Testing of Saccade Accuracy: Subjects’ ability to make saccadic eye movements to remembered locations, as a measure of the constancy of the spatial reference frame, was also tested, without measuring eye movements. The tablet computer presented multiple targets to the subject, and he or she was asked to make saccades between these targets. The subject then closed his or her eyes and continued to make saccades to the remembered target locations. After several seconds, the eyes re-opened and a grid of symbols appeared on the display. The subject indicated which of these symbols he or she was looking at most directly, which provided a rough measure of where the eyes are directed for comparison with the intended fixation point.
The hardware included a tablet computer, wireless motion and EMG sensors, and plastic red-blue eyeglasses. This test battery evaluated (1) vestibulo-ocular function, (2) vestibular-evoked myogenic potentials (VEMPs), (3) spatial orientation, (4) posture and locomotion, and (5) visual performance measures. In the vestibulo-ocular tests, subjects looked at visual targets (e.g., dots and lines, letters) displayed on a tablet computer and reported what they saw with touchscreen inputs. In some tests, they were asked to move their head while viewing these targets, and in other tests they wore plastic red-blue eyeglasses so that different information was seen by each eye. In the VEMP test, small surface EMG electrodes were placed on the head, neck, trunk, and limbs to measure muscle reflexes in response to auditory sounds (e.g., tones, clicks) or small taps to the forehead with a rubber clinical reflex hammer. In the spatial orientation task, subjects reported their perceptions of "down" with their eyes closed. In the posture and locomotion tests, changes in body sway and leg muscle activity were measured with the motion and EMG sensors when subjects stood, stood while making head movements, stood with eyes closed, walked, turned corners, and climbed stairs. In the visual performance measures, subjects were asked to view and respond to visual targets displayed on the tablet computer.
As the maturation plan developed (single user, independent testing) over the years and better LED tablets were available, investigators realized the critical need to ensure subjects were tested in complete darkness. Therefore, they initially designed a shroud to be built into the side of the aircraft for the parabolic flight experiments. From November 18-22 2013, they participated in a Parabolic Flight Campaign managed by the Flight Opportunities Program. They recruited seven naïve fliers and two highly experienced fliers. Each subject flew one 40-parabola flight. All subjects were screened for motion sickness (none or minimal motion sickness susceptibility on Earth) pre-flight, trained in Vertical and Torsional Alignment Nulling tests (VAN, TAN), and participated in baseline data collection.
Three out of the nine test subjects experienced severe motion sickness (nausea and vomiting), within the first several parabolas of their respective parabolic flights. As such, they were unable to perform the VAN and TAN tests during the actual parabolas. All (n=4) of the naive flyers showed significant g-level dependencies for both VAN and TAN tests (i.e. test scores varied depending on 0, 1, or 1.8 g levels). The experienced fliers did not show any significant differences in g level dependent misalignments; although this may be partially due to age effects (the two experience fliers were several decades older than naïve test subjects).
Next, investigators examined all nine subjects’ baseline 1g data to look for differences in ocular misalignments between the three individuals who experienced motion sickness inflight and the six who did not. There was no difference in the mean vertical or torsional ocular misalignments between these two groups. There was also no difference in the variability of the vertical ocular misalignments between these two groups. There was, however, a strong difference in the variability of the torsional ocular misalignments. The data suggests variability in torsional misalignment may be an indicator of motion sickness susceptibility.
Investigators then examined all nine subjects’ baseline 1g data to look for differences in ocular misalignments between the three individuals who experienced motion sickness inflight and the six who did not. There was no difference in the mean vertical or torsional ocular misalignments between these two groups. There was also no difference in the variability of the vertical ocular misalignments between these two groups.. There was, however, a strong difference in the variability of the torsional ocular misalignments. This finding is in agreement with a study that correlated instability of ocular torsion during the 0g phases of parabolic flight with space flight motion sickness. The data suggests variability in torsional misalignment may be an indicator of motion sickness susceptibility. Investigators are intrigued that this correlation result is only observed using the torsion data and not the vertical data. They presume that this is because static torsional eye positioning represents a vestigial reflex, much less subject to voluntary control than vertical eye movements.
During these November 2013 flights, investigators realized this version of the shroud would be untenable for the goals of their maturation plan. Therefore, they developed a portable shroud and participated in the July 18-30, 2014 Parabolic Flight Campaign, managed by the Flight Opportunities Program. They tested 12 subjects using their newly designed portable shrouds to measure VAN and TAN in 1 g across different head positions and separately across different g-levels (0, 1, 1.8) while positioned upright and during the different g-levels of parabolic flight. Data suggest most of the experienced subjects expressed significant differences in their VAN and TAN responses when upright versus lying supine. All subjects displayed significant differences in VAN and TAN when lying right ear down versus left ear down. Parabolic flight-testing revealed that eight subjects showed significant differences in TAN and seven subjects showed significant differences in VAN in 0g versus 1.8g. Furthermore, a significant correlation was found between TAN responses in-flight and TAN responses on the ground: subjects who showed significant differences in 0g versus 1.8g also showed significant differences in upright versus supine. Together, these data can be attributed to innate otolith asymmetries and suggest that VAN and TAN may have a role in identifying deficits in otolith signal processing. The portable shroud appears to sufficiently enclose subjects in an environment dark enough to ensure accuracy. These data are some of the most exciting of the results, as they suggest the VAN and TAN tests of ocular conjugacy can be used to monitor sensorimotor function across different gravitational levels. Additionally, this finding existed in both experienced and naïve flyers, suggesting VAN and TAN have good generalizability regardless of experience.
Head Impulse Dynamic Visual Acuity (hiDVA): For the hiDVA test, the subject wore a rate sensor while holding a computer tablet about 18 inches from the face. Static visual acuity was measured first, followed by dynamic (active head impulse) visual acuity during pitch and yaw head rotation with near (0.45m) and far (2m) targets. During each test, subjects viewed optotypes randomly rotated by 0, 90, 180, or 270 degrees) with Snellen acuity levels between 20/200 and 20/4 (far) or 20/17 (near). For the dynamic component of the test, the letter only flashed when head velocity was > 120 d/s for 80 ms duration. At each acuity level, subjects were presented with five optotypes and asked via forced choice paradigm to identify the orientation.
Investigators conducted validation experiments using the hiDVA test to ensure the body worn sensor would communicate with the tablet using Bluetooth to trigger the flashing optotype. Next, they measured static (head still) and dynamic (active head impulse) visual acuity during pitch and yaw head rotation with near (0.45m) and far (2m) targets in six healthy controls four patients with vestibular hypofunction.
Summary of HERA and NEEMO Flight Analogs
HERA Results: The procedures and operations were efficiently carried out during each of the four HERA missions. Each of the HERA crewmembers was able to complete the oculomotor and gait/postural measures. Investigators learned that the operations manual must be very terse and easy to understand. They also learned it is critical to have interaction with the crew during the mission, even if on delay. They realized the importance of ensuring a completely dark environment while completing the oculomotor portions of SARA (i.e. light ‘noise’ from emergency lighting can affect results).
Scientifically, the initial results suggest some oculomotor and gait metrics may exhibit changes over time, perhaps related the confinement of such an analog or with increased mission duration. Further analyses and additional subjects are needed for statistical significance.
NEEMO 18 Results: The NEEMO 18 crew was generally successful in self-administering SARA tests. Some of the oculomotor data was lost due to improper initialization of data recordings. This appears related to poor emphasis by investigators during limited training sessions and limited time for crew to read detailed procedures during a mission. Investigators will need to automate this feature for future missions. The crew recommended minor shroud improvements for increased comfort, which have since been implemented. The SARA Bluetooth sensors operated without interference from other Aquarius electronics.