Visual perceptions can lead to ambiguous interpretation of the reality. Such ambiguous perceptions are called visual illusionary perceptions. As an example, the picture "My wife and my mother-in-law" (Bohring (1930) Am J. Psychol) reveals two different contents within the same image, which are perceived sequentially, but not simultaneously.
Another example of illusionary perception is evoked by the fixation of the animated picture presented below. Here the impression is that of two dots moving up- and down (it is also possible to interpret the motion of the dots as a horizontal movement, or as a clock-wise movement).
This perception is a pure illusion produced by our brain. In fact, there is no movement of the dots at all. Instead the dots appear at one location and suddenly appear at one other location. Since our vision practically excludes "jumps" in objects in motions, the apparent perception is the one of objects in motion.
Such visual illusions are of great interest in the field of clinical- and basic neuroscience as it can be viewed as a potentially valuable probe of two different mechanisms of brain processing: top-down and bottom-up processing. Bottom-up processing is referred to the sequentially processing of visual information from the primary sensory organs via primary cerebral cortices to association cortices within the human brain. Top-down processing in the contrary, is a mechanism in which the perceptions are additionally influenced by stimuli that are not originated by the "outside-world".
We address these phenomena using EEG (optimal temporal resolution) and fMRI (optimal spatial resolution) in order to obtain information about the neurophysiological mechanism that is responsible for the occurrence of these perceptions. Moreover, we focus on the differences in temporal and spatial patterns that are present in humans with psychosis, personality disorders and healthy controls.
University Hospital of Psychiatry Bern, Switzerland
Institute of Neuroradiology, University of Bern, Switzerland
Members of the project group
University Hospital of Psychiatry Bern:
Helge Horn (Consultant)
Kay Jann (MR methodology and Electrophysiology)
Thomas Koenig (electrophysiology)
Insitute of Neuroradiology, University of Bern:
Roland Wiest (MR consultant)
Federspiel A, Volpe U, Horn H, Dierks T, Franck A, Vannini P, Wahlund LO, Galderisi S, Maj M (2005): Motion standstill leads to activation of inferior parietal lobe. Human Brain Mapping. 27(4): 340-349.
Müller TJ, Federspiel A, Horn H, Lövblad KO, Lehmann C, Dierks T and Strik WK (2005): The neurophysiological time pattern of illusionary visual perceptual transitions: a simultaneous EEG and fMRI study. Int journal of Psychophysiology. 55(3):299-31.
Müller TJ, Federspiel A, Fallgatter AJ, Strik WK (1999): EEG signs of vigilance fluctuations preceding perceptual flips in multistable illusionary motion. Neuroreport 10(16): 3423-3427.