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Biomedical subjects

C von der Malsburg

Publications and source records attributed to C von der Malsburg.

14 recordsLinked to original sources

Democratic integration: self-organized integration of adaptive cues.

Sensory integration or sensor fusion -- the integration of information from different modalities, cues, or sensors -- is among the most fundamental problems of perception in biological and artificial systems. We propose a new architecture for adaptively integrating different cues in a self-organized manner. In Democratic Integration different cues agree on a result, and each cue adapts toward the result agreed on. In particular, discordant cues are quickly suppressed and recalibrated, while cues having been consistent with the result in the recent past are given a higher weight in the future. The architecture is tested in a face tracking scenario. Experiments show its robustness with respect to sudden changes in the environment as long as the changes disrupt only a minority of cues at the same time, although all cues may be disrupted at one time or another.

Contrast Sensitivity↗

Improving object recognition by transforming Gabor filter responses.

Previous work described a biologically motivated object recognition system with Gabor wavelets as basic feature type. These features are robust against slight distortion, rotation and variation in illumination. We here describe extensions of the system that address image variance due to arbitrary in-plane rotation, substantial scale changes and moderate depth rotation of objects, and to background variation, using simple linear transformation of the Gabor filter responses. The performance of the system is enhanced significantly.

Journal Article↗

Binding in models of perception and brain function.

The development of the concept of feature binding as fundamental to neural dynamics has made possible recent advances in the modeling of difficult problems of perception and brain function. Major weaknesses of past neural modeling (most prominently its inability to work with natural stimuli and its 'learning-time' barrier) have been traced back to improper treatment of the binding issue. Signal synchrony is now seen as playing a major role in binding. Inclusion of temporal binding in neural models has led to recent breakthroughs in solving important perceptual problems. Among them is perceptual segmentation, invariant object recognition and natural language parsing, as well as overcoming the 'learning-time' barrier.

Animals↗

Sensory segmentation with coupled neural oscillators.

We present a model of sensory segmentation that is based on the generation and processing of temporal tags in the form of oscillations, as suggested by the Dynamic Link Architecture. The model forms the basis for a natural solution to the sensory segmentation problem. It can deal with multiple segments, can integrate different cues and has the potential for processing hierarchical structures. Temporally tagged segments can easily be utilized in neural systems and form a natural basis for object recognition and learning. The model consists of a "cortical" circuit, an array of units that act as local feature detectors. Units are formulated as neural oscillators. Knowledge relevant to segmentation is encoded by connections. In accord with simple Gestalt laws, our concrete model has intracolumnar connections, between all units with overlapping receptive fields, and intercolumnar connections, between units responding to the same quality in different positions. An inhibitory connection system prevents total correlation and controls the grain of the segmentation. In simulations with synthetic input data we show the performance of the circuit, which produces signal correlation within segments and anticorrelation between segments.

Animals↗

A neural cocktail-party processor.

Sensory segmentation is an outstanding unsolved problem of theoretical, practical and technical importance. The basic idea of a solution is described in the form of a model. The response of "neurons" within the sensory field is temporally unstable. Segmentation is expressed by synchronization within segments and desynchronization between segments. Correlations are generated by an autonomous pattern formation process. Neuronal coupling is the result both of peripheral evidence (similarity of local quality) and of central evidence (common membership in a stored pattern). The model is consistent with known anatomy and physiology. However, a new physiological function, synaptic modulation, has to be postulated. The present paper restricts explicit treatment to the peripheral evidence represented by amplitude modulations globally present in all components of a sound spectrum. Generalization to arbitrary sensory qualities will be the subject of a later paper. The model is an application and illustration of the Correlation Theory of brain function.

Action Potentials↗

Development of ocularity domains and growth behaviour of axon terminals.

Ontogenetic development of ocularity domains--stripes, patches and layers in cortex, colliculus superior and lateral geniculate nucleus--is the result of organization that may either be intrinsic to the postsynaptic structure or induced to it by the afferents. A specific type of axonal growth behaviour that was recently proposed as a basis for ontogenetic development of retinotopy is sufficient to account also for ocularity domains. No intrinsic organization in the postsynaptic structure is required. The latter merely serves as a propagating medium for markers carried by the presynaptic terminals. Computer simulations demonstrate the mechanism to be complete and consistent.

Animals↗

McCollough effect and eye optics.

Astigmatism induced by cylindrical lenses leads to colour sensations similar to the McCollough effect. Consequences for the design of experiments and a new interpretation of the McCollough effect are suggested.

Accommodation, Ocular↗

How to label nerve cells so that they can interconnect in an ordered fashion.

We present a method for setting up topographically ordered mappings between two sheets of nerve cells. A set of chemical markers that express the neighborhood relationships within the presynaptic sheet is induced by the fibers into the postsynaptic sheet. The markers are used to guide the fibers to their terminal sites. A case for which this idea may be relevant is the retinotectal projection; our model exhibits types of plasticity found experimentally. The fact that the postsynaptic markers remain after removal of the projecting fibers suggests an important difference between development and regeneration. This paper concentrates on explaining the basic idea, and in addition presents a set of preliminary computer simulations.

Cell Count↗