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Biomedical subjects

T Poggio

Publications and source records attributed to T Poggio.

At least 55 records · Page 3Linked to original sources
PubMed1980

On the respresentation of multi-input systems: computational properties of polynomial algorithms.

This paper introduces a theoretical frame-work for characterizing and classifying simple parallel algorithms and systems with many inputs, for example an array of photoreceptors. The polynomial representation (Taylor series development) of a large class of operators is introduced and its range of validity discussed. The problems involved in the polynomial approximation of systems are also briefly reviewed. Symmetry properties of the input-output map and their implications for the system structure (i.e. its kernels) are studied. Finally, the computational properties of polynomial mappings are characterized.

Mathematics↗
PubMed1980

Smallest channel in early human vision.

We suggest from the psychophysical data on two-point and line acuity that the smallest foveal channel in human vision must have an excitatory center with a diameter of around 1' 20". Taking into account the optics of the eye and the finite size of the receptors, we show that this would correspond well to the properties of a retinal ganglion cell receiving excitatory input from a single cone.

Humans↗
PubMed1979

A computational theory of human stereo vision.

An algorithm is proposed for solving the stereoscopic matching problem. The algorithm consists of five steps: (1) Each image is filtered at different orientations with bar masks of four sizes that increase with eccentricity; the equivalent filters are one or two octaves wide. (2) Zero-crossings in the filtered images, which roughly correspond to edges, are localized. Positions of the ends of lines and edges are also found. (3) For each mask orientation and size, matching takes place between pairs of zero-crossings or terminationss of the same sign in the two images, for a range of disparities up to about the width of the mask's central region. (4) Wide masks can control vergence movements, thus causing small masks to come into correspondence. (5) When a correspondence is achieved, it is stored in a dynamic buffer, called the 2 1/2-D sketch. It is shown that this proposal provides a theoretical framework for most existing psychophysical and neurophysiological data about stereopsis. Several critical experimental predictions are also made, for instance about the size of Panum's area under various conditions. The results of such experiments would tell us whether, for example, cooperativity is necessary for the matching process.

Humans↗
PubMed1979

Bandpass channels, zero-crossings, and early visual information processing.

Under appropriate conditions zero-crossings of a bandpass signal are very rich in information. The authors examine here the relevance of this result to the early stages of visual information processing, where zero-crossings in the output of independent spatial-frequency-tuned channels may contain sufficient information for much of the subsequent processing.

Humans↗
PubMed1978

Analysis of a cooperative stereo algorithm.

Marr and Poggio (1976) recently described a cooperative algorithm that solves the correspondence problem for stereopsis. This article uses a probabilistic technique to analyze the convergence of that algorithm, and derives the conditions governing the stability of the solution state. The actual results of applying the algorithm to random-dot stereograms are compared with the probabilistic analysis. A satisfactory mathematical analysis of the asymptotic behaviour of the algorithm is possible for a suitable choice of the parameter values and loading rules, and again the actual performance of the algorithm under these conditions is compared with the theoretical predictions. Finally, some problems raised by the analysis of this type of "cooperative" algorithm are briefly discussed.

Depth Perception↗
PubMed1977

Wiener-like system identification in physiology.

Applications of Wiener-like identification methods to biological systems have revealed several limitations of this technique. These practical limitations correspond to conceptual and mathematical problems intrinsic to this kind of identification of nonlinear systems.

Physiology↗
PubMed1976

Cooperative computation of stereo disparity.

The extraction of stereo-disparity information from two images depends upon establishing a correspondence between them. In this article we analyze the nature of the correspondence computation and derive a cooperative algorithm that implements it. We show that this algorithm successfully extracts information from random-dot stereograms, and its implications for the psychophysics and neurophysiology of the visual system are briefly discussed.

Depth Perception↗
PubMed1975

The Müller-Lyer figure and the fly.

In the Müller-Lyer illusion two horizontal line segments of equal length are perceived by humans as unequal. The gaze of a fly presented with Müller-Lyer figures corresponds to human eye movements and human (illusionary) evaluations of the segment lengths. It is suggested that a theory similar to the phenomenological theory which accounts for the fly's gaze may account for the human eye's movement during an observation of Müller-Lyer figures.

Animals↗