Effect of visual attention and horizontal vergence in three-dimensional space on occurrence of optokinetic nystagmus

Abstract

OKN corresponding to the motion of the fixating area occurs when a stimulus has two areas separated in depth containing motion in different directions. However, when attention and vergence are separately directed to areas with different motions and depths, it remains unclear which property of attention and vergence is prioritized to initiate OKN. In this study, we investigated whether OKN corresponding to motion in the attending or fixating area occurred when two motions with different directions were presented in the central and peripheral visual fields separated in depth. Results show that OKN corresponding to attended motion occurred when observers maintained vergence on the peripheral stimulus and attended to the central stimulus. However, OKN corresponding to each motion in the attending area and in the fixating area occurred when observers maintained vergence on the central stimulus and attended to the peripheral stimulus. The accuracy rate of the target detection task was the lowest in this condition. These results support the idea that motion in the attended area is essential for occurrence of OKN, and vergence and retinal position affect the strength of attention.

Keywords: Eye movement; attention; binocular disparity; eye tracking; optokinetic nystagmus; stereopsis; vergence.

Figure 1.

Stimulus configuration used in the experiment: Left and center panels are for cross fusion, and center and right panels are for parallel fusion. By means of free-fusing, both cross and parallel fusers can make an impression on the 3D structure of the stimulus. The numeral “1” indicates the target (presented near the center).

Figure 2.

Schematic illustration of stimulus: Left and right panels, respectively, show front and top view of stimuli. Arrows show direction of motion. Circle (not actually presented) show border of area where dots were presented. Central and peripheral areas have different depths.

Figure 3.

Time course of stimulus presentation in a trial: Left and center panels are for cross fusion, and center and right panels are for parallel fusion. By means of free-fusing, both cross and parallel fusers can make an impression of the 3D structure of the stimulus. The observer attended to the motion stimulus while maintaining vergence at the different (or same) depth plane from attended plane on the anteroposterior axis at the center of stimulus.

Figure 4.

Schematic illustration of stimulus in each condition. All panels show top view. Gray and black squares, respectively, show depth planes where attention was paid and vergence was directed. Dotted lines show the plane of display. See texts for the details.

Figure 5.

Trace of eye position in a trial for two observers (OB1 and OB2): The upper four panels depict results of vertical eye position. The lower four panels depict results of horizontal vergence. The line drawing inserted above each panel presents a schematic representation of OKN corresponding to the attended motion in the condition. Horizontal lines in the lower panel show the disparity of the plane to which vergence was instructed to direct, and dotted lines show that to which attention was instructed to direct.

Figure 6.

Mean frequency of OKN in the experiment for each condition of directed vergence and attention: The horizontal axis presents the position of stimulus motion to which OKN corresponded, and the parentheses under that indicate instruction for observers. The vertical axis presents the frequency of OKN corresponding to the motion of each area. Error bars show ± 1 SEM.

Figure 7.

Mean gain of OKN in the experiment for each condition of vergence and attention instructed to direct: The vertical axis presents the gain of OKN corresponding to the motion of each area. Other aspects of the figure are the same as those in Fig 6.