Correction of Saccade-Induced Midline Errors in Responses to Pure Disparity Vergence Stimuli.

Abstract

Purely symmetrical vergence stimuli aligned along the midline (cyclopean axis) require only a pure vergence response. Yet, in most responses saccades are observed and these saccades must either produce an error in the desired midline response or correct an error produced by asymmetry in the vergence response. A previous study (Semmlow, et al. 2008) has shown that the first saccade to appear in a response to a pure vergence stimulus usually increased the deviation from the midline, although all subjects (N = 12) had some responses where the initial saccade corrected a vergence induced midline error. This study focuses on those responses where the initial saccade produces an increased midline deviation and the resultant compensation that ultimately brings the eyes to the correct binocular position. This correction is accomplished by a higher level compensatory mechanism that uses offsetting asymmetrical vergence and/or corrective saccades. While responses consist of a mixture of the two compensatory mechanisms, the dominant mechanism is subject-dependent. Since fixation errors are quite small (minutes of arc), some feedback controlled physiological process involving smooth eye movements, and possibly saccades, must move the eyes to reduce binocular error to fixation disparity levels.

Target eccentricity and form influences disparity vergence eye movements responses: A temporal and dynamic analysis

“…The last observation from our study is the prevalence of saccades increased as the eccentricity of the target increased. Our results are similar to other studies which analyze saccades during symmetrical vergence step responses (Semmlow, Chen, Granger, Donnetti, & Alvarez, 2009;Semmlow, Chen, Granger-Donnetti, & Alvarez, 2008).…”

New device for taking nine-directional ocular photographs: “9Gaze” application

“…First, the sample size was limited, and further studies will be needed to verify our results. Second, the 9Gaze application requires that photographs are taken at about 20 cm from the participant; therefore, it is possible that the eyes’ vergence responses contained saccades that could influence the results ( , 8 , 9 ) However, since the 9Gaze application is a recording method rather than a rigorous examination, we considered it useful for recording purposes irrespective of vergence responses and saccades. Previously, a novel eye-tracking device with artificial intelligence was used for nine-directional ocular measurement ( 3 ); it was trained on nine-directional ocular photographs for diagnosis of eye position abnormalities ( 2 ).…”

Dynamics of the disparity vergence fusion sustain component

“…Isolating the slow component from the total vergence response is the first step in our analysis. While methods have been developed using independent component analysis to separate the initial and slow components, they operate on a group, or ensemble of movements, and identify component averages across the group (Alvarez et al, 2000;Semmlow, Chen, Alvarez, & Pedrono, 2007;Semmlow, Chen, Granger-Donetti, & Alvarez, 2008;Semmlow, Yuan, & Alvarez, 2002). Here, we need to identify the segment dominated by the late response in individual eye movements.…”