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This Article Full Text Full Text (PDF) All Versions of this Article: 102/1/513    most recent 00045.2009v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Joshi, A. C. Articles by Leigh, R. J. PubMed PubMed Citation Articles by Joshi, A. C. Articles by Leigh, R. J.

Effect of Vergence on Human Ocular Following Response (OFR)

¹Department of Biomedical Engineering and ²Department of Neurology, Daroff–Dell'Osso Laboratory, Veterans Affairs Medical Center and University Hospitals, Case Western Reserve University, Cleveland, Ohio

Submitted 15 January 2009; accepted in final form 15 May 2009

The human ocular following response (OFR) is a preattentive, short-latency visual-field–holding mechanism, which is enhanced if the moving stimulus is applied in the wake of a saccade. Since most natural gaze shifts incorporate both saccadic and vergence components, we asked whether the OFR was also enhanced during vergence. Ten subjects viewed vertically moving sine-wave gratings on a video monitor at 45 cm that had a temporal frequency of 16.7 Hz, contrast of 32%, and spatial frequency of 0.17, 0.27, or 0.44 cycle/deg. In Fixation/OFR experiments, subjects fixed on a white central dot on the video monitor, which disappeared at the beginning of each trial, just as the sinusoidal grating started moving up or down. We measured the change in eye position in the 70- to 150-ms open-loop interval following stimulus onset. Group mean downward responses were larger (0.14°) and made at shorter latency (85 ms) than upward responses (0.10° and 96 ms). The direction of eye drifts during control trials, when gratings remained stationary, was unrelated to the prior response. During vergence/OFR experiments, subjects switched their fixation point between the white dot at 45 cm and a red spot at 15 cm, cued by the disappearance of one target and appearance of the other. When horizontal vergence velocity exceeded 15°/s, motion of sinusoidal gratings commenced and elicited the vertical OFR. Subjects showed significantly (P < 0.001) larger OFR when the moving stimulus was presented during convergence (group mean increase of 46%) or divergence (group mean increase of 36%) compared with following fixation. Since gaze shifts between near and far are common during natural activities, we postulate that the increase of OFR during vergence movements reflects enhancement of early cortical motion processing, which serves to stabilize the visual field as the eyes approach their new fixation point.