Objective vs subjective measures of fixation disparity for short and long fixation periods.

Purpose: Fixation disparity, i.e. the vergence error for stationary fusion stimuli, can be measured objectively with eye trackers and subjectively with nonius lines.

Binocularity during reading fixations: Properties of the minimum fixation disparity.

The present study was based on the physiologically reasonable assumption that the binocular system aims for a reduction of fixation disparity during fixation and that the minimum amount of fixation disparity reflects the optimal binocular status. We measured eye movements (EyeLink II) of 18 participants, while they read 60 sentences from the Potsdam-Sentence-Corpus (PSC) at a viewing distance of 60cm. The minimum fixation disparity was frequently reached directly after the post-saccadic drift, sometimes at the end of fixation and sometimes somewhere in between.

Individual differences in the asymmetry of binocular saccades, analysed with mixed-effects models.

We analysed the reliability of individual differences in parameters of binocular saccadic eye movements. During saccades between isovergent targets, the movement of the right and left eye are not exactly symmetrical (conjugate). Typically, the abducting eye has a shorter latency and reaches a higher velocity, so that a transient divergence occurs during the saccade.

Horizontal fixation disparity measures with nonius lines.

Purpose: It has been reported that changes in visual direction and retinal correspondence may limit the validity of nonius lines as a subjective measure of vergence, at least in particular viewing conditions, e.g., dynamic or forced vergence.