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Biomedical subjects

T M Caelli

Publications and source records attributed to T M Caelli.

14 recordsLinked to original sources
PubMed1994

Lie transformation groups, integral transforms, and invariant pattern recognition.

This paper considers image representations based on integral transforms which are invariant under certain transformations, while preserving the uniqueness of the encoding. Necessary and sufficient conditions are determined for the existence of such representations and a method to determine the kernels of the related integral transforms is presented. Finally, the possible relevance of such considerations for the understanding of invariant recognition systems in biological vision is also explored.

Humans↗
PubMed1988

Underlying neural computations for some visual phenomena.

In this paper we examine how a large array of neurons, and their associated neural circuitry, may determine known receptive field profile types and some well-known visual phenomena including Mach bands, edge enhancement, and visual masking of one signal by another. The neural model has a spatio-temporal structure and is described by a nonlinear integropartial differential difference equation with an isotropic Gabor kernel - a Gaussian apertured cosine modulation. Several simulations are presented.

Computer Simulation↗
PubMed1987

On the identification of neural responses.

The most common form of measuring electrical responses of nerve cells is the recording of a given cell's "spike train" profile to the parameters of a given input signal. In this paper we consider the conditions under which it is possible to relate such response measures to the properties of the cell's underlying activity characteristics, the neural network, and the input signal.

Mathematics↗
PubMed1986

The relationship between signal response selectivity and the functional structure of complex retinal neural networks.

In this paper we simulate the simultaneous responses of 45 neurones within a hypothetical retina to a variety of spatio-temporal signals. Our results demonstrate how specific convergent and divergent excitatory and inhibitory connections are sufficient to determine signal response selectivity of specific ganglion cells and so delimit the known types of center-surround receptive fields.

Animals↗
PubMed1986

An inverse problem in neural processing.

Any neural network aimed at the coding sensory events must contain computational properties which generally allow the organism to reconstruct the input signals with some degree of accuracy--else the association between stimulus and response would, at best, be uncertain. In this paper we investigate the problem of reconstructing external input signals to neural networks when the activity profiles of only some of its member cells are known. The evolution and activities of such cells are defined by an earlier formulation of one of us (Oğuztöreli 1979) and, here, we restrict our application to local circuits within the vertebrate retina. Solutions to this inverse coding problem are presented for specific network equations and exemplified with 1, 3, and 5 neuron cases.

Mathematics↗
PubMed1986

Control mechanisms of a neural network.

In this paper we consider some classical control theoretic properties of a nonlinear neural network proposed by Oğuztöreli (1979) to represent the activities of constituent neurones in terms of the input signals and coupling (associative) properties. By breaking the network into linear and nonlinear components we have been able to localize the nonlinearities in the individual neural response latencies through the system.

Animals↗
PubMed1985

Control properties of perceptual transient and sustained mechanisms.

A second order control formulation describing the temporal responses of sustained and transient preceptual processes is investigated. Parametric configurations for the resulting transfer functions are determined from existing experimental data. These data include experiments on impulse response, flicker frequency, subthreshold summation, and masking.

Cybernetics↗
PubMed1981

Some psychophysical determinants of discrete Moiré patterns.

In a series of experiments we have investigated the perception of Moiré patterns as a function of spatial density, rotation and temporal display parameters. Results indicate that the local correlation extraction processes involved in the perception of these patterns is not feature specific, yet is driven by excitatory (correlated) and inhibitory (uncorrelated) information under a form of spatial summation. These results are comparable with recent results on texture discrimination where texture interpoint distance distributions (dipole statistics) have also been discovered to have excitatory and inhibitory components.

Form Perception↗
PubMed1980

Facilitative and inhibitory factors in visual texture discrimination.

In this paper we consider some spatial and temporal properties of visual textures which either inhibit of enhance their discrimination. From exposure time and texture mixing studies two findings emerge. First, it is clear that the spatial summation process involved in texture discrimination has a time course consistent with counting models for decision making. Secondly, the receptive field structures of salient texture features, in particular-orientation, seem to involve simple excitatory center and inhibitory surround mechanisms.

Humans↗
PubMed1980

On the contours of apparent motion: a new perspective on visual space-time.

Previous results on the perception of motion indicate that perceived motion paths cannot be explained solely in terms of simple feature-specific analyzers. This is particularly true of apparent (phi) motion. In this paper we develop a dynamic network, with simple filtering and summation properties, which can predict the geometric paths of apparent motion in various spatio-temporal configurations. The network assumptions predict a non-Euclidean metric for the visual space-time of motion perception and we consider the implications of such distortions for various visual displays, including illusions.

Humans↗
PubMed1975

The Poggendorff Illusion and estimates of transverse extent.

The underestimation of transverse extent relative to longitudinal extent, in the Poggendorff Illusion, was tested by varying oblique line orientation, interparallel line distance, and presence or absence of obliques. 20 subjects made estimates of the transverse extent on both a longitudinal and transverse extent. The results indicated that, although underestimation was found for some stimulus conditions, overestimation was found for others. It was argued that even though presence of obliques affected judgmental error the longitudinal-transverse illusion could not form a basis for the Poggendorff Illusion.

Humans↗