Binocular Onset Rivalry at the Time of Saccades and Stimulus Jumps

Recent studies suggest that binocular rivalry at stimulus onset, so called onset rivalry, differs from rivalry during sustained viewing. These observations raise the interesting question whether there is a relation between onset rivalry and rivalry in the presence of eye movements. We therefore studied binocular rivalry when stimuli jumped from one visual hemifield to the other, either through a saccade or through a passive stimulus displacement, and we compared rivalry after such displacements with onset and sustained rivalry. We presented opponent motion, orthogonal gratings and face/house stimuli through a stereoscope. For all three stimulus types we found that subjects showed a strong preference for stimuli in one eye or one hemifield (Experiment 1), and that these subject-specific biases did not persist during sustained viewing (Experiment 2). These results confirm and extend previous findings obtained with gratings. The results from the main experiment (Experiment 3) showed that after a passive stimulus jump, switching probability was low when the preferred eye was dominant before a stimulus jump, but when the non-preferred eye was dominant beforehand, switching probability was comparatively high. The results thus showed that dominance after a stimulus jump was tightly related to eye dominance at stimulus onset. In the saccade condition, however, these subject-specific biases were systematically reduced, indicating that the influence of saccades can be understood from a systematic attenuation of the subjects' onset rivalry biases. Taken together, our findings demonstrate a relation between onset rivalry and rivalry after retinal shifts and involvement of extra-retinal signals in binocular rivalry

Average eye dominance as function of time in the sustained rivalry motion task.

<p>A: subject FW. B: subject JB. C: subject TG. Right- and left-hand panels show data from trials in which the stimulus was in the right or the left hemifield, respectively. Black line: right eye. Gray line: left eye.</p

Example of eye movements.

<p>A: Saccade trial, B: stimulus jump trial. Horizontal (black) and vertical (gray) eye movements (here measured with a search coil) are shown as function of time. The gray bar indicates the horizontal position of the stimulus. The black dashed lines show the moment of the cue for the saccade or the stimulus jump, respectively. Note that the saccade and the stimulus jump result in the same retinal displacement. The double black line shows the moment the subject responded with two button presses indicating the dominance state before and after the shift, respectively. After this response, fixation was no longer required. Data from subject JG.</p

Eye predominance during sustained rivalry phase as function of eye dominance at stimulus onset.

<p>Right eye predominance in the sustained rivalry phase (Experiment 2) is plotted as function of right eye dominance probability at stimulus onset. Symbols identify the same subjects as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0020017#pone-0020017-g003" target="_blank">Figure 3</a>. Blue: motion stimulus (9 subjects), red: face/house (10 subjects) stimulus, green: grating stimulus (5 subjects). Black lines: linear regression lines for 9 subjects that completed the experiment with more than one stimulus type.</p

Illustration of the two trial types in Experiment 3.

<p>White circles indicate the subject's gaze position. Arrows denote a saccade or stimulus jump. Each panel shows the input for one eye only. A: Saccade trials. The subjects looked at the large, red cross until it shrunk. Then the subject made a saccade to the other cross, thus actively changing the retinal input. B: Stimulus jump trials. The subject looked at the green fixation cross at the center of the screen and kept fixation there during the whole trial. After a certain delay, the stimulus jumped to the opposite side, resulting in the same retinal displacement as in A, but this time the displacement was passive.</p

Time from last perceptual switch to the retinal image shift.

<p>Data are shown for all stimulus types (columns) and 4 subjects (rows). In each panel, the left bar show the data from saccade trials and the right bar from the stimulus jump trials. Error bars denote standard errors. Each subject completed 48–60 trials for each condition. Note the similarity of dominance durations in all subjects.</p

Odds ratio of eye dominance after saccades and stimulus jumps as function of onset dominance.

<p>A–C: Odds ratio of right eye dominance after saccades and stimulus jumps as function of right eye dominance after stimulus jumps, shown on a logit scale. Filled symbols: shift from left to right hemifield. Open symbols: shift from right to left hemifield. Data are from subjects FW (A) JB (B) and TG (C). D: Histogram of the regression slopes for all subjects that completed the experiment with two or three stimulus types (n = 9).</p

Three examples of the switch probability after stimulus jumps.

<p>Data is displayed separately for trials with left and right dominance before the shift, respectively. Left-hand panels show jumps from the right to the left hemifield and right-hand panels show jumps from the left to the right hemifield. Bars show the probability of a percept switch, P(switch) or no percept switch, P(no switch) by their position relative to zero, separately for trials in which the left eye (upper bars) or the right eye (lower bars) was dominant before the shift. Data from the face/house stimulus. A: subject FW. B: subject JV. C: subject TG.</p

Subject-specific onset preference.

<p>A: Data from three typical subjects (face/house stimulus). Each colored vertical line shows the onset response in a single trial: right eye or left eye dominance is indicated in red and green, respectively. Trials in which the stimulus was presented in the left or the right hemifield are presented on the left-hand and right-hand side of the center, respectively. The first trial is shown in the center, trial number increases outwards. Values marked <i>I_LR</i> and <i>I_NT</i> at the right hand side of the figure show preference indices (see text). B: Indices quantifying the left/right and nasal/temporal preference at trial onset. <i>I_NT</i> is plotted as a function of <i>I_LR</i> for each subject. Colors indicate different stimulus types. Blue: motion stimulus (9 subjects), red: face/house stimulus (10 subjects), green: grating stimulus (5 subjects).</p

Right eye dominance after shifts as function of right eye dominance at stimulus onset.

<p>Data are shown on a logit scale with logistic regression lines. Blue: motion stimulus. Red: face/house stimulus. Green: grating stimulus.</p