Article Figures & Data
Figures
- Figure 1.
Predictions for the horizontal saccade direction bias as a function of head tilt. Polar histograms indicate the frequency of each saccade direction as a function of angle in degrees. A, When the head is upright, the horizontal saccade bias looks the same for both the world orientation hypothesis and the head orientation hypothesis. B, When the head is tilted, it is possible that the saccade bias will either rotate with the head (head orientation hypothesis) or stay consistent with the world and Earth upright (world orientation hypothesis). Blue and orange lines indicate reference lines (i.e., the horizontal axis) for the world and head orientation hypotheses, respectively.
- Figure 2.
A, Head stabilization system for the FOVE virtual reality headset. B, Example fractal photosphere image. C, Example scene photosphere image licensed by Artem Svetlov and obtained from Flickr. The Flickr image was released with a CC-BY-2.0 license.
- Figure 3.
A, Main sequence of all saccades showing the stereotyped relationship between peak velocity and amplitude. B, Histogram showing the number of saccades as a function of amplitude. C, Histogram showing the number of saccades as a function of duration. D, Horizonal and vertical eye traces for one subject during one trial.
- Figure 4.
A, Polar distributions for a single subject during free viewing of fractal images for head tilt right (red) and head upright (black). The angles of the polar plots represent degrees while the radius indicates normalized frequency. B, The unwrapped polar distributions from A. C, The output of the circular cross-correlation that identifies the lag (in degrees) that results in the maximum correlation.
- Figure 5.
Saccade direction distributions during free viewing of fractal images for head tilt left, head upright, and head tilt right. The top row shows the data relative to the world (i.e., accounting for subject head tilt), while the bottom row shows the data relative to the head. Each polar plot is calculated by applying a circular kernel density estimate on saccade direction data. The angles of the polar plots represent degrees while the radius indicates normalized frequency. The black histogram line indicates the mean across subjects while the shaded gray indicates 95% CIs. The blue and orange lines indicate the orientation of the world and head hypotheses, respectively, showing the average measured head tilt.
- Figure 6.
Saccade polar histograms for all subjects during fractal viewing, shown in head coordinates, for (A) head upright and head tilt right distributions and (B) head upright and head tilt left distributions. C, Left, Bootstrapped average displacements for individual subjects with 95% CI error bars. Right, Bar plots showing the direction distribution displacement for all subjects. Circles represent individual data and error bar represents 95% CIs. D, Box and whisker plot showing the reference frame index derived by scaling the direction distribution displacement values for each subject by their head tilt amount in degrees.
- Figure 7.
A, Ocular counter roll traces from one subject from head tilt left, head upright, and head tilt right conditions. B, Change in median OCR values for each subject derived by subtracting the median OCR value of head tilt left (or right) from the median OCR value of head upright. Circles represent individual subjects. Error bars indicate 95% CIs. C, Change in median OCR as a function of the cross-correlation displacement values for each subject (negative values were reversed). D, Reference frame index found by scaling the direction distribution displacement values for each subject by their change in median OCR amount in degrees.
- Figure 8.
Saccade polar histograms for all subjects during Earth upright scene viewing, shown in world coordinates, for (A) head upright and head tilt right distributions and (B) head upright and head tilt left distributions. C, Left, Bootstrapped average displacements for individual subjects with 95% CI bars. Right, Bar plots showing the direction distribution displacement for all subjects. Circles represent individual data and error bar represents 95% CIs. D, Box and whisker plot showing the reference frame index derived by scaling the direction distribution displacement values for each subject by their head tilt amount in degrees.
- Figure 9.
Saccade direction polar histograms during head upright for scenes with (A) 0° and 30° tilt and (B) 0° and −30° tilt. C, Left, Bootstrapped average displacements for individual subjects with 95% CI bars. Right, Bar plots showing the direction distribution displacement for all subjects. Circles represent individual data and error bar represents 95% CIs. D, Box and whisker plot showing the reference frame index derived by scaling the direction distribution displacement values for each subject by the scene tilt amount in degrees.
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