Fig 1.
Schematic overview of important cortical regions and brainstem areas involved in the control of eye movements.
The sagittal cross section of the brainstem is showing the three oculomotor nuclei (III, IV, VI), the nucleus prepositus hypoglossi (NPH), the interstitial nucleus of Cajal (INC), the superior colliculus, the paramedian pontine reticular formation (PPRF), the medial longitudinal fasciculus (MLF) and the mediadorsal nucleus (MD) in the thalamus. The nucleus raphe interpositus (not shown) lies close to the midline, at the level of the abducens nucleus (VI) [modified from Petzold A, Paine M, Faldon M, Riordan-Eva P, Bronstein AM, Gresty MA, Plant GT. Synchronised paroxysmal ocular tilt reaction and limb dystonia. Neuroophthalmology 2009;33:217–236.].
Fig 2.
a. Picture of the device set-up. Participants were seated in front of a display monitor, with their head stabilized with a chin and forehead rest. The camera was located in front of the chin rest, just below the line of sight. b. Target used in the measurements, a black circle with a black cross in the center of the circle. c. Schematic overview of the set-up (view from above). The participant in the chin and forehead rest is located 92 cm in front of the display monitor and 55 cm in front of the camera. The examiner is located on the left of the participant and can check stability of the signal and performance of the participant on the host monitor.
Fig 3.
Assessments in the DEMoNS protocol.
All assessments start with a fixation period (F) at a central target (black dot), with a random duration between 1.0 and 3.5 seconds. After this, depending on the task, a gap period (G), one or two targets (T, T1, T2) and refixation targets (RF) are appearing (black dots) of different durations. The circles with the dashed lines show the other possible locations of the targets in this task. Afterwards, the central target re-appears, and the task will restart. All target steps (fixation position to target and target one to target two) encompass 8 degrees of visual angle, except for the vertical target steps in the fixation task (10 degrees of visual angle) and the most eccentric target steps in the pro-saccadic task (15 degrees of visual angle). In the top right corner, an enlarged example of one possible combination of target locations of the double-step saccadic task is shown.
Fig 4.
Example of two parameters of the DEMoNS protocol.
a. Scatterplot of left eye gaze positions of one subject (JNB) of the first central fixation trial. The 68% Bivariate Contour Ellipse Area (BCEA) is represented by the dashed line, which is the area of a bivariate ellipse encompassing 68% of the highest density samples. The arrows are indicating the distance of 0.1 degree of visual angle in the horizontal and vertical dimension. b. Schematic representation of the area under the curve (AUC) of the horizontal saccadic trajectory of a rightward saccade. The blue line represents the right eye and the red line represents the left eye. The AUC is assessed from the first starting saccade (left or right eye) until the last ending saccade (left or right eye). In this period the area is calculated for both eyes separately by summing the horizontal eye position at every time point minus the horizontal start position of the saccade.
Table 1.
Summary of analysis steps of the eye movement data.
Fig 5.
Intra-class correlation coefficients of pro-saccadic task.
Intra-class correlation coefficient (black dots) with 95% confidence interval (error bars) of parameters of the pro-saccadic task.
Fig 6.
Latency of pro-saccades and express saccades.
a. Latency of pro-saccades (black dots) and express saccades (white diamonds) of second measurement against first measurement of all subjects. The dotted line corresponds to absolute agreement between the two measurement. b. Latency of first measurement (black dots) and second measurement (white diamonds) of pro-saccades against express saccades. The linear fit (black line) with 95% confidence interval (dotted lines) of all measurements is shown.
Fig 7.
Proportion of errors and latency of anti-saccades.
a. Proportion of errors of second measurement against first measurement of all subjects (black dots). The dashed line corresponds to absolute agreement between the two measurement. b. Latency of correct anti-saccades of second measurement against first measurement of all subjects (black dots). The dashed line corresponds to absolute agreement between the two measurement.
Fig 8.
Proportion of correct double-step saccades and error of the final eye position.
a. Proportion of correct double-step saccades (DS) of second measurement against first measurement of all subjects (black dots). The dashed line corresponds to absolute agreement between the two measurement. b. Error of the final eye position (FEP) in degrees of visual angle of double-step saccades of second measurement against first measurement of all subjects (black dots). The dashed line corresponds to absolute agreement between the two measurement.
Fig 9.
Comparison of pro-saccadic parameters of center one and center two.
Box (25–75%)-and-whisker (0–100%) plots from pro-saccadic parameters of center one (both at sampling a frequency of 1000 Hz and downsampled to 500 Hz) and center two. The horizontal line in the box is plotted at the median and the plus sign indicates the mean.
Fig 10.
Bland Altman plots of pro-saccadic parameters of centerone and two.
On the x-axis, the mean of the two measurements for the three subjects tested at both centers is shown. On the y-axis the difference (center one minus center two) of the two measurements is shown. Both comparison with the original sampling frequency of center one of 1000 Hz (black dots) and downsampled to 500 Hz (white diamonds) is shown.