Biomedical subjects

W R Uttal

Publications and source records attributed to W R Uttal.

At least 19 recordsLinked to original sources

PubMed1996

An integrated computational model of three-dimensional vision.

This article presents the details of and background for a computational model of three-dimensional vision. The basic idea embodied in this model is that a veridical approximation to a three-dimensional scene can best be produced by combining several operators that act on acquired two-dimensional images to reconstruct surface shape and distance. Stereo, shape from shading (SFS), and shape from structured light (SFSL) operators are combined to produce a reconstruction that is superior to any that might be produced by one alone. The advantages and disadvantages of each independent operator and the generic difficulties faced by members of this class of operators are discussed. Collectively, this package of combined algorithms represents a functional model of human spatial vision.

Algorithms↗

PubMed1995

Dichoptic and physical information combination: a comparison.

Two experiments, in which information from two different kinds of degraded (low-pass filtered and regionally averaged or blocked) visual stimuli (aircraft silhouettes) was combined, are reported. In the first experiment, the degraded images were perceptually combined by being separately presented to each eye in a dichoptic viewing situation. Both stimuli in both presentations were masked by identical random visual interference. When the two stimuli were visually fused, performance in a discrimination task was enhanced over that in control situations in which only one of the two stimuli was presented. In the second experiment the two degraded stimuli were physically superimposed prior to binocular presentation, with a similar result. The results of this hybrid (masking/binocular summation) experiment suggest that true advantageous information pooling occurs when these two types of degraded stimuli are combined either physically or dichoptically.

Attention↗

PubMed1995

The effect of combinations of image degradations in a discrimination task.

This paper explores the ways in which combinations of image degradations affect discrimination. Nine experiments are described that examine the discriminability of visual images that are degraded with three types of information reducing transformations: random punctate visual interference, low-pass spatial frequency filtering, and local area (i.e., block) averaging. The results of these experiments characterize a powerful visual ability to discriminate highly degraded stimuli unless that ability is severely challenged by relatively high levels of random visual interference. Discriminative commutativity of the orders in which the other two degradations are imposed is demonstrated. That is, the order in which the degradations are applied does not affect the final discriminative outcome. This result is in contrast to predictions from relevant mathematics and direct examination of the images produced by both orders of degradation. The commutativity is attributed to the particularly strong effect of the low-pass spatial frequency filtering degradation on the discrimination process. This study also demonstrates that combinations of degradations in a discrimination task always result in a reduction in performance, and never in the improvement that has been reported for recognition. This difference is attributed to the fact that form discrimination is mediated mainly by local features and high-frequency spatial components, whereas recognition is mediated mainly by global features and low-frequency spatial components.

Adult↗

PubMed1995

Combining image degradations in a recognition task.

Six experiments are reported that investigate the effect on form recognition performance of combining three kinds of stimulus degradations: local area averaging of intensities, low-pass spatial frequency filtering, and random dot visual interference. The effects are shown to be more complicated than previously reported in simple demonstrations. The complexity of the results suggests that models based on single stimulus attributes such as energy or spatial frequency spectrum probably cannot account for the data. Eclectic theories that invoke combinations of redundant processes may be necessary for describing visual recognition phenomena, even within the limited domain examined in this study.

Adult↗

PubMed1994

Psychophysical foundations of a model of amplified night vision in target detection tasks.

In this article we examine some of the basic psychophysics relevant to amplified night vision devices. These devices produce images that are substantially different from ordinary visual scenes. Distortions in contrast and luminance and the introduction of visual interference and geometrical artifacts contribute to unusual viewing conditions. We carried out experiments to determine the effect of these parameters of the image on a highly controlled visual target detection task simulated on a computer graphics system that closely models a night vision device. Our results indicate that display luminance and geometrical artifacts degrade detection performance only slightly, whereas contrast and visual interference have a substantial degrading effect.

Adult↗

PubMed1994

Stereoscopic perception with brief exposures.

In this report we describe the results of an experiment in which we demonstrated that a powerful and compelling stereoscopic experience is elicited with very brief (< 1 msec) stimulus durations. The observers were highly successful in recognizing briefly flashed, stereoscopic, random-dot surfaces in the absence of monocular contours. The results are shown to be closely related to the range of depths for any stimulus form; however, the recognition thresholds were nonmonotonic as a function of disparity. Previous investigators have disagreed about the existence of a temporal threshold for stereopsis. We believe that prior findings suggesting that stereopsis cannot occur at short exposure durations are probably due to inadequate control of fixation disparity. Therefore, there is poor dichoptic image registration when a stereoscopic stimulus is presented. The present results also raise difficulties for any theory of stereopsis that requires eye movements.

Adult↗

PubMed1990

On some two-way barriers between models and mechanisms.

A number of recent as well as classic ideas suggest that there are constraints and limits on the explanatory role that computational, mathematical, and neural net models of visual and other cognitive processes can play that have not been generally appreciated. These ideas come from mathematics, automata theory, chaos theory, thermodynamics, neurophysiology, and psychology. Collectively, these ideas suggest that the neural or cognitive mechanisms underlying many kinds of formal models are untestable and unverifiable. Models may be good descriptions of perceptual and other cognitive processes, but they cannot in principle be reductive explanations nor can we use them to predict behavior at the molar level from what we know of the neural primitives. This discussion is an effort to clarify the appropriate meanings of these models, not to dissuade workers from forging ahead in the modeling endeavor, which I acknowledge is progressing and is making possible our increasingly deep appreciation of plausible and interesting cognitive processes.

Brain↗

PubMed1988