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At least 253 records · Page 14Linked to original sources
PubMed1983

A model for the monocular line orientation analyzer.

A model for monocular line perception by human Ss is based on three basic assumptions: (a) the line's inclination is coded by the maximally excited orientation detector's number; (b) the inclination of the perceived line is equivocally determined by the excitation vector in the subjective space; (c) the analyzer has a maximum differential sensitivity over the whole range of the line inclinations. This simple model for the line inclination analyzer, taking into account the optimization of its sensitivity, provides incomplex explanations for a wide range of psychophysical and neurophysiological data obtained from human and animal experiments.

Animals↗
PubMed1983

Analysis of nonlinear physiological systems with single or multiple spike inputs and analogue or spike outputs.

This paper outlines an extension of Krausz' (1975) approach to nonlinear analysis of physiological systems with random impulse train inputs. This extension concerns multiple (here two) inputs and spike train outputs in addition to analogue outputs. The respective theoretical formula are given, and the approach is illustrated by experimental data relating to the nonlinear interaction of cat motor units activated with random pulse trains. As outputs are considered muscle tension (as an example for an analogue signal) and discharge frequency of a Ia fibre (as an example for a spike output).

Animals↗
PubMed1983

The frequency of seeing square wave density modulations in random dot patterns.

A theoretical and experimental study on the detection of a square wave pattern of random dots is presented. Our theory applies to two-alternative forced choice experiments as well as to "seen"-"not seen" discrimination experiments. In our experiments we used the forced choice method. The theory provides a good description of the psychometric function of the percentage of correct decisions versus contrast. From these frequency of seeing (FOS) curves the apparent signal-to-noise ratio of the detection mechanism of human subjects can be derived. It is found that this ratio can have values of up to 100% and that it decreases with the number of dots in the stimulus and with the number of periods of the square wave. It is shown that a more precise description of the human performance can be obtained from the mid-points of the FOS-curves (i.e. the thresholds) rather than from the slopes.

Bionics↗
PubMed1983

Synchronization in chains of pacemaker cells by phase resetting action potential effects.

Interactions between pacemaker cells in a chain were calculated according to a "phase-reset" model. It is based on effects of action potentials in the cells on the cycle lengths of neighbouring cells. These effects were defined for each cell by a latency-phase curve (LPC), giving the latency time (L) until the onset of the next action potential in that cell, as a function of the phase (phi) at which a neighbour cell fired an action potential. Neighbour cells with simultaneous action potentials did not influence each others cycle length. We investigated how stable synchronization depends on the shape of the LPC's of the pacemaker cells and on chain length. Three types of interactive behaviour were distinguished. First, anti-phase synchrony, in which neighbouring cells fired with large phase differences with respect to the synchronized period Ps. Second, asynchrony, in which the periods of the cells did not become equal and constant. Third, in-phase synchrony, in which the phase differences between the neighbouring cells were zero or much smaller than the synchronized period Ps, depending on the differences between the intrinsic periods. Asynchrony and anti-phase synchrony may be seen as cardiophysiological arrhythmias, while in-phase synchrony represents the physiological type of synchrony in the heart. In-phase synchrony appeared to be strongly favoured by LPC's, which have a no-effect (refractory) part at early phases, a lengthened latency (or phase delay) part at intermediate phases and a shortened latency (or phase advance) part at late phases in the cycle. Such LPC-shapes are commonly found in preparations of cardiac pacemaker cells. When the pacemaker cells were identical, the synchronized period Ps during in-phase synchrony was equal to their intrinsic period P*i. For different intrinsic periods, Ps was equal to the intrinsic period of the fastest cell if the LPC's contained a sufficiently long initial no-effect period at early phases and a shortened latency part at late phases. When, on the other hand, such cell chains had a linear gradient in their intrinsic periods, "action potentials" started from the fast end and traveled along the chain. The propagation of an action potential wave slowed down as it reached the slower cells. When the gradient in the intrinsic periods was too steep, only the intrinsically fast end of the chain developed synchrony.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1983

Three dimensional arm trajectories.

Planar arm trajectories are characterized by a segmentation of the hand velocity profile and by a coupling between shape and speed. The question addressed in this paper is whether such coupling, observed in two dimensions, still holds in three dimensions. This matter was investigated experimentally by recording three dimensional "aimless" movements of the arm, particularly three dimensional scribbles, and the answer suggested by the experimental data is that only the "bending" of the trajectory is coupled with speed, whereas the "twisting" is independent of speed. The same behaviour was also found to characterize a computational model of trajectory formation which is based on the spatial composition of chains of planar strokes, overlapped in time.

Adult↗
PubMed1983

The silent period in the stretch response of Ia-activated dorsal spino-cerebellar tract neurons to sinusoidal muscle stretch in cats.

By means of extracellular recordings of action potentials the stretch responses of single neurons of Clarke's column were analysed. The neurons were monosynaptically activated from Ia afferents of both ipsilateral gastrocnemius muscles. When stretch cycles of more than 0.2 mm amplitude and frequencies above 2 Hz were applied to the gastrocnemius muscles, the discharging was found to cease during the period of stretch release, whereas the average discharge rate was found to increase. In the frequency range between 0.1 and 10 Hz a sinewave of stretch frequency - the response sinewave - fitted to the non-zero bins of cycle histograms described the stretch response at small and large amplitudes equally well. The amount of increase in the average firing rate corresponded quite well to the portion of the response sinewave below the zero discharge rate. This indicates that the occurrance of discharge pauses and the relation of the average discharge rate to frequency and amplitude of stretch can be described successfully by a half-wave rectification of the response at zero discharge rate. If one regards the shape of cycle histograms to be a nearly sinusoidal modulation plus a non-linear clipping at zero the application of linear systems analysis is worthwhile in describing the response not only at very small amplitudes but in the whole range of muscle stretch.

Action Potentials↗
PubMed1983

Model emulates human smooth pursuit system producing zero-latency target tracking.

Humans can overcome the 150 ms time delay of the smooth pursuit eye movement system and track smoothly moving visual targets with zero-latency. Our target-selective adaptive control model can also overcome an inherent time delay and produce zero-latency tracking. No other model or man-made system can do this. Our model is physically realizable and physiologically realistic. The technique used in our model should be useful for analyzing other time-delay systems, such as man-machine systems and robots.

Bionics↗