Biomedical subjects

F H Schuling

Publications and source records attributed to F H Schuling.

4 recordsLinked to original sources

PubMed1991

Circadian inputs influence the performance of a spiking, movement-sensitive neuron in the visual system of the blowfly.

Long-term extracellular recordings from a spiking, movement-sensitive giant neuron (H1) in the third optic ganglion of the blowfly Calliphora vicina (L.) revealed periodic endogenous sensitivity fluctuations. The sensitivity changes showed properties typical of an endogenous circadian rhythm. This was true for the responses in reaction to intensity changes of visual patterns as well as for the responses elicited by pattern movement. For these two types of stimuli, the circadian fluctuations were comparable, but the envelope in the case of responses to movement was more robust. A circadian fluctuation in responses to movement is, therefore, present at the level of single elementary movement detectors. The tonic activity of the neuron was also shown to be under circadian control. In constant darkness (DD) the fluctuation was circadian, whereas in constant light it was not. The subjective light-dark (LD) transitions in the tonic activity in DD closely followed the LD transitions in the holding cages initially; that is, there was low activity at night and high activity during the daytime. The sensitivity fluctuations in response to visual stimuli led the tonic spike activity fluctuations by several hours.

Animals↗

PubMed1990

The computational measurement of apparent motion: a recurrent pattern recognition strategy as an approach to solve the correspondence problem.

In short, the model consists of a two-dimensional set of edge detecting units, modelled according to the zero-crossing detectors introduced first by Marr and Ullman (1981). These detectors are located peripherally in our synthetic vision system and are the input elements for an intelligent recurrent network. The purpose of that network is to recognize and categorize the previously detected contrast changes in a multi-resolution representation of the original image in such a manner that the original information will be decomposed into a relatively small number N of well-defined edge primitives. The advantage of such a construction is that time-consuming pattern recognition has no longer to be done on the originally complex motion-blurred images of moving objects, but on a limited number of categorized forms. Based on a number M of elementary feature attributes for each individual edge primitive, the model is then able to decompose each edge pattern into certain features. In this way an M-dimensional vector can be constructed for each edge. For each sequence of two successive frames a tensor can be calculated containing the distances (measured in M-dimensional feature space) between all features in both images. This procedure yields a set of K-1 tensors for a sequence of K images. After cross-correlation of all N x M feature attributes from image (i) with those from image (i + 1), where i = 1,...,K-1, probability distributions can be computed. The final step is to search for maxima in these probability functions and then to construct from these extremes an optimal motion field. A number of simulation examples will be presented.

Algorithms↗

PubMed1989

Microprocessor-controlled vector scan display system for generation of real-time visual stimuli.

The paper describes a low-cost, versatile, widely applicable digital display system in which a high-resolution, high-intensity display unit is driven by a real-time vector scan controller. The actual online display control of this device is preceded by an offline software stimulus-frame editor, designed to create and support a library of stimulus patterns (standard frames without any timing information and without any referencing to a special display co-ordinate system). The display times can be set individually for each single frame (containing at maximum 1023 pixels) with relative ease. Display frequency is set to 1 kHz. Writing time per pixel is less than 1 microsecond. A graphic display system like the one presented in this paper can be applied to generate a variety of real-time optical stimuli, such as intensity modulation of single spots or distinct display areas, abrupt displacements of a certain pattern, continuous movement or onset and offset of steady motion of a pattern.

Animals↗

PubMed1984

Electrical activity in the red nuclei of rats and the effects of hemicerebellectomy at young ages.

Extracellular activity in the red nuclei in different behavioural states was investigated in control adult rats and in adults rats who had previously undergone a cerebellar hemispherectomy on their 2nd, 5th, 10th or 20th day. In addition to visual analysis, spectra and coherence functions were computed from the signals during quiescence and movements. Preceding and during movements a particular pattern, characterized by a regular rhythm between 7.5 and 8.0 Hz occurs. Inter-rubral coherences are high at the specific pattern frequency. In rats with a cerebellar hemispherectomy - irrespective of the age at lesioning - power spectra from both red nuclei differ markedly from each other during quiescence. When movements occur, rats operated at the 20th day show a pattern in both red nuclei similar to that found in control rats. However, in rats lesioned at the 5th or 10th day the specific pattern frequency is much lower while in rats operated at the 2nd day no specific patterning of red nuclei activity is evident.

Afferent Pathways↗