research interests

Spalte #col2

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visual direction constancy

In March 2008, I started a postdoc in the new lab ofPatrick Cavanagh. The topic that we both share a passion for is visual direction constancy, or, spatiotopy. That is, why seems visual perception so remarkably continuous in space and time despite the fact that eye-, head-, and body-movements produce large-scale transitions in the input stream on the retina? And how do we keep track of things are around us if they jump around on our receptors? Neurophysiology has provided a number of findings that may guide our way. Together withTomas Knapen, my office-mate who is also postdoc in our lab, we are probing in various ways how visual direction constancy may be achieved. I am confident that we will come up with insightful data to finally arrive at a model of transsaccadic perception that is able to account for all these mysteries. I also started a collaboration withThérèse Collins at the University of Hamburg on some interesting aspects of these issues.

fixational eye movements

Human visual perception almost completely relies on the fact that the eyes are able to fixate points within a visual scene. But the term fixation may easily be misunderstood. We never fixate perfectly and we can count ourselfes lucky in this regard, since small eye movements during fixation clearly mediate perception. Fixational eye movements prevent the visual world from fading. In my research I mainly focus on microsaccades, small flicks of the eye during intended fixation. For some decades, there was reasonable doubt in the purpose of these small movements. Over the last ten years, however, neurophysiological findings and improved eye-movement-recording techniques pushed the topic again and doubts diminished in the light of new evidence. But even if microsaccades are "busy work" of the oculomotor system occurring when participants are forced to fixate for unnaturally long times, their investigation may generate insight about basic mechanisms of the oculomotor system and probably about cognitive processes related to it. In one series of experiments, for instance, we (together withRalf Engbert &Reinhold Kliegl at the Universität Potsdam) linked microsaccade rate and direction to spatial attention in different modalities (vision and audition). In another study, we (together withJochen Laubrock &Reinhold Kliegl in Potsdam) found that microsaccades may be associated with both a shortening or a lengthening of subsequent saccade latencies, depending on the amplitude of the microsaccade and on when it was observed relative to the saccade. These results have important implications for the implementation of microsaccades and saccades and provided the basis for a model of microsaccade and saccade generation that was published recently.

oculomotor control

A related research area is concerned with the issue of eye-movement control. What are the basic processes underlying saccade generation? Some recent work of mine was concerned with the gap task, a classical oculomotor paradigm, in which a fixation stimulus disappears prior to the appearance of a new fixation target. We know that the oculomotor system is put in some state of readiness during the gap period. However, it is not entirely clear whether this preparation is purely temporal or whether there is spatially localized preparation (i.e., specific saccade metrics are prepared). Together withFrancoise Vitu (CNRS, Marseille), we have successfully developed a new version of the gap paradigm in which we aimed to distinguish between these two scenarios. It turned out that purely temporal preparation cannot account for saccadic behavior in the gap task.

learning of attention

Some people develop incredible skills in efficiently distributing their spatial attention across the visual field. For instance, linesmen in soccer games almost flawlessly report when players are offside (i.e., at the moment the ball is played by one of his team, a player involved in active play is nearer to his opponents' goal line than both the ball and the second to last opponent). Obviously, this ability requires learning to attend to a handful of relevant players distributed across the pitch while effectively ignoring most other information that is available. In a new project, Annette Kinder and I investigate how visual attention learns to effectively filter out important parts of a scene and disengage, respectively, if relevant information is unlikely.