Biomedical subjects

T Baruch

Publications and source records attributed to T Baruch.

6 recordsLinked to original sources

PubMed1997

A parametric study of face recognition when image degradations are combined.

This article expands and quantifies one of the classic reports of modern visual perception research--Harmon and Julesz' (1973) demonstration of an enhancement in recognition performance when area averaging (blocking) and spatial frequency filtering are sequentially applied. Our goals were twofold: first, to determine if the existence of the phenomena could be confirmed and replicated in a parametric study; second, to determine if the new results supported the critical band masking theory originally proposed by Harmon and Julesz. We confirmed the presence of the phenomenon for stimuli subtending approximately six deg of visual angle vertically, but observed a surprisingly different pattern of results for smaller stimuli subtending approximately one deg. These and other recent findings from other laboratories raise questions about their masking theory as a complete explanation of the phenomena.

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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.

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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↗

PubMed1988

Impaired fibrinolysis in coronary artery disease.

We assessed endogenous endothelial-dependent fibrinolysis in 99 subjects with coronary artery disease (CAD) documented by angiography and in 28 control subjects with normal coronary arteries on angiography. We used specific, sensitive assays for plasma tissue-type plasminogen activator (t-PA) antigen, t-PA activity, plasminogen activator inhibitor (PAI) activity, plasminogen, and alpha-2 plasmin inhibitor (alpha-2 PI). Mean PAI activity was significantly higher, and mean t-PA activity after venous occlusion of the upper arm (a standard test of the capacity of vascular endothelium to release t-PA) was significantly lower in subjects with CAD than in subjects with normal coronary arteries. The mean increment in t-PA antigen after venous occlusion was significantly lower than normal in subjects with CAD with onset of symptoms before age 45 years. Subjects with CAD had a significantly increased mean plasma fibrinogen level compared with control subjects, and a significant positive correlation was observed between PAI activity and plasma fibrinogen in subjects with CAD. No significant abnormalities of plasminogen or alpha-2 PI were observed in any subset of subjects with CAD. These data support an association between impaired fibrinolysis and CAD, with contributions from both increased PAI activity and in younger subjects from reduced endothelial t-PA release.

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