Cognitive and Computational Psychophysics
Sensorimotor Integration

Our nervous system is designed to interact with the environment. Therefore we need to integrate information that is presented by the senses. This enables us to successfully use our motor system to affect the world. There is a long tradition of speculation about the ways this integration of sensory information is accomplished. For example, René Descartes assumed that the pineal gland is the "seat of the soul". He assumed that it is a central interpretation-organ that integrates all information and initiates motor actions.

Descartes (20705 bytes) René Descartes, Principles of Philosophy, 1644.

In recent years there has been a renewed interest in this topic. Cognitive neuroscience has presented a wide variety of new insights. Evidence from psychophysical experiments, neurological patients, animal research, and new imaging techniques is available and has led to a more complete understanding of the ways humans solve the problem of integrating sensory informations to guide actions.

We use real, and virtual environments to investigate sensory motor integration. The rational is to break up the flow of information that feeds back the effects of our actions to the sensory input. Virtual environments enable us to open the "action-perception cycle" and to introduce experimental manipulations that are not possible in the "real" world.

To accomplish this goal we use a variety of tools. Central is the use of two PHANToM devices (SensAble Technologies), an Optotrak-3020 system (Northern Digital), and computer graphics using an SGI-ONYX workstation. The systems are integrated into a virtual environment that enables tracking of movements and the generation of virtual haptic, and visual objects. For more details follow the link to the SeMo lab.

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    Visual Illusions and Grasping

Several theories assume that visual information is processed in two different streams in the primate brain - the dorsal stream and the ventral stream. It has been proposed that the dorsal stream performs transformations that are neccessary for the visual guidance of actions and that the ventral stream performs transformations that are necessary for object recognition and conscious experience. Support for this view came from studies which found that grasping is less affected by visual illusions than perception. In a series of experiments we tested this claim and found contrary evidence: Grasping seems to be affected by visual illusions and the effects seems to be similar to the effects on perception.

For more details on visual illusions and grasping see selected publications:

  • Franz, V. H., Fahle, M., Bülthoff, H. H., & Gegenfurtner, K. R. (in press). The Effects of Visual Illusions on Grasping. Journal of Experimental Psychology: Human Perception and Performance.
  • Franz, V. H., Gegenfurtner, K. R., Bülthoff, H. H., & Fahle, M. (2000). Grasping visual illusions: No evidence for a dissociation between perception and action. Psychological Science, 11(1), 20-25.
  • Franz, V. H., Fahle, M., Bülthoff, H. H., & Gegenfurtner, K. R. (1999) The Effects of Visual Illusions on Grasping. Max-Planck Institute for Biological Cybernetics, TR-74. Abstract, postscript (489 K), pdf (552 K).

Contact: Volker Franz

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   Plasticity of human visuomotor coordination
To perform goal directed hand movements, we need to integrate visual and proprioceptive information concerning the position of the desired target in relation to our limb. Manipulating visual feedback, for example by wearing displacing prisms in front of the eyes, disturbs that computation and results in aiming errors. Plasticity of the human visuomotor system is demonstrated by gradually decreasing errors until stable aiming accuracy is reestablished and by a negative aftereffect when the prisms are removed.

We implement EEG recordings to study the effect of manipulated (i.e. left-right mirrored) visual feedback on neural activity during pointing movements. This is done in cooperation with the working group of PD Edmund Wascher (Max Planck Institute for Psychological Research, Munich). 

For more details on plasticity of human visuomotor coordination see selected publications:

  • Berndt, I., Wascher, E., Franz, V., Bülthoff H.H. (2000,October). A psychophysical and psychophysiological investigation of processing effort in manual pointing movements. Poster presented at the symposium on Neural Control of Movement Synergy, Ohlstadt, Germany.
  • Berndt, I., von Campenhausen, C. (2000). Eye-hand coordination. Extending Helmholtz'es prism study. In H. H. Bülthoff, M. Fahle, K. R. Gegenfurtner, & H. A. Mallot (Eds.), Beiträge zur 3. Tübinger Wahrnehmungskonferenz (p. 151). Kirchentellinsfurt: Knirsch.
  • Berndt, I. (1999). Studien zur Visuomotorik von Handbewegungen. Die Übertragung des Helmholtz'schen Prismenversuchs auf Bildschirmtechniken. Diplomarbeit. Unpublished. Johannes Gutenberg Universität, Mainz.

Contact: Isabelle Berndt

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    Vision and Haptics

Imagine you go to the optician and get a new pair of glasses. The first time you put on these new pair of glasses the world looks funny because the image of the world is somewhat distorted by the glasses. After wearing the glasses for several hours, however, the world looks normal again. This is an example of visuomotor adaptation. To adapt to these kind of situations, information from the visual system has to be compared with information from the motor system. Here we investigate the integration of visual and haptic information by the human brain. Specifically, we are interested what kind of information from the visual or haptic modality is used by the other modality.

For more details see the home page of Marc Ernst.

Contact: Marc Ernst

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Last modified: Wed Dec 20 17:42:46 MET 2000