Chapter 3 Exploratory Research On The Effects Of Sustained .
SIC- and SAS-susceptibility39Chapter 3Exploratory research on the effects of sustainedcentrifugation: an overviewThis chapter provides an overview of the research that was performed inthe past to characterize the effects of sustained centrifugation on posturalstability, motion and attitude perception and vestibularly driven ocularresponses. This is complemented with data on subjective verticalmeasurements that were performed within the framework of the presentthesis. Together, these data did not reveal significant effects of sustainedcentrifugation on perceptual measures, but ocular responses were foundto be affected.Apart from testing subjects for SIC-susceptibility, several vestibulartests have been performed over the years to quantify the effect ofsustained centrifugation on behavioural tasks, and elucidate themechanism underlying SIC. They all focused on the otolith system andrelated responses (see Table 3.1 for an overview). Below, the mostimportant results are summarized. For a detailed description of the resultsthe reader is referred to the original manuscripts listed in Table 3.1. Thisresearch is then complemented with some new data, described in thesecond part of this chapter.
40Chapter 3
SIC- and SAS-susceptibility41REVIEW OF PREVIOUS STUDIESPostural stabilityOf all tests performed on the D1-astronauts (Bles et al., 1989), posturalstability appeared to be the parameter that was most affected bycentrifugation. When deprived of visual information, postural sway wasgreatly increased during quiet stance. One astronaut showed a majorincrease in visual dominance after centrifugation, as assessed in a tiltingroom. The astronaut was standing on an Earth-fixed stabilometerplatform, while the visual surround (a 2.5u2.5u2 m cabin) wasdynamically tilted about the roll axis located at ankle height. Aftercentrifugation this astronaut was much more de-stabilized by the visualtilt than before centrifugation. Interestingly, similar results were alsofound in the same astronauts after spaceflight (Bles & Van Raay, 1988).The effect of sustained centrifugation on postural measurements wasfurther investigated by Bles & De Graaf (1993). They observed anincreased postural sway following centrifugation during standing uprightwith the eyes closed, that markedly increased when head movements weremade. In some subjects the head movements resulted in a complete loss ofpostural control. In addition, subjects reported that standing in thesharpened Romberg position (feet positioned in front of each other, heelto toe) remained very difficult until hours after centrifugation. In theseexperiments the SIC-susceptible subjects did not behave statisticallydifferent from the non-susceptible subjects.Albery & Martin exposed subjects to 2Gz stimulation and observed noreal changes in postural stability after a 40 minute exposure, but found asignificant reduction after an exposure of 90 minutes.Subjective VerticalIn addition to a deterioration of postural balance changes were observedby Bles and colleagues (1989) in the perception of the vertical. Theastronauts were seated in a chair that was put in a tilted position and the
42Chapter 3astronauts were to set the chair upright again. After centrifugation theyshowed a consistent backward bias, indicating that in the actual uprightposition, a forward tilt was perceived. Such a directional bias in theperceived direction of gravity was also suggested by the posturalmeasurements of Bles & De Graaf (1993) mentioned above, wheresubjects generally showed a tendency to fall backwards.Groen investigated the effect of sustained centrifugation on theperception vertical in the roll plane. Non-astronaut subjects were to aligna visual line with gravity under various angles of lateral body tilt. It wasobserved that subjects tended to underestimate the tilt at larger tilt angles(A-effect, that is, the visual line was tilted towards the body axis), but noeffect of centrifugation was found.Eye movementsTorsional eye movements were of particular interest, because they areassumed to be predominantly driven by otolith signals (see e.g. Miller,1962). Groen and colleagues (1996b) recorded ocular counter rollingduring static lateral body tilt and found a decrease in the gain of thisresponse after sustained centrifugation. The dynamic torsional responsewas assessed during angular oscillation of 0.25 Hz about an Earth-verticalaxis (no otolith stimulation) and about an Earth-horizontal axis. The gainof the response was found to be increased after centrifugation duringrotation about an Earth-horizontal axis (i.e., with otolith stimulation). Thismight seem to be contradictive with the results of the staticmeasurements, but they are explained by the finding that in these subjectsstimulation of semicircular canals alone led to a higher response gain thanstimulation of both semicircular canals and otoliths. Thus, apparently theotolith contribution counteracted the canal contribution. Therefore areduced otolith gain after centrifugation would decrease the counteractingeffect of the otoliths, thereby increasing the total gain of the response.This opposite effect of semicircular canals and otoliths on the torsionalresponse was however not replicated in a later study using the same
SIC- and SAS-susceptibility43subjects (Groen et al., 1999).Apart from the torsional vestibulo-ocular reflex (VOR), Groen (1997)also investigated the horizontal angular VOR during constant velocityEarth-vertical axis rotation. The gain of this response was unaffected bysustained centrifugation, but the dominant time constant of the decay-rateof slow phase velocity was found to be significantly decreased.Head movementsThe findings of Bles & De Graaf (1993) showed that in an erect postureonly pitch and roll head movements were provocative, while in a supineposture pitch and yaw movements were provocative. This indicated thatonly those head movements were provocative that changed the orientationof the head relative to gravity, in line with earlier reports of the D1astronauts.De Graaf and De Roo (1996) developed a head movement test thatincluded a psychomotor task. Subjects were to turn their head in avisually indicated direction (up, down, left, or right) where another visualtrigger was shown. Depending on the latter trigger they either were topress a button or to put a peg in a small hole. It was observed that subjectswho were suffering from SIC moved their heads significantly slower thansubjects who were not suffering from SIC. Although this velocitydecrease was present in both pitch and yaw movements, only the pitchmovements were rated provocative. Task performance was not affectedby centrifugation.Mode of centrifugationBles & De Graaf (1993) also tested whether the direction of the appliedgravitational load affected the aftereffects of centrifugation. To that endthey positioned the subjects in a supine body position in the centrifugewhile changing the position of the head relative to the GIA. Pitching thehead forwards over 90º yielded Gz-stimulation, rotating the head 90º
44Chapter 3about the longitudinal body axis yielded Gy stimulation and keeping thehead in line with the body yielded Gx stimulation. These three conditions,however, had comparable effects on postural stability. The onlydifference between conditions was that after Gx stimulation pitch headmovements were rated as more provocative than roll head movements(while erect) and after Gy stimulation roll was rated more provocativethan pitch. Yaw movements, that did not change the orientation of thehead relative to the vertical, were not provocative in both cases. Gzstimulation did not change the rank order of the provocativeness of headmovements and the effects of was similar to Gx stimulation.In three subjects the effect of vision on SIC was investigated and itwas observed that SIC-severity was increased when subjects kept theireyes open during centrifugation. (Bles & De Graaf, 1993).ADDITIONAL EXPLORATORY RESEARCHWithin the framework of this thesis, additional vestibular testing wasperformed both in the four astronauts who participated in a centrifugeexperiment between 2003 and 2007, and in a group of non-astronautsubjects. The two main experiments focused on the effect of sustainedcentrifugation on ocular responses and are described in Chapters 5 and 6.Here the results of the other additional tests are described.Provocativeness of head movementsEarlier results, as mentioned above, showed that after centrifugation onlythose head movements were provocative that changed the orientation ofthe head relative to gravity. Thus, pitch and roll when erect and pitch andyaw when supine. These results were replicated in a group of 4 astronautsubjects and 11 non-astronaut subjects. They all were exposed to 3Gx for60 min. and rated the provocativeness of yaw, pitch and roll headmovements (maximal 10 per axis, performed at a frequency of about 0.25Hz), both when standing and when lying supine. The effect of the head
SIC- and SAS-susceptibility45movements was scored on a 11-point numeric MISC scale (see Table 2.1)A nonparametric ANOVA (Friedman ANOVA by ranks) on these MISCscores showed that pitch movements were ranked as most provocative,while yaw and roll-movements were ranked equally provocative (Ȥ2 8.44,p .015). In a supine position there was a trend for roll to be ranked leastprovocative, while pitch and yaw were ranked about equally provocative,(Ȥ2 4.7, p .097). When subjects were asked afterwards what they foundthe most provocative movement, it was generally pitch, both in an erectand supine posture.Postural stability and visual-vestibular interactionPostural stability during quiet stance and during dynamic tilt of the visualsurround (in the tilting room) was also performed on two of the fourastronauts who were tested within the framework of this thesis (exposedto 60 min at 3Gx). One of them was susceptible to SIC and the other onewas not. During all recordings, the astronauts stood on a layer of foamrubber that was placed on the stabilometer platform to reduce the relativeweighting of proprioceptive cues. The sway of the centre of pressure wasrecorded in the fore-aft and the lateral direction, at a sample frequency of20 Hz. Recordings were obtained during quiet stance with eyes open, witheyes closed and with the neck extended (eyes closed). These conditionswere always performed in this order. Figure 3.1 displays the results of thestatic postural stability recordings of the two astronauts (i.e., stationaryvisual surround). Shown are values for sway in the fore-aft direction,lateral sway was generally smaller but followed a similar pattern. Theastronaut who was not affected by the centrifuge run in terms of SICexhibited very little postural sway. Only a little increase during the firstposttest in the ‘Neck extension’ condition was observed. In contrast, theother astronaut, who was reasonably affected by the centrifuge run,clearly showed a different pattern over sessions, especially in the ‘Neckextension’ condition. Instead of a steady decrease of the postural swayover sessions (which is normally observed in repeated recordings) the
46Chapter 3sway increased in the second and especially in the third session. The thirdsession was also the session were the highest MISC scores were observed.In this astronaut behaviour was not back to baseline within 4 hours afterthe centrifuge run.Figure 3.1: Postural stability recordings for the three experimental conditions in twoastronauts (Each panel shows the data of one astronaut). Postural sway is expressedas the root-mean-square value of the sway of the centre of pressure.The dynamic measurements (oscillation of the visual surround at 0.025Hz and 0.2 Hz) in pitch or roll showed no large increases in posturalsway, indicating that the astronauts were not affected by movement of theroom. This was also not deteriorated by sustained centrifugation.Subjective vertical measurements in the pitch planeIn two separate experiments it was investigated whether sustainedcentrifugation affected the perception of body orientation in space in thepitch plane, as was suggested by earlier findings (Bles et al., 1989; Bles &De Graaf, 1993). They were performed on a total of 10 subjects (2astronauts and 8 non-astronaut subjects) who were exposed to 60 min at3Gx. Both experiments were performed shortly before and aftercentrifugation.The first experiment focused on the perception of the vertical and ofbody orientation under different conditions of pitch body tilt, using a
SIC- and SAS-susceptibility47tactile indicator. Experiments were perfomed in the TNO tilt-chair, thatenabled rotation about the pitch axis through the center of the head.Blindfolded subjects were seated and secured with a five-point belt. Theywere oriented in different positions and in each position they were toalign the manual indicator first with their perceived longitudinal bodyaxis (Subjective Body axis, SB, defined as ‘parallel to your spine”) andsubsequently with the gravitational vertical (Subjective Vertical, SV).Figure 3.2 shows the error in these two measurements as a function of tilt.Figure 3.2: Errors in subjective vertical (SV) and subjective body axis (SB). Pretestvalues (mean and standard deviation) are indicated by the open symbols, values of thefirst posttest are indicated by the filled symbols.For backward body tilt a positive error in SV yields an underestimation oftilt, thus the SV is tilted towards the body-axis (A-effect). This is visiblefor larger tilt angles in the pretest, and appears to be changed into anoverestimation of tilt in the posttest. However, these effects of test sessionor tilt angle were not significant (Factorial ANOVA with Tilt and Testsession as within subject factors). Interestingly, for the SB a significanteffect of Tilt was found (F(4, 32) 5.46, p .01): the body axis wasperceived to be more tilted backwards (negative error) and this errorincreased with tilt angle. No significant effect of centrifugation could bedemonstrated. Similar trends for SV and SB were observed in six controlsubjects who did not undergo centrifugation (see Nooij et al., 2006).In a second experiment subjects were to reorient themselves to uprightafter a perturbation in pitch ( 30º forward or backward). As in theprevious experiment, subjects were blindfolded and seated in the tilt-
48Chapter 3chair. Each session consisted of six repetitions. The data showed that themagnitude of the error was weakly correlated with the magnitude of theperturbation (r 0.25, p .01), but because this effect was small incomparison with the error magnitude, the values were not corrected forthis trend. Analysis of variance revealed that the sign of the error in theperceived upright was dependent on the direction of the perturbation:when the perturbation was backwards, the perceived upright position wasalso tilted backwards and vice versa (F(1, 72) 50.5, p .001). No effect oftest-session (pre-/posttest) could be demonstrated for the error in theperceived upright, and also no differences between the behaviour of SICsusceptible subjects and non-susceptible subjects. Over all, the error inthe perceived upright ranged between 10.8º and 9.7º (mean 0.6º, SD4.0º), whereas the average absolute error equaled 3.2º (SD 2.42º). In thesecond session the variability of the responses (standard deviation overthe six repetitions) decreased significantly (F(1,7) 6.4, p .05), suggestingthat subjects got more acquainted with the task.DISCUSSIONBy recording the kinematic characteristics of the head movement, DeGraaf and De Roo (1996) nicely showed that head movements wererequired to provoke SIC following centrifugation: SIC susceptiblesubjects performed the head movements slower than non susceptiblesubjects, in an attempt to minimize or prevent increasing symptoms ofmotion sickness. The results of previous studies regarding theprovocativeness of head movements were replicated by new data: pitchhead movements were most provocative both when erect and supine. Yawmovements were not provocative when erect, and roll movements werenot provocative when supine. The observation that this provocativenesswas not altered following Gz stimulation (Bles & De Graaf, 1993)suggests that the magnitude of the G-load is more important than thedirection of stimulation, indicating the involvement of a centraladaptation process. However, that Gy stimulation altered the order of
SIC- and SAS-susceptibility49provocativeness when compared to Gx stimulation suggest that a directionspecific element should be involved as well, adding to the effect of the Gmagnitude.Next to symptoms of motion sickness, the second most obvious effectof sustained centrifugation is the deterioration of postural balance. Aslong as veridical visual information is available, balance could bemaintained, but in more challenging situations (with eyes closed or headextended) postural sway increased. Although there were large differencesbetween individuals (i.e., between the two subjects in Figure 3.1), norelationship between SIC-susceptibility and postural sway parameterscould be demonstrated (Bles & De Graaf, 1993). This is comparable withthe findings in astronauts following space flight. After space flight asimilar deterioration of postural balance is found, both in astronauts whosuffered from SAS and in astronauts who were free form SAS (e.g., Blacket al., 1995; Reschke et al., 1998; Young et al., 1993)Following centrifugation, head movements often resulted in posturalovercorrections and loss of balance (Bles & De Graaf, 1993) showing thatdynamic situations were more challenging than static situations. Thisfurthermore hints at a disturbed interaction between semicircular canalsand otoliths: both are involved in the estimation of the vertical in thissituation. As mentioned in Chapter 1, this is in accordance with thehypothesis that a disturbed perception of the vertical during dynamic headtilt is related to the occurrence of motion sickness after centrifugation.The perception of the vertical during static body tilt was not found tobe affected by sustained centrifugation, neither in the roll nor in the pitchplane. The same was true for the perceived body orientation. Manystudies demonstrated that the perception of the gravitational vertical canbe quite veridical, but that this does not guarantee a veridical perceptionof body orientation relative to that vertical. The latter requires both egoand allocentric information and thus, the perceived body orientation inspace cannot be inferred from the subjective vertical setting alone (e.g.,Mars et al., 2005; Mast & Jarchow, 1996; Van Beuzekom et al., 2001).This was also shown by the perceptual responses to pitch body tilt, as
50Chapter 3mentioned above. Subjects were able to indicate the vertical with onlyminor errors, but they made large errors in indicating their subjectivebody axis. Where subjective vertical settings are predominantly based onotolith input, somatosensory information is known to affect the perceptionof body posture in space (see e.g., Bisdorff et al., 1995; Bringoux et al.,2000; Ito & Gresty, 1997; Mittelstaedt, 1999). Somatosensoryinformation most likely dominated the perception of the postural verticalin the task where subjects were to set themselves upright.Although sustained centrifugation did not affect the perception of thevertical during lateral or pitch body tilt, it did affect the ocular response:the gain of ocular counterrolling was decreased. Because this response ismainly dependent on the magnitude of the utricular shear force (e.g.,MacDougall et al., 1999; Merfeld et al., 1996a; Miller & Graybiel, 1971;Moore et al., 2001), this would suggest a decrease in otolith sensitivity tohead tilt. The absence of an effect on the visual vertical, which is alsolargely dependent on otolith information, is however not in accordancewith this hypothesis. Another possibility is that the otolith
Chapter 3 Exploratory research on the effects of sustained centrifugation: an overview This chapter provides an overview of the research that was performed in the past to characterize the effects of sustained centrifugation on postural stability, motion and attitude perception and vestibularly driven ocular responses.
Part One: Heir of Ash Chapter 1 Chapter 2 Chapter 3 Chapter 4 Chapter 5 Chapter 6 Chapter 7 Chapter 8 Chapter 9 Chapter 10 Chapter 11 Chapter 12 Chapter 13 Chapter 14 Chapter 15 Chapter 16 Chapter 17 Chapter 18 Chapter 19 Chapter 20 Chapter 21 Chapter 22 Chapter 23 Chapter 24 Chapter 25 Chapter 26 Chapter 27 Chapter 28 Chapter 29 Chapter 30 .
TO KILL A MOCKINGBIRD. Contents Dedication Epigraph Part One Chapter 1 Chapter 2 Chapter 3 Chapter 4 Chapter 5 Chapter 6 Chapter 7 Chapter 8 Chapter 9 Chapter 10 Chapter 11 Part Two Chapter 12 Chapter 13 Chapter 14 Chapter 15 Chapter 16 Chapter 17 Chapter 18. Chapter 19 Chapter 20 Chapter 21 Chapter 22 Chapter 23 Chapter 24 Chapter 25 Chapter 26
DEDICATION PART ONE Chapter 1 Chapter 2 Chapter 3 Chapter 4 Chapter 5 Chapter 6 Chapter 7 Chapter 8 Chapter 9 Chapter 10 Chapter 11 PART TWO Chapter 12 Chapter 13 Chapter 14 Chapter 15 Chapter 16 Chapter 17 Chapter 18 Chapter 19 Chapter 20 Chapter 21 Chapter 22 Chapter 23 .
1.1 PURPOSE OF THE EXPLORATORY RESEARCH STUDY The purpose of this study was to conduct exploratory research on consumer-level food loss to help inform the development of a complete study to develop estimates of food loss for individual food categories. The exploratory research included reviewing published literature on consumer-level food loss,
Exploratory Data Analysis - Detailed Table of Contents [1.] This chapter presents the assumptions, principles, and techniques necessary to gain insight into data via EDA--exploratory data analysis. 1. EDA Introduction [1.1.] 1. What is EDA? [1.1.1.] 2. How Does Exploratory Data Analysis differ from Classical Data Analysis?
for automated suggestions for portions of the exploratory data analysis process. Many intuitive user interface features that would be ideal to have for an exploratory data analy-sis tool are available in Tableau [1] which is descended from earlier research in exploratory data analysis such as Polaris [14] and Mackinlay's earlier work [9].
About the husband’s secret. Dedication Epigraph Pandora Monday Chapter One Chapter Two Chapter Three Chapter Four Chapter Five Tuesday Chapter Six Chapter Seven. Chapter Eight Chapter Nine Chapter Ten Chapter Eleven Chapter Twelve Chapter Thirteen Chapter Fourteen Chapter Fifteen Chapter Sixteen Chapter Seventeen Chapter Eighteen
18.4 35 18.5 35 I Solutions to Applying the Concepts Questions II Answers to End-of-chapter Conceptual Questions Chapter 1 37 Chapter 2 38 Chapter 3 39 Chapter 4 40 Chapter 5 43 Chapter 6 45 Chapter 7 46 Chapter 8 47 Chapter 9 50 Chapter 10 52 Chapter 11 55 Chapter 12 56 Chapter 13 57 Chapter 14 61 Chapter 15 62 Chapter 16 63 Chapter 17 65 .
