- Email: [email protected]
Mental performance during short-term and long-term spaceflight
Brain Research Reviews 28 Ž1998. 215–221
Short review
Mental performance during short-term and long-term spaceflight Dietrich Manzey ) , Bernd Lorenz German Aerospace Center (DLR), Institute of AÕiation and Space Medicine, Department of AÕiation and Space Psychology, Sportallee 54a, D-22335 Hamburg, Germany
Abstract During the last years several attempts have been made to describe changes in the mental efficiency of astronauts during space missions by means of performance monitoring studies. These studies are characterized by repeated multivariate assessment of different functions of the human information-processing system. In the present paper, a first review of performance monitoring studies during short-term and long-term spaceflight is given. Despite the comparatively small number of studies, a fairly consistent pattern of effects can be derived: Whereas no or only slight impairments of elementary and complex cognitive functions or spatial processing were found in space, clear disturbances could be identified in visuo-motor tracking and dual-task performance. Both of these latter effects appear to be closely related to adaptation to altered gravity conditions. General issues of this strategy of research are discussed which concern the disentanglement of microgravity-related effects and unspecific stress effects on mental performance under conditions of spaceflight. In addition, possible mechanisms which may be responsible for tracking disturbances under microgravity are discussed, and some directions for future human performance research in space are outlined. q 1998 Elsevier Science B.V. All rights reserved. Keywords: Spaceflight; Microgravity; Mental performance; Tracking; Dual-task; Cognitive processes
Contents 1. Introduction .
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2. Results of performance monitoring studies during short-term and long-term spaceflight . 3. Inherent problems of performance monitoring studies during spaceflight
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4. Impairments of tracking performance under microgravity: possible mechanisms .
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5. Directions of further research . 6. References .
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1. Introduction During manned spaceflight mental performance of astronauts may be affected by several external stressors. The most prominent of these stressors is microgravity which, among others, induces complex changes in the vestibular and sensory-motor system w20x. In addition, myriad others ) Corresponding author. Fax: q49-40-51-30-96-60; E-mail: [email protected]
stressors such as altered dark–light cycle, elevated CO 2 concentration in the ambient air, confinement, and high mental and physical workload are present during spaceflights, and may also entail detrimental effects on cognitive and perceptual-motor processes. Two lines of research on the impact of space-related stressors on mental performance can be distinguished. The first approach focuses on analyses of the impact of space conditions and microgravity, in particular, on specific functions of human information-processing. This research includes specific experi-
0165-0173r98r$ - see front matter q 1998 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 5 - 0 1 7 3 Ž 9 8 . 0 0 0 4 1 - 1
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D. Manzey, B. Lorenzr Brain Research ReÕiews 28 (1998) 215–221
ments on, e.g., visual information processing w12x, spatial visualization w12,13x, cognitive representation of space w8x, or mass discrimination w21x. A second approach is represented by a broad-band strategy of mental performance assessment w3,15–17,23x. This approach, referred to as performance monitoring, aims at describing a whole pattern of performance changes in the course of a space mission, and is characterized by probing a variety of mental performance functions repeatedly during spaceflight. Performance assessment is conducted by applying batteries of performance tasks which are based on theoretical models of information processing and which have been shown to react sensitively to environmental stressors, or can be assumed to be affected by alterations in the sensory-motor system induced by altered gravity conditions. The performance functions assessed include elementary and complex cognitive processes involving working memory Že.g., choice-reaction time, memory-search, logical reasoning, or mathematical processing. or spatial processing functions Že.g., mental rotation, spatial memory., perceptual-motor functions Že.g., tracking., andror higher attentional functions Že.g., attention switching, dual-task performance.. In the following a summary of recent results from performance monitoring studies during short-term and long-term spaceflight will be given. Based on this review some general conclusions will be drawn, and problems related to this strategy of research will be described. Finally, some directions for future human performance research in space will be outlined which follow from the results of performance monitoring during spaceflight.
2. Results of performance monitoring studies during short-term and long-term spaceflight During the last decade several attempts have been made to describe the time-course of different aspects of mental efficiency during spaceflights. Most of these studies were conducted during short-term space missions w3,15,16,23x. Benke et al. w3x assessed the performance of one cosmonaut in several cognitive tasks at three times during a six-day mission to the Russian space station MIR. The performance tasks used included a simple-reaction time task, a choice-reaction time task, a Stroop-like interference task, a spatial memory task, and a spatial perception task. Comparing inflight performance with pre- and postflight performance, none of these tasks revealed any significant performance decrements during the stay in space. Manzey et al. w15,16x adopted a similar but more extended singlesubject approach during an eight-day MIR mission. This experiment included six preflight and six postflight assessments, as well as a total of 13 inflight assessments during both, the approach phase in the Soyuz spacecraft, and the stay onboard MIR. In order to probe elementary cognitive functions Ži.e., logical reasoning, memory retrieval., per-
ceptual-motor functions and higher attentional functions, a subset of four task were selected: Ž1. grammatical reasoning, Ž2. memory-search, Ž3. unstable tracking, and Ž4. a dual-task consisting of unstable tracking with concurrent memory-search w1x. In accordance with the results of Benke et al. w3x speed and accuracy of short-term memory retrieval and logical reasoning were found unimpaired under conditions of spaceflight. However, clear disturbances of fine manual control movements emerged in the unstable tracking task. These performance decrements showed a striking tri-phasic time-course with most severe disturbances during the first two days in space, an intermediate recovery to preflight performance level, and a re-appearance of disturbances at the last four days on MIR. In addition, dual-task interference effects reflected in singleto-dual performance decrements in tracking andror memory-search increased considerably during the whole stay in space. From the tri-phasic time-course of tracking impairments it was concluded that they may have been caused by both, microgravity-related alterations in the sensory-motor system, as well as effects of accumulated fatigue, with the former factor primarily responsible for the large increase of tracking error at the first four assessments in space w15x. The dual-task performance decrements were proposed to result from a distortion of attentional processes known as attentional selectivity effect w9,16x. The single-subject findings of Manzey et al. were confirmed by two American experiments conducted during short-term Shuttle flights w11,23x. Although the ‘Mental Performance and Workload’ experiment of Lathan and Newman w11x during IML-1 focused primarily on the evaluation of different input devices Žjoystick, trackball. for control of a computer screen cursor, their results are worth noting here because their approach included the assessment of discrete tracking movements and memory-search performance. In accordance with the results presented above, Lathan and Newman w11x did not find any impairments of memory-search performance, but clear disruptions of tracking movements reflected by increased movement times across all input devices. Schlegel et al. w22x and Schiflett et al. w23x conducted a performance monitoring study which included daily assessments of different mental functions of three astronauts during a 13-day Shuttle mission. Using very similar tasks as Manzey et al. w15,16x they found impairments of tracking performance and time-sharing efficiency in space in two of their subjects. However, deviating from the studies cited above they also found impairments of memory-search performance in two astronauts. Given these results Schiflett et al. w23x raised the question whether their results are microgravity related or just present some sideeffects of decreased alertness and fatigue. This question arose particularly because they found some correlation between dual-task tracking performance and fatigue ratings in one of their subjects. Further converging evidence for disturbances of tracking performance and higher attentional functions has also
D. Manzey, B. Lorenzr Brain Research ReÕiews 28 (1998) 215–221
been provided by a first performance monitoring experiment during a long-term spaceflight which was conducted during a 438-days Russian space mission w17x. The results of this study are particularly interesting because they suggest a close relation of tracking disturbances and attentional selectivity effects to adaptation to altered gravity
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conditions. In this experiment the same set of tasks was used as in the study of Manzey et al. w15,16x. In addition, several subjective ratings concerning mood and workload were collected. The experiment included a total of 41 experimental sessions Ž4 preflight baseline assessments, 29 inflight assessments, 6 postflight assessments, and 2 fol-
Fig. 1. Results from performance monitoring study during long-term spaceflight w17x. ŽA. Mean response rates Žline graph. and mean error rates Žbars. for grammatical reasoning task across preflight, inflight, and postflight assessments. ŽB. Time-course of mean tracking error across preflight, inflight, and postflight assessments. ŽC. Time-course of subjective fatigue-ratings across preflight, inflight, and postflight assessments. The horizontal lines in A and B correspond to the upper and lower confidence limits for pairwise comparisons ŽBonferroni contrasts. between average preflight performance at days y87 and y34 and all subsequent sessions.
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low-up assessments six months after landing.. Comparisons of inflight and postflight assessments with preflight baseline assessments y87 and y34 days prior to launch revealed the following pattern of statistically reliable effects Žsee Fig. 1.: Ž1. Significant impairments of elementary cognitive functions as assessed by the grammatical reasoning task were found only during the last three days prior to launch. After entering the space environment, performance in this cognitive task recovered rapidly to preflight baseline level and remained more or less stable afterwards until follow-up assessments ŽFig. 1a.. A quite similar picture also emerged for the memory-search task. Ž2. In contrast, tracking performance declined significantly during the first week in space. As becomes evident from Fig. 1b this effect turned out to represent a transient phenomenon, and a complete recovery of tracking performance to preflight baseline level was achieved within the first three weeks in space. After this period, tracking performance remained impressively stable throughout the following 13 months of the mission. However, clear tracking disturbances re-appeared during the first two postflight assessments. Again a recovery of tracking performance could be observed within two weeks, and tracking disturbances were not seen any more at follow-up assessments half a year after the mission. Ž3. Impairments of dual-task performance were observed only during some single experimental sessions. Even though this did not confirm the far more pronounced impairments found during short-term flights, it was striking that these dual-task effects, if any, also occurred during the first two weeks in space and after return to Earth. Ž4. Corresponding to the impairments of tracking and dual-task performance, the subjective data indicated feelings of raised workload and increased fatigue ŽFig. 1c. during the first three weeks in space and the first two weeks after landing. In summary, the different performance monitoring studies conducted so far clearly prove the feasibility of this approach to describe the impact of the environmental changes in space on different mental functions. Moreover, the performance effects observed in these studies present a fairly consistent pattern of results. Whereas no or only slight impairments of basic and complex cognitive functions or spatial processing were found, clear disturbances could be identified in several studies for visuo-motor tracking and higher attentional functions involved in dualtask performance. And both of these latter effects appear to be related to the adaptation to altered gravity conditions.
3. Inherent problems of performance monitoring studies during spaceflight Major problems of performance monitoring studies concern the small sample size, the generalizability of results and the explanation of effects. Small sample sizes which raise the problem of lack of statistical power represent a
problem which is common to all kinds of life science experiments during spaceflight and which is not limited to performance monitoring studies alone w5x. However, in contrast to other experiments, performance monitoring approaches provide the advantage of a number of repeated measurements which allow for an application of statistical single-subject methods with comparatively high statistical power. One example of these approaches combine a general linear model approach to analysis of variance with a test on autocorrelated residuals w14x, and has been used by Manzey et al. w15–17x. Another approach is based on fitting learning curves to results of repeated preflight performance assessments in order to derive predicted performance scores for comparison with inflight performance and has been applied by Schiflett et al. w23x. Thus, most of the findings reviewed above can be regarded as reliable results for the individual astronauts involved in the different studies. More difficult to evaluate is the generalizability of these findings. Given the comparatively small number of performance monitoring studies during spaceflight covering results from only a few astronauts, the currently available data base is too small to warrant any definite conclusions about mental efficiency during spaceflight. Therefore, even though the convergence of results is impressive, the conclusions drawn above have to be regarded as preliminary. The third and most important problem, however, concerns the identification of the specific causes for the performance effects found in the different studies. Firstly, it remains unclear whether unimpaired cognitive performance in space indeed reflects absence of any spacerelated influence upon a given performance component. Alternatively, it could be argued that possible performance effects have been masked by some compensatory effort of the astronauts in performing the given tasks. The strategy pursued up to now, to rely on comparatively global performance scores in order to identify performance changes, may not be adequate to detect such effects. Similarly, also differences in the structure of cognitive processes which may not necessarily lead to overt performance decrements may have remained undetected by this kind of research. Secondly, even though disturbances of tracking performance and higher attentional functions emerged primarily during adaptation to changed gravity conditions, they do not necessarily reflect direct effects of altered gravity on sensory-motor processes. For example, during adaptation to space, generally, two different factors may have contributed to these effects Žan analogous confounding of effects may be expected during re-adaptation to 1 g after prolonged spaceflight.: Ža. microgravity induced changes in the sensory-motor system which may call for an accommodation of previously learned visuo-motor skills to the new gravity conditions, and Žb. unspecific stress effects of the environmental conditions in the space habitat which, among other things, lead to impaired well-being and decreased alertness during adaptation Že.g., secondary effects
D. Manzey, B. Lorenzr Brain Research ReÕiews 28 (1998) 215–221
of physiological adaptation, effects of altered darkrlight cycle, effects of limitations of life-support system, effects of confinement.. A disentanglement of these two factors can hardly be achieved. The obvious correlation of mood ratings and performance effects in some of the studies reviewed above w17,23x suggest that tracking and dual-task disturbances in space are primarily related to disturbances of attentional processes induced by adverse effects on subjective well-being and alertness during the demanding adaptation to the living conditions in space. However, at least with regard to tracking impairments found at the very first assessments in space and after return from long-term spaceflight, there exist some evidence that also microgravity-related changes in the sensory-motor system may have contributed to these effects. For example, a comparison of preflight and inflight fatigue ratings and performance data reported by Schiflett et al. w23x showed that, although there was an obvious correlation between dual-task tracking performance and fatigue during inflight sessions in one subject, the comparatively small increment of fatigue ratings at the first inflight sessions cannot explain the clear decrement of tracking performance at this time of the mission. Similarly, some obvious dissociations of tracking performance and fatigue ratings were also found in the long-term study of Manzey et al. w17x. Even though, fatigue ratings in this study were comparatively high at days 4, 5, 11, 12, 19 and 27, large tracking performance decrements were only found at the first three assessments Ždays 4, 5, and 6. in space. In addition, also the striking tracking performance decrement at the first postflight assessment clearly could not be explained by an accompanying effect of fatigue Žcompare Fig. 1b and c.. Finally, Lathan and Newman w11x did not find effects on movement times in discrete tracking comparable to those found during IML-1 when they repeated their experiment during a ground based simulation of a 7-day Shuttle flight which resembled a real flight in almost all important aspects but microgravity. 4. Impairments of tracking performance under microgravity: possible mechanisms Lacking more specific experiments on the impact of gravitational changes on visuo-motor processes as those involved in tracking, the mechanisms which may cause microgravity-related impairments of tracking performance are not well understood, so far, and represent a matter of speculation. Since tracking represents a closed-loop visuomotor task, microgravity-related effects on tracking performance may be due to both, effects on the visual and ocular system as well as effects on motor control processes. In compensatory tracking, continuous feedback of tracking error is provided by visually pursuing the position of the continuously moving cursor which directly displays the direction and amplitude of tracking error w24x. Consequently, it might be supposed that distortions of pursuit
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eye-movements due to microgravity-induced changes in the vestibulo-ocular system may contribute to impairments of tracking performance during the first days in space. However, pursuing the cursor of compensatory tracking tasks as used in the studies cited above typically includes a range of only some 3 to 4 degrees in the horizontal plane where first studies have been shown that microgravity does not alter the characteristics of pursuit eye-movements w2x. More likely, then, the tracking impairments seen in the first assessments after gravitational changes may be attributed to alterations in the motor system under microgravity. This assumption gets support from results of space experiments and ground based studies which suggest that changes in gravity conditions require adjustments of existing central motor programs and cause substantial changes of proprioceptive processes associated with execution of precise voluntary movements w4,6,7x. In tracking tasks proprioceptive information from joint-position and muscle-tension related receptors provides feedback about the system dynamics of the task w25x. Distortions of this feedback under microgravity would convey information that the dynamics of the task have been altered which, in turn, would conflict with unchanged visual cues from the task. Such a conflict between proprioceptive and visual cues would cause some confusion and could be responsible for disturbances of tracking performance at least at the first performance of the task after gravitational changes. In addition, also changes in the kinematics of movements may affect tracking performance. Analyzing visually guided pointing arm movements in the horizontal plane, Berger et al. w4x found no effects on accuracy but significant alterations of kinematics of these movements in space. In particular, they found a general slowing of movement times, a decrease of peak velocity, and alterations of the acceleration time-profile of movements compared to preflight values, indicating more slow and cautious movements under microgravity. Berger et al. w4x attribute these results to enhanced demands on ‘intra-movement control’ ww4x, p. 786x associated with the need to elaborate and establish new motor patterns in order to adapt to microgravity-induced changes in the sensory-motor system. Similar effects of microgravity on fine manual control movements in tracking tasks which typically involve a complex pattern of accelerative and decelerative phases may cause increments in tracking error by increasing the ‘effective time delay’ and decreasing the tracking gain Ži.e., ratio of amplitude of compensatory movement to amplitude of tracking error. in the control-loop w24x. However, it must be taken into account that most of the research concerning adjustments of central motor programs and distortions of proprioception associated with precise voluntary movements under changed gravity, so far, has largely been limited to discrete aimed arm movements. It remains to be shown whether similar effects indeed are to be expected in fine continuous control movements as those involved in tracking tasks.
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5. Directions of further research What may be concluded from the results of performance monitoring studies during spaceflight for future research? First, the strategy of multivariate performance monitoring studies in space, i.e., the analysis of changes in performance patterns in the course of a space mission, represents a suitable approach to identify specific effects of the space environment on human information processing functions and its time-course of adaptation, and should be continued in order to enlarge the existing data base and to cross-validate the previous results. For this purpose, a standardized battery of performance tasks should be defined which would assure comparability of different studies. Second, the results from the long-term study w17x suggest that at least the first three weeks in space and the first two weeks back on Earth after a prolonged spaceflight may represent critical adaptational periods which may be associated with degraded efficiency of perceptual-motor and higher attentional processes. This fact should be taken into account in scheduling and interpreting any kind of behavioral experiments on human cognition during spaceflight. Third, the tracking results of the performance monitoring studies suggest that experimental research should be conducted which describe more clearly the effects of changed gravity on fine manual control movements. Analyses of tracking performance appear to be one promising approach in this regard. Varying the directions of cursor movements to be tracked Žhorizontal, vertical, diagonal., the bandwidth of forcing functions, and the system dynamics of the control-loop provides a large spectrum of possible experimental variations inducing different demands on gaze control, cognitive involvement, and motor control. In addition, the mathematical and psychological models which have been developed to describe human tracking behavior, e.g., quasi-linear cross-over models w18x or optimal control models w10x are well validated and provide a sound theoretical basis for modeling and predicting human performance in manual control. Furthermore, they provide sophisticated methodological approaches for microanalyses of tracking behavior which yield precise descriptions of different human characteristics in manual control Že.g., time-delay, gain, non-linear elements. w24x, and which may be used to identify fundamental changes in the sensory-motor system under the impact of altered gravity conditions. Fourth, in order to obtain a more clear picture of possible changes of cognitive and attentional processes in space, analyses of cognitive task performance should be enriched by analyses of accompanying changes in brain electrical activity. Particularly, analyses of event-related brain potentials like P300, slow DC-potentials, or even more sophisticated approaches of brain mapping may offer new insights in this regard. Such an approach could be based on the large amount of data and experience which have been accumulated in the field of cognitive psychophysiology during the last 20 years. Ground-based simulation studies w19x have
already proven the suitability of this approach under conditions comparable to those of spaceflight.
References w1x Advisory Group of Aerospace Research and Development ŽEd.., Human performance assessment methods ŽAGARDograph No. 308., AGARD, Neully Sur Seine, 1989. w2x C. Andre-Deshays, I. Israel, O. Charade, A. Berthoz, K. Popov, M. Lipshits, Gaze control in microgravity: 1. Saccades, pursuit, eye-head coordination, J. Vestibular Res. 3 Ž1993. 331–343. w3x T. Benke, O. Koserenko, N.V. Watson, F. Gerstenbrand, Space and cognition: the measurement of behavioral functions during a six-day space mission, Aviat. Space Environ. Med. 64 Ž1993. 376–379. w4x M. Berger, S. Mescheriakov, E. Molokanova, S. LechnerSteinleitner, N. Seguer, I. Kozlovskaya, Pointing arm movements in short- and long-term spaceflight, Aviat. Space Environ. Med. 68 Ž1997. 781–787. w5x P.A. Bishop, M. Greenisen, Limitations to the study of man in space in the U.S. space program, Aviat. Space Environ. Med. 64 Ž1993. 238–242. w6x O. Bock, Joint position sense in simulated changed-gravity environments, Aviat. Space Environ. Med. 65 Ž1994. 621–626. w7x O. Bock, I.P. Howard, K.E. Money, K.E. Arnold, Accuracy of aimed arm movements in changed gravity, Aviat. Space Environ. Med. 63 Ž1992. 994–998. w8x A. Friederici, W.J.M. Levelt, Resolving perceptual conflicts: the cognitive mechanism of spatial orientation, Aviat. Space Environ. Med. 58 Ž1987. A164–A169. w9x G.R.J. Hockey, Changes in operator efficiency as a function of environmental stress, fatigue, and circadian rhythms, in: K.R. Boff, L. Kaufman, J.P. Thomas ŽEds.., Handbook of Perception and Human Performance, Vol. 2, Wiley, New York, 1986, pp. 44-1–4449. w10x D.L. Kleinman, S. Baron, W.H. Levison, An optimal control model of human response, parts 1 and 2, Automatica 6 Ž1970. 337–369. w11x C.E. Lathan, D.J. Newman, Quantification of human performance in extreme environments, Adv. Hum. Fact.rErgono., Design of Comput. Syst.: Soc. and Ergono. Consid. 21B Ž1997. 1005–1008. w12x G. Leone, M. Lipshits, V. Gurfinkel, A. Berthoz, Influence of graviceptive cues at different levels of visual information processing: the effect of prolonged weightlessness, Acta Astron. 36 Ž1995. 734–751. w13x G. Leone, M. Lipshits, V. Gurfinkel, A. Berthoz, Is there an effect of weightlessness on mental rotation of three-dimensional objects?, Cogn. Brain Res. 2 Ž1995. 255–267. w14x B. Lorenz, Cognitive and psychomotor performance of divers under simulated deep-sea conditions: Methodology and results of human performance monitoring based on single-case analyses ŽDLR-FB 94-07, in German., Technical Report, DLR, Cologne, 1994. w15x D. Manzey, B. Lorenz, A. Schiewe, G. Finell, G. Thiele, Behavioral aspects of human adaptation to space: analyses of cognitive and psychomotor performance in space during an 8-day space mission, Clin. Inv. 71 Ž1993. 725–731. w16x D. Manzey, B. Lorenz, A. Schiewe, G. Finell, G. Thiele, Dual-task performance in space: Results from a single-case study during a short-term space mission, Human Factors 37 Ž1995. 667–681. w17x D. Manzey, B. Lorenz, V.V. Polyakov, Mental performance in extreme environments: results from a performance monitoring study during a 438-day space mission, Ergonomics 41 Ž1998. 537–539. w18x D.T. McRuer, H.R. Jex, A review of quasi-linear pilot models, IEEE Trans. of Hum. Fac. in Elec. 8 Ž1967. 231–249. w19x A. Mecklinger, A. Friderici, T. Gussow, Confinement affects the ¨ detection of low frequency events: An event-related potential analysis, J. Psychophys. 8 Ž1994. 98–113.
D. Manzey, B. Lorenzr Brain Research ReÕiews 28 (1998) 215–221 w20x M.F. Reschke, J.J. Bloomberg, W.H. Paloski, D.L. Harm, D.E. Parker, Neurophysiologic aspects: sensory and sensory-motor function, in: A.E. Nicogossian, C.L. Huntoon, S.L. Pool ŽEds.., Space Physiology and Medicine, Lea and Febiger, Philadelphia, 1994, pp. 261–285. w21x H.E. Ross, E. Schwartz, P. Emmerson, The nature of sensorimotor adaptation to altered G-levels: evidence from mass-discrimination, Aviat. Space Environ. Med. 58 Ž1987. A148–A152. w22x R. Schlegel, R. Shehab, S.G. Schiflett, J. French, D. Eddy, The NASA performance assessment workstation: Astronauts vs. a ground-based reference group, Paper presented to the 11th Man in Space Symposium. Toulouse, March 27–31, 1995, ŽAbstract..
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w23x S. Schiflett, D. Eddy, R. Schlegel, J. French, R. Shehab, Performance assessment workstation ŽPAWS.. Final science report to NASA, 1995. w24x C.D. Wickens, The effects of control dynamics on performance, in: K.R. Boff, L. Kaufman, J.P. Thomas ŽEds.., Handbook of Perception and Human Performance, Vol. 2, Wiley, New York, 1986, pp. 39-01–39-60. w25x C.D. Wickens, C. Kessel, The effects of participatory mode and task workload on the detection of dynamic system failures, IEEE Trans. Systems, Man, Cybern. SMC 9 Ž1979. 24–34.
Short review
Mental performance during short-term and long-term spaceflight Dietrich Manzey ) , Bernd Lorenz German Aerospace Center (DLR), Institute of AÕiation and Space Medicine, Department of AÕiation and Space Psychology, Sportallee 54a, D-22335 Hamburg, Germany
Abstract During the last years several attempts have been made to describe changes in the mental efficiency of astronauts during space missions by means of performance monitoring studies. These studies are characterized by repeated multivariate assessment of different functions of the human information-processing system. In the present paper, a first review of performance monitoring studies during short-term and long-term spaceflight is given. Despite the comparatively small number of studies, a fairly consistent pattern of effects can be derived: Whereas no or only slight impairments of elementary and complex cognitive functions or spatial processing were found in space, clear disturbances could be identified in visuo-motor tracking and dual-task performance. Both of these latter effects appear to be closely related to adaptation to altered gravity conditions. General issues of this strategy of research are discussed which concern the disentanglement of microgravity-related effects and unspecific stress effects on mental performance under conditions of spaceflight. In addition, possible mechanisms which may be responsible for tracking disturbances under microgravity are discussed, and some directions for future human performance research in space are outlined. q 1998 Elsevier Science B.V. All rights reserved. Keywords: Spaceflight; Microgravity; Mental performance; Tracking; Dual-task; Cognitive processes
Contents 1. Introduction .
.......................................................................
2. Results of performance monitoring studies during short-term and long-term spaceflight . 3. Inherent problems of performance monitoring studies during spaceflight
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216
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218
4. Impairments of tracking performance under microgravity: possible mechanisms .
...................................
219
..............................................................
220
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5. Directions of further research . 6. References .
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1. Introduction During manned spaceflight mental performance of astronauts may be affected by several external stressors. The most prominent of these stressors is microgravity which, among others, induces complex changes in the vestibular and sensory-motor system w20x. In addition, myriad others ) Corresponding author. Fax: q49-40-51-30-96-60; E-mail: [email protected]
stressors such as altered dark–light cycle, elevated CO 2 concentration in the ambient air, confinement, and high mental and physical workload are present during spaceflights, and may also entail detrimental effects on cognitive and perceptual-motor processes. Two lines of research on the impact of space-related stressors on mental performance can be distinguished. The first approach focuses on analyses of the impact of space conditions and microgravity, in particular, on specific functions of human information-processing. This research includes specific experi-
0165-0173r98r$ - see front matter q 1998 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 5 - 0 1 7 3 Ž 9 8 . 0 0 0 4 1 - 1
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D. Manzey, B. Lorenzr Brain Research ReÕiews 28 (1998) 215–221
ments on, e.g., visual information processing w12x, spatial visualization w12,13x, cognitive representation of space w8x, or mass discrimination w21x. A second approach is represented by a broad-band strategy of mental performance assessment w3,15–17,23x. This approach, referred to as performance monitoring, aims at describing a whole pattern of performance changes in the course of a space mission, and is characterized by probing a variety of mental performance functions repeatedly during spaceflight. Performance assessment is conducted by applying batteries of performance tasks which are based on theoretical models of information processing and which have been shown to react sensitively to environmental stressors, or can be assumed to be affected by alterations in the sensory-motor system induced by altered gravity conditions. The performance functions assessed include elementary and complex cognitive processes involving working memory Že.g., choice-reaction time, memory-search, logical reasoning, or mathematical processing. or spatial processing functions Že.g., mental rotation, spatial memory., perceptual-motor functions Že.g., tracking., andror higher attentional functions Že.g., attention switching, dual-task performance.. In the following a summary of recent results from performance monitoring studies during short-term and long-term spaceflight will be given. Based on this review some general conclusions will be drawn, and problems related to this strategy of research will be described. Finally, some directions for future human performance research in space will be outlined which follow from the results of performance monitoring during spaceflight.
2. Results of performance monitoring studies during short-term and long-term spaceflight During the last decade several attempts have been made to describe the time-course of different aspects of mental efficiency during spaceflights. Most of these studies were conducted during short-term space missions w3,15,16,23x. Benke et al. w3x assessed the performance of one cosmonaut in several cognitive tasks at three times during a six-day mission to the Russian space station MIR. The performance tasks used included a simple-reaction time task, a choice-reaction time task, a Stroop-like interference task, a spatial memory task, and a spatial perception task. Comparing inflight performance with pre- and postflight performance, none of these tasks revealed any significant performance decrements during the stay in space. Manzey et al. w15,16x adopted a similar but more extended singlesubject approach during an eight-day MIR mission. This experiment included six preflight and six postflight assessments, as well as a total of 13 inflight assessments during both, the approach phase in the Soyuz spacecraft, and the stay onboard MIR. In order to probe elementary cognitive functions Ži.e., logical reasoning, memory retrieval., per-
ceptual-motor functions and higher attentional functions, a subset of four task were selected: Ž1. grammatical reasoning, Ž2. memory-search, Ž3. unstable tracking, and Ž4. a dual-task consisting of unstable tracking with concurrent memory-search w1x. In accordance with the results of Benke et al. w3x speed and accuracy of short-term memory retrieval and logical reasoning were found unimpaired under conditions of spaceflight. However, clear disturbances of fine manual control movements emerged in the unstable tracking task. These performance decrements showed a striking tri-phasic time-course with most severe disturbances during the first two days in space, an intermediate recovery to preflight performance level, and a re-appearance of disturbances at the last four days on MIR. In addition, dual-task interference effects reflected in singleto-dual performance decrements in tracking andror memory-search increased considerably during the whole stay in space. From the tri-phasic time-course of tracking impairments it was concluded that they may have been caused by both, microgravity-related alterations in the sensory-motor system, as well as effects of accumulated fatigue, with the former factor primarily responsible for the large increase of tracking error at the first four assessments in space w15x. The dual-task performance decrements were proposed to result from a distortion of attentional processes known as attentional selectivity effect w9,16x. The single-subject findings of Manzey et al. were confirmed by two American experiments conducted during short-term Shuttle flights w11,23x. Although the ‘Mental Performance and Workload’ experiment of Lathan and Newman w11x during IML-1 focused primarily on the evaluation of different input devices Žjoystick, trackball. for control of a computer screen cursor, their results are worth noting here because their approach included the assessment of discrete tracking movements and memory-search performance. In accordance with the results presented above, Lathan and Newman w11x did not find any impairments of memory-search performance, but clear disruptions of tracking movements reflected by increased movement times across all input devices. Schlegel et al. w22x and Schiflett et al. w23x conducted a performance monitoring study which included daily assessments of different mental functions of three astronauts during a 13-day Shuttle mission. Using very similar tasks as Manzey et al. w15,16x they found impairments of tracking performance and time-sharing efficiency in space in two of their subjects. However, deviating from the studies cited above they also found impairments of memory-search performance in two astronauts. Given these results Schiflett et al. w23x raised the question whether their results are microgravity related or just present some sideeffects of decreased alertness and fatigue. This question arose particularly because they found some correlation between dual-task tracking performance and fatigue ratings in one of their subjects. Further converging evidence for disturbances of tracking performance and higher attentional functions has also
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been provided by a first performance monitoring experiment during a long-term spaceflight which was conducted during a 438-days Russian space mission w17x. The results of this study are particularly interesting because they suggest a close relation of tracking disturbances and attentional selectivity effects to adaptation to altered gravity
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conditions. In this experiment the same set of tasks was used as in the study of Manzey et al. w15,16x. In addition, several subjective ratings concerning mood and workload were collected. The experiment included a total of 41 experimental sessions Ž4 preflight baseline assessments, 29 inflight assessments, 6 postflight assessments, and 2 fol-
Fig. 1. Results from performance monitoring study during long-term spaceflight w17x. ŽA. Mean response rates Žline graph. and mean error rates Žbars. for grammatical reasoning task across preflight, inflight, and postflight assessments. ŽB. Time-course of mean tracking error across preflight, inflight, and postflight assessments. ŽC. Time-course of subjective fatigue-ratings across preflight, inflight, and postflight assessments. The horizontal lines in A and B correspond to the upper and lower confidence limits for pairwise comparisons ŽBonferroni contrasts. between average preflight performance at days y87 and y34 and all subsequent sessions.
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low-up assessments six months after landing.. Comparisons of inflight and postflight assessments with preflight baseline assessments y87 and y34 days prior to launch revealed the following pattern of statistically reliable effects Žsee Fig. 1.: Ž1. Significant impairments of elementary cognitive functions as assessed by the grammatical reasoning task were found only during the last three days prior to launch. After entering the space environment, performance in this cognitive task recovered rapidly to preflight baseline level and remained more or less stable afterwards until follow-up assessments ŽFig. 1a.. A quite similar picture also emerged for the memory-search task. Ž2. In contrast, tracking performance declined significantly during the first week in space. As becomes evident from Fig. 1b this effect turned out to represent a transient phenomenon, and a complete recovery of tracking performance to preflight baseline level was achieved within the first three weeks in space. After this period, tracking performance remained impressively stable throughout the following 13 months of the mission. However, clear tracking disturbances re-appeared during the first two postflight assessments. Again a recovery of tracking performance could be observed within two weeks, and tracking disturbances were not seen any more at follow-up assessments half a year after the mission. Ž3. Impairments of dual-task performance were observed only during some single experimental sessions. Even though this did not confirm the far more pronounced impairments found during short-term flights, it was striking that these dual-task effects, if any, also occurred during the first two weeks in space and after return to Earth. Ž4. Corresponding to the impairments of tracking and dual-task performance, the subjective data indicated feelings of raised workload and increased fatigue ŽFig. 1c. during the first three weeks in space and the first two weeks after landing. In summary, the different performance monitoring studies conducted so far clearly prove the feasibility of this approach to describe the impact of the environmental changes in space on different mental functions. Moreover, the performance effects observed in these studies present a fairly consistent pattern of results. Whereas no or only slight impairments of basic and complex cognitive functions or spatial processing were found, clear disturbances could be identified in several studies for visuo-motor tracking and higher attentional functions involved in dualtask performance. And both of these latter effects appear to be related to the adaptation to altered gravity conditions.
3. Inherent problems of performance monitoring studies during spaceflight Major problems of performance monitoring studies concern the small sample size, the generalizability of results and the explanation of effects. Small sample sizes which raise the problem of lack of statistical power represent a
problem which is common to all kinds of life science experiments during spaceflight and which is not limited to performance monitoring studies alone w5x. However, in contrast to other experiments, performance monitoring approaches provide the advantage of a number of repeated measurements which allow for an application of statistical single-subject methods with comparatively high statistical power. One example of these approaches combine a general linear model approach to analysis of variance with a test on autocorrelated residuals w14x, and has been used by Manzey et al. w15–17x. Another approach is based on fitting learning curves to results of repeated preflight performance assessments in order to derive predicted performance scores for comparison with inflight performance and has been applied by Schiflett et al. w23x. Thus, most of the findings reviewed above can be regarded as reliable results for the individual astronauts involved in the different studies. More difficult to evaluate is the generalizability of these findings. Given the comparatively small number of performance monitoring studies during spaceflight covering results from only a few astronauts, the currently available data base is too small to warrant any definite conclusions about mental efficiency during spaceflight. Therefore, even though the convergence of results is impressive, the conclusions drawn above have to be regarded as preliminary. The third and most important problem, however, concerns the identification of the specific causes for the performance effects found in the different studies. Firstly, it remains unclear whether unimpaired cognitive performance in space indeed reflects absence of any spacerelated influence upon a given performance component. Alternatively, it could be argued that possible performance effects have been masked by some compensatory effort of the astronauts in performing the given tasks. The strategy pursued up to now, to rely on comparatively global performance scores in order to identify performance changes, may not be adequate to detect such effects. Similarly, also differences in the structure of cognitive processes which may not necessarily lead to overt performance decrements may have remained undetected by this kind of research. Secondly, even though disturbances of tracking performance and higher attentional functions emerged primarily during adaptation to changed gravity conditions, they do not necessarily reflect direct effects of altered gravity on sensory-motor processes. For example, during adaptation to space, generally, two different factors may have contributed to these effects Žan analogous confounding of effects may be expected during re-adaptation to 1 g after prolonged spaceflight.: Ža. microgravity induced changes in the sensory-motor system which may call for an accommodation of previously learned visuo-motor skills to the new gravity conditions, and Žb. unspecific stress effects of the environmental conditions in the space habitat which, among other things, lead to impaired well-being and decreased alertness during adaptation Že.g., secondary effects
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of physiological adaptation, effects of altered darkrlight cycle, effects of limitations of life-support system, effects of confinement.. A disentanglement of these two factors can hardly be achieved. The obvious correlation of mood ratings and performance effects in some of the studies reviewed above w17,23x suggest that tracking and dual-task disturbances in space are primarily related to disturbances of attentional processes induced by adverse effects on subjective well-being and alertness during the demanding adaptation to the living conditions in space. However, at least with regard to tracking impairments found at the very first assessments in space and after return from long-term spaceflight, there exist some evidence that also microgravity-related changes in the sensory-motor system may have contributed to these effects. For example, a comparison of preflight and inflight fatigue ratings and performance data reported by Schiflett et al. w23x showed that, although there was an obvious correlation between dual-task tracking performance and fatigue during inflight sessions in one subject, the comparatively small increment of fatigue ratings at the first inflight sessions cannot explain the clear decrement of tracking performance at this time of the mission. Similarly, some obvious dissociations of tracking performance and fatigue ratings were also found in the long-term study of Manzey et al. w17x. Even though, fatigue ratings in this study were comparatively high at days 4, 5, 11, 12, 19 and 27, large tracking performance decrements were only found at the first three assessments Ždays 4, 5, and 6. in space. In addition, also the striking tracking performance decrement at the first postflight assessment clearly could not be explained by an accompanying effect of fatigue Žcompare Fig. 1b and c.. Finally, Lathan and Newman w11x did not find effects on movement times in discrete tracking comparable to those found during IML-1 when they repeated their experiment during a ground based simulation of a 7-day Shuttle flight which resembled a real flight in almost all important aspects but microgravity. 4. Impairments of tracking performance under microgravity: possible mechanisms Lacking more specific experiments on the impact of gravitational changes on visuo-motor processes as those involved in tracking, the mechanisms which may cause microgravity-related impairments of tracking performance are not well understood, so far, and represent a matter of speculation. Since tracking represents a closed-loop visuomotor task, microgravity-related effects on tracking performance may be due to both, effects on the visual and ocular system as well as effects on motor control processes. In compensatory tracking, continuous feedback of tracking error is provided by visually pursuing the position of the continuously moving cursor which directly displays the direction and amplitude of tracking error w24x. Consequently, it might be supposed that distortions of pursuit
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eye-movements due to microgravity-induced changes in the vestibulo-ocular system may contribute to impairments of tracking performance during the first days in space. However, pursuing the cursor of compensatory tracking tasks as used in the studies cited above typically includes a range of only some 3 to 4 degrees in the horizontal plane where first studies have been shown that microgravity does not alter the characteristics of pursuit eye-movements w2x. More likely, then, the tracking impairments seen in the first assessments after gravitational changes may be attributed to alterations in the motor system under microgravity. This assumption gets support from results of space experiments and ground based studies which suggest that changes in gravity conditions require adjustments of existing central motor programs and cause substantial changes of proprioceptive processes associated with execution of precise voluntary movements w4,6,7x. In tracking tasks proprioceptive information from joint-position and muscle-tension related receptors provides feedback about the system dynamics of the task w25x. Distortions of this feedback under microgravity would convey information that the dynamics of the task have been altered which, in turn, would conflict with unchanged visual cues from the task. Such a conflict between proprioceptive and visual cues would cause some confusion and could be responsible for disturbances of tracking performance at least at the first performance of the task after gravitational changes. In addition, also changes in the kinematics of movements may affect tracking performance. Analyzing visually guided pointing arm movements in the horizontal plane, Berger et al. w4x found no effects on accuracy but significant alterations of kinematics of these movements in space. In particular, they found a general slowing of movement times, a decrease of peak velocity, and alterations of the acceleration time-profile of movements compared to preflight values, indicating more slow and cautious movements under microgravity. Berger et al. w4x attribute these results to enhanced demands on ‘intra-movement control’ ww4x, p. 786x associated with the need to elaborate and establish new motor patterns in order to adapt to microgravity-induced changes in the sensory-motor system. Similar effects of microgravity on fine manual control movements in tracking tasks which typically involve a complex pattern of accelerative and decelerative phases may cause increments in tracking error by increasing the ‘effective time delay’ and decreasing the tracking gain Ži.e., ratio of amplitude of compensatory movement to amplitude of tracking error. in the control-loop w24x. However, it must be taken into account that most of the research concerning adjustments of central motor programs and distortions of proprioception associated with precise voluntary movements under changed gravity, so far, has largely been limited to discrete aimed arm movements. It remains to be shown whether similar effects indeed are to be expected in fine continuous control movements as those involved in tracking tasks.
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5. Directions of further research What may be concluded from the results of performance monitoring studies during spaceflight for future research? First, the strategy of multivariate performance monitoring studies in space, i.e., the analysis of changes in performance patterns in the course of a space mission, represents a suitable approach to identify specific effects of the space environment on human information processing functions and its time-course of adaptation, and should be continued in order to enlarge the existing data base and to cross-validate the previous results. For this purpose, a standardized battery of performance tasks should be defined which would assure comparability of different studies. Second, the results from the long-term study w17x suggest that at least the first three weeks in space and the first two weeks back on Earth after a prolonged spaceflight may represent critical adaptational periods which may be associated with degraded efficiency of perceptual-motor and higher attentional processes. This fact should be taken into account in scheduling and interpreting any kind of behavioral experiments on human cognition during spaceflight. Third, the tracking results of the performance monitoring studies suggest that experimental research should be conducted which describe more clearly the effects of changed gravity on fine manual control movements. Analyses of tracking performance appear to be one promising approach in this regard. Varying the directions of cursor movements to be tracked Žhorizontal, vertical, diagonal., the bandwidth of forcing functions, and the system dynamics of the control-loop provides a large spectrum of possible experimental variations inducing different demands on gaze control, cognitive involvement, and motor control. In addition, the mathematical and psychological models which have been developed to describe human tracking behavior, e.g., quasi-linear cross-over models w18x or optimal control models w10x are well validated and provide a sound theoretical basis for modeling and predicting human performance in manual control. Furthermore, they provide sophisticated methodological approaches for microanalyses of tracking behavior which yield precise descriptions of different human characteristics in manual control Že.g., time-delay, gain, non-linear elements. w24x, and which may be used to identify fundamental changes in the sensory-motor system under the impact of altered gravity conditions. Fourth, in order to obtain a more clear picture of possible changes of cognitive and attentional processes in space, analyses of cognitive task performance should be enriched by analyses of accompanying changes in brain electrical activity. Particularly, analyses of event-related brain potentials like P300, slow DC-potentials, or even more sophisticated approaches of brain mapping may offer new insights in this regard. Such an approach could be based on the large amount of data and experience which have been accumulated in the field of cognitive psychophysiology during the last 20 years. Ground-based simulation studies w19x have
already proven the suitability of this approach under conditions comparable to those of spaceflight.
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