SHORT COMMUNICATION
Reaction Time in Pilots During Intervals of High Sustained G Olaf Truszczynski, Rafal Lewkowicz, Mieczyslaw Wojtkowiak, and Marcin P. Biernacki TRUSZCZYNSKI O, LEWKOWICZ R, WOJTKOWIAK M, BIERNACKI MP. horizontal bar at a fixed distance from the eyes. A center Reaction time in pilots during intervals of high sustained G. Aviat red light is used as fixation point and the criterion for Space Environ Med 2014; 85:1114–20. central vision loss (blackout) is when intensity dims conIntroduction: An important problem for pilots is visual disturbances siderably or disappears. Peripheral light loss is estaboccurring under +Gz acceleration. Assessment of the degree of intensification of these disturbances is generally accepted as the acceleration lished by disappearance of flashing green lights placed tolerance level (ATL) criterion determined in human centrifuges. The aim at 15–25° on each side of the center red light (17). One of of this research was to evaluate the visual-motor responses of pilots durthe newest types of devices for the subjective assessment ing rapidly increasing acceleration contained in cyclic intervals of +6 Gz of loss of peripheral vision is a 180° curved light bar to the maximum ATL. Methods: The study involved 40 male pilots ages 32–41 yr. The task was a quick and faultless response to the lightby stimuli Delivered Ingentawhich to: jacob wasbusch used at the Naval Air Development Center presented on a light bar during exposure IP: to acceleration until reaching 91.198.127.151 On: Wed, 2016 11:57:24 for13 theJul dynamic tracking of a subject's peripheral vision the ATL. Simple response time (SRT) measurements were performed Copyright: Aerospace Medical Association in acceleration physiology (9). during experiments using a visual-motor analysis system throughout the exposures which The key indicator recorded during the examination allowed assessment of a pilot’s ATL. Results: There were 29 pilots who tolerated the initial phase of interval acceleration and achieved +6 Gz, of the impact of acceleration is simple reaction time completing the test at ATL. Relative to the control measurements, the (SRT) to visual stimuli. Measurements of this indicator, obtained results indicate a significant effect of the applied acceleration together with the assessment of cardiovascular indices on response time. SRT during +6 Gz exposure was not significantly londuring acceleration with different parameters, can be ger compared with the reaction time between each of the intervals. SRT and erroneous reactions indicated no statistically significant differences the basis for the initial and periodic assessment of peobetween the “lower” and “higher” ATL groups. Conclusion: SRT meaple susceptible to this factor. Empirical data can also be surements over the +6-Gz exposure intervals did not vary between gathered which, subjected to analysis and interpreta“lower” and “higher” ATL groups and, therefore, are not useful in pretion, can also help explore the psychological meaning dicting pilot performance. The gradual exposure to the maximum value of +6 Gz with exposure to the first three intervals on the +6-Gz plateau of the revealed dependencies (7,10,13). This issue was effectively differentiated pilots. addressed by many researchers (8,11,26), who found Keywords: +Gz tolerance, acceleration tolerance level, simple response reduced ability to perform tasks under conditions of time, repeated exposure, simulated air combat maneuver.
A
PILOT’S FUNCTIONING during flight requires continuous observation of objects in the visual field, analysis of the onboard instruments’ indications related to the control system, and perception of different stimuli and information provided by other participants involved in the task being performed. Working conditions in the changing environment of flight require the ability to concentrate, divided attention, a sense of spatial orientation, very good eye-hand coordination, and a fast and reliable response to the threat from the pilot. These facts underlie the need to analyze changes in eye function while examining the impact of acceleration on humans in centrifuges. The basis for this kind of research was, in addition to the standard physiological parameters, the introduction of equipment that records the perception of light signals using a perimeter. Loss of peripheral vision measured by the subject tracking his peripheral vision on a light bar is an accepted measure of tolerance limits (Air Standardization Coordinating Committee, Joint Base Andrews, MD). The first centrifuges used a fixed set of three colored light signals arranged on a
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acceleration. Numerous published studies on repeated +Gz exposure to simulated aerial combat maneuvers (SACM) (1,5,6) focused mainly on assessing the impact of SACM on changes of physiological parameters and G tolerance. However, in these articles, there is no reference to the impact of repeated accelerations on the SRT. The interval program developed in the Polish Military Institute of Aviation Medicine (MIAM) in Warsaw (25), similarly to the ones used by other authors (4), meets the criteria for selection and training. The program, named “Selective interval program for the acceleration From the Department of Flight Safety, the Aeromedical Training Division, the Department of Aviation Physiology, and the Department of Aviation Psychology, Military Institute of Aviation Medicine, Warsaw, Poland. This manuscript was received for review in March 2014. It was accepted for publication in August 2014. Address correspondence and reprint requests to: Mieczyslaw Wojtkowiak or Rafal Lewkowicz, Krasinskiego 54/56, 01-755 Warszawa, Poland; [email protected] or [email protected]. Reprint & Copyright © by the Aerospace Medical Association, Alexandria, VA. DOI: 10.3357/ASEM.4009.2014
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+GZ INTERVALS & REACTION TIME—TRUSZCZYNSKI ET AL. tolerance level (ATL) assessment,” is complemented by preparatory training and characterized by rapid escalation of acceleration. The increase in the speed of high-performance aircraft has led to the introduction of new research programs in human centrifuges characterized by intervals of rapidly increasing acceleration. In connection with this, the above-mentioned selection program required supplementation of the tests for pilots involved in high acceleration flights. The aim of our study was to evaluate the visual-motor responses of pilots during rapidly increasing acceleration contained in cyclic intervals of +6 Gz to the maximum acceleration tolerance level (ATL). In addition, we adopted two hypotheses: 1) with each subsequent interval of acceleration at +6 Gz, SRT will statistically significantly increase; and 2) development of a research program, based on the measurement of SRT, will allow the selection of pilots while assessing their suitability to air combat.
found in Biernacki et al. (2). Response time measurements were performed using the visual-motor analysis system developed at MIAM (22,24,28). The device consists of a computer, sending and receiving stochastically programmed visual stimuli, and a light bar located on both sides of the examined person at the eye level. The bar has three rows of 64 white, green, and red lights (3mm diameter LEDs), but in this study we used only the green light. The ambient light level in the cabin, LEDs, and central light were constant. The bar has a field-ofview of 185°. The system was equipped with the device, ensuring the possibility of selecting the presented stimuli with a light intensity of 50 cd · m22 with moves at a randomly selected speed of 2 m · s21 along the side arms of the device in the direction from the periphery to the central point of visual fixation. The light bar was described in detail elsewhere (19). The program of light stimuli presentation was started from the same point of examination for each pilot. During the exposure, the participants were told to concenMETHODS trate their gaze on the central light point. The subjects’ task was a quick and accurate response to the changes Subjects Delivered by Ingentaobserved to: jacob in busch the presentation of the visual stimuli. When IP: 91.198.127.151 13 Jul 2016 11:57:24 Tested in the human centrifuge at MIAM wereOn: 40 Wed, the subject could no longer see the stimuli and there was Copyright: Association male volunteer pilots, ages 32-41 yr (35 6 3),Aerospace highly Medical no response while the visual stimuli were moving along qualified in aerial combat, and actively engaged in the arms of the perimeter, it was assumed the subject high-acceleration flights. After the research program had lost eye-level blood pressure and, thus, also periphwas approved by the Ethics Committee at MIAM, each eral vision, and the centrifuge was stopped. When the participant was thoroughly familiarized with the methlight stimulus appeared in the peripheral field of view, odology of the research, security conditions, and the the pilot pressed the circuit breaker to signal this to the light stimuli task, and signed a consent form. As a next computer. The computer sent back the next signal accordstep, the pilots were tested by the Central Military ing to the experimental profile program. The range beAviation Medical Commission and accepted as able to tween stochastically sent signals was from 0.8 to 3.0 s. The tolerate accelerations in the centrifuge. The subjects subjects always responded at the moment they noticed were experienced in acceleration endurance during conthe visual stimuli appearing on the side arms. The movtinuous flight training or from yearly centrifuge examiing points of light presented on the arms of the device nations of their ATL. The subjects did not wear an anti-G were extinguished after the button was pressed, or when suit. They did not perform an L-1 anti-G straining mathe light reached the central point of visual fixation. neuver (AGSM), but employed mainly muscular strainFor the study, we defined a range of correct SRT. For ing of the lower limbs and abdomen. The subjects were fast SRT we have taken 200 ms on the basis of previous seated at a reclined angle of 12° relative to the vertical, research results (3). For the upper limit of the correct rewith the arms supported at the heart level. The feet were sponse we assumed 800 ms, applied and validated in supported on the rudder pedals, making it possible to studies (25). Response times not within the range of 200 perform a muscular strain. Before the test, each pilot exto 800 ms were classified as wrong responses or a lack of erted pressure on the pedals at maximal effort, in this reaction. This group of erroneous responses was defined way determining the baseline level. The baseline value as SRT errors. Therefore, the number of errors in each of of the pressure was presented on a monitor installed in the measuring points was a sum of three incorrect rethe cab and the displayed pressures were monitored in sponses: too fast (, 200 ms), too slow (. 800 ms), and the control room. At the onset of visual symptoms, the lack of reaction. pilots were instructed to perform a muscular strain at Procedure about 50% of their maximum strain until normal vision reappeared. Due to the need for research conducted unThe testing began with a briefing. Under the accelerader the conditions of acceleration, only those subjects tion conditions, the subjects became acquainted with the who endured the applied acceleration of at least three exposure and how to respond to the stochastically ex+6 Gz acceleration intervals were selected to participate hibited stimuli in the peripheral field of vision. The in the study. mode of operation of the centrifuge, with the self-control Equipment The research was conducted in the human centrifuge at MIAM. More details about this centrifuge can be
option switched on, made it possible for the subjects to increase or decrease the acceleration values at their will within the range from 1.4 (baseline) to +3 Gz, with a constant rise in speed of 1.5 G · s21. The training time
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+GZ INTERVALS & REACTION TIME—TRUSZCZYNSKI ET AL. Statistical Analyses was 3 min. After 30 min of rest, the pilots were subjected to the experimental protocol of the study. For comparative analysis, SRT arithmetic mean and The main part of the test including SRT measurements erroneous reactions were calculated for the following was conducted via a control phase, during operation of phases of the study: 1 min before centrifugation (control the interval acceleration in the initial phase and main measurement); the first, middle, and last level of conprogram phase, and after its completion. The SRT meastant acceleration at +6 Gz; and 1 min after stopping the surements were commenced 60 s before the start of the centrifuge. SRT and error reaction variations during the centrifuge (control measurement) and continued uninexperiment were analyzed by means of two-way ANOVA terrupted until 60 s after the centrifuge stopped. The with repeated measures. The measurement time point pilots had to react to the light stimuli exhibited stochaswas the within-subject variable during the experiment. tically in the peripheral field of vision. The recorded reThe number of intervals tolerated at a constant +6 Gz (the sponse time was considered the SRT. In the initial phase, “lower” ATL group, ATL 3-5 intervals, and the “higher” the pilots were progressively subjected to increasing acATL group, ATL 6-8 intervals) served as the betweenceleration in the range of 4, 4.5, 5.1, and 5.3 +Gz. In the subjects variable. interval acceleration of the main program phase, the Each significant result was calculated using the ŋ2 meamethod used applied a gradual increase of the system sures. The assumption of normality was tested using the load up to the maximum limit of +6 Gz. The acceleration Kolmogorov-Smirnov test. Huynh-Feldt epsilons were interval achieved at a stable +6 Gz was repeated until the used in case of sphericity assumption violation. Post hoc tested person reached ATL. This level was determined comparisons were performed with the Bonferroni test. based on the lack of response to two following stimuli IBM SPSS 17 was used for all analyses. presented in the peripheral field of vision. The speed of increase and decrease of the acceleration in the interval IngentaRESULTS to: jacob busch acceleration program was 1.5 G · s21, theDelivered duration by of the IP: 91.198.127.151 On: Wed, 13 Jul 2016 11:57:24 The tests revealed that 11 pilots did not obtain the refixed acceleration 15 s, and the breaksCopyright: between the interAerospace Medical Association quired minimum of three acceleration intervals at +6 Gz, vals were also 15 s. Fig. 1 presents the acceleration opexperiencing loss of vision before three intervals and eration program. It should be noted that during the thereby finishing the tests. The remaining 29 pilots toltests, in all centrifuge runs, other physiological paramerated the initial intervals with no disturbances and, in eters were routinely recorded which are not reported in the course of further acceleration increases in successive this paper.
Fig. 1. Experimental acceleration program. The circles with numbers in them represent the number of pilots who obtained the maximum values of Gz (ATL) in each interval.
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+GZ INTERVALS & REACTION TIME—TRUSZCZYNSKI ET AL. intervals, they achieved the maximum planned level of were close to those obtained in the control measurements. It is worth noting that SRT during +6 Gz expo+6 Gz, completing the test at ATL. Fig. 1 presents the resure was not significantly longer (P . 0.05) compared sult of the number of participants who passed the given with the reaction time between each of the intervals exposure to acceleration on the consecutive levels of the (first, middle, and last). applied acceleration program. Thus, this figure shows The analysis of intergroup differences was performed the changes in the number of the subjects in each interwith the division of the experimental results taking the val ranging from +5.3 Gz to the last interval at +6 Gz, ATL obtained by the participants (number of intervals of which was achieved by seven pilots. +6 Gz) into account. There were 17 subjects compared in Fig. 2 presents the results of SRT and the relative numthe “lower” ATL group with 3-5 intervals and 12 subber of erroneous responses for the 29 subjects qualified jects in the “higher” ATL group with 6-8 intervals. Fig. 3 for further analysis. In comparison with the control test, a graphically shows the changes in mean response time marked increase in SRT in the first interval of +6 Gz did and reaction errors in each phase of the test (measurenot undergo significant changes during the course of the ment point) for each ATL group. test (the middle and the last interval). Reaction time SD, The main effect of the ATL group was not statistically comparable with one another in these points of measuresignifi cant [F(1,27) 5 0.095, P 5 0.761]. The effect of the ment, was two times higher than the value for the control interactions between the measurement point and the measurement and the measurement made 60 s after stopnumber of intervals was not statistically significant ping the centrifuge. The percentage of SRT errors in the [F(3,87) 5 0.82, P 5 0.494, e 5 0.811]. This means that analyzed group of 29 pilots is shown in Fig. 2, while the reaction time was the same in the “lower” and “higher” results for the intergroup analysis (number of ATL intercentrifugation groups. Analysis of erroneous reactions vals) are presented in Fig. 3. showed similarity to SRT results, indicating no statistiThe analysis of the obtained results indicates a signifi Delivered by Ingentacally to: jacob busch signifi cant differences in the incorrect responses cant effect of the applied acceleration on response time IP: 91.198.127.151 On: Wed, 13 Jul 2016 11:57:24 2 between each ATL group. Analysis of the Spearman e 5 0.776]. The Medical Association [F(3,87) 5 164.864, P , 0.001, ŋ 5 0.855, Copyright: Aerospace rank correlation coefficient showed no significant relaanalysis of the SRT shows that, with the next interval, tionship between SRT and SRT errors in each of the ATL the response time is not significantly different. The regroups. sponse times recorded in the first interval, the middle interval, and the last interval of +Gz exposure were sigDISCUSSION nificantly longer (P , 0.001) compared with the control values. However, in the first minute after stopping the During the development of the interval acceleration procentrifuge, the SRT shortened significantly compared gram presented in Fig. 1, its authors sought to obtain information on the changes in SRT during stochastically with the last interval of +6 Gz (P , 0.001). The values
Fig. 2. SRT and SRT errors in response (N 5 29). Squares are SRT measurements and triangles are SRT errors. Aviation, Space, and Environmental Medicine x Vol. 85, No. 11 x November 2014
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+GZ INTERVALS & REACTION TIME—TRUSZCZYNSKI ET AL.
Delivered by Ingenta to: jacob busch IP: 91.198.127.151 On: Wed, 13 Jul 2016 11:57:24 Copyright: Aerospace Medical Association Fig. 3. SRT and SRT errors in response in the “lower” and “higher” ATL groups.
presented visual stimuli. To this end, in our study we used +6 Gz acceleration values in intervals lasting 15 s. According to Burton et al. (4), the values of these parameters are referred to as high sustained G (HSG) and, thus, they should be classified as a significantly high organism load. The authors suggest the desirability of seeking ways to increase HSG, which could alleviate the difficulty of tolerating the effort during +Gz. It should be emphasized that in our tests, forming the HSG acceleration threshold, we used a suitably calibrated tensioning force of the skeletal muscle, which facilitated the +6 Gz interval tolerances. From the studies of other authors (12,16,23), it is known that in the first period of exposure to +Gz acceleration, shortening of the simple response time to light stimulus occurs. During this time, increased heart rate provides better blood circulation in the eyes, allowing efficient and quick response. This is why the interval acceleration program used in our research included the initial phase of exposure (four +Gz plateaus prior to the first +6 Gz plateau) for pilots who achieved acceleration values above +6 Gz. The expected outcome of the applied acceleration program was an increase, progressing with the next exposure to +6 Gz, in SRT. However, the obtained results do not confirm these assumptions. The reaction time at each of the measuring points in the +6 Gz level (first, middle, and last) was not significantly different. Lalande (15) showed a similar finding in pilot visual performance, that visual rating during SACM exposure with short and long +Gz pauses did not change significantly. It must be assumed, therefore, that the 15-s intervals used between each +6 Gz exposure were an appropriate 1118
period to prepare the pilots for the next acceleration stimulus. It is worth noting that the variability of reaction time during exposure to +6 Gz [SD (first; middle; last) 5 80.9; 64.3; 79 in Fig. 2] is more than two times higher than the value set for the control measurement (SD 5 30.4) and the final measurement (SD 5 24.6) after stopping the centrifuge. During exposure to acceleration intervals at the constant level of +6 Gz, a statistically significant increase occurs in SRT compared with the time registered at the baseline measurement. Similar differences were obtained with respect to measurements taken 1 min after stopping the centrifuge. In this case, a statistically significant difference was seen at each of the three analyzed measurement points recorded during exposure to +6 Gz acceleration. We found that immediately after exposure to acceleration, visual-motor simple reaction time reached values similar to the baseline. This is confirmed by the results of our other studies (18), which show that after the cessation of acceleration stimulus, response time returns to the state observed in the period prior to acceleration exposure. The results of the analysis of response times in comparison with the intergroup ATL factor showed no statistically significant differences. This means that in the course of the study, the nature of the reaction time changes proceeded in a manner slightly different both in the group with high ATL (6–8 intervals) and low ATL (3–5 intervals). The number of erroneous responses made during the maximum effect of individual intervals, including too quick reactions, too slow reactions, and no single response to stimuli, varied in all subjects. On the basis of
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+GZ INTERVALS & REACTION TIME—TRUSZCZYNSKI ET AL. however, use the gradual exposure to the maximum the literature and our studies (20,27), we found that the value of +6 Gz (initial phase) with exposure to the first erroneous responses observed in our study are indicathree intervals on a +6 Gz plateau to effectively differentors of the functional scope of attention. We excluded tiate pilots who are highly qualified in aerial combat. In no-response reactions indicating a loss of visual field order to enhance the credibility of the research program and immediately preceding the ATL, which resulted in with respect to the qualifications of pilots in air combat, stopping the centrifuge, from the calculation. the authors suggest increasing the number of research The gradual exposure of the body to the maximum groups in this program and performing comparative value of +6 Gz (initial phase) with exposure to the first three intervals on the +6 Gz plateau effectively differentests using methods of increasing G tolerance (for extiated pilots who are highly qualified in aerial combat. ample, the anti-G suit, or the L-1 AGSM). This is confirmed by the 11 pilots, representing nearly ACKNOWLEDGMENT 25% of the study group, who did not achieve the exAuthors and affiliations: Olaf Truszczynski, Ph.D., Department pected minimum of three intervals of +6 Gz. of Flight Safety, Rafal Lewkowicz, M.Sc., Aeromedical Training The problem of mental load during substantial physiDivision, Prof. Mieczyslaw Wojtkowiak, M.D., Ph.D., Department cal load affecting the body was studied by Jaśkowski of Aviation Physiology, and Marcin P. Biernacki, Ph.D., Department of Aviation Psychology, Military Institute of Aviation Medicine, (10), who argued that changes in visual perception, exWarsaw, Poland. pressed by time change in the physical factor, make it possible to specify the functional scope of attention. AcREFERENCES cording to some authors (14,18,21), the measurement of 1. Bain B, Jacobs I, Buick F. 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Reaction Time in Pilots During Intervals of High Sustained G Olaf Truszczynski, Rafal Lewkowicz, Mieczyslaw Wojtkowiak, and Marcin P. Biernacki TRUSZCZYNSKI O, LEWKOWICZ R, WOJTKOWIAK M, BIERNACKI MP. horizontal bar at a fixed distance from the eyes. A center Reaction time in pilots during intervals of high sustained G. Aviat red light is used as fixation point and the criterion for Space Environ Med 2014; 85:1114–20. central vision loss (blackout) is when intensity dims conIntroduction: An important problem for pilots is visual disturbances siderably or disappears. Peripheral light loss is estaboccurring under +Gz acceleration. Assessment of the degree of intensification of these disturbances is generally accepted as the acceleration lished by disappearance of flashing green lights placed tolerance level (ATL) criterion determined in human centrifuges. The aim at 15–25° on each side of the center red light (17). One of of this research was to evaluate the visual-motor responses of pilots durthe newest types of devices for the subjective assessment ing rapidly increasing acceleration contained in cyclic intervals of +6 Gz of loss of peripheral vision is a 180° curved light bar to the maximum ATL. Methods: The study involved 40 male pilots ages 32–41 yr. The task was a quick and faultless response to the lightby stimuli Delivered Ingentawhich to: jacob wasbusch used at the Naval Air Development Center presented on a light bar during exposure IP: to acceleration until reaching 91.198.127.151 On: Wed, 2016 11:57:24 for13 theJul dynamic tracking of a subject's peripheral vision the ATL. Simple response time (SRT) measurements were performed Copyright: Aerospace Medical Association in acceleration physiology (9). during experiments using a visual-motor analysis system throughout the exposures which The key indicator recorded during the examination allowed assessment of a pilot’s ATL. Results: There were 29 pilots who tolerated the initial phase of interval acceleration and achieved +6 Gz, of the impact of acceleration is simple reaction time completing the test at ATL. Relative to the control measurements, the (SRT) to visual stimuli. Measurements of this indicator, obtained results indicate a significant effect of the applied acceleration together with the assessment of cardiovascular indices on response time. SRT during +6 Gz exposure was not significantly londuring acceleration with different parameters, can be ger compared with the reaction time between each of the intervals. SRT and erroneous reactions indicated no statistically significant differences the basis for the initial and periodic assessment of peobetween the “lower” and “higher” ATL groups. Conclusion: SRT meaple susceptible to this factor. Empirical data can also be surements over the +6-Gz exposure intervals did not vary between gathered which, subjected to analysis and interpreta“lower” and “higher” ATL groups and, therefore, are not useful in pretion, can also help explore the psychological meaning dicting pilot performance. The gradual exposure to the maximum value of +6 Gz with exposure to the first three intervals on the +6-Gz plateau of the revealed dependencies (7,10,13). This issue was effectively differentiated pilots. addressed by many researchers (8,11,26), who found Keywords: +Gz tolerance, acceleration tolerance level, simple response reduced ability to perform tasks under conditions of time, repeated exposure, simulated air combat maneuver.
A
PILOT’S FUNCTIONING during flight requires continuous observation of objects in the visual field, analysis of the onboard instruments’ indications related to the control system, and perception of different stimuli and information provided by other participants involved in the task being performed. Working conditions in the changing environment of flight require the ability to concentrate, divided attention, a sense of spatial orientation, very good eye-hand coordination, and a fast and reliable response to the threat from the pilot. These facts underlie the need to analyze changes in eye function while examining the impact of acceleration on humans in centrifuges. The basis for this kind of research was, in addition to the standard physiological parameters, the introduction of equipment that records the perception of light signals using a perimeter. Loss of peripheral vision measured by the subject tracking his peripheral vision on a light bar is an accepted measure of tolerance limits (Air Standardization Coordinating Committee, Joint Base Andrews, MD). The first centrifuges used a fixed set of three colored light signals arranged on a
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acceleration. Numerous published studies on repeated +Gz exposure to simulated aerial combat maneuvers (SACM) (1,5,6) focused mainly on assessing the impact of SACM on changes of physiological parameters and G tolerance. However, in these articles, there is no reference to the impact of repeated accelerations on the SRT. The interval program developed in the Polish Military Institute of Aviation Medicine (MIAM) in Warsaw (25), similarly to the ones used by other authors (4), meets the criteria for selection and training. The program, named “Selective interval program for the acceleration From the Department of Flight Safety, the Aeromedical Training Division, the Department of Aviation Physiology, and the Department of Aviation Psychology, Military Institute of Aviation Medicine, Warsaw, Poland. This manuscript was received for review in March 2014. It was accepted for publication in August 2014. Address correspondence and reprint requests to: Mieczyslaw Wojtkowiak or Rafal Lewkowicz, Krasinskiego 54/56, 01-755 Warszawa, Poland; [email protected] or [email protected]. Reprint & Copyright © by the Aerospace Medical Association, Alexandria, VA. DOI: 10.3357/ASEM.4009.2014
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+GZ INTERVALS & REACTION TIME—TRUSZCZYNSKI ET AL. tolerance level (ATL) assessment,” is complemented by preparatory training and characterized by rapid escalation of acceleration. The increase in the speed of high-performance aircraft has led to the introduction of new research programs in human centrifuges characterized by intervals of rapidly increasing acceleration. In connection with this, the above-mentioned selection program required supplementation of the tests for pilots involved in high acceleration flights. The aim of our study was to evaluate the visual-motor responses of pilots during rapidly increasing acceleration contained in cyclic intervals of +6 Gz to the maximum acceleration tolerance level (ATL). In addition, we adopted two hypotheses: 1) with each subsequent interval of acceleration at +6 Gz, SRT will statistically significantly increase; and 2) development of a research program, based on the measurement of SRT, will allow the selection of pilots while assessing their suitability to air combat.
found in Biernacki et al. (2). Response time measurements were performed using the visual-motor analysis system developed at MIAM (22,24,28). The device consists of a computer, sending and receiving stochastically programmed visual stimuli, and a light bar located on both sides of the examined person at the eye level. The bar has three rows of 64 white, green, and red lights (3mm diameter LEDs), but in this study we used only the green light. The ambient light level in the cabin, LEDs, and central light were constant. The bar has a field-ofview of 185°. The system was equipped with the device, ensuring the possibility of selecting the presented stimuli with a light intensity of 50 cd · m22 with moves at a randomly selected speed of 2 m · s21 along the side arms of the device in the direction from the periphery to the central point of visual fixation. The light bar was described in detail elsewhere (19). The program of light stimuli presentation was started from the same point of examination for each pilot. During the exposure, the participants were told to concenMETHODS trate their gaze on the central light point. The subjects’ task was a quick and accurate response to the changes Subjects Delivered by Ingentaobserved to: jacob in busch the presentation of the visual stimuli. When IP: 91.198.127.151 13 Jul 2016 11:57:24 Tested in the human centrifuge at MIAM wereOn: 40 Wed, the subject could no longer see the stimuli and there was Copyright: Association male volunteer pilots, ages 32-41 yr (35 6 3),Aerospace highly Medical no response while the visual stimuli were moving along qualified in aerial combat, and actively engaged in the arms of the perimeter, it was assumed the subject high-acceleration flights. After the research program had lost eye-level blood pressure and, thus, also periphwas approved by the Ethics Committee at MIAM, each eral vision, and the centrifuge was stopped. When the participant was thoroughly familiarized with the methlight stimulus appeared in the peripheral field of view, odology of the research, security conditions, and the the pilot pressed the circuit breaker to signal this to the light stimuli task, and signed a consent form. As a next computer. The computer sent back the next signal accordstep, the pilots were tested by the Central Military ing to the experimental profile program. The range beAviation Medical Commission and accepted as able to tween stochastically sent signals was from 0.8 to 3.0 s. The tolerate accelerations in the centrifuge. The subjects subjects always responded at the moment they noticed were experienced in acceleration endurance during conthe visual stimuli appearing on the side arms. The movtinuous flight training or from yearly centrifuge examiing points of light presented on the arms of the device nations of their ATL. The subjects did not wear an anti-G were extinguished after the button was pressed, or when suit. They did not perform an L-1 anti-G straining mathe light reached the central point of visual fixation. neuver (AGSM), but employed mainly muscular strainFor the study, we defined a range of correct SRT. For ing of the lower limbs and abdomen. The subjects were fast SRT we have taken 200 ms on the basis of previous seated at a reclined angle of 12° relative to the vertical, research results (3). For the upper limit of the correct rewith the arms supported at the heart level. The feet were sponse we assumed 800 ms, applied and validated in supported on the rudder pedals, making it possible to studies (25). Response times not within the range of 200 perform a muscular strain. Before the test, each pilot exto 800 ms were classified as wrong responses or a lack of erted pressure on the pedals at maximal effort, in this reaction. This group of erroneous responses was defined way determining the baseline level. The baseline value as SRT errors. Therefore, the number of errors in each of of the pressure was presented on a monitor installed in the measuring points was a sum of three incorrect rethe cab and the displayed pressures were monitored in sponses: too fast (, 200 ms), too slow (. 800 ms), and the control room. At the onset of visual symptoms, the lack of reaction. pilots were instructed to perform a muscular strain at Procedure about 50% of their maximum strain until normal vision reappeared. Due to the need for research conducted unThe testing began with a briefing. Under the accelerader the conditions of acceleration, only those subjects tion conditions, the subjects became acquainted with the who endured the applied acceleration of at least three exposure and how to respond to the stochastically ex+6 Gz acceleration intervals were selected to participate hibited stimuli in the peripheral field of vision. The in the study. mode of operation of the centrifuge, with the self-control Equipment The research was conducted in the human centrifuge at MIAM. More details about this centrifuge can be
option switched on, made it possible for the subjects to increase or decrease the acceleration values at their will within the range from 1.4 (baseline) to +3 Gz, with a constant rise in speed of 1.5 G · s21. The training time
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+GZ INTERVALS & REACTION TIME—TRUSZCZYNSKI ET AL. Statistical Analyses was 3 min. After 30 min of rest, the pilots were subjected to the experimental protocol of the study. For comparative analysis, SRT arithmetic mean and The main part of the test including SRT measurements erroneous reactions were calculated for the following was conducted via a control phase, during operation of phases of the study: 1 min before centrifugation (control the interval acceleration in the initial phase and main measurement); the first, middle, and last level of conprogram phase, and after its completion. The SRT meastant acceleration at +6 Gz; and 1 min after stopping the surements were commenced 60 s before the start of the centrifuge. SRT and error reaction variations during the centrifuge (control measurement) and continued uninexperiment were analyzed by means of two-way ANOVA terrupted until 60 s after the centrifuge stopped. The with repeated measures. The measurement time point pilots had to react to the light stimuli exhibited stochaswas the within-subject variable during the experiment. tically in the peripheral field of vision. The recorded reThe number of intervals tolerated at a constant +6 Gz (the sponse time was considered the SRT. In the initial phase, “lower” ATL group, ATL 3-5 intervals, and the “higher” the pilots were progressively subjected to increasing acATL group, ATL 6-8 intervals) served as the betweenceleration in the range of 4, 4.5, 5.1, and 5.3 +Gz. In the subjects variable. interval acceleration of the main program phase, the Each significant result was calculated using the ŋ2 meamethod used applied a gradual increase of the system sures. The assumption of normality was tested using the load up to the maximum limit of +6 Gz. The acceleration Kolmogorov-Smirnov test. Huynh-Feldt epsilons were interval achieved at a stable +6 Gz was repeated until the used in case of sphericity assumption violation. Post hoc tested person reached ATL. This level was determined comparisons were performed with the Bonferroni test. based on the lack of response to two following stimuli IBM SPSS 17 was used for all analyses. presented in the peripheral field of vision. The speed of increase and decrease of the acceleration in the interval IngentaRESULTS to: jacob busch acceleration program was 1.5 G · s21, theDelivered duration by of the IP: 91.198.127.151 On: Wed, 13 Jul 2016 11:57:24 The tests revealed that 11 pilots did not obtain the refixed acceleration 15 s, and the breaksCopyright: between the interAerospace Medical Association quired minimum of three acceleration intervals at +6 Gz, vals were also 15 s. Fig. 1 presents the acceleration opexperiencing loss of vision before three intervals and eration program. It should be noted that during the thereby finishing the tests. The remaining 29 pilots toltests, in all centrifuge runs, other physiological paramerated the initial intervals with no disturbances and, in eters were routinely recorded which are not reported in the course of further acceleration increases in successive this paper.
Fig. 1. Experimental acceleration program. The circles with numbers in them represent the number of pilots who obtained the maximum values of Gz (ATL) in each interval.
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+GZ INTERVALS & REACTION TIME—TRUSZCZYNSKI ET AL. intervals, they achieved the maximum planned level of were close to those obtained in the control measurements. It is worth noting that SRT during +6 Gz expo+6 Gz, completing the test at ATL. Fig. 1 presents the resure was not significantly longer (P . 0.05) compared sult of the number of participants who passed the given with the reaction time between each of the intervals exposure to acceleration on the consecutive levels of the (first, middle, and last). applied acceleration program. Thus, this figure shows The analysis of intergroup differences was performed the changes in the number of the subjects in each interwith the division of the experimental results taking the val ranging from +5.3 Gz to the last interval at +6 Gz, ATL obtained by the participants (number of intervals of which was achieved by seven pilots. +6 Gz) into account. There were 17 subjects compared in Fig. 2 presents the results of SRT and the relative numthe “lower” ATL group with 3-5 intervals and 12 subber of erroneous responses for the 29 subjects qualified jects in the “higher” ATL group with 6-8 intervals. Fig. 3 for further analysis. In comparison with the control test, a graphically shows the changes in mean response time marked increase in SRT in the first interval of +6 Gz did and reaction errors in each phase of the test (measurenot undergo significant changes during the course of the ment point) for each ATL group. test (the middle and the last interval). Reaction time SD, The main effect of the ATL group was not statistically comparable with one another in these points of measuresignifi cant [F(1,27) 5 0.095, P 5 0.761]. The effect of the ment, was two times higher than the value for the control interactions between the measurement point and the measurement and the measurement made 60 s after stopnumber of intervals was not statistically significant ping the centrifuge. The percentage of SRT errors in the [F(3,87) 5 0.82, P 5 0.494, e 5 0.811]. This means that analyzed group of 29 pilots is shown in Fig. 2, while the reaction time was the same in the “lower” and “higher” results for the intergroup analysis (number of ATL intercentrifugation groups. Analysis of erroneous reactions vals) are presented in Fig. 3. showed similarity to SRT results, indicating no statistiThe analysis of the obtained results indicates a signifi Delivered by Ingentacally to: jacob busch signifi cant differences in the incorrect responses cant effect of the applied acceleration on response time IP: 91.198.127.151 On: Wed, 13 Jul 2016 11:57:24 2 between each ATL group. Analysis of the Spearman e 5 0.776]. The Medical Association [F(3,87) 5 164.864, P , 0.001, ŋ 5 0.855, Copyright: Aerospace rank correlation coefficient showed no significant relaanalysis of the SRT shows that, with the next interval, tionship between SRT and SRT errors in each of the ATL the response time is not significantly different. The regroups. sponse times recorded in the first interval, the middle interval, and the last interval of +Gz exposure were sigDISCUSSION nificantly longer (P , 0.001) compared with the control values. However, in the first minute after stopping the During the development of the interval acceleration procentrifuge, the SRT shortened significantly compared gram presented in Fig. 1, its authors sought to obtain information on the changes in SRT during stochastically with the last interval of +6 Gz (P , 0.001). The values
Fig. 2. SRT and SRT errors in response (N 5 29). Squares are SRT measurements and triangles are SRT errors. Aviation, Space, and Environmental Medicine x Vol. 85, No. 11 x November 2014
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Delivered by Ingenta to: jacob busch IP: 91.198.127.151 On: Wed, 13 Jul 2016 11:57:24 Copyright: Aerospace Medical Association Fig. 3. SRT and SRT errors in response in the “lower” and “higher” ATL groups.
presented visual stimuli. To this end, in our study we used +6 Gz acceleration values in intervals lasting 15 s. According to Burton et al. (4), the values of these parameters are referred to as high sustained G (HSG) and, thus, they should be classified as a significantly high organism load. The authors suggest the desirability of seeking ways to increase HSG, which could alleviate the difficulty of tolerating the effort during +Gz. It should be emphasized that in our tests, forming the HSG acceleration threshold, we used a suitably calibrated tensioning force of the skeletal muscle, which facilitated the +6 Gz interval tolerances. From the studies of other authors (12,16,23), it is known that in the first period of exposure to +Gz acceleration, shortening of the simple response time to light stimulus occurs. During this time, increased heart rate provides better blood circulation in the eyes, allowing efficient and quick response. This is why the interval acceleration program used in our research included the initial phase of exposure (four +Gz plateaus prior to the first +6 Gz plateau) for pilots who achieved acceleration values above +6 Gz. The expected outcome of the applied acceleration program was an increase, progressing with the next exposure to +6 Gz, in SRT. However, the obtained results do not confirm these assumptions. The reaction time at each of the measuring points in the +6 Gz level (first, middle, and last) was not significantly different. Lalande (15) showed a similar finding in pilot visual performance, that visual rating during SACM exposure with short and long +Gz pauses did not change significantly. It must be assumed, therefore, that the 15-s intervals used between each +6 Gz exposure were an appropriate 1118
period to prepare the pilots for the next acceleration stimulus. It is worth noting that the variability of reaction time during exposure to +6 Gz [SD (first; middle; last) 5 80.9; 64.3; 79 in Fig. 2] is more than two times higher than the value set for the control measurement (SD 5 30.4) and the final measurement (SD 5 24.6) after stopping the centrifuge. During exposure to acceleration intervals at the constant level of +6 Gz, a statistically significant increase occurs in SRT compared with the time registered at the baseline measurement. Similar differences were obtained with respect to measurements taken 1 min after stopping the centrifuge. In this case, a statistically significant difference was seen at each of the three analyzed measurement points recorded during exposure to +6 Gz acceleration. We found that immediately after exposure to acceleration, visual-motor simple reaction time reached values similar to the baseline. This is confirmed by the results of our other studies (18), which show that after the cessation of acceleration stimulus, response time returns to the state observed in the period prior to acceleration exposure. The results of the analysis of response times in comparison with the intergroup ATL factor showed no statistically significant differences. This means that in the course of the study, the nature of the reaction time changes proceeded in a manner slightly different both in the group with high ATL (6–8 intervals) and low ATL (3–5 intervals). The number of erroneous responses made during the maximum effect of individual intervals, including too quick reactions, too slow reactions, and no single response to stimuli, varied in all subjects. On the basis of
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+GZ INTERVALS & REACTION TIME—TRUSZCZYNSKI ET AL. however, use the gradual exposure to the maximum the literature and our studies (20,27), we found that the value of +6 Gz (initial phase) with exposure to the first erroneous responses observed in our study are indicathree intervals on a +6 Gz plateau to effectively differentors of the functional scope of attention. We excluded tiate pilots who are highly qualified in aerial combat. In no-response reactions indicating a loss of visual field order to enhance the credibility of the research program and immediately preceding the ATL, which resulted in with respect to the qualifications of pilots in air combat, stopping the centrifuge, from the calculation. the authors suggest increasing the number of research The gradual exposure of the body to the maximum groups in this program and performing comparative value of +6 Gz (initial phase) with exposure to the first three intervals on the +6 Gz plateau effectively differentests using methods of increasing G tolerance (for extiated pilots who are highly qualified in aerial combat. ample, the anti-G suit, or the L-1 AGSM). This is confirmed by the 11 pilots, representing nearly ACKNOWLEDGMENT 25% of the study group, who did not achieve the exAuthors and affiliations: Olaf Truszczynski, Ph.D., Department pected minimum of three intervals of +6 Gz. of Flight Safety, Rafal Lewkowicz, M.Sc., Aeromedical Training The problem of mental load during substantial physiDivision, Prof. Mieczyslaw Wojtkowiak, M.D., Ph.D., Department cal load affecting the body was studied by Jaśkowski of Aviation Physiology, and Marcin P. Biernacki, Ph.D., Department of Aviation Psychology, Military Institute of Aviation Medicine, (10), who argued that changes in visual perception, exWarsaw, Poland. pressed by time change in the physical factor, make it possible to specify the functional scope of attention. AcREFERENCES cording to some authors (14,18,21), the measurement of 1. Bain B, Jacobs I, Buick F. Respiratory muscle fatigue during reaction times to light stimuli is particularly important simulated air combat maneuvering (SACM). Aviat Space Environ Med 1997; 68:118–25. during the occurrence of hemodynamic changes in the 2. Biernacki MP, Jankowski KS, Kowalczuk K, Lewkowicz R, Dereń critical phase of acceleration, as it indicates loss of visual M. +Gz centrifugation and mood. Aviat Space Environ Med by is Ingenta to: jacob busch perception. Ciarkowska (7) underlinesDelivered that there a 20122016 ; 83:136 –9. IP: 91.198.127.151 On: Wed, 13 Jul 11:57:24 fixed regularity between the periodCopyright: of changes in the Medical 3. Brebner JT, Welford AT. Introduction: an historical background Aerospace Association sketch. In: Welford AT, ed. Reaction times. New York: Academic perception of light stimuli on a physiological level and Press; 1980:1–23. the simple response time. Therefore, we can assume that 4. Burton RR, Leverett SD, Michaelson RD. 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