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H J Reitboeck

Publications and source records attributed to H J Reitboeck.

8 recordsLinked to original sources
PubMed1996

A neural network for position invariant pattern recognition combining spiking neurons with the Fourier-transform.

We present an approach for position invariant recognition of individual objects in composite scenes, combining neural networks and algorithmic methods. A dynamic network of spiking neurons is used to generate object definition and figure/ground separation via temporal signal correlations. A shift invariant representation of the network spike activity distribution is subsequently realized via the amplitude spectrum of the Fourier-transform. Objects and their transformed representations are therefore linked in the time domain. The model segregates scenes and classifies individual patterns independent of their position in the input scene.

Algorithms↗
PubMed1993

Construction of concepts by the nervous system: from neurons to cognition.

Neurophysiological studies have recently identified a pattern of synchronized slow-wave activity in the visual cortex which characteristically encompasses groups of neurons activated by similar or closely related stimulus attributes. This slow-wave activity appears to tag clusters of neurons to form aggregates representing in their totality more complex, higher-order stimulus attributes across disparate positions in the cortical representation. The notion is advanced that the function of these aggregates is analogous to that ascribed to the subsymbolic computational level in connectionist networks. On this basis, the argument is presented that the synchronized cortical activity is an important aspect of the construction of symbolic representation by the nervous system and, thus, a step from neural information processing to the symbolic processes stipulated by classical cognitivism.

Animals↗
PubMed1991

Adaptation of the Reitboeck method of multiple microelectrode recording to the neocortex of the waking monkey.

We adapted to the neocortex of waking monkeys a method for multiple microelectrode recording devised by Reitboeck. A sliding platform allows micropositioning of 7 electrodes independently, in 2 microns steps. Microelectrodes are quartz glass filaments (80 microns o.d.) with central metal cores (30 microns) of tungsten-platinum alloy. Filaments are drawn in a high temperature chamber, and ground to the desired form and tip size. The microdrive is held over the region to be explored, and the microelectrodes passed through 300 microns o.d. guide tubes fixed in implant thimbles of chosen size an and x - y arrangement of tubes, sealed by an O-ring into a small craniotomy opening. A microprocessor controlled recording system provides gain, noise and wave-shape filtering, impedance testing, and differential amplitude discrimination for each channel. Electrode movement is obtained via the microprocessor which displays and updates on the console terminal the electrode depth, impedance, and the channel assignment of each electrode. A second microprocessor based system is used to collect, buffer, and encode in real time all event data, which are transferred whenever convenient to a minicomputer that controls the experiment. Exploratory recordings were made in the posterior parietal, somatic sensory, and motor cortical areas. The system has now been used successfully in a number of investigations.

Action Potentials↗
PubMed1988

Coherent oscillations: a mechanism of feature linking in the visual cortex? Multiple electrode and correlation analyses in the cat.

Primary visual coding can be characterized by the receptive field (RF) properties of single neurons. Subject of this paper is our search for a global, second coding step beyond the RF-concept that links related features in a visual scene. In recent models of visual coding, oscillatory activities have been proposed to constitute such linking signals. We tested the neurophysiological relevance of this hypothesis for the visual system. Single and multiple spikes as well as local field potentials were recorded simultaneously from several locations in the primary visual cortex (A17 and A18) using 7 or 19 individually advanceable fiber-microelectrodes (250 or 330 microns apart). Stimulus-evoked (SE)-resonances of 35-85 Hz were found in these three types of signals throughout the visual cortex when the primary coding channels were activated by their specific stimuli. Stimulus position, orientation, movement direction and velocity, ocularity and stationary flicker caused specific SE-resonances. Coherent SE-resonances were found at distant cortical positions when at least one of the primary coding properties was similar. Coherence was found 1) within a vertical cortex column, 2) between neighbouring hypercolumns, and 3) between two different cortical areas. We assume that the coherence of SE-resonances is mediated by recurrent excitatory intra- and inter-areal connections via phase locking between assemblies that represent the linking features of the actual visual scene. Visually related activities are, thus, transiently labelled by a temporal code that signalizes their momentary association.

Action Potentials↗
PubMed1988

Visual receptive fields of local intracortical potentials.

We have developed a method to define a spatial-temporal receptive field (RF) for local, intracortically recorded field potentials in the visual cortex. In analogy to the classic RF concept, a relation between stimulus position and a single recording location is evaluated. Our receptive field cinematogram (RF-Cine) approach, additionally, includes the temporal dynamics between stimulus and response: A sequence ('movie') of successive 'frames' is calculated, which shows the field potential amplitudes plotted with reference to the position in visual space of a randomly moving stimulus. The exploration of the receptive fields via a randomly jumping disk stimulus is especially suitable for multi-electrode cortex mapping, because the RF-Cines of all electrodes can be evaluated simultaneously within a single stimulation period of 100 s duration. Field potential RF-Cines showed concentrical or ellipsoidal antagonistic center-surround structures with biphasic or triphasic time courses. The size of these structures increases with retinal eccentricity. The cortical surface coverage of the RF-Cine centers was calculated to be 0.8 mm2 for area 17 and 1.3 mm2 for area 18, being nearly constant within the 0-10 degrees cortical representation of the lower visual field. These values approximately correspond to the extent of one hypercolumn. The absolute positions of the RF-Cine structures can be determined with an accuracy of 0.1-0.2 mm in cortical coordinates.

Animals↗
PubMed1984

A model for size- and rotation-invariant pattern processing in the visual system.

The mapping of retinal space onto the striate cortex of some mammals can be approximated by a log-polar function. It has been proposed that this mapping is of functional importance for scale- and rotation-invariant pattern recognition in the visual system. An exact log-polar transform converts centered scaling and rotation into translations. A subsequent translation-invariant transform, such as the absolute value of the Fourier transform, thus generates overall size- and rotation-invariance. In our model, the translation-invariance is realized via the R-transform. This transform can be executed by simple neural networks, and it does not require the complex computations of the Fourier transform, used in Mellin-transform size-invariance models. The logarithmic space distortion and differentiation in the first processing stage of the model is realized via "Mexican hat" filters whose diameter increases linearly with eccentricity, similar to the characteristics of the receptive fields of retinal ganglion cells. Except for some special cases, the model can explain object recognition independent of size, orientation and position. Some general problems of Mellin-type size-invariance models-that also apply to our model-are discussed.

Animals↗
PubMed1983

Fiber microelectrodes for electrophysiological recordings.

Methods for the fabrication of tungsten-glass and platinum-rhodium-quartz fiber microelectrodes and of fiber pipettes are described and the electrical and mechanical properties of fiber electrodes are discussed. These properties (minimal tissue damage, good single unit isolation and temporal stability) make them particularly suited for multielectrode recordings from the central nervous system.

Animals↗