Table 1.
Averaged clinical parameters of optometric examination for positive (base-out) and negative (base in) fusional range, the break and recovery point of near point of convergence.
Fig 1.
A) A graphical representation of the experimental setup. LEDs (light-emitting diodes) were placed at eye level on isovergent circles at two distances from the observer: 20 cm and 100 cm. Eye movements were elicited for both distances, depending on the combination of the fixation and the target LED. Each trial started with the onset of the fixation LED in the midline (position 2 or 5) which was followed by the onset of one of the lateral target LEDs. Eye movements were triggered by redirecting the eyes as following: saccades at far–from LED 5 to LED 4 (leftward saccades) or 6 (rightward saccades); saccades at near–from LED 2 to LED 1 (leftward saccades) or 3 (rightward saccades); combined convergences–from LED 5 to LED 1 (leftward combined convergences) or 3 (rightward combined convergences); combined divergences–from LED 2 to LED 4 (leftward combined divergences) or 6 (rightward combined divergences). B) The design of the experiment as a function of time. Each trial started with the fixation LED, displayed for a random duration between 2,000 to 3,000 Subsequently the target LED was presented for 2,000 ms, which was followed by a 1,000-ms intertrial interval.
Fig 2.
Electrode placement for EOG data collection.
First, the saccade signal was registered separately for left and right eyes. Subsequently, they were averaged using the following formula: EOGsacc = (hEOGleft + hEOGright)/2.
Fig 3.
Electro-oculographic (EOG) signals measured from the electrodes attached to the outer and inner canthi of both the right and the left eyes.
The grand averages, based on 14 participants, are presented for each condition from -400 to 400 ms relative to the saccade onset of each eye movement.
Table 2.
Mean latencies for exogenously triggered saccades, divergences, and convergences based on 14 participants.
SE represents the standard error.
Fig 4.
Topographical maps of event-related potentials for the three eye movement types from -180 ms to -60 ms before eye movement onset.
The first two rows display the maps for pure left and right saccades, the third and fourth row show the maps for combined left and right convergences, and the two lower rows represent the maps for left and right combined divergences.
Fig 5.
Grand average waveforms of event related potentials for three eye movement types in time intervals from -180 ms to 10 ms relative to eye movement onset.
The grand averages waveforms of the response-locked activity are presented for 12 relevant electrodes located in the frontal, parieto-occipital and occipital cortex.
Fig 6.
Estimated pairs of source locations based on event-related potentials (ERPs) observed preceding lateral exogenous saccades, convergences, and divergences.
A model was built based on the averaged ERPs obtained for combined convergences using the BESA algorithm. Based on the GFP inspection, the fitting procedure was performed for the three time windows selected from the onset of a peak to the local maximum of the GFP: (1) -180 to -154 ms, (2) -132 to -96 ms, and (3) -86 to -60 ms. Three pairs of regional sources (RS) were fitted to subsequent time intervals: RS1, RS2, and RS3, respectively.
Table 3.
Talairach coordinates of regional sources related to the execution of saccades, convergences, and divergences.
The regional sources were determined for the time window -180 ms to -60 ms before the eye movement onset. A model was built and based on the averaged ERPs obtained for combined convergences using the BESA algorithm. Cortical regions were estimated using the Talairach Client software (version 2.4.3).
Fig 7.
Source waveforms elicited by activity preceding the different eye movement types for each regional source.
Source waveforms were prepared per participant by calculating the RMS (root mean square) for each condition within each of the three regional sources per hemisphere. Then, the averages of all individuals per condition were computed, the result of which is shown in the figure. The obtained individual averages for each type of eye movement per condition were used for statistical analyses.
Fig 8.
Source waveforms comparing stimulus-locked and response-locked activities in each regional source for saccades, combined convergences and combined divergences.
Fig 9.
Contralateral source activity elicited by eye movement preparation in occipital source RS2.
Source waveforms were prepared per participant by calculating the RMS (root mean square) for each condition within a regional source. Then, the averages of all individuals per condition and contralateral activity were computed. Finally, the result is shown in the figure. The obtained averages for each type of eye movement were used for statistical analyses.