In the Active Perception Laboratory, experiments with human observers are designed to investigate the perceptual consequencs of eye movements and the mechanisms gaze control. Because of their direct and impact on the retinal input, eye movements provide an ideal arena to study the influences of motor activity on vision.

Our experimental and theoretical work is tightly integrated: experiments are almost always designed on the basis of modeling predictions and their results in turn used to refine models. Much of our experimental work relies on new tools and techniques for better measuring eye movements and manipulating visual input signals that have been developed in the laboratory.

(Top) An example of normal eye movements. The enlargement shows the incessant microscopic eye movements present during the periods of fixation. (Right) The visual input to the retina resulting from exploring the scene by means of eye movements.

An important component of research has been dedicated to the most common, yet elusive, oculomotor behavior: the microscopic eye movements (the microsaccades and ocular drift) that humans continually perform in the periods in between voluntary relocations of gaze. These movements provide a great example of the importance of behavior in perception. Vision is still possible when fixational eye movements are the only source of input modulations, whereas the percept fades away when retinal image motion is eliminated, a laboratory procedure known as retinal stabilization. Thus, fixational eye movements are sufficient for enabling vision of stationary scenes, but how they do so has been the subject of long and fierce debates. Research in the Active Perception Laboratory has led to multiple new findings on the mechanisms and functions of fixational eye movements.

Another important line of research is the analysis of the joint perceptual consequences of head and eye movements under natural head-free viewing conditions. We have demonstrated that, during natural fixation, involuntary microscopic head movements yield useful parallax and interact with fixational eye movements to give a retinal input signal with specific characteristics. We are currently studying the function of ocular drift during normal head-free fixation and its relation to the vestibulo-ocular reflex.

Research in the Active Perception Laboratory has also elucidated some of the mechanisms underlying perceptual stability and the establishment of stable visual representations despite eye movements. We have recently shown that, in the presence of saccades, this process relies on the statistically optimal integration of retinal and extra-retinal signals, including eye muscle proprioception.