TY - THES A1 - Rolfs, Martin T1 - In-between fixation and movement : on the generation of microsaccades and what they convey about saccade generation T1 - Zwischen Fixation und Bewegung : zur Generierung von Mikrosakkaden und was sie über die Vorbereitung von Sakkaden mitteilen N2 - Microsaccades are an important component of the small eye movements that constitute fixation, the basis of visual perception. The specific function of microsaccades has been a long-standing research problem. Only recently, conclusive evidence emerged, showing that microsaccades aid both visual perception and oculomotor control. The main goal of this thesis was to improve our understanding of the implementation of microsaccade generation within the circuitry of saccade control, an unsolved issue in oculomotor research. We make a case for a model according to which microsaccades and saccades result from mutually dependent motor plans, competing for expression. The model consists of an activation field, coding for fixation at its center and for saccades at peripheral locations; saccade amplitude increases with eccentricity. Activity during fixation spreads to slightly peripheral locations in the field and, thus, may result in the generation of microsaccades. Inhibition of remote and excitation of neighbouring locations govern the dynamics of the field, resulting in a strong competition between fixation and saccade generation. We propose that this common-field model of microsaccade and saccade generation finds a neurophysiological counterpart in the motor map of the superior colliculus (SC), a key brainstem structure involved in the generation of saccades. In a series of five behavioral experiments, we tested implications of the model. Predictions were derived concerning (1) the behavior of microsaccades in a given task (microsaccade rate, amplitude, and direction), (2) the interactions of microsaccades and subsequent saccades, and (3) the relationship between microsaccadic behavior and neurophysiological processes at the level of the SC. The results yielded strong support for the model at all three levels of analysis, suggesting that microsaccade statistics are indicative of the state of the fixation-related part of the SC motor map. N2 - Mikrosakkaden sind ein wichtiger Bestandteil der kleinen Augenbewegungen, aus denen Fixationen, die Basis der visuellen Wahrnehmung, bestehen. Neuere Arbeiten erbrachten schlüssige Evidenz dafür, das Mikrosakkaden eine wichtige Rolle in der Wahrnehmung und der Blickbewegungskontrolle spielen. Hauptanliegen dieser Dissertation war es, unser Verständnis der Implementierung der Generierung von Mikrosakkaden im Kreislauf der Sakkadensteuerung zu vertiefen. Wir schlagen ein Modell vor, in dem Mikrosakkaden und Sakkaden konkurrierende Bewegungsprogramme darstellen, die um ihre Umsetzung wettstreiten. Das Modell besteht aus einem Aktivationsfeld, in dem Fixation im Zentrum und Sakkaden in der Peripherie repräsentiert sind (Sakkadenamplitude steigt mit der Exzentrizität). Aktivität während der Fixation breitet sich zu leicht peripheren Orten im Feld aus und kann so zur Generierung von Mikrosakkaden führen. Hemmung von entfernten und Erregung von benachbarten Orten bestimmen die Dynamik im Feld, was zu einem starken Wettstreit zwischen Fixation und Sakkadengenerierung beiträgt. Wir schlagen vor, dass dieses common-field model of microsaccade and saccade generation ein neurophysiologisches Pendant in der Bewegungskarte des colliculus superior (CS) findet, einer Struktur im Hirnstamm, die im starken Zusammenhang mit der Entstehung von Sakkaden steht. In fünf behavioralen Experimenten wurden Implikationen des Modells überprüft. Vorhersagen wurden auf drei Ebenen abgeleitet: (1) Verhalten der Mikrosakkaden in bestimmten Aufgaben (Mikrosakkadenrate, -amplitude und -richtung), (2) Interaktionen von Mikrosakkaden und nachfolgenden Sakkaden, (3) der Zusammenhang zwischen Mikrosakkadenverhalten und neurophysiologischen Prozessen auf der Ebene des CS. Die Ergebnisse unterstützten das Modell auf allen drei Analyseebenen. Mikrosakkaden scheinen ein Indikator der Fixationsaktivität in der Bewegungskarte des CS zu sein. KW - Blickbewegung KW - Aufmerksamkeit KW - Wahrnehmung KW - Blickbewegungskontrolle KW - Sakkade KW - Eye movement KW - Attention KW - Perception KW - Oculomotor control KW - Saccade Y1 - 2007 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-14581 ER - TY - GEN A1 - Dambacher, Michael A1 - Rolfs, Martin A1 - Göllner, Kristin A1 - Kliegl, Reinhold A1 - Jacobs, Arthur M. T1 - Event-related potentials reveal rapid verification of predicted visual input N2 - Human information processing depends critically on continuous predictions about upcoming events, but the temporal convergence of expectancy-based top-down and input-driven bottom-up streams is poorly understood. We show that, during reading, event-related potentials differ between exposure to highly predictable and unpredictable words no later than 90 ms after visual input. This result suggests an extremely rapid comparison of expected and incoming visual information and gives an upper temporal bound for theories of top-down and bottom-up interactions in object recognition. T3 - Zweitveröffentlichungen der Universität Potsdam : Humanwissenschaftliche Reihe - paper 180 KW - Interactive activation model KW - Top-down influences KW - Word form area KW - Spatial attention KW - Brain potentials Y1 - 2009 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-44953 ER - TY - GEN A1 - Kliegl, Reinhold A1 - Rolfs, Martin A1 - Laubrock, Jochen A1 - Engbert, Ralf T1 - Microsaccadic Modulation of Response Times in Spatial Attention Tasks N2 - Covert shifts of attention are usually reflected in RT differences between responses to valid and invalid cues in the Posner spatial attention task. Such inferences about covert shifts of attention do not control for microsaccades in the cue target interval. We analyzed the effects of microsaccade orientation on RTs in four conditions, crossing peripheral visual and auditory cues with peripheral visual and auditory discrimination targets. Reaction time was generally faster on trials without microsaccades in the cue-target interval. If microsaccades occurred, the target-location congruency of the last microsaccade in the cuetarget interval interacted in a complex way with cue validity. For valid visual cues, irrespective of whether the discrimination target was visual or auditory, target-congruent microsaccades delayed RT. For invalid cues, target-incongruent microsaccades facilitated RTs for visual target discrimination, but delayed RT for auditory target discrimination. No reliable effects on RT were associated with auditory cues or with the first microsaccade in the cue-target interval. We discuss theoretical implications on the relation about spatial attention and oculomotor processes. T3 - Zweitveröffentlichungen der Universität Potsdam : Humanwissenschaftliche Reihe - paper 249 Y1 - 2009 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-57098 ER - TY - GEN A1 - Rolfs, Martin A1 - Engbert, Ralf A1 - Kliegl, Reinhold T1 - Crossmodal coupling of oculomotor controland spatial attention in vision and audition N2 - Fixational eye movements occur involuntarily during visual fixation of stationary scenes. The fastest components of these miniature eye movements are microsaccades, which can be observed about once per second. Recent studies demonstrated that microsaccades are linked to covert shifts of visual attention [e.g., Engbert & Kliegl (2003), Vision Res 43:1035-1045]. Here,we generalized this finding in two ways. First, we used peripheral cues, rather than the centrally presented cues of earlier studies. Second, we spatially cued attention in vision and audition to visual and auditory targets. An analysis of microsaccade responses revealed an equivalent impact of visual and auditory cues on microsaccade-rate signature (i.e., an initial inhibition followed by an overshoot and a final return to the pre-cue baseline rate). With visual cues or visual targets,microsaccades were briefly aligned with cue direction and then opposite to cue direction during the overshoot epoch, probably as a result of an inhibition of an automatic saccade to the peripheral cue. With left auditory cues and auditory targets microsaccades oriented in cue direction. Thus, microsaccades can be used to study crossmodal integration of sensory information and to map the time course of saccade preparation during covert shifts of visual and auditory attention. T3 - Zweitveröffentlichungen der Universität Potsdam : Humanwissenschaftliche Reihe - paper 234 KW - Microsaccades KW - Covert orienting KW - Fixational eye movements KW - Multisensory Y1 - 2005 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-56804 ER - TY - GEN A1 - Rolfs, Martin A1 - Kliegl, Reinhold A1 - Engbert, Ralf T1 - Microsaccade orientation supports attentional enhancement opposite to a peripheral cue: Commentary on Tse, Sheinberg, and Logothetis T3 - Zweitveröffentlichungen der Universität Potsdam : Humanwissenschaftliche Reihe - paper 248 Y1 - 2004 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-57081 ER - TY - GEN A1 - Thiel, Marco A1 - Romano, Maria Carmen A1 - Kurths, Jürgen A1 - Rolfs, Martin A1 - Kliegl, Reinhold T1 - Generating Surrogates from Recurrences N2 - In this paper we present an approach to recover the dynamics from recurrences of a system and then generate (multivariate) twin surrogate (TS) trajectories. In contrast to other approaches, such as the linear-like surrogates, this technique produces surrogates which correspond to an independent copy of the underlying system, i. e. they induce a trajectory of the underlying system visiting the attractor in a different way. We show that these surrogates are well suited to test for complex synchronization, which makes it possible to systematically assess the reliability of synchronization analyses. We then apply the TS to study binocular fixational movements and find strong indications that the fixational movements of the left and right eye are phase synchronized. This result indicates that there might be one centre only in the brain that produces the fixational movements in both eyes or a close link between two centres. T3 - Zweitveröffentlichungen der Universität Potsdam : Humanwissenschaftliche Reihe - paper 238 KW - Æ Recurrence Plots KW - Surrogate Data KW - Hypothesis Test KW - Phase Synchronization Y1 - 2006 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-56906 ER - TY - GEN A1 - Rolfs, Martin A1 - Laubrock, Jochen A1 - Kliegl, Reinhold T1 - Shortening and Prolongation of Saccade Latencies Following Microsaccades N2 - When the eyes fixate at a point in a visual scene, small saccades rapidly shift the image on the retina. The effect of these microsaccades on the latency of subsequent large-scale saccades may be twofold. First, microsaccades are associated with an enhancement of visual perception. Their occurrence during saccade target perception should, thus, decrease saccade latencies. On the other hand, microsaccades likely indicate activity in fixation-related oculomotor neurons. These represent competitors to saccade-related cells in the interplay of gaze holding and shifting. Consequently, an increase in saccade latencies after microsaccades would be expected. Here, we present evidence for both aspects of microsaccadic impact on saccade latency. In a delayed response task, participants made saccades to visible or memorized targets. First, microsaccade occurrence up to 50 ms before target disappearance correlated with 18 ms (or 8%) faster saccades to memorized targets. Second, if microsaccades occurred shortly (i.e., < 150 ms) before a saccade was required, saccadic reaction times in visual and memory trials were increased by about 40 ms (or 16%). Hence, microsaccades can have opposite consequences for saccade latencies, pointing at a differential role of these fixational eye movements in preparation of motor programs. T3 - Zweitveröffentlichungen der Universität Potsdam : Humanwissenschaftliche Reihe - paper 242 KW - Fixational eye movements KW - Memory-guided saccades KW - Visually-guided saccades Y1 - 2006 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-57012 ER - TY - GEN A1 - Thiel, Marco A1 - Romano, Maria Carmen A1 - Kurths, Jürgen A1 - Rolfs, Martin T1 - Twin Surrogates to Test for Complex Synchronisation N2 - We present an approach to generate (multivariate) twin surrogates (TS) based on recurrence properties. This technique generates surrogates which correspond to an independent copy of the underlying system, i. e. they induce a trajectory of the underlying system starting at different initial conditions. We show that these surrogates are well suited to test for complex synchronisation and exemplify this for the paradigmatic system of R¨ossler oscillators. The proposed test enables to assess the statistical relevance of a synchronisation analysis from passive experiments which are typical in natural systems. T3 - Zweitveröffentlichungen der Universität Potsdam : Humanwissenschaftliche Reihe - paper 264 Y1 - 2006 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-57231 ER -