Optokinetic responses (OKRs) are reflexive eye movements induced by a moving visual pattern (Collewijn, 1991; Distler and Hoffmann, 2003; Stahl, 2004; Leigh and Zee, 2006; Buttner and Kremmyda, 2007; Kodama and du Lac, 2016). When a visual pattern starts to move, the eyes begin to move toward the direction of the stimulus motion to produce an initial phase OKR. If the movement of the visual pattern continues for a longer duration, slow tracking eye movements are interrupted by prompt eye movements that reset the eye to its primary position, thus constituting a late-phase OKR. This ocular response of alternating slow tracking and quick resetting eye movements is also known as optokinetic nystagmus (OKN).
This task is designed to assess optokinetic tracking responses in the presence of a motion stimuli consisting of continuous or intermittent optic flow. The optic flow consists of two types of stimuli that differ in the motion pattern: 1) circles/rotations, and 2) bars/transitions. The transition stimuli are designed to assess visual preference for a motion pattern with a specific speed, whereas the rotation stimuli are designed to assess visual preference for a motion pattern with a specific time. The optokinetic tracking was measured in response to the two types of flow stimuli, with two different stimulus durations (4 or 8 sec for transition stimuli, 20 or 40 sec for circle/rotation stimuli).
The number of stimuli with each pattern of motion is 6 for eight seconds, and this results in a total of 48 stimuli in a trial. For the transition stimuli the speed is varied between the four stimuli. For the rotation stimuli the number of 60 degree pulses in a circle are varied between the six stimuli. The stimulus offsets are marked on screen with a yellow line, and the maximum speed is 2.0 deg/sec. The task is divided into a start phase and an OKR phase (n). Each trial starts with a fixation phase of 1000 ms, during which a white fixation dot (radius 0.3 deg) is presented at the fixation point on the middle of the screen center. During the next step a stimulus presentation begins, and the fixation dot is displayed again at the screen center for another 1000 ms. d2c66b5586