interval substantial difference between the startle stimuli, preceding stimulation) was 20.4 b.p.m. for the there did appear to be a subjective difference HE group and 8.3 b.p.m. for the LE group. between them. ·A five-point rating scale with This difference was significant (t=2.54; p<.05). endpoints consisting of "not startled at all" A similar trend was found for 8 2, but the differ (scale value of 5) to "extremely startled" (scale ence between the mean HE change of 17.2 b.p.m. value of 1) was administered following the ex and mean LE change of 9.7 b.p.m. was not sig periment. The mean rating for 81 was 4.5 and nificant (t=1.95; p>.05). 5 for 82 3.6. A sign testi indicated this difference With regard to the subjective ratings obtained to be significant (p<.001). from the post-experiment questionnaire, the HE Individual differences. To enable comparison group rated 81 more startling than did the LE of the characteristics of those Ss whose tracking group (U=3; p=.004). Although the trends performance was poorest following startle with were the same, the two groups did not differ those whose performance was best, the distribu significantly with respect to their ratings of s2 tions of absolute error scores (integrator resets) ( U=13; p=.l8). were obtained for the first 5-second interval fol lowing S1 and 82. A correlation of 0.60 (p<.01) IV. Discussion. between these two distributions revealed a mod erate degree of consistency among Ss in their The results of the present study revealed the performance following startle. Since primary recovery of tracking performance following concern was only with examination of the char startle to be quite rapid. Upon initial presenta acteristics of extreme reactors, two groups were t~on of the startle stimulus, maximum disruption formed. Those Ss whose scores were in the top was found to occur during the first 5 seconds third of both distributions were designated as after stimulation, with significant, but consider high error (HE) Ss and those in the bottom ably less disruption during the second 5-second third of both distributions as low error (LE) interval. Interpretation of the effects of the Ss. Eight HE and six LE Ss were obtained in second startle on tracking was difficult because this manner. For S1 the obtained mean error of the elevated level of tracking error prior to scores were 12.87 for the HE group and 4.08 for the stimulus. Neither presentation of the startle, the LE group. For 8 2 the comparable values however, yielded any indication of adverse effects were 13.56 and 4.00 for the HE and LE groups after the initial 5- to 10-second post-stimulus respectively. interval. Beyond this, startle appeared to have In comparing the two groups with respect to an alerting effect in which performance was gen possible differences prior to startle, neither the erally improved relative to pre-stimulus levels. pre-startle values for conductance .level nor for Recently, Vlasak19 has reported a study which maximum heart rate approached significance. also dealt with recovery of motor performance There were, however, significant differences be- following startle. He employed a simple task in 8 which the S attempted by means of a stylus, to paired for 15 seconds following stimulation. For trace an irregular line. Startle resulting from the reaction time tasks, there were insufficient a "klaxon" horn was reported to produce only data given to determine the precise duration of momentary disruption of performance lasting impairment, although both were impaired tem approximately 1 to 2 seconds. It should be noted, porarily following startle. As noted earlier, though, that Vlasak chose to examine perform Woodhead20 21 found decrements on a decision ance only during the first few seconds following task following sudden noise stimulation which startle. Thus, the possibility of subsequent dis lasted from 17 to 31 seconds. It would appear ruption of lesser magnitude was ignored. In from the results of the present study and from addition, he used what would appear to be a the few others which also have investigated per much simpler "tracking task," and one which formance recovery, that the major performance might reveal more rapid recovery from startle. decrement following startle probably occurs Nevertheless, the tracking data of the present within the first few seconds. However, a lesser study were re-examined to determine whether the but significant decrement may last for periods of increase in error during the initial 5-second in from 10 to 30 seconds after startle. There is terval following startle could be attributed pri some indication that following startle, recovery marily to an increase occurring during the first of performance on motor tasks may be somewhat 1 or 2 seconds. The total number of integrations more rapid than recovery of performance on within each successive second of this interval tasks which are more cognitive in nature, al was obtained and expressed as a percentage of though this must be considered a tentative con the total. For the initial interval following S1, clusion at present. the percentages were 28, 28, 17, 15, and 12 for Reaction times to the startle stimuli them 1, 2, 3, 4, and 5 seconds, respectively. Comparable selves were :found to be :facilitated relative to the percentages for s2 were 30, 26, 17, 13, and 14. nonstartle reaction times. This was an unex These data indicate that over 50 percent of the pected finding, since two previous studies17 18 ob error during the initial 5-second interval occurred tained lengthened reaction times to startle. One during the first 2 seconds, and thus tend to sup possibility might be that the thumb flexion re port Vlasak's findings. Since the total startle quired as a response in this study was :facilitated reflex may last from 0.3 to 1.5 seconds,8 this sug by the startle reflex itself, although the mean gests that at least some of the performance dis reaction times to 81 and 82 ( 402 and 401 msecs., ruption which takes place within the 5-second respectively) were considerably longer than the interval following startle may be attributable to times (145 to 195 msecs.) reported by Landis and direct mechanical effects of the startle reflex on Hunt8 :for the muscular startle reflex to reach the motor control. However, the fact that the present hand. This would suggest that the obtained study showed performance to be significantly reaction times, while possibly :facilitated by impaired during the second 5-second interval startle, were not simply reflex responses. Puro following startle as well, at least for the first hiP2 13 has recently argued that reaction time to presentation of the stimulus, would also suggest startle may be either inhibited or facilitated de that not .all of the increase in error can be at pending on the extent to which the voluntary tributed entirely to a disruption of motor control response employed is compatible with the reflex resulting from the mechanical effects of the startle response. This would appear to offer a startle reflex*. reasonable explanation for the discrepancy be In addition to tracking, Vlasak also studied tween the reaction time data of the present study the effects· of startle on continuous mental sub and the findings of both Sternbach17 and Thack traction and on simple and choice reaction time. ray,tB since these earlier studies employed arm Subtraction was found to be significantly im- or hand responses which likely were partially inhibited by the total startle pattern. *Since reaction times were also obtained in the present study, it could be argued that the response of pressing the With regard to individual differences, there button to the startle stimulus may have contributed to tracking was a direct relationship between tracking pro impairment during the first second following startle. Although this may have had some effect upon tracking, it is likely that ficiency before and after startle, i.e., the group the effect was quite small, since pilot data indicated that the which revealed the greatest error immediately actual button response itself resulted in no apparent increase in tracking error. following startle also had significantly higher 9 error before startle and vice· versa. These find ment with the previous findings of 8ternbach17 ings are consistent with those of several previous and Thackray.18 Both earlier studies found a studies. Thus, Vlasak19 found a similar relation tendency for slowness of response to startle ship between performance disruption following (greater impairment) to be associated with startle and level of prior proficiency, with less greater autonomic response. Also, like the pres proficient Ss being considerably more disrupted ent study, neither of these previous ones found by startle. This held for three out of the four any relationship between the extent of perform tasks studied. These included mental subtraction, ance disruption to startle and pre-startle levels choice reaction time, and simple tracing. As of physiological activity. noted earlier, Thackray18 also found evidence to Evidence of an apparent covariation between suggest that,· with the particular reaction time the recovery curves for heart rate and tracking task employed, startle tended to exaggerate pre was found for both 8 1 and 8 2 • For both stimuli existing differences between individuals in their the significant increase in heart rate and tracking "nonstartle" response time, i.e., the slow became error immediately after startle was followed by slower and the fast responded with ev-en shorter parallel decreases in heart rate and error. The latencies to startle. Taken together with the subsequent secondary heart ~ate acceleration was present findings, these results suggest the general accompanied again by an increase in error, al hypothesis that the extent of disruption following though this was a considerably weaker effect as startle is dependent upon the level of task pro shown by the general lack of statistical signifi ficiency prior to startle with greatest disruption cance. Nevertheless, there are reasons to believe occurring among those who are least proficient that the secondary rise in tracking error was prior to startle. real. Not only did it appear following both Although there was some indication of greater stimuli, but it was also present in the data of subjective and physiological response to startle pilot Ss run prior to the experiment. Why the by the HE Ss, the differences were not pro apparent coupling between these two variables nounced and appeared somewhat inconsistent. continued for the initial 20- to 25-second period Thus, while the differences between the groups following stimulation, and then appeared to dis in heart rate response and subjective judgment sipate is an interesting question. Certainly there is evidence to suggest that cardiac-behavioral were significant for 8 1 , they were not for 8 2 • coupling can and does occur. 3 5610 Lacey6 7 has Also, the two groups did not differ in their con reviewed the evidence for a mechanism whereby ductance change to either 8 1 or 8 2 • Nevertheless, cardiac change can either facilitate or inhibit with the exception of this lack of difference be sensory input via baroreceptor feedback to the tween the groups in conductance change, the central nervous system, and the present data may trends of these differences were in general agree- reflect the operation of such a mechanism. 10 REFERENCES 1. BERG, R. L. and BEEBE-CENTER, J. G.: Cardiac startle on a perceptual task and a sensory-motor task. in man. Journal of Experimental Psychology, 28:262- Perceptual and Motor Skills, 18:753-762, 1964. 279, 1941. 11. PEARSON, R. G.: Performance tasks for operator 2. DAVIS, R. C.: Motor effects of strong auditory skills research. 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