The Warped Geometry of Visual Space Near a Line Assessed Using a Hyperacuity Displacement Task

Badcock & Westheimer (Spatial Vision, 1(1), 3-11, 1985) showed that a thin vertical line induces nearby zones of attraction and repulsion; this study extends those results by more closely examining the horizontal and vertical extents of the repulsion zone and by using an illusory contour to induce repulsion. The experimental paradigm measures perceived hyperacute displacements of a thin vertical line 10' tall. Halfway through the stimulus, the bright target line was shifted and a lower contrast flanking line added. Conditions equivalent to Badcock & Westheimer replicate their results. Repulsion is observed horizontally from separations of 5' to at least 30' and becomes minimal at 50'. Repulsion also decreases with increasing vertical separation. Another experiment shows that symmetry is not required for repulsion when the flanking line is split into two vertically separated fragments; one fragment alone causes the same amount of repulsion as both fragments together. Finally, it is shown that a flanking contour formed by the grating illusion causes repulsion of the target line in the same manner as a target line defined by luminance.British Petroleum (89A-1204); Defense Advanced Research Projects Agency (90-0083); Air Force Office of Scientific Research (90-0175

Automated construction of a hierarchy of self-organized neural network classifiers

This paper documents an effort to design and implement a neural network-based, automatic classification system which dynamically constructs and trains a decision tree. The system is a combination of neural network and decision tree technology. The decision tree is constructed to partition a large classification problem into smaller problems. The neural network modules then solve these smaller problems. We used a variant of the Fuzzy ARTMAP neural network which can be trained much more quickly than traditional neural networks. The research extends the concept of self-organization from within the neural network to the overall structure of the dynamically constructed decision hierarchy. The primary advantage is avoidance of manual tedium and subjective bias in constructing decision hierarchies. Additionally, removing the need for manual construction of the hierarchy opens up a large class of potential classification applications. When tested on data from real-world images, the automatically generated hierarchies performed slightly better than an intuitive (handbuilt) hierarchy. Because the neural networks at the nodes of the decision hierarchy are solving smaller problems, generalization performance can really be improved if the number of features used to solve these problems is reduced. Algorithms for automatically selecting which features to use for each individual classification module were also implemented. We were able to achieve the same level of performance as in previous manual efforts, but in an efficient, automatic manner. The technology developed has great potential in a number of commercial areas, including data mining, pattern recognition, and intelligent interfaces for personal computer applications. Sample applications include: fraud detection, bankruptcy prediction, data mining agent, scalable object recognition system, email agent, resource librarian agent, and a decision aid agent

Мовна ситуація в українських засобах масової комунікації в оцінках громадян (за результатами масового опитування)

У статті проаналізовано результати масового опитування щодо мовної ситуації в українських ЗМК. З’ясовано, що диференціація преференцій українців у сфері ЗМІ й культури обумовлена мовою повсякденного спілкування, рідною мовою та регіоном проживання, найменшою мірою віком, освітою та типом населеного пункту

Estimation of the parameters of a boundary contour system using psychophysical hyperacuity experiments

Dissertation (Ph.D.)--Boston UniversityVisual hyperacuity enables observers to make accurate judgments of the relative positions of stimuli when the differences are smaller than the size of a single cone in the fovea. Because hyperacuity can serve as a gauge for precisely measuring characteristics of the visual system, it can provide stringent tests for models of the visual system. A variant of the Boundary Contour System (BCS) model is here used to clarify previously unexplained psychophysical hyperacuity results involving contrast polarity, stimulus separation, and sinusoidal masking gratings. Two-dot alignment thresholds were studied by Levi & Waugh (1996) by varying the gap between the dots, with same and opposite contrast polarity with respect to the background, and also with and without band-limited sinusoidal grating masks of different orientations. They found that when the gap between the dots is small (6 arcmin), different patterns of misalignment thresholds are obtained for the same and different contrast polarity conditions. However, when the gap is large (24 arcmin), the same pattern of thresholds was obtained irrespective of contrast polarity. The simulations presented here replicate these findings, producing the same pattern of results when varying the gap between the dots, with same and opposite contrast polarity with respect to the background, and also with and without sinusoidal grating masks of different orientations. The vision model used (BCS) is able to produce these patterns because of its inherent processing using contrast insensitivity, spatial and oriented competition, and long-range completion layers. A novel aspect of the model is the use of sampled field processing, which simplifies the model's equations. Modified Hebbian learning and a neural decision module are proposed as mechanisms that link the vision model's outputs to a decision criterion. All model parts have plausible neurobiological correlates. In addition, psychophysical hyperacuity experiments served to map the limits of inhibitory spatial interactions. The results show that inhibition occurs even when only half of the split flanking line of Badcock & Westheimer (1985b) is used, suggesting that subthreshold activity in units representing the line extends beyond the end of the line. Furthermore, strong inhibition was observed with a flanking illusory line grating

1995 The Analysis

https://jdc.jefferson.edu/analysis/1022/thumbnail.jp