@article{OhlBrandtKliegl2011, author = {Ohl, Sven and Brandt, Stephan A. and Kliegl, Reinhold}, title = {Secondary (micro-)saccades the influence of primary saccade end point and target eccentricity on the process of postsaccadic fixation}, series = {Vision research : an international journal for functional aspects of vision.}, volume = {51}, journal = {Vision research : an international journal for functional aspects of vision.}, number = {23-24}, publisher = {Elsevier}, address = {Oxford}, issn = {0042-6989}, doi = {10.1016/j.visres.2011.09.005}, pages = {2340 -- 2347}, year = {2011}, abstract = {We examine how the size of saccadic under-/overshoot and target eccentricity influence the latency, amplitude and orientation of secondary (micro-)saccades. In our experiment, a target appeared at an eccentricity of either 6 degrees or 14 degrees of visual angle. Subjects were instructed to direct their gaze as quickly as possible to the target and hold fixation at the new location until the end of the trial. Typically, increasing saccadic error is associated with faster and larger secondary saccades. We show that secondary saccades at distant in contrast to close targets have in a specific error range a shorter latency, larger amplitude, and follow more often the direction of the primary saccade. Finally, we demonstrate that an undershooting primary saccade is followed almost exclusively by secondary saccades into the same direction while overshooting primary saccades are followed by secondary saccades into both directions. This supports the notion that under- and overshooting imply different consequences for postsaccadic oculomotor processing. Results are discussed using a model, introduced by Rolfs, Kliegl, and Engbert (2008), to account for the generation of microsaccades. We argue that the dynamic interplay of target eccentricity and the magnitude of the saccadic under-/overshoot can be explained by a different strength of activation in the two hemispheres of the saccadic motor map in this model.}, language = {en} } @article{RolfsOhl2011, author = {Rolfs, Martin and Ohl, Sven}, title = {Visual suppression in the superior colliculus around the time of microsaccades}, series = {Journal of neurophysiology}, volume = {105}, journal = {Journal of neurophysiology}, number = {1}, publisher = {American Chemical Society}, address = {Bethesda}, issn = {0022-3077}, doi = {10.1152/jn.00862.2010}, pages = {1 -- 3}, year = {2011}, abstract = {Miniature eye movements jitter the retinal image unceasingly, raising the question of how perceptual continuity is achieved during visual fixation. Recent work discovered suppression of visual bursts in the superior colliculus around the time of microsaccades, tiny jerks of the eyes that support visual perception while gaze is fixed. This finding suggests that corollary discharge, supporting visual stability when rapid eye movements drastically shift the retinal image, may also exist for the smallest saccades.}, language = {en} } @inproceedings{OhlBrandtKliegl2012, author = {Ohl, Sven and Brandt, S. and Kliegl, Reinhold}, title = {Post-saccadic location judgments after presentation of multiple target-like objects}, series = {Perception}, volume = {41}, booktitle = {Perception}, number = {1}, publisher = {Sage Publ.}, address = {London}, issn = {0301-0066}, pages = {171 -- 171}, year = {2012}, language = {en} } @inproceedings{OhlBrandtKliegl2013, author = {Ohl, Sven and Brandt, S. and Kliegl, Reinhold}, title = {Immediate preparatory influences on microsaccades before saccade onset to endogenously vs. exogenously defined targets}, series = {Perception}, volume = {42}, booktitle = {Perception}, number = {4}, publisher = {Sage Publ.}, address = {London}, issn = {0301-0066}, pages = {37 -- 38}, year = {2013}, language = {en} } @article{OhlBrandtKliegl2013, author = {Ohl, Sven and Brandt, Stephan A. and Kliegl, Reinhold}, title = {The generation of secondary saccades without postsaccadic visual feedback}, series = {Journal of vision}, volume = {13}, journal = {Journal of vision}, number = {5}, publisher = {Association for Research in Vision and Opthalmology}, address = {Rockville}, issn = {1534-7362}, doi = {10.1167/13.5.11}, pages = {23}, year = {2013}, abstract = {Primary saccades are often followed by small secondary saccades, which are generally thought to reduce the distance between the saccade endpoint and target location. Accumulated evidence demonstrates that secondary saccades are subject to various influences, among which retinal feedback during postsaccadic fixation constitutes only one important signal. Recently, we reported that target eccentricity and an orientation bias influence the generation of secondary saccades. In the present study, we examine secondary saccades in the absence of postsaccadic visual feedback. Although extraretinal signals (e.g., efference copy) have received widespread attention in eye-movement studies, it is still unclear whether an extraretinal error signal contributes to the programming of secondary saccades. We have observed that secondary saccade latency and amplitude depend on primary saccade error despite the absence of postsaccadic visual feedback. Strong evidence for an extraretinal error signal influencing secondary saccade programming is given by the observation that secondary saccades are more likely to be oriented in a direction opposite to the primary saccade as primary saccade error shifts from target undershoot to overshoot. We further show how the functional relationship between primary saccade landing position and secondary saccade characteristics varies as a function of target eccentricity. We propose that initial target eccentricity and an extraretinal error signal codetermine the postsaccadic activity distribution in the saccadic motor map when no visual feedback is available.}, language = {en} } @article{OhlKliegl2016, author = {Ohl, Sven and Kliegl, Reinhold}, title = {Revealing the time course of signals influencing the generation of}, series = {Vision research : an international journal for functional aspects of vision.}, volume = {124}, journal = {Vision research : an international journal for functional aspects of vision.}, publisher = {Elsevier}, address = {Oxford}, issn = {0042-6989}, doi = {10.1016/j.visres.2016.06.007}, pages = {52 -- 58}, year = {2016}, abstract = {Saccadic eye movements are frequently followed by smaller secondary saccades which are generally assumed to correct for the error in primary saccade landing position. However, secondary saccades can also occur after accurate primary saccades and they are often as small as microsaccades, therefore raising the need to further scrutinize the processes involved in secondary saccade generation. Following up a previous study, we analyzed secondary saccades using rate analysis which allows us to quantify experimental effects as shifts in distributions, therefore going beyond comparisons of mean differences. We use Aalen's additive hazards model to delineate the time course of key influences on the secondary saccade rate. In addition to the established effect of primary saccade error, we observed a time-varying influence of under- vs. overshooting - with a higher risk of generating secondary saccades following undershoots. Moreover, increasing target eccentricity influenced the programming of secondary saccades, therefore demonstrating that error-unrelated variables co-determine secondary saccade programs. Our results provide new insights into the generative mechanisms of small saccades during postsaccadic fixation that need to be accounted for by secondary saccade models.}, language = {en} } @article{OhlWohltatKliegletal.2016, author = {Ohl, Sven and Wohltat, Christian and Kliegl, Reinhold and Pollatos, Olga and Engbert, Ralf}, title = {Microsaccades Are Coupled to Heartbeat}, series = {The journal of neuroscience}, volume = {36}, journal = {The journal of neuroscience}, publisher = {Society for Neuroscience}, address = {Washington}, issn = {0270-6474}, doi = {10.1523/JNEUROSCI.2211-15.2016}, pages = {1237 -- 1241}, year = {2016}, abstract = {During visual fixation, the eye generates microsaccades and slower components of fixational eye movements that are part of the visual processing strategy in humans. Here, we show that ongoing heartbeat is coupled to temporal rate variations in the generation of microsaccades. Using coregistration of eye recording and ECG in humans, we tested the hypothesis that microsaccade onsets are coupled to the relative phase of the R-R intervals in heartbeats. We observed significantly more microsaccades during the early phase after the R peak in the ECG. This form of coupling between heartbeat and eye movements was substantiated by the additional finding of a coupling between heart phase and motion activity in slow fixational eye movements; i.e., retinal image slip caused by physiological drift. Our findings therefore demonstrate a coupling of the oculomotor system and ongoing heartbeat, which provides further evidence for bodily influences on visuomotor functioning.}, language = {en} }