Figure 2: Summary of 48 participants’ data showing SPQ and SATQ trait measures and vertical RMSE for the slow tracking condition. (a) and (b) show the frequency distributions of SPQ and SATQ scores with descriptive statistics. (c) Strong correlation between SPQ and SATQ scores. (d) to (e) Weak correlation between SPQ and onset, 0ms, RMSE for both gravity and antigravity conditions, and (f) moderate correlation between gravity and antigravity RMSE. (g) to (i) weak correlation between SATQ and onset, 0ms, RMSE for both conditions, G and AG, and then the distributions of the onset y-RMSE values for gravity (darker) and antigravity (lighter) showing separation between condition performance. (j) to (l) show moderate correlation between gravity and antigravity RMSE, increasing strength through 80ms, 160ms and 240ms. (m) to (o) show distributions of y-RMSE distributions for gravity (darker) and antigravity (lighter) which become less distinct over time from 80ms to 240ms.
Eye tracking differences across gravity conditions
Tracking was measured separately across G and AG conditions both for the constant speed component – x and the accelerating component – y. We first considered the relationship between the tracking measures for the accelerating direction RMSE – y and for the G and AG conditions. We carried out four Pearson’s correlations to track this relationship dynamically from onset (0ms) through to the closed-loop response at 240ms in four windows. Alpha was adjusted to 0.0125 for four comparisons. There was a significant correlation between individual RMSE – y values across all the time windows: at 0ms, r = 0.422, p = 0.00282; near response onset at 80ms r = 0.472, p = 7 x 10-4; during the open loop at 160ms r = 0.481, p = 5.47 x 10-4; and during the closed loop r = 0.532, p = 9.8 x 10-5. Interestingly, the correlations increase in strength over time from onset, suggesting that the earliest anticipatory responses have less shared processing between the G and AG stimulus cases than the later closed-loop response (Figure 2F, J-L). We then tested for a difference in the RMSE – y responses between the G and AG conditions for the same sequential time windows. We used a Wilcoxon signed rank test because of the non-parametric distributions (see Figure 2I, M-O). There was a significant difference between the G and AG responses for the earliest two windows, with the values at 0ms for G: Median = 0.41° and for AG: Median = 0.73°, with W = 167, p = 0.0000157, and at 80ms for G: Median = 0.37° and for AG: Median = 0.56°, with W = 265, p = 0.000923. At 160ms and 240ms, there was no significant difference between G and AG responses, with W = 513, p = 0.44, and W = 550, p = 0.70 respectively. Early responses in the gravity direction are consistently best for the G condition and initially poorer for the AG condition (Figure 2I, M-O). Similar differences are found between the G and Control conditions. The pattern of results showing better performance under G and delays under AG replicates previous findings (Meso et al., 2020). We then compared the values of both saccade measures under the two gravity conditions, adjusting alpha for the two tests. For the rates, significantly fewer saccades are produced per second under G: Median = 1.36 than under AG: Median = 1.58, W = 245, p = 0.000735. For the amplitudes, there is no significant difference in the size of saccades produced under the G and AG conditions, W = 448, p = 0.15 (Figure 3I and J). Finally, we looked at the effect of learning across trials for both the constant speed motion with RMSE – x and the motion subject to acceleration RMSE – y and adjusted alpha for two comparisons to 0.025. For the first (x), there is a difference between the conditions with less learning under G: Median = -0.06° than AG: Median = 0.03°, W = 319, p = 0.0058. For the accelerating condition (y), learning is again lower for G: Median = -0.02° than AG: Median = 0.19°, W = 248, p = 0.000488. This result suggests that performance in the gravity condition did not generally improve over the course of trials while that under the antigravity condition generally did, especially under acceleration (Figure 3K-L).