Temporal Neighborhood Research Articles

The influence of saccade length on the saccadic suppression of displacement detection

The decrease in sensitivity to spatial displacement which accompanies a voluntary horizontal saccadic eye movement was measured as a function of the length of the saccade. Threshold for detecting the displacement increased linearly from about 0.3 degrees to 1.2 degrees as saccade length increased from 4 degrees to 12 degrees. The variability (standard deviation) of the discrimination increased linearly with saccade length as well, and hence also linearly with the displacement threshold. These results, along with our previous finding that the increase is not a consequence of the saccadically generated spatiotemporal smearing of the retinal image (Li & Matin, 1990), support the proposal that displacement detection is based on a constant internal signal/noise ratio whose denominator is a measure of the variability of the extraretinal signal regarding eye position, and that the reduction in sensitivity is a result of a transient increase of this variability in the temporal neighborhood of a saccade.

Nonlinear smoothing filters based on rank estimates of location

A class of nonlinear filters that are based on the rank estimates (R-estimates) of location parameters in statistical theory is introduced. It is shown how moving-window rank filters (R-filters) can be defined starting from rank estimates of location. These filters utilize the relative ranks of the observations in each window to produce an output value. The idea of rank Winsorization is extended to that of averaging only observations which lie within small temporal neighborhoods. This leads to a definition of the class of generalized Wilcoxon (GW) filters, which are parameterized by three parameters, namely the degrees of temporal and rank Winsorization and the degree of averaging. The GW filters can be defined to have desirable characteristics of edge preservation, detail retention, and impulse rejection, in addition to the property of Gaussian noise smoothing. Performance characteristics of these filters are considered through analysis and simulation. The filters show that all three well-known classes of robust location estimates, the L-, M-, and R-estimates, can be applied to nonlinear smoothing of signals. >

VLSI architecture for computer vision based on neurobiological principles of organization : Ran Ginosar and Yehoshua Y. Zeevi. Electrical Engineering Department, Technion - Isracl Institute of Technology, Haifa 32000, Israel

Biological and technological (wide-field-of-view) vision systems are confronted with the formidable task of managing data sets at a rate in excess of 10/sup 0/10 bits per second. In both cases, however, considering the required tasks, it appears that the data are highly redundant, and therefore must be reorganized before any type of higher level processing is applied to them. Reorganizations may include compression, and dimensional reduction according to the various relevant parameters. Biological processing at both the retinal and cortical levels often consists of repetitive simple operations applied to spatial and/or temporal neighborhoods, limited in their extend and duration. These are most adequate for the very high image data rates, in spite of the fact that those neurobiological systems actually consists of simple components which are several orders of magnitude slower than electronic components. It is the authors' goal to follow biological algorithms and principles of organization in the design of VLSI architectures, and to achieve similar or better performance in image processing and machine vision. Their efforts have yielded the following families of VLSI devices and systems. A highly parallel Intelligent Scan Image Acquisition VLSI sensing device has been constructed. It selectively scans only the relevant areas of interestmore » in each image, thus effectively providing a compressed image for later processing stages. The device is controlled by an algorithm which is highly sensitive to image content. This sensor imitates the capability of the eye to concentrate on (attend) certain parts of the image, and even extends this by processing multiple focal points simultaneously. This is an example of how we applied the nonuniform sample-and-process algorithm, characteristic of biological vision, in a highly parallel architecture which surpasses the performance of the human eye.« less

Nonrandom Price Changes in Association with Trading in Large Blocks

This paper investigates price movements in the immediate transaction and temporal neighborhood of the sale of a large block of stock on the New York Stock Exchange (NYSE).' Our working hypothesis is that this conspicuous happening can establish a distinct regime of price behavior that differs significantly from that of the ordinary round-lot market and that for a time at least, prices have a memory. Our analysis is based on the view that the price-memory hypothesis does not require that all prices have a memory or that all prices get remembered. What is required is a means of identifying the prices that do get remembered and, of course, a theory of market reactions. The trade of a block is an easily identified event, and as we will see, it is associated with strains on the market mechanism and the exposure of information of great potential value.2 It is not unreasonable to expect that significant market effects will accompany this occurrence. Our procedure will be to start with the immediate transaction neighborhood of the event, the single trades which take place just before and just after the block, and then progressively extend the scope